Carb Tuning

[Adarcy]

Hi All,

I've got the factory 2 barrel carb on my 302 and I "think" it needs to be tuned. It requires a decent amount of throttle/rpm to get moving in first or reverse from a stop otherwise the engine bogs down and dies or comes close to it.

Does this sound like a carb problem? If so can anyone offer some tuning tips for someone who has never tuned a carb?

I just finished replacing all of the fuel lines, fuel filter, fuel pump, and cleaned out both gas tanks so i'm confident that I don't have any restrictions there.

Thanks,

Andy

 

[needabronco]

Sounds like you might need a clutch adjustment. Try that first, unless I misread your question...

Find the clutch adjusment fork, it's attached to the bar going from the frame to he engine block. There will be (sould be) two nuts loosen them up and lengthen the rod until you have about a 1/4" or so of play, which shoul be about a 1/2" or so of pedal play before the clutch starts to engage.

After that I'd double check your timing and that it's advancing properly. If it's off your carb will likely need some fine tuning to adjust idle again.

If it idles fine and rev's up ok, without massive clouds of smoke your carb is probably 'ok'. But it never hurts to hook up a vacuum gauge to it and tune it anyway.

There used to be a link (I think) in the FAQ section.

 

[broncnaz]

X2 check your timing and points gap. You may also have a bad accelerator pump. look down the throat of the carb and open the throttle if you see gas squirt then your good if no gas then you accelerator pump is bad. I'd get a rebuild kit and go through the carb. Also make sure your choke is operating properly.

I dont think its your clutch as if the clutch was slipping the engine would rev up but the bronco wouldnt pick up speed.

 

[SKOOTER]

I recently re-built and fined tuned my carb with the help of this site. a timing lite and vacuum gauge made a huge diference for my rig. Took a while to figure out what I was doing but what a difference it made. Good luck

 

[DirtDonk]

How does it idle? Smooth or a little rough? If rough, you could also have a vacuum leak or three.
Along with a possible bad accelerator pump in the carb, the condition of the PCV valve can do this as well. If the valve is stuck open for instance, you could get a lean-bog off idle like you're experiencing.
And like they said, ignition timing can make a huge difference.

Have you done a full tune-up on it first? If not, that's the place to start. It may still be entirely the fault of the carb, like you're thinking, but if you don't have the rest of it in good tune, you might never know.

Good luck.

Paul

 

[Adarcy]

X2 check your timing and points gap. You may also have a bad accelerator pump. look down the throat of the carb and open the throttle if you see gas squirt then your good if no gas then you accelerator pump is bad. I'd get a rebuild kit and go through the carb. Also make sure your choke is operating properly.

I dont think its your clutch as if the clutch was slipping the engine would rev up but the bronco wouldnt pick up speed.

Checked the accelerator pump and it is functioning properly. I didn't think of the choke..I'll check that next, thanks.

 

[Adarcy]

How does it idle? Smooth or a little rough? If rough, you could also have a vacuum leak or three.
Along with a possible bad accelerator pump in the carb, the condition of the PCV valve can do this as well. If the valve is stuck open for instance, you could get a lean-bog off idle like you're experiencing.
And like they said, ignition timing can make a huge difference.

Have you done a full tune-up on it first? If not, that's the place to start. It may still be entirely the fault of the carb, like you're thinking, but if you don't have the rest of it in good tune, you might never know.

Good luck.

Paul

I'll go check the pcv valve now.

Speaking of tune up...Does anyone have good suggestions on replacement spark plugs and wires? (how much gap is needed for the 302?)

 

[broncnaz]

Stock points igintion? plug gap is .034 point gap is .021(although I like to run .017 gap). I like Autolite plugs and just about any good aftermarket spiral core wires. I wouldnt waste money on high dollar fancy spark plugs on a carbed engine as they tend to need plugs replaced every year or 12,000 or so miles anyhow.

 

[DirtDonk]

Lot of people here like the Ford Racing replacement wires. Don't know what they cost now, but for a time they seemed like a good deal on a very nice set of wires.

Paul

 

[Justafordguy]

Lot of people here like the Ford Racing replacement wires. Don't know what they cost now, but for a time they seemed like a good deal on a very nice set of wires.

Paul

I have them on both of my Mustangs. They are really nice wires.

 

[broncnaz]

I believe all the ford motorsports wires require the use of the larger HEI style cap but still a good upgrade overall. The wires only run about $50 and you can get the HEI style cap, rotor and cap adpater at your local parts store. Just ask for a 77 -85 cap,rotor and adapter.

 

[Adarcy]

Ok,

My plugs, wires and dist all check out ok. PCV, choke, and accelerator pump are good as well.

I have also noticed that my idle seems to be quite high. Could be related? Not having a tach I don't know for sure, but it feels like it idles around 1krpm's and then when you engage a gear it drops down. This is the case when the engine is both cold or warm.

How do you adjust the idle?

 

[dbevans2249]

Adarcy you have one nice clean Bronco there. I looked at your gallery to figure out weather you had a manual or automatic transmission. The statement that the RPM's dropped down when you put it in gear threw me. Since you have three on the tree puting it in gear should not do anything to the RPM.

Have you done a compression test on this engine? It is the first step in a tune up according to many of the old Motor Manuals etc. The reason is that you cant tune an engine that is not mechanically healthy. The results of compression test can give you an idea if the timing chain is badly streched etc. If the cam timing is late all the cylinders will have low compression. That realy kills the bottom end and wont let the engine idle.

A Vacuume Gage can also be used to get an idea of what is going on in the engine.

 

[Adarcy]

Adarcy you have one nice clean Bronco there. I looked at your gallery to figure out weather you had a manual or automatic transmission. The statement that the RPM's dropped down when you put it in gear threw me. Since you have three on the tree puting it in gear should not do anything to the RPM.

Have you done a compression test on this engine? It is the first step in a tune up according to many of the old Motor Manuals etc. The reason is that you cant tune an engine that is not mechanically healthy. The results of compression test can give you an idea if the timing chain is badly streched etc. If the cam timing is late all the cylinders will have low compression. That realy kills the bottom end and wont let the engine idle.

A Vacuume Gage can also be used to get an idea of what is going on in the engine.

Thanks!

With a little more investigation I found the culprit of the high idle. The dashpot wasn't allowing the throttle to come all the way back down. I've attached a picture of the lil bugger. The fix? Remove it and adjust the idle screw so it runs fine at idle.