18 replies to this topic

[Jay92]

Hi all,
Any suggestions on a HIF 44 1275 1992 mini (carb conversion)
Can’t keep the engine running unless it’s warm and set crazy rich at 12% CO (even then it bogs out and cuts out when little throttle). If set around 2.5% /3.5% with warm engine then engine is revved and left to settle the mixture goes to 0.5% and cuts out. I recently put the standard air box with k&n and drilled holes instead of a cone filter . Set timing with strobe light and changed the dash pot oil from what looks like ATF to 20/50 but still no difference, spark plugs changed to BP6ES and gapped correctly. Su rebuild kit is on the way to try this week.
Cheers

[alpder]

On mine, my troubles - running far too rich - were the starter ('choke') seals leaking fuel and permanently enriching it. Trying to set mixture was a complete headscratcher until it was fixed.

 

It's also worth looking for air leaks into the manifold, from the usual places including servo if you have one.

[68+86auto]

Check that the piston always returns correctly. I have seen one that wouldn't fully return in certain situations. It felt fine but showed up on an exhaust gas analyser.

 

Do you have the readings from the other three gasses?

 

Can you post some photos of the engine bay?

[Jay92]

Thanks, I’ve checked for vacuum leaks and blocked off the servo but still no joy, the choke seal is in that rebuild kit so will give that a go.
I’ve cleaned the piston and it returns fairly smoothly when not running.

[Jay92]

Sorry can’t seem to load picture as file is to big

[andyapanel]

Have you tried returning the car to the state where it was running?

I think a K+N in a drilled airbag will improve the fuelling; the old air filter set up you describe usually leans out the fuel mixture. Maybe the carb had been set to compensate for the extra air.

 

Do you have a Haynes to set the idle speed?

 

Good luck with the rebuild.

[Jay92]

Engine picture

Attached Files

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[Jay92]

I set the idle speed when I managed to get it to idle and adjusted the air/fuel mix to get to the 2.5/3 % co (lambda around 950/1000) but as soon as it’s revved up and allowed to idle again the co is goes to0.5% and the really lean mix causes it to idle really rough and cut out. Should the carb piston drop completely down as soon as the revs are dropped off ? (I’m wondering if it’s sticking somewhere on the return back down even though by hand it returns smoothly by itself)

Edited by Jay92, 22 June 2026 - 01:42 PM.

[Ethel]

If I've read it correctly and you have to set it rich to get it to run I'd suspect there's an air leak that reduces as the manifold vacuum decreases - crankcase breather & throttle spindle seals/bushes being prime suspects.

Float chamber venting, piston communication ports, spring & damping also possibilities.




...Saw the piccy so adding brake servo to the possible air leak list.

[Jay92]

That does make sense, il check them out. Will keep you posted.
I have had that stripped down as the brake pedal was sticking down intermittently, maybe I’ve fixed a fault and created one. Il get the smoke tester out.
Thanks for your help

Edited by Jay92, 22 June 2026 - 02:25 PM.

[Jay92]

Thanks for all your help, it was a blocked float valve vent pipe/over flow pipe from the side of the carb (thanks Ethel great suggestion) unblocked and running at 2.5/3%. Might be able to make a couple of mini meets this weekend now.
Cheers 👍🏻

[68+86auto]

I just came across someone on FB who doesn't understand that restricting the vent with a filter is a bad idea. Apparently a filter looks nice.

[Jay92]

😆 some just don’t listen to advice.
My first job was getting rid of the small filters on the breather pipes and getting a standard air filter housing for it

[68+86auto]

some just don’t listen to advice.
My first job was getting rid of the small filters on the breather pipes and getting a standard air filter housing for it

 

It was connected to the overflow/vent fitting on the carb. Made no sense and would easily cause issues even if it appears to run fine to the typical owner.

 

It is good that you understand how the breather system should be connected. Most seem to have no clue, even "mechanics".

Edited by 68+86auto, 23 June 2026 - 11:08 PM.

[Jay92]

After a bit more advice if possible, thought I’d get out to some mini meets this weekend to celebrate the mini being ready to drive and on the way home have noticed the drain pipe off the carb (the one that was blocked) is a little wet at the end with a bit of a strong petrol smell from it , is that normal? And whilst engine under load up a very steep hill (foot to floor) the engine bogged out, coughed and spluttered. Would that be needle profile that’s incorrect? It runs beautifully throughout the rest of the driving range and very responsive.
Cheers all (anyone else going to the MED in Lutterworth tomorrow or the caffeine and machine event?)