meeklay812

I recently did a 305 TBI to 350 carb swap. The problem I am having is around 1800 - 2500 somewhere in there, a bog occurs and the RPMS drop really fast and I have to pump the gas pretty hard to get it to pop over the bog. This usually only happens in 1st gear and one in a great while in second. Is this a fuel issue?

five7kid

iTrader: (14)

Probably. Have you put a fuel pressure gage on it so you can watch what it does before or as this event occurs?

meeklay812

Yeah i have one of the 1.5" under the hood fuel pressure guages. Something is messed up in my fuel system though because it only reads 3 - 3.5psi. With 3psi, i dont even think the car would stay running. When I adjust my AFPR, it doesnt move the guage one bit, but when i grab a wrench and squeeze the return feed, once i hit a certian point it goes way up and i can get it to 12 psi. When i rev the motor in park / neutral, the psi goes down just a LITTLE under 3. Any ideas?

five7kid

iTrader: (14)

3-3.5 is plenty at idle. The carb doesn't need pressure to run, it needs the fuel bowl(s) to stay at the proper level.

I was trying to ask if you knew what fuel pressure is doing when this symptom shows up. You can't know that with an under-hood gage. You need to get one extended to the windshield and taped on at least temporarily so you can answer the question.

What I'm suspecting is the fuel pressure drops to zero under load. That means the pump can't keep the fuel bowl(s) at the proper level when demand is high.

Carbs need fuel pressure only to insure the gas continues to flow enough to keep the bowl(s) full.

meeklay812

"What I'm suspecting is the fuel pressure drops to zero under load. That means the pump can't keep the fuel bowl(s) at the proper level when demand is high."

If that was the case, would i need a new fuel pump!?!?

five7kid

iTrader: (14)

You may just need a new fuel filter, or the pick-up sock may be plugged.

Or, you may have a "hot gas" issue, where the fuel in the system, especially in the secondary fuel bowl (if a Holley or Demon - you never said what kind of carb you have), has gotten hot and when you ask for it, it isn't dense enough to give the proper mixture ratio under load. Or fuel that has been sitting in the fuel line has gotten hot, and when it gets to the carb, same effect.

Or, you may need a new fuel pump.

meeklay812

Well, I replaced the fuel filter about 2 weeks ago. My carb is the edelbrock #1407, its a 750 cfm with a mechanical choke.... Is the "hot gas" problem likely in this carb?

five7kid

iTrader: (14)

I have no personal experience with them. However, it does have separate primary and secondary fuel bowls, so it could be.

Does this happen repeatedly and predicably? I.E., if you went through 2nd, slowed down and started the same routine all over again, would it happen in exactly the same way? If not, it could be hot fuel. If it repeats each and every time, it's not hot fuel.

meeklay812

It definately does it each time, but sometimes it varies how much it "stalls"... Sometimes it just WAY down and sometimes it gets down just a little...kinda crazy

five7kid

iTrader: (14)

Most likely it's a fuel delivery problem. The primary suspects have already been fingered.