ChrisC

So, for the past couple of weeks now, my non cc 305 ho has been stumbling quite bad. I have a new-ish Edelbrock 1406 on it, and for the first 15-20 minutes of driving, the car falls flat on its face, bogs, stumbles, stammers, stalls, all of the above. After I get the car running for a solid 15 minutes, it runs perfect. The chokes coming off within a normal time but the problem keeps happening afterward. When the problem occurs, the car will idle down extremely low, pop through the exhaust, and appears to be running very rich. Thus far I have replaced my fuel filter, cleaned the needle, floats, and all internals of the carburetor, as well as my fuel pressure regulator. All internals were as brand new as they should have been. I'm thinking that it could be a problem with the choke, any thoughts guys? The car will start every time and I am running 5-5.5 lbs of fuel pressure.

Apeiron

The choke would be a place to start.

Edwardgp

The choke is maybe staying on to long, or opening up to fast. That is adjustable. You can, if you do not have the instructions, look them up on line.

ChrisC

I haven't calibrated it since the hot weather has started. I think it's just a matter of loosening the bolts on the choke housing and increasing or reducing the amount of tension on the spring. I can't remember which way does which though, so I will double check. Thanks gentlemen

Edwardgp

On the Edelbrock [spelling] it makes a big difference when you adjust them. Do the idle screws and choke adjustment and let me know how it works.

ChrisC

I adjusted the choke this morning but by the time that all was said and done, the car was fully warmed up anyways so I wasn't able to see if that fixed my problem..We'll see once it cools down!

ChrisC

To bring up this post again, I've been trying to figure out this issue for about 3 weeks now with absolutely no luck. Upon adjusting the choke, the car won't stall on initial start up anymore. However, within the first 15 mins of driving, before the car is completely warm, the stalling, sputtering, and falling on its face still happens everytime without fail. I have noticed that it will always happen after I take the car for a short drive, shut it off, and then start and attempt to drive it. 9 out of 10 times the first cold start it will drive fine but as soon as I shut it off and try to drive again it happens. The jets are all fine, as are the needles and floats. I thought it might have been ignition break up when the coil was cold but after swapping coils there's no change. Just to say I did it I also inspected all of the plugs and timing's fine.

Any other ideas would be great because I'm completely stumped.

Additional info: I also was thinking that it could be the accelerator pump, but if it was it wouldn't be an intermittant problem it would occur during both cold operating temperatures. Another comment, I have a cheapo fuel pressure gauge that runs inline with the fuel inlet going to the carb. The gauge reads 0 lbs of fuel pressure when the problem occurs, however the gauge is a piece of junk and fluctuates every way that it wants. My next step is to legitimatly test the fuel pressure. Anyway, I just felt like I should add this additional info in.

Edwardgp

And we thank you for the update, no new ideas to give you. Keep up the fight you will find out whats wrong pretty soon, let us know what it was. PS you might try and adjust that accelerator pump.

ChrisC

Thanks for the support, I adjusted the accelerator pump last week and the car was running awesome. Then I shut it off and went out again 10 minutes later and sure enough, it instantly started running awful. Earlier, I looked at the accelerator pump while working the throttle when the problem was occuring and it looked like there was no fuel squirting into the carb from it. I've heard of fuel pumps doing weird things in cold weather but never anything about a fuel pump acting up only before the engine has warmed up..on a non cc car that is. By the way, it's an electric in tank pump. Not sure if I mentioned that.

ChrisC

After checking the fuel pressure both before and after the return style regulator, I have come up with this: Fuel pressure is where it should be until the problem begins. Once the problem begins, fuel pressure both before and after the regulator drops to almost 0lbs of pressure. As soon as the problem starts to clear, the fuel pressure returns to its normal PSI. I know on the later third gens the pump relay is located on the firewall in between the booster and the fender. There are a couple of relays there on mine, one for the pump and one for the fan I think. Does anyone know which one is which or if this is the same as my early third gen? Missing out on all of these prime beach cruise nights is really putting a damper on my summer!

ChrisC

Nevermind, found out my answer to the relay location question.

ChrisC

No update on the solution because I have not found it yet. To walk through this for my own benefit: The problem has to be before the carburetor. Lack of fuel pressure has to be either a clogged filter, a fuel line, the relay, or the pump itself. I have replaced the fuel filter that sits under-hood. I am gonna replace the one that lies in line under the car next and take it from there I guess.

ChrisC

I took the car out last night while it was only 60 degrees out and it ran like a dream. This morning started it up and it ran great again. After warming up, absolute junk. I know that I have an in tank electric pump and vapor lock is less likely, but this problem is starting to turn into something that resembles just that, vapor lock. Any thoughts?

five7kid

iTrader: (14)

It is possible the in-tank pump isn't doing its job. I've seen them work fine when cold, and crap out when warm.

ChrisC

Yes I think that the pump is more than likely the culprit as well. The only thing that was hindering me from replacing it was the sporadic manner of the problem but I agree that it more than likely is the pump. Any recommendations as far as pumps go? I remember hearing when I bought the car way back when something about upgrading to a Corvette pump. It may have just been a friend rambling but I can't remember now.

ChrisC

To pull this thread back to life again, I replaced the pump with no luck. I re checked my fuel pressure and the pressure is still good. I even by passed my 4309 regulator and ran 13 lbs of fuel straight to the carburetor BUT even with this much fuel pressure, there was still 0lbs of pressure reading to the carb. In terms of the fuel pump, I know that the ecm primes the pump and once a few lbs of oil pressure are detected, the oil pressure sending unit takes over in terms of powering the pump. My oil pressure gauge has been busted since I have owned the car a couple of years now, but I have never had a problem in terms of fuel. I guess what my question is, is if there is something wrong with the OPSU, then how is the pump powered? I've heard of the opsu going bad and the fuel pump constantly staying on but I've never heard any tales of the opposite.

FtrSpeedy

Check for exhaust leaks by the fuel line, sounds like tryin to vapor lock.

ChrisC

The only reason I'm straying away from vapor lock is because it has an electric pump opposed to the vapor lock **** mechanical pump. Does anyone know about the oil pressure sending unit? If it were to fail then in theory wouldn't the pump still prime with no problem from the ecm but since the opsu had failed, the pump would no longer get power after initial priming and the motor would not receive more fuel..Or does that work a different way?

ChrisC

Or does the fuel pump relay stay on as a constant to power the pump as well?