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MG MGA - Ethonol and SU carbs

Hi I 've had a problem with needle valve seating and flooding on my SU carbs. When I inspected the float chamber there are deposits of salts. I'm assuming this is corrosion of the alloy from the water in modern unleaded petrol. Also the float arm is starting to corrode.

Does anyone else have this problem ? Is it worth draining the petrol tank over winter ? should I run it more often over winter ?

Any solution to this ( no pun intended) Thanks
DJ Joy

More likely to be muck out of your tank, rust being one of them. If your tank is low over winter, condensation can form and that leads to rust. The solution to your problem is, fit a fuel filter between the tank and your fuel pump. This will stop rust particles from playing havoc with your fuel pump and float chamber valves, and keep your fuel tank filled to the brim over winter.
Lindsay Sampford

It's not the ethanol. Ethanol actually prevents free water accumulation.
Art Pearse

There should not be a filter between the fuel pump and tank.
If the filter becomes clogged then the pump will try to pump until it burns itself out.
You can install the filer after the fuel pump and if the filter becomes clogged the pump will stop as normal.
S Sanders

Oh wrong again, I give up!
Lindsay Sampford

DJ - see the article, Float Lever Drop Adjustment in the Other Tech Articles section of my Homepage, at: If the float lever is allowed to drop to far, it will jam against the float and will not shut off the flow of fuel.

Lindsay - "The solution to your problem is, fit a fuel filter between the tank and your fuel pump." Sandy is correct, If a filter between the fuel tank and pump clogs sufficiently that fuel cannot be pulled through the filter, the pump (if it is a SU pump) will stall in a current on condition. Usually this results in the swamping resistor (that is in parallel with the pumps coil) will burn out, resulting in excessive arching across the points and will burn the points contacts to the extent that the pump will no longer work reliably (this is also covered in my Homepage, linked above). Cheers - Dave

DW DuBois

I see the point that Sandy and Dave are making but in reality, how long would you actually have to leave the fuel pump running in its "stalled" state to burn out the resistor and the points?

I would have thought that most owners would notice the engine wasn't running, switch off the ignition and look for the problem. (Probably in the ignition system😁.)

I admit to running a Facet solid-state pump (which has a built in fuel filter) and an aftermarket in-line fuel filter which is fitted between the fuel tank and the pump.
It is one of those glass tube designs and you can usually see if there is dirt in there at a glance.
I has worked fine for over 10 years, I check it out and clean it every year and don't see any need to re site it after the pump.

Colyn Firth

I've been told that the Super premium fuel available at various petrol stations under different names ( Ultimate etc.) not only has a higher octane rating (97 to 99) but seems to have lower ethanol content - I've started using it and the engine seems to run better.
Cam Cunningham

Cam, higher octane makes for a slower more even burn. This eliminates 'ping'.

Everyone remember "No Knock"?

DJ A thread on this site earlier this year about Engine temperatures gave this link

Some interesting information here about Ethanol & corrosion seen in the float chambers.

I notice that my float chambers are not at the same electrical potential as the rest of the car. Im no expert but could it be that we are beginning to see some form of electrolytic action taking place between two metals at a different potential separated by a better electrolyte (ethanol fuel)!

R A Evans

Colyn - "how long would you actually have to leave the fuel pump running in its "stalled" state to burn out the resistor and the points?"

Judging from the chard remains of the damping resistor on the coils that I have observed, I would suspect that some leave the ignition on quite a long time while trying to troubleshoot the problem (the resistor is a very fine resistance wire wrapped around a fiber card soldered to the ends of the coil). The only indication that the swamping resistor is burned, is the accelerated pitting of the points. Without the swamping resistor and even with the various devices used to reduce the arching at the points, I have seen the voltage spike across the coil when the points open go as high as 500 volts (think of the ignition coil).
D.W. DuBois

Local Weber specialist told me ethanol fuels cause corrosion of the solder joints on the floats over time. A lot more solder joints on weber floats but something to bear in mind
Mike Ellsmore

Spraying carb cleaner on dry aluminum and then not rinsing it off with gasoline or the like will cause a formation of whitish salts.
J MacDonald

Thanks for the replies , what is the best filter to fit ?.

I believe you can get a float valve that has a ball bearing and spring rather than a needle valve , has any one tried this ?
DJ Joy

You have opened the flood gates now DJ (pun intended)😊.

Lots of divided opinions on the use of Gross Jets instead of needle valves in SUS.
Some swear by them and others prefer the needle valves.
Probably, whichever you choose, just buy the best quality you can get and fit a fuel filter to keep any dirt from jamming them open.

My needle valves worked pretty well most of the time and so I never felt the need to try Gross jets.
Colyn Firth

Every grose jet I have seen has been faulty - my recommendation is to use the viton tipped version of the standard needle valve.
Chris at Octarine Services

Sorry DJ I forgot to answer your fuel filter question.

I use a transparent glass filter made by Sytec, it is very effective, really easy to dismantle for cleaning and pretty low cost too. I think they are about 7.00 on-line.
See Demon Tweeks link below.

They come in different fuel pipe diameters too and I would choose one which has an INTERNAL diameter at least the same size as your fuel pipe which continues on to the carbs.

Otherwise you are introducing a restriction into your fuel line which may possibly cause fuel starvation at high revs.
(The filters come in 6-8- and 10mm internal diameter)

Chris at Octarine Services is one of the leading experts in the country on tuning the B-Series engine, so I would take his advice on not fitting Grose Jets (I spelled it correctly this time Chris! but maybe "Gross" is a more suitable spelling! :-)


PS if the link above doesnt work, cut and paste it into your search engine.
Colyn Firth

The PO of my car fitted the Grose jets - I have now had the car for 14 years and they still seem ok.
Cam Cunningham

I suffered frequent sticking of the needle valve. I fitted Grose valves and have had no recurrence in 7 years.

I know that Burlen now make unsinkable floats to overcome the failure of the Brass floats due to Ethanol attack of the solder joint.

Colin Manley

I don't have any additional filter and fitted Grose Valves at least 10 years and no problems with sticking valves since. All UK driving though.

I did have a float fail a couple of years back and I suspected ethanol but people on here said they have always failed occassionally.

Paul Dean

Grose jets for 15 years. Faultless!
B Mayo

Perhaps I only see cars when they are giving problems - certainly I don't open up the float chambers on a routine service.

In every case the problem has been dirt in the jet causing it to stay open - sometimes it can be cleared sometimes not or it resticks again soon after.

Part of the problem is that you cannot disassemble the grose jet to clean it whereas the viton tipped valves are self cleaning and if you do get a bit of rubber from the fuel line lodged in there you can clear it.

Give me "serviceable" over "replace" when anything goes wrong!
Chris at Octarine Services

Running Gross Jets 300,000 miles or so since 1989, no problem, and they will likely last forever. The fuel has to be clean. Also avoid "Gross type jets" made by other manufacturers (since the patent ran out). Those are often shoddy workmanship and faulty parts.

Been running groese jets 6 months and never a hitch. Any time dirty fuel is run through the system you can expect those valves to potentially have a problem, no matter what brand or style of manufacture.. The fuel tank has a filter for outgoing fuel, and the SU pump has a finer screen on the intake side and if either of those get clogged they will also burn up the pump. Don;t see the big deal about no filter before the pump as long as you have a tank that is not rusting out, and you check the added filter often enough to not let it dirty solid.
J MacDonald

Thanks , I'll think I'll try putting a inline filter on the bulk head and see if it cures the problem thanks again
DJ Joy

I have had grose jets fitted for the last 5 or 6 years, and never had an issue with the carbs. Just make sure the fuel tank is free from debris of any kind. Once I tried the viton tipped needles, but experienced fuel overflow leakage very soon after. I'm all for grose jets now.

F. Camilleri

The people who bad mouth grose jets seem to have an agenda, and usually let people tell their good experiences with them and then jump in and say only the original old groseys made 5 or more years ago are any good and the new ones are junk. Think is they always say the groseys get clogged up and stick, when in fact the original needle style are much more prone to getting things stuck in there than the ball type grose jets. So I am happy to see several people who have got them recently see them working just fine.
J MacDonald

I kind of had a feeling that DJs question would bring the RSPCGJ faction to the fore! (Royal Society for Prevention of Cruelty to Grose Jets") :-)

It does seem though that the response this time is much more pro than con though and I suppose that is a good thing.

Sorry if everyone thought that I had a bad opinion of Grose jets but in truth I have never tried them on my previous SUs and so I dont really have an opinion.

My present carb is a Weber 45 DCOE and I must admit that I am not certain if its float chamber level is controlled needle jets or Grose Jets. I will dig out the exploded diagram and have a look.

Colyn Firth

Nothing wrong with liking the original SU style components. Either work well when things are not rotting out of the tank and getting clogged in there.

Thing is there are fake grose jets available, just like there have been fake SU needle valves I have seen over the years. Not the sort of thing to buy off ebay unless it is a reputable peddler? I recall a time or two over the years where SU was selling needles made of a plastic material for their body, and also (experimental I guess) needles and seats of a design that looked overly complex, yet cheap. It is the penny saving ideas to watch out for in either design, which often you can spot with the eye.

J MacDonald

All the SU-fitted MGs we have owned have had a small plastic fuel filter in the engine bay. I know the MGB filters were factory fitted. Many MGA owners have followed suit. The OE brass needle valves do eventually wear and the viton tipped replacements seem to last well. The UK ethanol based fuel does melt the earlier types of hose and we all need to up-grade and the same goes for the floats. Burlens new stay-up range has been ethanol proofed. Many owners have cars sitting around through the Winter when water can condense. In the past, I have seen the effect on the V8's injectors. The advice given me has been to use 97 "super" (without ethanol)in UK and all three cars run only on it. And.....popular anecdotal evidence suggests we should only buy fuel from the oil companies.
Roger Walker

This thread was discussed between 23/04/2017 and 30/04/2017

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