I'm running a double pumper holley carb on my 400, with a performance cam. When I mash on the gas, the car builds speed very slowly and then a popping or coughing sound comes through the car, like a misfire. The timing is set to 12TDC and the float levels seem to be fine. Any help would be appreciated, I know nothing about carbs.

Thanks again.

Seth

Did it just start doing this? Has it been sitting for any amount of time without starting? How old is the gas? My first thought was your timing is not advancing when you "get on it". I had a vaccum problem with the vaccum advance a while back on 1 of my cars. Just a thought.... Joe

It did just start doing this. I have driven it since the winter and it just started doing it. And it's just getting worst. Do you think if I put carb cleaner through it? I guess it's worth a try. I wonder if the advance canister is broken?

Definitely sounds like a timing issue. How old is your timing chain? I had only 25k miles on my rebuild and the chain was stretched big time. I had a lot of misfiring up the carb.

Just a thought...

Using E10 fuel? Longshot but it causes all kinds of carb related problems. Go to pure-gas.org to find decent fuel.

Timing may have slipped. Has the idle changed at all?

If the idle is ok, check the total timing with an adjustable timing light.

Check that you're getting full throttle, make sure both the primaries and secondaries are vertical. Could be the secondaries are jammed.

Do you run a good fuel filter? With today's gas, modern fuel tends to clean the fuel system well, but it also rots rubber pieces. Check your fuel filter or filters. I've had a Fram canister filter clog after only about 200 miles.

There are many things that can cause that effect with a Holley. First off, when you hit the gas, the carb is going from the idle circuit to the main circuit and there is a lot of transitional things happening between the jets, power valve, and squirters. If it just started doing this, and every other time in the past when you mashed the gas, I would look at dirt in the main circuit. I would recommend taking off the float bowls and metering blocks, cleaning and blowing out all the passages then replacing the power valve and putting it back together. I have run, built, and raced many Holley carbs ad when they work they are great, but they can be a real pain when they get dirt or bad fuel in them.....

mine does that but i just put it together after 20 years so don't know yet what it is. i put some 93 octane fuel in it to see if that helps. if that doesn't help, i'm going to retard my timing from 12 BTDC to 10 BTDC. it does seem like its pop and cough on moderate to heavy accel which could be detonation caused by overavanced spark or poor fuel quality. hopefully one of those works, i'll let you know.

I brought up the thing about the e10 crap fuel they are selling nowdays because I have been doing nothing but rebuilding/cleaning out power eq. carbs all spring. The ethanol picks up the water and crap in your tank, and is corrosive to some parts including some rubber. Lots of info out there on it, even on my 67 I ended up having to put a fuel pressure regulator set at about 6 to stop the needle/seat from getting stuck and I use non ethanol fuel. I too have had a new filter clog real quick and send water to the carb, start with the simple stuff perhaps swap a know good carb on there to rule out that as a potential problem.

It's been 25 years since I have had to deal with a Holley 4 Bbl, but your problems sound strangely familiar.

Are you using an in-line fuel filter? Is it a good one?

I had a lot of problems with trash in the gas jamming my float needles open and causing symptoms like you describe.

Have you used a fuel pressure gauge?

Thanks for all of the advice. I'm up at a show this weekend, but as soon as I get back I'm going to try looking at all of these things.

I'm wonder if it could also because by a coil. I just replaced my coil a few weeks ago with a NAPA brand one. Could it be I got a bad one. It seems to coincidental.

so everything was fine until you replaced the coil ? was that just for preventive maintenance that you changed the coil ? could be a poor connection or a lower output coil that doesn't have the juice to keep the spark strong under high output demands. seems doubtful but you could put the old one back in and see if it makes a difference. also on mine, the wire came loose inside the distributor cap (I think thats where the one side goes to from the coil). doublecheck that. i tried 93 octane and it didn't help my issue, next up retard timing from 12 to 10 BTDC.

Will try. Thanks