4Ac Stalling Issue

[Willacy70]

Hi guys,

 

as the topic suggests my 4ac stalls once it is warm while coming to a stop (e.g: pulling up to an intersection). On occasion when stopping, the car will idle at around 500-700 rpm, and other times it will idle fine. I have realised that it only happen on really cold days. During summer the car ran fine and I hadn't had this issue for 6 or so months but it seems to have come back now that weather is getting cooler. The problem is really annoying. I have read the thread about one of the diaphragms in the carby being faulty but I'm not 100 percent sure this is the issue. I am certain though that this is a carb issue. The carby has had a vacuum delete. Any help would be appreciated.

 

Thanks

[ke70dave]

How did it go before the "vacuum delete" ?

 

I'd start by giving it a good cleanout with some of that carby cleaner. spray it into the carby and clean it all, then fire up the engine (it will be VERY hard to start), then once the engine is going go to town with the carby cleaner with the engine running, you will have to keep the engine going with the throttle as the carby cleaner tends to kill the engine.

 

Its unlikely this will solve your issue (unless the idle jet is blocked with dirt?), but it will clean the thing thats for sure.

[altezzaclub]

Does it have an automatic choke or a manual one?

[Willacy70]

How did it go before the "vacuum delete" ?

 

I'd start by giving it a good cleanout with some of that carby cleaner. spray it into the carby and clean it all, then fire up the engine (it will be VERY hard to start), then once the engine is going go to town with the carby cleaner with the engine running, you will have to keep the engine going with the throttle as the carby cleaner tends to kill the engine.

 

cheers, I cleaned it with carby cleaner not too long ago as that was my first suspicion but it doesn't seem to have helped the problem, Also i didn't do the vacuum delete so I'm not sure how it ran.

 

Its unlikely this will solve your issue (unless the idle jet is blocked with dirt?), but it will clean the thing thats for sure.

Does it have an automatic choke or a manual one?

 

Its the stock carb and has an auto choke.

 

As i said It runs perfect in warm weather, but has this idling and staling issue in cold weather. Here is a picture of the carby if it helps anything.

 

Edited May 28, 2013 by Willacy70

[altezzaclub]

The amount of choke it delivers is adjustable. I've never played with this particular carb but it looks like most of its generation.

 

There is a choke idle screw that will need a touch up where the choke mechanism works on the throttle to hold it open at cold idle. Just screw it in a 1/4turn and see if that is enough. There will be a series of steps in the steel quadrant that holds the idle open in the various stages of warming up.

 

Usually the black plastic cover on the back of the choke in that photo can be turned when you undo the three screws. It has a bimetallic coil inside that unwinds as it gets hot, so you just need to put more tension on the coil spring to close it slightly more. Make sure it comes back to completely vertical when warm.

[Willacy70]

The amount of choke it delivers is adjustable. I've never played with this particular carb but it looks like most of its generation.

 

There is a choke idle screw that will need a touch up where the choke mechanism works on the throttle to hold it open at cold idle. Just screw it in a 1/4turn and see if that is enough. There will be a series of steps in the steel quadrant that holds the idle open in the various stages of warming up.

 

Usually the black plastic cover on the back of the choke in that photo can be turned when you undo the three screws. It has a bimetallic coil inside that unwinds as it gets hot, so you just need to put more tension on the coil spring to close it slightly more. Make sure it comes back to completely vertical when warm.

 

There is no issue when the car is cold and the choke is still on. it is when the choke comes off and the car is warm that is doesn't want to idle. It is intermittent as well which is annoying. I will try and post a video later on to show better what the situation is.

[ke70dave]

I'd suggest, find your nearest carburetta shop and give them a call or better yet drop in.

 

I suspect poor hot idle is very very common, and they can probably give you some tips over the phone.

 

Most guys at carburetta shops are old, and old guys love to talk!

 

edit: i think what altezza club was getting at, was that the choke is not 'unchoking' once the engine gets hot. if its an automatic choke, its quite possible that the automatic bit does not pull the choke off once it gets hot, so you are essentially choking the engine continually.

 

And choking a hot engine doesnt go down to well, which is probably causing your drama.

Edited June 13, 2013 by ke70dave

[Willacy70]

I have tried to adjust the auto choke to no avail. I have realised a pattern though and that is the car will only stall once after a cold start and will run perfectly after it has stalled once. I'm not sure what everyone else thinks but i find this a bit strange. If all else fails i will be bringing it to a carby shop.

[Willacy70]

Thanks to the above posters for your input. I dropped the car off at the mechanic today and for the sake of people who have such symptoms with their car in the future, ill post the solution here after i pick up the car. Hopefully the mechanic can pinpoint the problem.

[Willacy70]

so after taking my car into a mechanic who told me the accelerator cable needed adjusting, I decided to replace the auxillary pump diaphragm in the carby which has improved the issues slightly but has quite fixed it. I think the car floods during cold operation and fouls the plugs. I say this because after 10 or 15 minutes of driving there is no issue and the car runs fine but before this period wont idle nicely. The previous owner told me the carby was re-jetted with bigger jets? could this be an issue? Will adjusting the choke so it stays on for longer improve the issue? any help would be appreciated, thanks

[altezzaclub]

I think the car floods during cold operation and fouls the plugs. I say this because after 10 or 15 minutes of driving there is no issue and the car runs fine but before this period wont idle nicely.

 

Ok, is there a screw acting on a quadrant that adjusts choke idle?? It is separate from the warm idle screw that does the main work of idle speed. If you screw up the choke idle speed that may solve it. If you reckon it is flooding, ie- too much choke, then have another go at adjusting the choke mechanism and reduce it's effect.

 

If the carb has been rejetted with larger jets you might need less choke just from that alone. It will always run richer when driving, hot or cold. However, unless they richened the idle jet as well the idle mixture will stay as lean as it was.

[Willacy70]

Ok, is there a screw acting on a quadrant that adjusts choke idle?? It is separate from the warm idle screw that does the main work of idle speed. If you screw up the choke idle speed that may solve it. If you reckon it is flooding, ie- too much choke, then have another go at adjusting the choke mechanism and reduce it's effect.

 

If the carb has been rejetted with larger jets you might need less choke just from that alone. It will always run richer when driving, hot or cold. However, unless they richened the idle jet as well the idle mixture will stay as lean as it was.

 

Thanks for the reply, funnily enough I tried this today to see what would happen, adjusted the choke and leaned the fuel mixture a bit as well, it worked to a certain extent but it still wants to stall or idle at a significantly low rpm (around 500rpm) after long sustained periods of driving. In saying that i haven't driven for a period of longer than 10 minutes or so after the initial warm up. Was thinking of maybe buying some hotter plugs to see if they would improve anything? not sure if its a good idea or not but may give it a go anyway. But like i said from the start, this is only a problem in cold weather which completely puzzles me.

[Willacy70]

still have this issue. Any idea's?

[altezzaclub]

I say this because after 10 or 15 minutes of driving there is no issue and the car runs fine but before this period wont idle nicely.

 

Is this still how it happens??

 

So it is fine when started cold (on full choke) stalls as it warms up (on part choke) then fine once it is warmed up...

 

It certanly sounds like the choke is coming off too fast, its not richening it for quite long enough. Next time it stalls leap out and check the choke,see if it is completely off or partly off.

 

Did you have success with turning the choke bi-metallic mechanism?? That will determine how long the choke stays on for.

 

The choke throttle screw determines how high the idle is while its on choke.

[lexsmaz]

I think you will find that the carby is icing up around the throttle butterfly area, hence cold mornings & stalling only once & then its fine, I have experienced it on quite a few cars over the years, you can sometimes actually see if you are quick enough after it stalls the ice around the outside of the carby base & if not just feel it & it will be super Cold .. First thing to do is make sure your Stove / Hot air pipe off the exhaust to the air cleaner is there & working & the flap if its adjustable is set to Winter, sometimes too if the carby throttle butterfly linkage are worn badly It can make things a bit worse too, but the Stove pipe is number one ... To test the theory if you let the car stall & so no air flow the ice will melt after about 10-15 seconds & the car will be fine after that, I you don't let it stall out it will carry on idling poorly for quite a while until there is enough heat soak in the carby & engine bay etc to melt off the ice .. That's a Impressive Mechanic saying to adjust your throttle cable !!!!! Gives us Mechanics a bad name ..