1985 2.8 Carb Adjustments

[Uncle Gump]

Does the choke snap full closed when you pump the pedal on a stone cold engine?

All your symptoms sound like they're coming from a misadjusted choke.

 

[RonD]

+1, ^^^^
Classic symptoms of mis-adjusted Choke

All gasoline engines need to be choked when cold, that basically just means Rich fuel mix and high idle until coolant temp gets to about 150degF, just above 1/4 on temp gauge

The Choke plate on a carb restricts air flow into the engine so increases vacuum at the Jets, thats where the RICH mix comes from, more fuel is SUCKED out of the jets, the greater the restriction the Richer the mix
The high idle comes from the Choke cam on throttle linkage

Depending on where you live you may need to adjust Choke twice a year because of average outside temps, once for winter driving, colder temps needs more Choke, and once for summer warmer temps less choke

For the non-high tech fix, we used to adjust the choke for winter and then in the summer put a wooden clothes pin on the choke plate to hold it open farther, lol

 

[ford4wd08]

I'll confirm choke settings, but it did snap close when I adjusted it last.

 

[ford4wd08]

I think I'm going to set the choke thermostat a little tighter and see what happens.

On another note I decided to throw a vacuum gage on it when I got home. It was reading about 21 inches HG, I know that is good, but the mixture screws are pretty loose. And it didn't seem to make much difference how loose I went until they came all the way loose. I could tighten them in and get a difference in idle and drop of vacuum. I just assume if I kept going looser it would stumble a little as well.

Does this mean I should look into rejetting the carb? Maybe go up a size?

@Uncle Gump @RonD @19Walt93

 

[Uncle Gump]

Before you adjust the choke tighter.... ensure it fully closes cold. If it does... start the engine and see how far the choke pull off opens the choke plate. It could be a pull off adjustment and not a choke adjustment giving you problems.

I would suggest before you do any more messing around with the choke... set the mixtures screws. I set them buy warming up the engine and then turning the screws (one at a time) inward until you notice a perceptible drop in RPM. This will indicate that the mixture is to lean. Then turn the same screw out until you achieve the highest RPM. Try 1/4 turns both in and out. Once the first screw is set... adjust the second one.

 

[ford4wd08]

Before you adjust the choke tighter.... ensure it fully closes cold. If it does... start the engine and see how far the choke pull off opens the choke plate. It could be a pull off adjustment and not a choke adjustment giving you problems.

I would suggest before you do any more messing around with the choke... set the mixtures screws. I set them buy warming up the engine and then turning the screws (one at a time) until you notice a perceptible drop in RPM. This will indicate that the mixture is to lean. Then turn the same screw out until you achieve the highest RPM. Try 1/4 turns both in and out. Once the first screw is set... adjust the second one.

Understood on your comments. You and I have been over that procedure a bunch on here together lol.

Let's start with the choke: i believe it is fully snapping close when cold. I've set it and marked it with a line. Still lines up.

I have adjusted the pull of in the past. I adjusted it to a drill bit. It might be possible it needs to be smaller? That is an easy one to adjust as well.

I'm daily driving this rig now. I have done the 1/4 turn adjustment on the idle mixture screws on a warm engine. My point is once I go to rich side after going in lean I never notice any change.except for the initial one after I back off lean. RPM's stay the same. It on changes once I screw in until it leans out. Rich side seems to be all the same. Shouldn't I experience a change in idle or vacuum if too rich?

 

[Uncle Gump]

So you turn the screw in until it starts to miss and loses RPM... then back it out until it stops missing and the highest idle is achieved. It won't keep raising RPM the richer you go. Once you see no more increase in RPM... stop turning the screw. if you don't see a drop in RPM... turn it in until you do.

 

[ford4wd08]

So you turn the screw in until it starts to miss and loses RPM... then back it out until it stops missing and the highest idle is achieved. It won't keep raising RPM the richer you go. Once you see no more increase in RPM... stop turning the screw. if you don't see a drop in RPM... turn it in until you do.

Understood. Time to try it again. I feel like the springs on the screws are very worn. Might be worth replacing.

 

[19Walt93]

Understood. Time to try it again. I feel like the springs on the screws are very worn. Might be worth replacing.

Just stretch them out a little, the tension is to prevent the screws from turning by themselves, it isn't a critical measurement. I agree with setting the idle mixture before you tweak on the choke and making sure the choke closes fully. In the 60's choke pull down was around 1/4"(#2 phillips), you probably want less than that. If you let it run for a minute or 2 to warm up you'll want it open a little more that if you fire it up and drive away.

 

[ford4wd08]

So you turn the screw in until it starts to miss and loses RPM... then back it out until it stops missing and the highest idle is achieved. It won't keep raising RPM the richer you go. Once you see no more increase in RPM... stop turning the screw. if you don't see a drop in RPM... turn it in until you do.

Just stretch them out a little, the tension is to prevent the screws from turning by themselves, it isn't a critical measurement. I agree with setting the idle mixture before you tweak on the choke and making sure the choke closes fully. In the 60's choke pull down was around 1/4"(#2 phillips), you probably want less than that. If you let it run for a minute or 2 to warm up you'll want it open a little more that if you fire it up and drive away.

So, I set the idle mixtures screws maximum vacuum with smooth idle. 21 inch of vacuum. Did the 1/4 turn and I could see it better. So I'm confident in that.

I did tighten up the pull off slightly. I'll see how it does in the morning.

I'm not trying to fix something that doesn't need fixing as the old saying goes, but how do you know if a carb is jetted correctly?

Would a pinto and B2 be jetted the same way?

 

[19Walt93]

If yours is the original feedback carb it is probably jetted different than a non feedback carb on a Pinto. Too lean a jet will cause surging at steady speeds and stumbling on easy accell, a little too rich might feel like it's running OK but the mileage and power will both suffer. Have you heard the expression "lean is mean?"

 

[ford4wd08]

If yours is the original feedback carb it is probably jetted different than a non feedback carb on a Pinto. Too lean a jet will cause surging at steady speeds and stumbling on easy accell, a little too rich might feel like it's running OK but the mileage and power will both suffer. Have you heard the expression "lean is mean?"

Guess I'm too young for "lean is mean"....

I ditched the feedback carb when I converted to a duraspark distributor. I swapped it for a 2150 off of a Pinto with an auto trans that I bought off a member on here. I rebuilt it before installing it on my B2. I think it could be running slightly rich. I know it is easy to change jets.

How would you recommend confirming jet size? Trial and error?

 

[Uncle Gump]

The old rule of thumb I used for main jet sizes was Venturi size X 4. That will put you into the ball park. Fine tuning is a bit mare complicated... a cross between seat on your pants feel... reading your spark plugs and trial and error.

I do think though you should focus on one thing at a time. Get your warm idle mixture set... then focus on cold starting... then worry about main jetting. If you keep doing multiple adjustments everytime under the hood... it's extremely hard to determine what made the changes worse or better.

 

[Uncle Gump]

I actually say start with the idle circuit... because in most instances/carbs... the idle circuit is also supplying fuel when the main circuits are working. This would mean if the idle circuit is rich.... this rich condition carries over into cruise speeds and vice versa.

 

[ford4wd08]

The old rule of thumb I used for main jet sizes was Venturi size X 4. That will put you into the ball park. Fine tuning is a bit mare complicated... a cross between seat on your pants feel... reading your spark plugs and trial and error.

I do think though you should focus on one thing at a time. Get your warm idle mixture set... then focus on cold starting... then worry about main jetting. If you keep doing multiple adjustments everytime under the hood... it's extremely hard to determine what made the changes worse or better.

I actually say start with the idle circuit... because in most instances/carbs... the idle circuit is also supplying fuel when the main circuits are working. This would mean if the idle circuit is rich.... this rich condition carries over into cruise speeds and vice versa.

You mean times 40? 1.08 X 40 = 43.2 so a 43 jet size? I believe the feedback carb came with a 50, but had the solenoid to add in air. I'm not sure what this carb has, but I will check soon. I suspect around the same.

Warm idle mixture is set, I'm confident in that.

Cold starting was better this morning, but still required me to start it twice, after second start it ran fine. I'll try adjusting the pull off a little more. I did not stumble from the stop sign at all this morning out of my neighborhood, so that is a plus.

I just feel like it might be a little rich running, but I won't know until I play with the jetting some.