Misfiring when driving hard

[76_Cobra_II]

I have a 1976 Cobra II with a 302 4 speed. When Im gunning the engine it misfires or "gurgles". I Really noticed it when I tried to dyno my car. I couldnt complete a full pull cause it was so bad. I have replaced the plugs and wires, but Im thinking I may need a coil, cap or possibly a distributor. What are y'alls thoughts on this? It has an edelbrock manifold with an edelbrock 4bbl Carb. Am I possibly trying to push too much fuel through? I am clueless, any help is appreciated!

 

[Cool Wheels]

Is that like a hesitation? If so, I replaced my accelerator pump not long ago and that solved all hesitation problems.

 

[chaka]

What size carb? Have you tuned it?

I would start there.

 

[Wart]

What they said.

And/ Or:

The secondaries could be opening too fast/ quickly.

 

[dmoody]

Have you checked your timing? Which way is it misfiring.. does it make a very loud bang out the exhaust or back through the carburetor?

>Am I possibly trying to push too much fuel through?

What did your plugs look like before you replaced them? Adjust the enrichment on your carburetor and/or the jet sizes if you think this is the problem.

d

 

[1970impala]

I have a 1976 Cobra II with a 302 4 speed. When Im gunning the engine it misfires or "gurgles". I Really noticed it when I tried to dyno my car. I couldnt complete a full pull cause it was so bad. I have replaced the plugs and wires, but Im thinking I may need a coil, cap or possibly a distributor. What are y'alls thoughts on this? It has an edelbrock manifold with an edelbrock 4bbl Carb. Am I possibly trying to push too much fuel through? I am clueless, any help is appreciated!

exhaust clogged?
how many miles on the engine? possibly the cam?
i would try the ol' cap and wire and plug and rotor routine. be sure the wires aren't cross arching!!! look at them at night for sparks to be sure they are not too close together.

 

[76_Cobra_II]

Let me start out by saying, "Tis is the first 8cyl I have owned and I dont know alot about it."
COOL WHEELS: Acc. pump? Please explain more.
CHAKA: I have NO Idea, will it say somewhere on the Carb?
WART: Secondaries? Please explain.
D MOODY: Havent checked the timing yet, but the car idles fine! When I get on it hard it seems to shudder and kinda rapidly backfire/pop. But not very loud. Kinda sounds like its coming from the Carb though....Plugs seemed fine, what would I have needed to look for?
1970 IMPALA: I dont have any cats on my dual exhaust so I kinda doubt the pipes are clogged, but then again, I dunno! 54,000 on rebuilt engine. Not sure about the cam. Havent checked the wires at night. I dont like to start her up at night since its So Loud with No Cats and 2 dual chamber Flowmasters. My apt. complex wouldnt like it!

 

[Cool Wheels]

If it's your accelerator pump you would notice symptoms of inadequate fuel delivery when the throttle is actuated under load, like when you hit it hard, while in gear, the car will bog out or "hesitate" then will go as normal after the hesitation. Not sure if this is your problem. Depends on the symptoms. I'm not a mechanic or anything so listen to some of the other advice on here. The AP is located on your carburator and will be somehow connected to the throttle - not sure how to test it though...

 

[chaka]

To test the acclerator pump you can push the throttle while looking down the carb. (while the car is not running, you don't want it to backfire and have your face over that) and see if gas gets squirted out. You will notice see it. I am sure there is a better way, but if that happens you should be good.

I am not sure if it will say on the carb. really don't know, but a lot of people overcarb their cars and it makes them run worse. bigger is not always better.

To tune it you need a vacuum gauge. You hook it up to the manifold and adjust the mixture screws until you get the highest vacuum. (There are usually more then one mixture screws. If you screw one in you have to screw the others in the same amount) most carbs are set to run rich out of the box.

Secondaries are just that. on a 4 barrel carb you have two primaries and two secondaries, which open up under a load to add more gas, You can have vaccum secondaries which are activated by vacuum from the manifold or mechinicals which are just hooked up to the throttle linkage. If the secondaries are set wrong they will open too soon and add excess gas.

For the timing. I usually just let the car warm up then spin the dist. until I get the highest rpm. then adjust the idle to the accordingly.

hope this helps

 

[dmoody]

In my experiences with Fords I've rarely had the Accel Pump, secondaries, etc be faulty on a carb. I think your problem stems from one of a couple common problems:

1) Carb float set to low and/or trash and/or old gas buildup in your float bowls.
2) Fuel pump is about to go out on you. This happens when the pump gets old and the internal gaskets start to tear apart. There may be enough gas pumping for the car to idle but not much more than that.
3) Your timing is off. You can adjust the timing and the car can idle great through a fairly large range of settings. However when you accelerate hard if your timing is off then the engine will hesitate and/or bog down.

d

 

[76_Cobra_II]

Wow guys, All great advice! Im gonna check all that out as soon as I can get a free WARM weekend. Thanks to EVERYONE for their $.02!

 

[COBRA 7]

A camshaft with a bad lobe will pop out the carb. under acceleration.

Put a vacuum guage on the intake manifold and see if the needle is steady. If it jumps around alot, maybe a bad cam. lobe.

 

[76_Cobra_II]

Pump is fine, I tested it and gas came flowing out very well! I messed with the 2 screws a little bit, got it idleing alot better, but didnt take it on a test run due to the rain, I dont need to skid out of control! I also noticed instead of a Spring on the accelerator return, there is a lock strap (the kind U slide into a square end and it clicks into place but cant be pulled back out) I need to get a misc. spring kit from the parts store this week!