76 YF carb problems...

Please help!

I had trouble with one brrl carb on my 76, the YF style. So i went and purchased a rebuilt one just so i wouldnt have to tear it down. It wasnt that expensive anyway. Well i got it on, and the jeep runs but when i take off down the road it shutters like its starving for fuel? When its idleing its fine, and out of gear it just revs up fine. If i just barely depress the pedal it will accelerate smoothly but if i get past say 1/3 down it will shutter.

Ive tried different positions on the idle mixture screw with no luck, id thought that might be it...but if you dont already know..i just dont have the experience with carbs yet, i need some help so i came to you guys.

What do i need to do to adjust for this?

 

Sounds like you need a new fuel filter or the fuel pump is crapping out. Of course the rebuilt carb's float may not be opening enough too. I would start with the fuel filter and pump then proceed to the carb. Good luck

 

Good advice - replacing the fuel filter is a good maintenance proctice, so I'd replace it anyway.

Re the fuel pump, you can check how much fuel it is pumping by directing the outlet into a pint jar and cranking the engine. Take the coil wire off so the engine won't start. You should be able to fill the jar in 20-30 seconds of cranking. There's a pressure spec too - IIRC 3-4 psi, if you have a suitable gauge.

No great loss if you buy a new fuel pump and that's not the problem - every Jeeper needs to carry a spare fuel pump anyway.

 

Sounds like a float level problem. Bowl gets enough gas to start, but not enough to run under load.

 

OK replaced fuel pump, didnt mind that, filter as well, then tried my hand at adjusting the float level using the Haynes manual i have. The float needed a little tweaking but wasnt anything major. Still having problems with motor running under a load. Seems i can get it to idle ok, adjust it around even and it changes rpm smooth, but when i jump in and try to drive it its terrible. The motoer even revs up fine when not in gear. Whats my next plan of attack? The tank maybe?? The fuel line from the tank?

One more question...When should fuel come out from the overflow back to the tank? I took my hoses off and saw no excess fuel escaping anywhere, is this an issue?

 

Ok you may have to investigate new fuel lines. Just check them visually to determine what condition they are in. You can try adjusting the metering rod inside the carb. If you need the directions on how they are in the FSM (someone here has a link to a 72 FSM online, anyone have that?) also visually examine the accelerator pump while your adjusting the metering rod. With the engine off, take the air cleaner off and look down the throat of the carb while opening the the throttle all the way. You should see a squirt of gas spray into the carb throat. If not, the accel pump is bad. Before tearing into the carb all the ignition parts are in working order right?? Inspect all wires, etc.

 

If the problem wasn't there before you replaced the carb, then the carb is most likely the problem. It's possable that somebody misinstalled a checkball or linkage during the rebuild. If this is a reman'd unit as you stated, then return it for another. The proper operation of the carb is their responsibility.

 

Well, i worked on the old carb some and put it back on, it was flooding and the gaskets seeping before. It seems to be having the same "starving" trouble as the new carb now. Im just causing the old stuff to fail as i upgrade the rest i guess. Im thinking the fuel lines may be the culprit, gonna try that next, maybe run a rubber fuel line temporarily from the tank to the fuel pump to check that. Well thats where im at, ill let ya know what happens next.

Steve

 

If I recall correctly, isn't the movable metering rod/needle adjustable inside the carb? Unless I am thinking about the wrong carb. I once had an IH Scout with the AMC 232 engine that I cured the flat spot/stumble by a slight adjustment of the metering rod. If I remember right it only took about a half turn of the screw to correct it. This may or may not help. Worth a try.

 

I have eliminated the fuel lines from the equation now, finally swapping for another carb now, like others had suggested.

hopefully a good one!

 

OK this is a long shot but my '74 was doing the same thing... I thought it was a carb problem but it turned out to be a cracked exhaust manifold. If you've tried everything else, check the intake and exhaust manifold for cracks or holes and make sure they're tight. You also might have a bad intake and/or exhaust manifold gasket(s). Double check timing/dwell and make sure your spark advance isn't sticking.

Wil.........

 

My '81 CJ5 is doing the same thing. It runs great around town but when I take it out on the fwy. it bogs down. I also have tried two carbs, fuel filter fuel lines etc. etc. I also recently replaced the exhaust.
This is all after I swapped out the entire block and head.

I'm thinking that it may have someting to do with spark / timing. I will be replacing the distributor next. I know we have different engines but we may be able to help each other out. I'll let you know how this distributor works out.

 

Hey, that sounds good, i finally got a decent Carb from "Advance", but still having a small sputter in mine. My choke isnt connected to anything so i need to figure a way around that since i just put on a new header myself. Anybody had solutions for that? The old carb had a wire running to the choke...electric choke?, but the replacement has no spade for a connector, can these be swapped between the two?

The Distributor is my next target as well. I will report back as ive been calling the salvage yards lately looking for the HEI item. No luck just yet.

A question about timing/dwell... When i set my timing to about 8deg ATDC, where the manual says, what should the timing mark do when reving the engine while watching it with the timing gun? Im new to this i guess, but the mark goes off the scale for timing and completely out of site. Is this correct?


Steve

 

I believe thats normal. I think you should be adjusting the timing at idle. (around 700 - 900 RPM?) But when you rev the engine it will change.

By the way, what engine do you have?

 

Its the 258-AMC

 

This is normal, as the vacuum advance mechanism kicks in and a advances the timing a bunch to keep up with the motor. The method I will usually use when adjusting all this stuff is as follows.

1. new parts (plugs, wires, cap, points, etc.)
2. Adjust carb (choke, mixture, idle, etc.)
3. Adjust timing

I think unless the timing is waaaayyy off do it last.

I idle my 74 258 at 600-675 (curb idle fully warmed up), disconnect and block the vacuum advance and set timing. I may touch up the idle mixture or idle speed if it changed signficantly.

 

Mine has the GM 151 "Iron Duke" 4cyl. But you mentioned HEI. I also have HEI. My manual calls for 17degrees above top dead center for my engine? Seems like a lot.

I disconnected the electric choke and put in a manual choke.

My plugs and wires are all new. I replaced them when I swapped out the engine (block and head) with a rebuilt in September but I used the old distributor, carb etc. When I noticed the problem, the first thing I tried was my spare carb that I had in the garage.

 

Try this.... Wil mentioned the intake gasket. With the engine at idle, I sprayed a small shot of ether (starting fluid) at the base of my carb. and at the intake gasket (where it bolts to the head). I found that the RPMs increased thus indicating an intake leak. This would cause air to enter the carb. and cause the mixture to be too lean. I found that one of the nuts that hold my carb. down was loose.
I'll drive it today and if the problem still exists I'll replace the carb gasket. I'll let you know......

 

HOLY COW!!! Hey WSG; I went 75 on the freeway this morning....That's fast for my Jeep! No sputtering either. I guess it was an intake leak due to a loose nut. I'm going to replace the carb. gasket tomorrow.

I would suggest checking your carburator and intake manifold for leaks.

 

I will do that.. maybe the intake, as i replaced the exhaust not long ago.. new header maybe, new gasket and flange mating problem maybe.

pretty sure of the carb bolts as i replaced the carb though.

Thanks, glad yours is running better too!

Steve