429 carbed studder problem

[Krafty]

429 with 2 bbl carb, stock fuel pump, fuel filter not that old. coil off 79.

here is my problem it will idle all day long, in park and neutral i can rev the engine and hold it anywhere without problem.

when its in gear and under load ( usually after its warmed up a bit) it'll studder and drop rpm then jump back up sometimes once or twice, but lately its been doing it almost constantly for like 10 minutes at a time. I can always put it into neutral and rev the engine fine, and it never drops idle or stalls.

blocked line?, fuel filter?, Coil?, clogged carb? Fuel Pump?

either spark of fuel for sure, underload thing makes me lean toward fuel,

the good idle and reving makes me think there isn't enough pressure in the line, ie pump.

 

[Bronc76]

how old is fuel pump and has carb been rebuilt?

 

[Krafty]

fuel pump is original 69 I think. and no the carb hasn't been rebuilt. the carb is a 79.

I've had absolutely no problem with it for over a year of driving, but now its started doing the studdering.

I can try running some carb cleaner or something through it. the fuel filter is only $4 so I'm going to do that first.

 

[Broncobill78]

Sounds an awful lot like a carb problem. I'd also make sure the engine is in good tune, timing is OK and vacuum is good but if all that has been done or ck's out then I'd say it's most definitely time to rebuild/replace the carb. If you *do* replace the carb keep in mind that almost none of the (Holley's in particular) will run well right out of the box. Holley's are notorious for runing rich & needing a good carb-tune before they'll run well. Dropping & stumbling when in gear might be pointing you towards a vacuum issue. Make sure all yous vacuum lines are in good shape & everything that *should* be capped is capped. Don't forget to ck the large line running from the rear of the intake to the brake booster. Do you still have an EGR on this engine ?

You might have a fuel flow problem, especially with an old/original tank but I'd take care of the carb before I started dropping the tank or replacing fuel lines. It sure *sounds* like a carb problem.

 

[Krafty]

I just picked up a fuel filter and some carb cleaner so im gonna try that before anything else. if that desn't fix it then i might try the 2bbl off my mustang and see if that works. The carb on it is original 79, and the one on the mustang was replaced last year so maybe that will fix it.

I put a new tank on it last winter.

 

[Krafty]

okay so as far as I know its an autolite 2100. with a the 302ci size main jet. now I think there are jets for the low mid and high.

the fuel pump is good cause when I pulled the fuel line off the carb it sprayed at me.

I have a 351W that has the same carb but its mostly seized together, im gonna try to get it apart if I can.

it wouldn't be a vacuum problem cause all my major systems run on vacuum and all is well.

the problem only occurs sparraticly after its warmed up. and only at mid throttle acceleration or cruising. if i let off the throttle it stops and if I floor it it stops.

and only when its in gear.

 

[Krafty]

I tried a different carb on it that I know works. and that did not fix it at all. no change pretty much.

im gonna look at getting a different fuel pump on the engine just in case. if that doesn't work then its either some unseen vacuum issue or something with my distributor or ignition system.

 

[Krafty]

okay my 429 seems to have a double vacuum advance timing setup one hot one cold, I don't know why.

But anyways, im gonna look into swapping it out for a regular one, or just a new one like that. wish me luck, im at my wits end here