26 replies to this topic

[Chekako]

Hello everyone,

 

I have started to face quite an annoying problem with me 1986 998 Single SU HS4 carb mini: It does not want to idle and it stalls from time to time when I decelerate.

It does that when it's cold or warm, the choke is set up correctly (believe) and the cable/linkage doesn't get stuck anywhere.

 

The only way to keep it running is to pull the choke a bit before it stalls. Acceleration is absolutely fine and without stuttering.

 

There is enough dashpot oil in the carb.

 

 

Could it be connected to fuel pressure or do I have to take apart the carb and clean everything up first?

 

 

Thanks a lot in advance

[MiniMadRacer]

I would start by taking the lid off the fuel bin ( 3 screws) an have a look if there is any crud in it

[cal844]

Check for crud in the float bowl and valve then whilst you have the screw driver out remove the dash pot and make sure there isn't crud around the needle. You'll now need to top up the dash pot oil, yes you've already checked it but as you've just inspected the carb the oil will run out. Is there a spring around the dash pot, if not there should be.

Road test the car. If no change try a heavier weight oil in the dash pot.

Test the car again. If its idling too low or stalling turn the idle up very slightly.

When road testing the car make sure you use the same route every run time.

If you suspect the mechanical fuel pump has failed, remove the oil dipstick and sniff it. It shouldn't smell like petrol, if it does then you need to replace the fuel pump.


Hope this is of some help.

Cal

Edited by cal844, 08 July 2020 - 08:19 PM.

[Chekako]

The fuel bin is clean, the float boal is good and the needle is new (I dropped the old one and couldn't find it anymore). The oil I put in the dash is Penrite Carb oil for SU carbs. The spring is indeed still in the carb and it sits correctly

[MiniMadRacer]

Maybe it need s "flat" richening up

[MiniMadRacer]

And at what revs is it idling at?

[Chekako]

Somewhat between 900 and 1200 RPM.

[Chekako]

Spark Plugs look good, definitely not too rich or too lean when I last drove it

[Chris1275gt]

Had same problem in my hs4 on my 75 1275gt. The Piston wasn't falling smoothly as the piston and dashpot had light scoring marks. Run your finger inside the dashpot and on the outside of the piston if it's marked lightly smooth it with fine wet and dry paper, did the trick for mine.

[Spider]

There's many variables and possibilities as to a cause or it could be a combination of issues.

 

I'd suggest starting off with a detailed tune up, if the engine is standard, as per the book.

 

Also, with the Penrite Oil is sold as 'SU Dashpot Oil' it is not what BMC / Leyland / Rover recommend, I'd suggest using engine oil here.

[cal844]

There's many variables and possibilities as to a cause or it could be a combination of issues.

I'd suggest starting off with a detailed tune up, if the engine is standard, as per the book.

Also, with the Penrite Oil is sold as 'SU Dashpot Oil' it is not what BMC / Leyland / Rover recommend, I'd suggest using engine oil here.

I agree with using 20/50 engine oil, it's all my minis will run on, if I use anything else it causes stuttering or it'll blow back through the carb, I've destroyed many an air filter this way ??

[sonscar]

I would check the throttle spindle for play,may not be the problem but it is cheap to try.If this is worn anything else is a band aid.Steve..

[andyapanel]

Check the Carb Piston moves up and falls easily; it may just need a bit of cleaning in there.

[PACINO]

The best oil is the specific to S.u Carbs or sewing machine oil.

[cal844]

Pacino

In all respects every carb is different and will take experimenting to get the carb running well