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MG MGA - Float Chamber Level

I am hanging my head in shame on this one and only going into print in case anyone has done likewise.

I am overhauling the carbs to get the mixture sorted once and for all. My brother-in-law is assisting me and he used to tune SUs in his past life. When I came to check the 7/16" gap in the float fork with the cover inverted he pointed out that I was checking the gap with the fork at rest rather than with the valve closed - pressure needs to be applied to the fork while taking the measurement!

Ho hum, no wonder I have been running rich over these last years and struggled to lean the jet enough.

Another one for the Gyles book of engineering cock-ups.

Steve
Steve Gyles

The carbs tuned up brilliantly as per the John Twist video. Road test was excellent.

To give an example of the altered float level; before the adjustment my front carb jet nut was 2 flats from fully lean. Now it is 9 flats.

Steve
Steve Gyles

Steve, I very much appreciate you sharing this info. Simple when you know how!
Richard
Richard Atkinson

Steve,

What video did you watch? Link?

I am under the impression that the float should be set with the lid inverted and the float resting on the spring but not compressing it. Can't find anything to the contrary...

Source?

Thanks.

JIM in NH
AJ Mail

I do not understand the reference to a spring. What spring?
Why is the float involved?
With the lid inverted the valve is closed under it's own weight.
The gap between the fork and the lid should then be 7/16".

Image attached.


Mick

M F Anderson

My valve is spring loaded open, so I had to push the fork with slight pressure to close it when making the measurement. The difference is significant, in the order of about 3/16 ".

The workshop manual does not state that the valve should be closed, leading to my confusion when looking at the diagram that Mick has posted. However, the S U toolkit instructions state clearly that the measurement is with the valve closed.

Stevd
Steve Gyles

If I understand this right I share MF's puzzlement, my MK 2 valves have no spring and I've not seen one detailed in the WSM. Surely the float does not have to struggle against a spring loaded fork.
J H Cole

John

Exactly my thoughts over the last 14 years, hence my error. I have always assumed that when the float cap was inverted the valve needle closed. Not so. At least not so with my valves which I have always assumed to be standard. The valve certainly pushed in quite a way, then returned to open when the pressure was released.

This is the Jon Twist video on Youtube: http://www.youtube.com/watch?v=ASeMfXfjNpw

He has a number of interesting videos. This one is for the MGB, but the principle is the same.

Steve
Steve Gyles

The issue is explained here:

http://tinyurl.com/9kroku3

Steve
Steve Gyles

I had those spring loaded float needles on my midget and never pushed down on the spring when adjusting the fork height, I just let it sit on the valve by gravity. The carb mixtures adjusted up fine with leeway in either direction.
Steve, I would say that something else is wrong if you were unable to lean the carbs out sufficiently. Do you have the correct carb jets and needles? Are the needles fitted to the pistons correctly, i.e. shoulder should be flush with the bottom of the piston? Are the correct piston springs fitted? Is there fuel inside the floats? Are the float needles worn out? I recommend grosse jets for the float chambers, they have never stuck open on mine; unlike the tapered needles!
Lindsay Sampford

Lindsay

They lean out beautifully now. The high fuel level as explained in my "Tiny" link summed it all up.

Steve
Steve Gyles

Steve,

This is even more confusing.
The article on your "Tiny" link says that the spring holds the valve seated.
You say that the spring holds it open.
If it stops flooding as stated in the article the spring must be holding the valve closed when the float moves down, but this is when it should be open.
Does the pump pressure then open the valve and if so how does the spring stop flooding?

I am off to take some of those tablets that my psychiatrist prescribed.

Mick
M F Anderson

Mick

No idea about all the reasoning etc. Fact is that a spring holds the valve extended (open) and the fork has to have pressure applied to it to close it - float pushing upwards. When calibrating though, finger pressure needs to be applied to the fork to hold the valve closed while making adjustments to the fork.

Steve
Steve Gyles

This is what Burlen says about the Spring loaded valve:

Now P/N: VZX 1101

This Needle Valve controls the flow of fuel into the float chamber and shuts off when the float reaches the correct height. Original versions were a brass body and used a steel needle.

These were replaced around 1960 by the Delrin type which had a nylon spring loaded body (anti vibration) with a steel needle tip.

This has now been replaced (2009) by an aluminium body, still spring loaded but with a viton tip. This version is far superior to any other type on the market including the double ball type.

Steve
Steve Gyles

Steve,

I was confused by the statement in the article on your "tinyurl".
It states:

"The spring-loaded arrangement allows the needle to exert a constant pressure on the seating".

However, the spring pushes the needle away from the seating, not towards it.

All that aside the spring loaded valves do exist.

The attached Burlen image explains.

Mick

M F Anderson

Thanks for the additional diagram Mick. However, it does not acoount for our carb with the the Delrin needle. I might drop Burlen an email for clarification.

I also do not understand what the spring achieves. I might take one out examine.

Nevertheless, I am delighted that I spotted the variation on my carbs. Having now lowered the fuel level in the bowls by about 3/16" I have finally managed to tune the carbs to perfection.

Steve
Steve Gyles

Steve,

You have a combination of two different systems.
If you have an old style float and forked arm but a spring loaded Delrin valve you are correct to depress the spring and set it at 7/16" with the valve seated.
By depressing the spring you are creating the original arrangement, as you would with the non-spring needle falling under it's own weight.

I believe the spring just acts as an anti-vibration shock absorber.

Vibration in SU's, affecting fuel level in the bowl, was the main problem for the mga twin cam engine.

Mick


M F Anderson

Steve, I really think it is time for you to come out to Aus. again soon! Maybe then you could meet Mick and me (and a few others) and sort this out!! I have not seen these 'spring loaded devices'! I will happily make my car available for testing.
Cheers, Barry.
Barry Gannon

Mick and all

My carbs were an exchange reconditioned unit, bought through Bob West when I rebuilt the car in 1997. I have never altered the float forks during that time, just checked them. That is how the reconditioner built them (with spring valve) and set them up. If it has happened to me it has surely happened to many others who have bought reconditioned carbs in recent years.

Have I unwittingly opened a can of worms?

Steve
Steve Gyles

Just done a few measurements. With my fork adjusted with the valve closed the gap is 7/16" as per the workshop diagram. When just at rest (valve open) the gap is 19/32". This lowers the fuel level in the bowl by 5/32".

The spring appears to act as a damper for the valve as can be seen in the attached photos.

Steve

Steve Gyles

Some of you are missing the point and the function of the spring in the valve pin. The spring does not hold the valve open, it holds the valve closed when the float rises. In Steve's photos (immediately above), the valve is closed in both cases, whether the spring is compressed or not. The valve is closed whenever the needle tip touches the seat.

In operation when the valve is closed the spring is only compressed a very short distance, and it applies enough force to the needle tip to stop the fuel flow. The spring then serves as a shock absorber, so if the carburetor vibrates and the float is vibrating the valve can say closed and nor flood.

When setting height of the arm arm you turn it upside down and let the arm rest gently on the spring loaded pin (not compressed). This is the operating position when the valve closes and stops fuel flow. Motion of the arm when you press it to compress the spring is irrelevant, and it will never see full travel there in operation. Go back to the image in Mick's note. The instructions clearly state do not depress the spring loaded needle.

If you depress the needle spring, and then bend the arm to set the calibration space to 7/16-inch, when you release the arm it will spring back to leave a much larger space. That makes the fuel level too low, in which case it will run excessively lean. Once more, do not depress the spring loaded needle when setting the float arm height.
Barney Gaylord

Hi Barney

I agree with all the basic logic. I have done bench tests with my mouth and confirm what you say. Now drinking some wine to get rid of the petrol!

However (yes there has to be one), in practice I have been unable to lean out the carbs by conventional means until I reset the forks as described above. The apparent slightly lower fuel level in the bowls now allows me to set the jets absolutely spot on. First time I have ever been able to do this. All practical indications are counter to your comment about "....will run excessively lean."

Why should this be? Is the sprung valve exactly the same length as the standard valve? Or, is my facet fuel pump delivering a higher pressure than the SU, overcoming the initial spring resistance when the valve closes? i.e. the chamber continues to fill until the spring resistance becomes too great?

Steve
Steve Gyles

Steve are your floats still fully buoyant? If they have leaked slightly or have too much solder from previous repairs...?
N McGurk

Plastic floats can get saturated and sink. Metal floats can leak and sink. If a main jet is not properly centered the jet and needle can wear enough to make the fuel mixture too rich. It is possible to have the wrong needle installed. If throttle shaft is work and leaks air, you adjust richer to have good idle, but that can make the mixture too rich at any speed higher than idle. If there is not enough oil in the dashpot damper it will run lean on acceleration, and it may idle bad even with the correct mixture.
Barney Gaylord

Standard metal floats, both dry, one small solder repair in one float; Jets checked and centred time and time again; correct needles; brand new shafts etc when supplied reconditioned. No air leaks (vacuum gauge spot on at idle) The only thing that I have never played with was the float level, but often checked.

I have never been able to adjust the fuel richness to my satisfaction for the last 14 years until yesterday. Then, with 2 small adjustments to the forks the carbs tuned up perfectly; the choke is right; the plug colours are right; and the performance is a quantum leap better than before, similar to when I fitted those stub stacks a year ago. Running lean? definitely definitely not.

Steve
Steve Gyles

Steve there is something weird going on with your float valves. Both on the "A" I had around 1963 and my present 1600, the 7/16" dimension has always been checked with the fork just resting on the needle with the cap inverted. The carbs have always tuned up dead easy.
I mean tuned too, seems I quite upset a twinky owner back in the old "A" by passing him in a bit of a burn-up with my bog standard 1600, which could easily get to 110mph! Before all these speed limits I might add...
Pete
P N Tipping

Pete

Getting it all in perspective, the issues with my carbs are very minor, but when I get my teeth into something I am not content until I know the reasons. In reality my car has been running great over the last 14 years. Ask Barry Gannon. He drove it for about about 60 miles and was very impressed with the performance. I have also had it up to 100mph and that was before the sports windscreen. The only issue that I have always had is that when tuning the carbs at idle I have never been able to achieve that small momentary rmp increase when one dashpot is raised 1/16". Other than that the plugs have always shown the correct colour. The big difference this week has been with the fork alteration. Suddenly I find I get all the correct answers as published in the books and demonstrated on the video. Better performance? It feels like it, just as I felt with the stub stacks.

I have a couple of experiments I am going to try this afternoon. I will let you know the result.

Steve
Steve Gyles

Pete,

A standard MGA doing 110 MPH?
Have you ever calibrated your speedometer in the upper range?
You need to use a GPS or roadside markers.
Steve got his to 100 MPH but he has an 1800 engine and 5 speed gearbox.
I think that the Twin Cam needs to check whether he has one spark plug lead missing.

Mick
M F Anderson

Done a most interesting experiment. It's always interesting to prove or disprove theories by putting them into practice.

I ran the engine and then measured the fuel level in the float chambers with my altered forks. I then put them back to the standard setting as per the book. Ran the engine same as before, then measured the fuel level again. It was 0.2" (4.26mm) higher.

Conclusions: On my car fitted with a facet fuel pump, fuel continues to be forced into the float chambers until the needle has fully compressed the spring, not just until the valve closes without spring compression. Therefore, my opening statement about needing to alter the forks is quite correct - at least for my car and fuel pump set-up.

What I could really do with now is for someone to tell me the correct depth of fuel in the chamber so that I can calibrate my set-up, because at the moment I have to assume that when the needle is compressed against the spring it protrudes the same distance into the chamber as the fixed needle.

Steve
Steve Gyles

Steve,

It is the correct fuel level at the jet that is important.
The bowl level is just a means to set it.

I have attached some SU Manual information.

Mick

M F Anderson

Thanks Mick

Having thought about it, my first experiment was meaningless. So I tried a different tack.

Without touching the bend in the forks I measured what the fuel level, or rather the float height, should be when the fork was just in contact with the needle. I then measured the actual height of the float and it was 3.8mm higher than calculated. Therefore the sprung needle was compressed significantly until the fuel flow was completely shut off.

Steve
Steve Gyles

Sorry Mick I meant an indicated 110mph (hood up 103 with it down) - before the sat navs the revs were well into the red. The current speedo recently fitted is spot on with the old sat nav, but Mr Plod won't let us go that quick anymore...
Steve - from your description, surely the Facet pump must be stalling at too high a pressure compared to an SU - requiring the extra force to close the valve.
With the standard 7/16" lever setting and my SU, the fuel level can be seen just below the jets faces.(say 2mm) Tuning is just as you and the book describe - perfick!
Pete
P N Tipping

Pete

I am now totally convinced that the sprung valve is the issue. I guess it is up to the individual to notice the effects of this damped valve. Trawling the web I have come across a number of forum discussions on the topic, so I suspect it is more of an issue than many suspect. I have now compromised and set the fork at rest position to 9/16" and it has made the world of difference.

I had always assumed that my sprung valve was standard for the MGA, having no knowledge of the other. I had no idea that a solid valve existed. That is why I always set the fuel levels up as published.

It's brilliant now. All my previous ramblings on this forum about starting issues, choke, mpg, etc are out of the window. Delighted.

Steve
Steve Gyles

Steve, your problem has made me start to think about my carbs.
They are the same H4s on an MGB motor and from the same supplier. So probably they have the same float valves fitted too.

I have had occasional hot starting problems and symptoms of being over rich at low throttle openings. I recently decided to slightly weaken the mixture very slghtly to see if this would help the very lumpy tick-over but when I screwed up the jet screws by only 2 flats I discovered that on the front carb, the jet was then screwed fully up to the top!

So I think like you, I have some further investigations to do.

The strange thing is that a couple of months ago I took the car to be set up on a rolling road dyno and it ran really well, showing 106 bhp at the flywheel.
I suppose that this is checking out max power at full throttle openings and doesnt really do a lot to sort out the running at lower throttle levels.

I too have the Facet fuel pump fitted and I wonder if fitting a pressure regulator would make it easier on the float valves?

Colyn
Colyn Firth

Colyn

My car has always pulled well. It was the fact that I could never fine tune it by the book that niggled me. I have rebuilt and inspected the carbs so many times over the years but always took it as read that my carbs were totally standard and I tried to set them up accordingly. I am now wondering if this has had an impact on my MPG. Only once since I started my MPG spreadsheet in 2006 have I returned an MPG over 30 mpg. My normal figure on a tank load is between 21-25mpg. My average since 2006 is 24.14.

I have had a Fuel King regulator for the best part of 10 years. I need to read the books to check what pressure I am delivering to the carbs.

Steve
Steve Gyles

With a fuel pressure regulator you would need to find out the maximum pressure that the float chamber needle valves can cope with.
Too much fuel pressure would push the fuel past the valves and over fuel the carbs which would really mess up the mixture.

Can you get float valves with different pressure settings?
When I raced 2-stroke karts I used an Amal carb for which you could get low pressure valves for gravity fed fuel systems and higher pressure valves for pumped fuel systems.
I seem to recall that the fuel pressure regulator was set to 2.5 to 3 psi.

I will try to find out what fuel pressure you should run with SU H4s.

Colyn
Colyn Firth

Steve, now you've come up with another non standard fitment! Are you sure you need it, what's the efficacy of this little item?
J H Cole

John

Always had the Facet pump since the rebuild in 1997. the SU pump was beyond redemption when I got the car as a barn find. At the time, the local MG racer/rebuilder/supplier in Preston recommended the pump as being less troublesome than the SU (believed what I was told in those days). I fitted the regulator (as also recommended). The pump puts out between 6 - 7.5psi according to the blurb. The MGOC supplied me with regulator to suit the H4.

Steve
Steve Gyles

I see in the MGA Workshop Manual that the SU is a high pressure type and its 'output lift' should be 48", while its 'suction lift' should be 33". If that was with water 48" is only 1.7psi and 33" suction is 1.2psi. Added together (I assume this is correct) that's a total of only 2.9psi. If the SG of petrol is 0.7 that means the total is really only about 2psi..!
Any good?
Pete
P N Tipping

Pete,

The two lifts, suction and output, should not be added.
The suction lift is a test of the solenoid specification and the output lift is a test of the spring specification.
Fuel is drawn by the solenoid into a chamber and then is expelled by the spring.
Only the spring sets the pressure. A heavier spring will give a greater pressure.
The output lift is the pressure.
This is assuming that the valves are 100% efficient.

Mick
M F Anderson

Steve, I just found the info on fuel pressure on Barneys website (why do I never think to look on there first??)

The SU runs ok with fuel pressure between 1.5 and 3.5 psi with a recommended max of 4.5 psi. Anything over 5 psi will lift the float valves and flood the carbs.

If anyone fits a fuel pressure regulator, make sure that it has a big enough pipe diameter to flow enough fuel to feed the carbs.

So far I have not been able to find any information about using a manometer to set the fuel pressure but as soon as I do I will post it.

I used to use a combined fuel pressure/vacuum gauge to set my pressure regulator. in my racing days.

Colyn
Colyn Firth

Colyn

I have a pressure gauge that I fix to the delivery side of the regulator. The Filter King is supplied with a tapping for this purpose..

Steve
Steve Gyles

Mick - You're dead right, I was thinking about this after having written that last entry. That pump is divided into two entirely separate units. So that 48" of (petrol) lift for this SU equates to about 1.2psi? That's a pretty low pressure...
Pete
P N Tipping

"with the float arm resting on the needle plunger but not depressing it". What I thought.

Jim
AJ Mail

Jim

Absolutely. That is what this discussion has all basically been about and certainly what I have been doing all these last dozen years or so.

From what I can gather from all the responses the SU set-up instruction was originally written alongside the diagram back in the days of a fixed length needle valve. Subsequently, the sprung needle (variable length) was introduced but the instruction remained the same. This is where there has been some discussion in various forums.

My own practical experience with the sprung needle is that the float camber has continued to fill approx 3/16" from that "float arm resting" position. I presume this is caused by my pump pressure overriding the valve spring for about half its compression. This is despite my regulator controlling delivery pressure to 2.5 PSI which I understand is inside The H4 tolerances.

Steve
Steve Gyles

Have been fitting SU spring loaded needle valves since they came out, and setting float levels by the book. Always tunes fine. The spring loaded valve works as Barney said. Throw the damned pump and regulator away and fit the correct pump. SU or Facet or whatever - they all except SU come in 1.5-3.5 or so and 5-7 or so. You need the lower range. An SU "high pressure" pump is just higher than the "low pressure" one, but they are both in the "Low Pressure" range.

FRM
FR Millmore

FRM

Just checked my Facet, it is in fact the lower range 4 - 5.5 psi.

Question for you on how the sprung valve works as you have been working with them a long time. It seems to me that they are designed to slightly over fill. i.e. the spring will compress a bit against fuel pressure until an equilibrium is found. Is this correct? If the fuel always shuts off immediately the fork touches the sprung needle there would, in my mind, be no need for the spring. I understand from all the blurb that the design is to stop the needle sticking, but surely this can only happen if there is compression on the spring?

Steve
Steve Gyles

Steve - that spring surely is just to prevent the needle bouncing on the seat and over filling when there are road shocks or vibrations. The Twinkies float chambers originally flothed up which I think is why the rubber float chamber mountings were fitted, probably all part of sorting fuel level issues.
Is your 2.5psi a bit high? I agree you say its within the H4 spec but it appears to be double the HP SU's output pressure?
Pete
P N Tipping

Pete

But that's my whole point, the bumps in the road are either going to be positive or negative 'G', or assuming all that goes up has to come down, a combination of both in short order. For the spring compensated needle to ride those conditions without unduly affecting fuel flow/ fuel level it has to be balanced mid-range under normal smooth/at rest running conditions.

Steve
Steve Gyles

It is simpler than that. The spring seems pretty soft, but it is much stronger than the fuel pressure (because the shut-off orifice is so small). In normal running conditions the spring doesn't compress at all, as the fuel pressure is not enough to depress the spring. The spring only comes into effect with vibration and jiggling of the float, in which case the spring allows the float arm to jiggle without disturbing the shut-off plunger on the top end. Otherwise the spring loaded pin works same as a solid pin.

I just pulled two spring loaded fuel shut-off valves out of inventory. One has square nylon plunger with stainless steel tip and spring loaded tail pin. The other has stainless steel plunger and rubber (Viton) tip with spring loaded tail pin. I measured the bore of the shut-off orifice with pin gauges (drill bits). Both jets have 3/32 (0.094")inch diameter orifice.

(0.094/2)^2 x pi = 0.007 sq-in orifice

With 5 psi fuel pressure,
5 psi x 0.007 in^2 = 0.035 pounds force.
0.035 x 16 = 0.56 ounces force
0.035 x 454 = 15.9 gm force

My digital letter scale says the spring force is 25 grams initial and 35 grams at fill stroke of the spring loaded tail pin, same for both models. There is no way that fuel pressure can compress these springs until it hits 8 to 10 psi pressure (unless assisted by some strange vibrations and harmonic frequencies).
Barney Gaylord

Barney

You have missed one major point. The positioning of the valve on the lever arm allows the fork to exert a greater force on the spring than your measured force. This is borne out by my chambers filling to a semi compressed spring height.

Steve
Steve Gyles

Ignore my last. Too early in the morning. I was thinking that that the extra pressure would open the valve. Of course it provides greater pressure to close it. Nevertheless the fact that my chambers fill beyond the at rest position remains fact. And no, they do not appear worn. Wish I could get to the bottom of this because my car is now running better and the carbs tune up likewise since altering the fork height.

Steve
Steve Gyles

Stripped the carbs again. Inspected everything and made absolutely certain that the forks are absolutely true with no bends in wrong places etc. Front one still fills to 3/32" above the closed position and the rear one to 1/8" above the closed position. Valve hole as per Barney's measurement. My springs are stronger than Barney's. At rest 50g and compressed 80g.

Next step is to recheck my regulator pressure. Unfortunately my gauge is out on loan and I won't get it back for another day or so.

Steve
Steve Gyles

I'm right there with you Barney. Have you got an old SU to try out Steve to test what happens at the designed pressure? You certainly have something strange there mate. In my experience there's nothing wrong with these electronic SU's; mine came with the car and it has not missed a beat since I got it in 1997.
Pete
P N Tipping

Pete

It is frustrating me. Everything looks absolutely tickety boo! But the fact is that the carbs will only tune up correctly as per the book once I lower the float levels a tadge. Nevertheless, the car has always run well. The Facet has never skipped a beat either! I will report back once I have checked the regulator output pressure again. I am pretty sure it was set at 2.5 PSI. If so,I will try lowering it to 1.5 psi and see what happens.

Steve
Steve Gyles

Steve, are you sure your carbs are correct for the 1800 engine? Surely the carb set-up should be the same as the MGB with regard to choke, jet size, throttle needle type and spring colour code? Also wear on the jets caused by them not being correctly centred would give a rich mixture.
When I overhauled my carbs I replaced the jets, needles and springs just to be sure I had the correct unworn items and it made a world of difference.
Lindsay.
Lindsay Sampford

Steve-
Sorry, been busy, not paying attention. As Barney says. Note that the WSM do not give pressures, rather delivery head at 4 ft. That would be somewhat less than 2 psi, so your pump is out of range. However, I've had plenty of cars running 5 psi pumps without problem, as you might predict from Barney math.
I think you are using H4? If so, it is possible that you have a scrambled float bowl mounting, which might alter the height of the actual bowls relative to the jet. There were two systems of mounting, and you need all the matching pieces for it to come out correctly. Bowls are the same, but: One uses a banjo bolt and grommets and a steel washer; the other is a hollow stud/nut with grommets and different washers. And there are older forms with flat fibre washers - I've seen all sorts of goofy combinations of these parts.

FRM
FR Millmore

Thanks FRM. Yes, H4. The blurb I have read about fuel height refers to the fuel level relative to the height of the jet in the main body. During this last week I have felt that a more suitable guideline would be the height of the fuel (with float in place) inside the chamber as this is far easier to measure. But I accept of course that this could be meaningless in the light of what you say. I will check the banjo arrangement today and report back. However, I do recall replacing the grommets and washers to no effect.

Referring to Lindsay's questions. Yes the jet needles are spot-on. Regards the correct set-up for the 1800, I asked the very same question when I installed the 1800 and was advised that there was no need to change any of the hardware in the first instance. Just retune as normal and, only then, if problems were experienced to experiment with other needles etc. So, in summary, it is bog standard MGA H4 hardware, but I have always had that problem of not being able to do that extra fine tuning (1/32" pin lift momentary acceleration) on both the 1500 and then the 1800.

I spoke with Bob West yesterday but he offered nothing exciting other than confirming that delivery pressure should be very low, down at 1.5psi. But he did suggest that once I had identified the problem to replace the float with the latest version that does not get attacked by fuel and also to replace my float valves with the viton tipped version - mine have what looks like brass tips.

I am coming to the conclusion that the likely issue is the fuel pressure. Can't wait to get my gauge back to check this one out.

Steve
Steve Gyles

Eureka. Or to quote her indoors: "It's only taken you 14 years of the chat room to sort that one out!".

The regulator was set at 3 PSI. I lowered it to 1.5 PSI; reset the float forks to 7/16"; did my measurements of fuel levels in the chambers and they balanced out instead of the previous 1/8" overfill; fired her up; and she tuned up perfectly as per the book.

So, it would seem that the H4 likes 1.5 PSI and no more.

Pity we are currently suffering the back end of the recent typhoon from across the pond. Proper road test will have to wait, but all looks good.

Sorry if I have rambled on for the past week, but for me it has been all worth while with all the inputs received. May be a few lessons and information has come out of it for the benefit of others.

Cheers

Steve
Steve Gyles

Thats good to hear Steve

I had a feeling it was a fuel pressure issue and I am now even more determined to check fuel pressure that my Facet pump is delivering.

I am fairly certain that my un-regulated pump will be pumping out much more than 1.5 psi and I will start to look around for a fuel pressure regulator.

Colyn
Colyn Firth

Steve,
Highly delighted it is now sorted. I have followed the thread with interest, though never had anything worthwhile to chip in with!
Graham M V

Colyn

If I had known years ago what I have learned this week I would have bought an SU pump rather than a regulator. The cost difference is not that much. The Facet has been superbly reliable but I was not aware of the pressure issues.

I might get my derelict SU out of the junk box and see if anything can be done.

Steve
Steve Gyles

Well done Steve,

I would like to mirror Graham's comments, a very interesting thread and a good result in the end. I admire and appreciate your persistence in this, as in all things MGA. I have learned an enormous amount through these forums.
N McGurk

What was nice about this long thread is that it came to a positive conclusion. So many threads for a number of reasons just 'peter out'
J H Cole

Hi Steve , I'll add my thanks for your thorough research. Like Graham I have read with interest all the posts ,but not joined in as I have no experience with "fiddling" with carbs. Good to note that the good old SU pump comes out well from all of this - confirming my choice to replace mine with the standard one a few years ago - and recommending fellow club members to do the same - even when the Facet had been recommended by others.
Interesting that Bob West recommends changing to an "ethanol resistant" float too. Will have to consider that when I next clean mine out - sometime over the winter. cheers Cam
Cam Cunningham

If the SU pump has poor contacts or a stiff diaphragm, it is relatively easy to repair.

If the coil is damaged, it's toast.

I would recommend the electronic mod. which is very very reliable and not too expensive.
dominic clancy

Go on Steve, get out there mate with your tuned-up carbs, your blower at the ready, deflector correctly set and a Shelley in the boot and enjoy the MGA'ing...
Pete(r Out)
P N Tipping

Thanks all. Road test fine. Feels smoother at lower revs, otherwise identical performance.

Dominic. I will look at the SU pump next week. I need to give you all a break! The pump was in a corner of a foreign field that is for ever England for 22 years and has been in my junk box for 16 years.

Now to celebrate my birthday. Cheers.

Steve
Steve Gyles

Why is everybody talking about "fuel resistant" floats etc?? I've never seen an H4 with anything but brass floats, and never had a problem with one. HS4 have plastic (nylon) floats, but again no problems. HIF are another story entirely.

H4 series are slightly different internally to HS4. The closest H4 MGA application to HS4 MGB is the 1622 MKII, and I use that setup as a start point, usually is about perfect.

FRM
FR Millmore

The H4 floats are brass with solder which are both attacked by ethanol. At 5% it is OK, but more vulnerable as the percentage rises. Using 5% ethanol I found the bottom half of the floats were a differnt colour to the dry(?) top half, so there is some corrosion even at this level. At 10% they will need changing as will the seals, jets, needles, tank, sender unit and perhaps carb bodies too? Appreciate you guys in the states have a start on us and maybe in practice there isn't so much of a problem, we can only go on the facts over here.
Pete
P N Tipping

Pete-
We have had ethanol to/near/at 10% for almost 35 years now, and now it is all you can get most places. It has not proved to be a problem, other than increased fuel consumption. Such problems as I have had were in the late 80s, and went away by the early 90s, so they were clearly some other ingredient in the fuel. Have not had to replace any of that stuff, for any reason that could by blamed on ethanol. Possibly old fuel hoses, but they deteriorate with age anyway. I observed the same colour changes in floats, solder corrosion, etc. long before ethanol - I think it has more to do with free water, or old oxidised fuel; it is arguable that having the water in solution as with ethanol, may actually reduce these things.
Your "facts" are bogus.

FRM
FR Millmore

I've been dealing with 10% gasohol for about 20 years and 200,00 miles on mg MGA. It is the only fuel available in the Chicago area. I have never had any problems with metal parts in the fuel system, still running the factory issue floats, throttle bodies, fuel sender unit, etc.

Rubber parts in the fuel system will deteriorate. Change the float bowl grommets to Viton material. You can use Teflon O-rings for the jet seals. Install Teflon lined fuel hoses at the carburetors (mine have been in service for 26 years now). Any other standard type hoses used in the fuel system need to be changed at 10 year intervals (possibly more often depending on quality of the hoses.

Modern fuel will likely attack the diaphragm in the SU fuel pump. Modern replacement parts might be more fuel resistant (maybe). My Airtex type electronic fuel pump seems to be maintenance free indefinitely. I have changed it at about 10 year 100,000 mile intervals as periodic maintenance when it looks rusty on the outside and needs new hoses. I recently saw one fail on someone else's car, but that pump had the appearance of being very old (and a slightly different shell style that I had never seen before).
Barney Gaylord

This thread was discussed between 17/09/2012 and 28/09/2012

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