Technical Cutting out when hot!!

[dtodd2112]

heres the symptom, cuts out when at junctions (idle) or if clutch held in too long when changing gears when its been under load / up to temperature,, leaving choke on stops it. holding the revs would also stop it.

Ive replaced dizzy cap and arm, all leads and plugs and fitted new vacuum advance unit.

car was fine until tonite when I drove it a few miles ( without the heater on and with 5 passengers at motorway speed ) it reached half on temp guage ( which it rarely gets the chance too) and this started.
I dont usually use the car enough and/or when I do use it it has the hot heater on all the time ( not the blower motor just the heat bit keeps coming through dash eg off the opposing wind ) so never goes above 60 degrees so the problem rarely happens

any ideas?????
the car has 39k miles and is in exceptional condition
Im a vehicle technician and this still has me stumped!!!
its a uno 45 Fire carb with electronic ignition 1988

 

[dtodd2112]

update its doing this all the time now

 

[lewey]

Stalling between gears is pretty bad. Whatever it is, it has happened fast. You have replaced ignition parts, so fuelling has to be on the hit list. Remove jets and blast them and the body with compressed air. Perhaps too little fuel is getting through, which you can compensate for with the choke open. Other issues could be the mechanics of the carb, like the choke flap is loose and flaps shut to literally choke the engine into a stall.

Otherwise, perhaps a poor earth to coil or the ignition module. Poor earths often get worse as the area around them warms- it naturally increases resistance. If your carb has a fuel cut-off solenoid, clean the contact on it and inspect the often battered wire going to it.

 

[dtodd2112]

I blanked off the fuel cutoff solonoid lol the earths havent been checked yet so thats a possability!! was thinking that there might be another vacuum leak as it seems like its getting too much air??? ive changed inlet manifold gasket 3 times and it usually goes away for a while then comes back again,,,:bang:

 

[dtodd2112]

was also gonna ask,, is the vaccum advance pipe supposed to have a strong vacuum all the time??

 

[alexGS]

Yes - on the FIRE engines, that strong vacuum tends to break the vacuum advance diaphragm, which you've already replaced. Consider drilling out the idle jet to 0.5mm with a suitable tiny drill - then the mixture adjustment will have more of an effect. This is after re-setting the timing to 5 degrees BTDC at a slow idle, without vacuum advance. Connecting the vacuum advance should then advance the timing to about 13 degrees, which lifts the idle speed quite a lot.

The reason for drilling out the idle jet is to compensate for air leaks around the throttle spindle. The original 0.40 or 0.45 idle jet was very lean in the first place and I've only seen one engine (a low-mileage minter) where adjusting the mixture screw actually richened the mixture enough to guarantee a really smooth idle under any conditions. Most of the time they are slightly uneven with a tendency to die when moving away if the accelerator is pressed in a hurry.

-Alex

 

[dtodd2112]

theres two jets, is it the one on the left that you mean,, ??, ive also ordered a new ignition module ,,, but i think that the problem is too much air getting in???? needs more fuel in me thinks

 

[lewey]

Too much air and too little fuel has the same symptoms of course.

 

[dtodd2112]

its got me thinking about going down the bike carb route,, anyone got any tips / opinions on this??:devil:

 

[dtodd2112]

update uno running idle without choke now,,, I tightened manifold bolts and replaced 2 gaskets on the plastic spacer with paper ones with hymolar sealant ( fuel resistant), now idles without choke,,, not purfect but ittl do for now:idea: