Choke, cold running misfire question

[BigBrother-84]

Nice write-up on the choke, Lariat! Thank you for that contribution. Frankly, this should go into a "How To" section, as the requests for choke adjustment are frequent.

Completely agree!

I am curious about the "multiple pedal depress" advice. I suppose it is about a "slow" movement, since the goal is to «clip» the choke flap closed... If "pumping" vigorously, won't it open de flap immediately after the second shot? If the pedal is depressed multiple times, slowly, is it certain that the choke will remain fully closed after the last shot?

On my side, Big Brother has the following starting behaviour:

1- Depress pedal completely and release;

2- Start the engine;

3- Motor starts immediately... but after 2-3 seconds running, RPM drops and it stalls.

4- Redo step 1.

5- This time, motor starts and continue as expected. But sometimes, it doesn't run smoothly and seems to have a "slightly" opened choke flap.

6- Choke often omit to disengage when the motor builds its heat, so I have to give a fast shot to the pedal, to slow down the RPM. Sometimes a second time after couple of minutes, to drop to the "normal" idle speed.

The bad idea I tried was, at step 3, to slightly pump the pedal in order to "help" the motor stay fuelled and avoid a stall: Yep, it doesn't stall, but I have to stay in the vehicle to keep it running, since the choke seems now to be slightly opened.

I would be very happy to find a starting sequence (and/or an adjustment) that enables Big Brother to start as... well let's admit... a fuel injected one.

[Gary Lewis]

Nice write-up on the choke, Lariat! Thank you for that contribution. Frankly, this should go into a "How To" section, as the requests for choke adjustment are frequent.

Completely agree!

I am curious about the "multiple pedal depress" advice. I suppose it is about a "slow" movement, since the goal is to «clip» the choke flap closed... If "pumping" vigorously, won't it open de flap immediately after the second shot? If the pedal is depressed multiple times, slowly, is it certain that the choke will remain fully closed after the last shot?

On my side, Big Brother has the following starting behaviour:

1- Depress pedal completely and release;

2- Start the engine;

3- Motor starts immediately... but after 2-3 seconds running, RPM drops and it stalls.

4- Redo step 1.

5- This time, motor starts and continue as expected. But sometimes, it doesn't run smoothly and seems to have a "slightly" opened choke flap.

6- Choke often omit to disengage when the motor builds its heat, so I have to give a fast shot to the pedal, to slow down the RPM. Sometimes a second time after couple of minutes, to drop to the "normal" idle speed.

The bad idea I tried was, at step 3, to slightly pump the pedal in order to "help" the motor stay fuelled and avoid a stall: Yep, it doesn't stall, but I have to stay in the vehicle to keep it running, since the choke seems now to be slightly opened.

I would be very happy to find a starting sequence (and/or an adjustment) that enables Big Brother to start as... well let's admit... a fuel injected one.

The choke is only controlled by temperature and, on some carbs, vacuum. So pumping the pedal several times while the engine is off will have no effect on the choke since the temp won't change and there is no vacuum.

But once the engine is running several carbs have a vacuum pulloff, and that includes most 2150's and the Holley 4180C you have on your truck. And that does just what it's name implies - pulls the choke off a bit. Basically it is a feedback or closed-loop system - if it pulls the choke off too much the engine will slow and the vacuum will drop, which will add some choke back in. The trick is to have it pulled off just enough, and it sounds like yours is coming off too much.

As for the fast idle, as long as you don't depress the throttle the fast idle cam will be captured by the throttle linkage and can't change. But if you open the throttle the fast idle screw will release the fast idle cam. So when you say you have to "give a fast shot to the pedal to slow down the RPM" that is exactly to be expected.

You can see the adjustment procedures below on those two systems from Ford's document on our page at Documentation/Fuel & Air Systems/Carburetors, Chokes, & EFI/Holley 4180C and then the Ford's Service Manuals tab followed by the 4180C-4V tab. And from your description I'd say you need to do the pulldown if not the fast idle adjustment.

[BigBrother-84]

The choke is only controlled by temperature and, on some carbs, vacuum. So pumping the pedal several times while the engine is off will have no effect on the choke since the temp won't change and there is no vacuum.

But once the engine is running several carbs have a vacuum pulloff, and that includes most 2150's and the Holley 4180C you have on your truck. And that does just what it's name implies - pulls the choke off a bit. Basically it is a feedback or closed-loop system - if it pulls the choke off too much the engine will slow and the vacuum will drop, which will add some choke back in. The trick is to have it pulled off just enough, and it sounds like yours is coming off too much.

As for the fast idle, as long as you don't depress the throttle the fast idle cam will be captured by the throttle linkage and can't change. But if you open the throttle the fast idle screw will release the fast idle cam. So when you say you have to "give a fast shot to the pedal to slow down the RPM" that is exactly to be expected.

You can see the adjustment procedures below on those two systems from Ford's document on our page at Documentation/Fuel & Air Systems/Carburetors, Chokes, & EFI/Holley 4180C and then the Ford's Service Manuals tab followed by the 4180C-4V tab. And from your description I'd say you need to do the pulldown if not the fast idle adjustment.

Thanks!

Next weekend, I'll read with great care and pay attention to my carb/choke adjustments and behaviours. There is no reason I cannot adjust and fine-tune it, since it runs very smoothly when hot.

[Gary Lewis]

Thanks!

Next weekend, I'll read with great care and pay attention to my carb/choke adjustments and behaviours. There is no reason I cannot adjust and fine-tune it, since it runs very smoothly when hot.

Yes, you can do it. But I'd suggest making one change at a time so you know what to back out if it doesn't work.

And don't miss the other tab with the other Ford document on the carb. They are slightly different so it would be good to have your head around both of them.

[rcarlisle]

Yes, you can do it. But I'd suggest making one change at a time so you know what to back out if it doesn't work.

And don't miss the other tab with the other Ford document on the carb. They are slightly different so it would be good to have your head around both of them.

I fiddled with mine on Saturday and Sunday. Found a couple things out of adjustment. Choke plate doesn't always close completely on pedal to floor at cold start. So it is remaining at the pull down opening when cold if it doesn't close completely. I can lightly touch the choke plate linkage and it will snap shut. Not sure if it's got a little stickiness in there or what. Will continue to investigate.

I removed the cap and cleaned the edges a bit and notched the case to know where the spring is at rest. the cap was taking two hands to twist. The gasket was sticking.

First testing I discovered that the choke plate isn't opening fully as it warms and still at pull off position for too long. So it would be running pretty darn rich when I was experiencing the missing. I think I am about to get it all adjusted. I had the adjuster too slack. The one that goes into the plastic piece behind the cap that determines how fast it comes off fast idle cam.

So check, drive, check, drive. I had it really bad at one point. Missing at speeds and any measureable throttle opening, but idling at about 2500. Ugh. Roadside adjustment.

Also found that when I open the throttle all the way, it leaks about 3 drops of gas off the throttle linkage. It's leaking a little somewhere. One of my dudes at work says I probably need to rebuild the carb. Wonder if I need to rebuild or just get a new carb. If it's leaking around the throttle shaft, does a kit have the parts to fix that?

I installed a tach too. Just to get and idea of engine speeds. At 55 ish, tach reads 2000 rpm. Shouldn't I be getting better mpg than 10? It's a 5 spd, so 2000 is in the realm of possibility. I don't think the tach is necessarily wrong.

What should idle speed be on a manual trans when warm? I"m going to go looking for that and a carb kit. It's got a reman tag so not sure what carb is set for, but surely a kit for 81 302 manual trans?

 

[FuzzFace2]

I fiddled with mine on Saturday and Sunday. Found a couple things out of adjustment. Choke plate doesn't always close completely on pedal to floor at cold start. So it is remaining at the pull down opening when cold if it doesn't close completely. I can lightly touch the choke plate linkage and it will snap shut. Not sure if it's got a little stickiness in there or what. Will continue to investigate.

I removed the cap and cleaned the edges a bit and notched the case to know where the spring is at rest. the cap was taking two hands to twist. The gasket was sticking.

First testing I discovered that the choke plate isn't opening fully as it warms and still at pull off position for too long. So it would be running pretty darn rich when I was experiencing the missing. I think I am about to get it all adjusted. I had the adjuster too slack. The one that goes into the plastic piece behind the cap that determines how fast it comes off fast idle cam.

So check, drive, check, drive. I had it really bad at one point. Missing at speeds and any measureable throttle opening, but idling at about 2500. Ugh. Roadside adjustment.

Also found that when I open the throttle all the way, it leaks about 3 drops of gas off the throttle linkage. It's leaking a little somewhere. One of my dudes at work says I probably need to rebuild the carb. Wonder if I need to rebuild or just get a new carb. If it's leaking around the throttle shaft, does a kit have the parts to fix that?

I installed a tach too. Just to get and idea of engine speeds. At 55 ish, tach reads 2000 rpm. Shouldn't I be getting better mpg than 10? It's a 5 spd, so 2000 is in the realm of possibility. I don't think the tach is necessarily wrong.

What should idle speed be on a manual trans when warm? I"m going to go looking for that and a carb kit. It's got a reman tag so not sure what carb is set for, but surely a kit for 81 302 manual trans?

If you have gas leaking out between the throttle shaft & carb base plate a rebuild kit will not fix this.

There is wear on the shaft and / or base plate and I see this as something beyond the normal person.

Even I would not try to fix as bushings would need to be installed and the shaft turned and if you dont get the blades back in the same place you can have even more issues with the throttle sticking.

Then add a choke not working right I would look into a new carb.

I did not say rebuilt as rebuilds may have the same issues with the throttle shaft.

So a 302 with a stick so you dont have to play with auto kick down linkage and that is good.

Check with local parts stores and Rock Auto for new carbs and prices.

If you dont have smog check you may want to look into Holley 2300 carb.

It comes as a 350 CFM and a 500 CFM and should be a bolt on to your intake.

You will have to deal with the gas line as it may feed differently and hooking up the throttle cable, may need a ball it snaps on to on the carb.

I have a 500 CFM on a AMC 304 to replace a Motorcraft carb and it was the best thing I did to the car.

With a new carb the choke should work,may need a little adjusting, and no more gas leak at the throttle shaft and should run a lot better.

Dave ----

[Gary Lewis]

If you have gas leaking out between the throttle shaft & carb base plate a rebuild kit will not fix this.

There is wear on the shaft and / or base plate and I see this as something beyond the normal person.

Even I would not try to fix as bushings would need to be installed and the shaft turned and if you dont get the blades back in the same place you can have even more issues with the throttle sticking.

Then add a choke not working right I would look into a new carb.

I did not say rebuilt as rebuilds may have the same issues with the throttle shaft.

So a 302 with a stick so you dont have to play with auto kick down linkage and that is good.

Check with local parts stores and Rock Auto for new carbs and prices.

If you dont have smog check you may want to look into Holley 2300 carb.

It comes as a 350 CFM and a 500 CFM and should be a bolt on to your intake.

You will have to deal with the gas line as it may feed differently and hooking up the throttle cable, may need a ball it snaps on to on the carb.

I have a 500 CFM on a AMC 304 to replace a Motorcraft carb and it was the best thing I did to the car.

With a new carb the choke should work,may need a little adjusting, and no more gas leak at the throttle shaft and should run a lot better.

Dave ----

/\ /\ What he said!

To fix a worn carb that way would require pulling the butterflies off the shaft, pulling the shaft out, boring the carb base out, pressing bushings in, reaming the bushings to the right diameter and alignment, and reinstalling & aligning the throttle shaft and butterflies. Not something just everybody should attempt.

[rcarlisle]

/\ /\ What he said!

To fix a worn carb that way would require pulling the butterflies off the shaft, pulling the shaft out, boring the carb base out, pressing bushings in, reaming the bushings to the right diameter and alignment, and reinstalling & aligning the throttle shaft and butterflies. Not something just everybody should attempt.

THanks gentlemen. That's kinda what I was thinking as well, from what I do know. That is not a place that can be fixed easily.

I'll start looking. The reman tag on mine says 2015, so it's probably done its time and is ready to be a shelf piece.

[rcarlisle]

/\ /\ What he said!

To fix a worn carb that way would require pulling the butterflies off the shaft, pulling the shaft out, boring the carb base out, pressing bushings in, reaming the bushings to the right diameter and alignment, and reinstalling & aligning the throttle shaft and butterflies. Not something just everybody should attempt.

Take a close look at base of carb - there is an extra piece in there. It has some sort of thing on rear of extra piece. What is this plate? Do I need to keep it if I replace carb? I'm going in search of docs on this.

Also below the vac pulloff in this photo.

Under carb here.

Feel free to comment if you see something that needs to be addressed. I didn't install this old reman carb on the new reman engine. I haven't touched anything except dist cap and rotor because cap was cracked at tower 3.

 

[Gary Lewis]

Take a close look at base of carb - there is an extra piece in there. It has some sort of thing on rear of extra piece. What is this plate? Do I need to keep it if I replace carb? I'm going in search of docs on this.

Also below the vac pulloff in this photo.

Under carb here.

Feel free to comment if you see something that needs to be addressed. I didn't install this old reman carb on the new reman engine. I haven't touched anything except dist cap and rotor because cap was cracked at tower 3.

That is the EGR valve/plate. I don’t remember what you need to do to eliminate that on that engine/carb setup. But if you do the ignition timing should be changed as it will be advanced a long ways at part throttle.