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MG Midget and Sprite Technical - HIF 44 woe!

Chaps

Fitting the HIF 44 in accordance with Chris' intruction off the web, I have had a bit of bother getting the car running smoothly and with seemingly no effect at all from the choke on cold.

The carb itself is an EBay purchase - caveat emptor rears its ugly head for sure - stamped 1982 on the float body, and the only departure from seemingly an otherwise standard carb is to have swapped out the original BFZ needle for the recommended BDL.

The breather connection goes to crankcase filter, vac addvance to the central nipple on the carb near the butterfly, all other manifold ports blocked off. Fuel flow is fine.

Head is modified, larger valves, higher compression.

Issues are

Car simply will not start - despite strong starter. Use of choke appears to have nil effect. The only way I can get it to start is raise the dashpot piston by about half inch with a bit of tube stuck into the inlet.

When running, it appears very rich. Of course, I adjusted the mix as per the SU manual. Some advantageous effect, but it does not run at all smoothly.

Questions then before I take the carb all apart for a damn good thrashing, and lose some vital part.....

Will the change of needle be responsible for the effects noted. Is it worth trying the original BFZ needle?

Copious amounts of carb cleaner have not helped. Thus on the basis that choke has little ffect, and if stuck, I guess it could foul things up, would the choke mechanism be a good place to start.

Why does it only start with the dashpot piston raised? Is this indicative of an underlying problem?

Is a 1982 HIF 44 suitable? Seems OK on the surface.....


Many thanks as always.....






Mark O

If it's running rich (check your plugs after one of your starting attempts) it could be the choke. After standing for a year or two the seals on my choke mechanism were shot and caused flooding.

Have you serviced the carb with one of the kits you can get? A good idea if you've got an unknown carb.

What filter are you using? When I fitted one to a mildly tuned car it ran straight away with a BDL and K&N filter. On the road it ran weak so I filed the needle to richen it up. Just needed another tweek with a file when Peter B set it up on the rolling road. I think the BDL should be on the weak side rather than rich.

The 1982 carb should be fine, especially if it's off a Mini or Metro.
John Payne

Another thought - have you got a filter fitted while testing it? I don't think mine would run without a filter fitted.
John Payne

John

Many thanks for the reply. Brand new K&N cone filter currently off - for initial tuning purposes. Cannot believe it makes that much difference surely! ...will try again with it fitted anyways...

Take your point about the choke seals and will check them. Allegedly it was serviced on Ebay description, but depends what one means by serviced of course.

Another thought was float height - which I will check out.


Must be something obvious other than mix setting. SU Carbs are not that complex ---apparently!
Mark O

Another thought was filter back plate. I'm not 100% sure but I think there are a couple of holes on the face of the carb (where the filter bolts to it) that should match up to holes on the filter back plate. There are two other holes that I think should be covered as well. Not sure on that though - anyone else know?
John Payne

Good thought about the two extra holes in the filter that must match up with holes in the carb flange. Also it is worth upending the carb and taking off the bottom of the float chamber. You can then see if the choke mechanism is working. There is a sort of fork that pulls the jet down when you twiddle the adjustmnent screw. See if it works too.
Mike Howlett

Mark, I've had a couple of HIF6's apart and they're not that difficult to strip, clean and rebuild. Get a rebuild kit and follow the instructions carefully.

But before you do...
it sounds like your choke isn't working at all and lifting the piston simulates a rich mixture to allow the car to start.
Daft questions first, when you pull the choke cable does the mechanism rotate as expected and does the cam open the throttle slightly (fast idle screw should run against the cam).
You can't really do any more to check the choke system without stripping the bottom end of the carb. When you do, squirt carb cleaner through the choke feed hole in the float chamber and, with the choke in the fully on position, you should see it come out of the other end which (IIRC) is a small hole on the engine side of the butterfly. If you don't get cleaner through it's a full strip down. Easy enough with the kit just be careful to note the orientation of the choke spindle and body when you remove them. You will need new seals and paper washers to put it all back together again.
My knowledge of needle selection isn't great but if the car runs rich once the engine is warm, I'd check the float height is correct and the mixture adjusting screw is actually moving the jet. This can be done by simply removing the dashpot and observing the jet while turning the screw. After that you need to speak to someone with a similar spec car, more knowledgeable and/or possibly a RR session.

Best of...

MGmike
M McAndrew

Mark,

The BDL is a good starting point and will not be the reason it won't run. I understand it was the MG Metro needle.

I recently fitted a HIF6 with a BDL and after the Aldon r/r session I'm now running with a BDK which is a bit richer from mid to full throttle (1293 road cam).
richard boobier

Gents


All useful info which I will follow. Many thanks

Mark
Mark O

Chaps

Bit confused by this hole thing mentioned. The two holes for the bolts affixing back plate of filter to carb inlet face, will of course be blocked off.

Is the suggestion the other two should be open also -even when filter back plate is on?

Ta

Mark

Mark O

Yes, the back plate should be drilled to match the position of the other two holes (air holes, not bolt holes)
Guy W

Thanks Guy...I was fiddling about with the filter off, but back plate on...and I think these holes are blocked by the plate/gasket. I'll get the drill out thren....Do you believe the consequence of them being blocked explains my woes?
Mark O

Should have added:
When you open the butterfly on an SU the manifold depression lifts the piston in the dashpot, which in turn lifts the needle and opens the choke (venturi tube) But as the piston rises against the spring the space below the piston itself needs to be able to draw air in from outside, otherwise it will be working against a vacuum here. The two extra holes on the flange that the air filter bolts to need to be clear to allow air into the void created below the piston as it rises. If they are blocked the engine will still run, after a fashion, but acceleration is sluggish and the engine quickly reaches a flat spot as the choke and fuel jet won't open fully
Guy W

Thats right, on one of the ones I did the filter was maybe for a HS series carb and the backplate didn't have the holes. I remember having to drill them out or elongate some that didn't line up. If you still have the airbox adaptor (casting that bolts onto the back of the carb for the standard filter) you will see it leaves the other two holes open.
John Payne

The magnificence of explanation continues to impress.. We are not worthy.....
Mark O

Mark,
Sorry to hear you are having problems. Have you got a little valve on the butterfly? Is it leaking? I soldered mine up until I got a new butterfly. Just a thought. Note that the choke mechanism is different to the ones you took off and the O ring seals may be shot. Any slop in the throttle spindle?

Just my 2p worth.
Steve Church

I bet its the blocked holes.
Mike Howlett

Mike, I agree that having the holes covered will cause a rich mixture when running but can't see how it would prevent it starting. Perhaps two faults? We'll be waiting with bated breath for an update :0)

MGmike
M McAndrew

...and the update is....I had a look last night, and lo, the two air holes mentioned are free and open - Holes in both gasket and filter backplate to accomodate. So after a moment's deep sorrow, yours truly decided to remove the backplate and gasket....and lo, another third air hole in the inlet face of the carb, to the right and down a little of the right hand original air hole mentioned.

This was clearly being bloked by gasket and plate - so a bit of work on pillar drill and snips opened it up....turn of the key, and blinking marvellous. Brief fiddle with idle and mix, and a superb sounding engine which hardly needs any choke. Can't wait for the snow and ice to disappear so I can test in anger......

Again, many thanks to all for pointing me in the right direction.....
Mark O

Excellent news! Welcome to better economy, better running and less tune ups!
John Payne

I'd recommend fitting a stub stack inside the filter if not already done so:

http://www.med-engineering.co.uk/catalogue/ancillaries/med-stub-stacks

John Payne

John - Thanks, and yes I had thought about a stub stack, but is there a measurable advantage in fitting one?
Mark O

I'm sure it would be measurable on a rolling road but maybe not driving. I'm sure when I fitted one to a mildly tuned car it seemed to rev better but that could just have been the 'I've just spent some money so it MUST be faster' factor!!

I keep meaning to upgrade mine to this set up from MED:

http://www.med-engineering.co.uk/catalogue/ancillaries/med-hif-44-stub-stack-system

I've got the larger pancake K&N on mine which I think is better than the cone type but that ITG one looks like it would be very good. Looks a bit modern though.
John Payne

Mark O
Great news that you finally got there.

Anybody know what the third hole is? I've not come across that before and it does not exist on my HI44.

Chris
Chris H (1970 Midget 1275)

I took my car to Peter Burgess for some tests with different thickness insulator blocks between my HIF44 and the manifold, to theoretically lengthen the inlet tract. During the course of the tests Peter removed the stub stack that I had fitted and there was no difference at all on the rolling road read out. Also, not much difference whichever thickness of insulator was used.
Vizard however, has charts in his book that indicate stubb stacks do improve performance. Maybe they work better on larger capacity tweaked engines

Bernie.
b higginson

Chris, Yes its very odd that Mark's HIF should have 3 breather holes. I have only ever come across the two that provide the vacuum balancing function that I described. In fact I don't think I have seen any H series carb with anything other than the two breather holes and two air filter bolt holes.

The normal gaskets are usually made with 4 holes. But inadvertently putting the gasket on upside down and blocking those holes must be a common mistake as they also make gaskets with 6 holes so that they are fully reversible without causing a blockage.
Guy W

I think a lot (not all) of tuning up twin carbs is because the carbs are worn or is unnecessary fiddly with them

get the car fully serviced, set up the rebuilt/reconned carbs and leave them alone, sure whenever you set them won't be exactly spot on totally right for all conditions but that's carbs for you

stop fiddling with with your bits, I mean carbs !
Nigel Atkins

I have a deep K&N round filter with a short (about 30mm) ram pipe within on my HIF6.

Similar to this link

http://www.pipercross.net/competition/products_rampipes.asp
richard boobier

The 1.3 (1275) Maestro had an unusual reverse flow over the top of the engine intake tract because the engine fitted "backwards" when the VW Golf Type gearbox was fitted on production cars. The carb is fitted to the "wrong" side of the manifold because of this.

Part/spec number for the Maestro carb is FZX 1428.

I wonder if the "third hole" is a legacy from that particular type of SU HIF?

Anyway, whichever it is good news that now you have a fun car to drive that will be sure to give good economy and rather decent running too.


(well mine does) :-)
Bill1

Nigel
your quote " carbs are worn or is unnecessary fiddly with them get the car fully serviced, set up the rebuilt/reconned carbs and leave them alone "
That's fine if you have a service centre that understands 'old' cars and service and set them up correctly.
Most mechanics these days plug a pc in to the ecu and it tells them what to replace. Hence a large number of 'modern' technicians wouldn't know an SU carb if it bit them on the #rse.
Most people decide to fettle their carbs to keep the car running as it should because moving parts wear in time and need adjustments to maintain efficency & performance, or the engine has been modified which effects the mixture required.
The other reason is why pay someone else when you can fix it yourself, especially if you have limited funds. But if you can afford it and don't like getting your hands dirty then your method is fine its just not for everyone.
Ed
Ed H

Related to the last comment (modern mechanic services) - I'm often asked (e.g. at MoT time) "when was the car last serviced?". When I say "it's serviced on a continuous basis" they can't get their heads round that and keep asking. I generally end up saying "about 3 months and 750 miles ago" just to keep them happy.
Chris H (1970 Midget 1275)

There was a thread running on the MGA section where stub stacks were made by one contributor and rolling road tested by another. The stacks were then optimised to give a small increase on the larger MGA engine. Several batches were made due to demand at £25 a set for HS4 carbs.
Alan
Alan Anstead

Chaps

To satisfy your curiosity, image of a similar carb with the third air hole previously mentioned....This must be kept open.. It is the obvious extra hole on the right hand side - without a corresponding one on the left.


Mark O

Mark, the question we would like answering is "where does it go"? any chance you could poke around and find out?

MGmike
M McAndrew

I have a carb that I intended fitting that has the extra hole, but its off a metro turbo. My carb also has the groove machined around the neck of the dashpot, which I'm told is a distinguishing mark for a turbo HIF. The sealing O ring is present, but of course you can't see that without taking the dashpot off. There's no ident tag.

Mark
M Crossley

Ed,
resetting the carbs after changes isn't unnecessary fiddling I was thinking of getting the car properly serviced and carbs properly set up and then leaving them alone unless really required, I did allow for worn carbs but if the carbs or any other parts or components are that badly worn then they need repairing

in the same way that classic cars don't have to be slow, poor handling and unreliable their twin carbs don't have to need constant fiddling with

if you keep fiddling with them they will drop off !! :)
Nigel Atkins

Nigel

I thought the old saying was "If it ain't broke fix it " or have I got that wrong ............?

Ed ;-)
Ed H

If it ain't broke - fix it until it is !

R.
richard boobier

Nigel, I hesitate to agree with you on this but I agree! And would you now it, I might even refer to the owners manual ;0) Carb's should only need checking every major service and if you need to keep fiddling with them to get the best out of the csr.... something else is wrong!!!! Carb's (su's) rarely go out of tune and should be the last thing adjusted. Fix the ignition, timing, tappets and everything else before adjusting the (standard) carb's.

Ed, I also agree it's hard to find a workshop who understand our old cars. I recently had occasion to "borrow" set of feeler gauges from a young mechanic only to be presented with "wot's one of them like? Never used them, never bought them...." So, you pick your workshop carefully and if the starting position is "I think you Carb's running rich" ... walk away.

best of

MGmike
M McAndrew

Nigel, mine never did, and I've been fiddling with them ever since I got 'em.

Mind you, I'm careful in the cold weather. :)
Lawrence Slater

Hole layout on the inlet flange gasket from the Burlen website:

http://www.sucarb.co.uk/ProductDetail.aspx?Id=27408

HTH


Doug Plumb

This thread was discussed between 11/12/2012 and 16/12/2012

MG Midget and Sprite Technical index

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