too much or too little fuel?

[Ahays000]

Okay, Here's the break down... I have an 86 K5 Blazer, originally a 305 4brl. carburetor truck. The previous owner has swapped in a 350 (10054727) out of a 93 3/4 ton chevy truck (originally a TBI motor). He also added an edelbrock cam, intake and 1406 600cfm carb, removing all the TBI and emissions controls.

The truck idle's good and the carb is tuned in perfectly for easy starts and great acceleration, the problem lies in top speed, as soon as the truck gets into 3rd gear (TH350 trans) it starts surging, running good, bogging down, running good, bogging down. doing so almost every other second, as soon as you let off the gas the engine clears up and does fine until you need it to pull a hill or any other open throttle acceleration.

The truck is running a 5-7 psi electric fuel pump inline near the tank. I was going to swap it over to a mechanical pump hoping this would solve my problem but soon realized this engine has no provisions for a mechanical pump.

My question is... Do you think high fuel pressure is a problem? there is no fuel regulator and the truck stinks of unburnt fuel. Also maybe its not fuel pressure but rather not enough fuel to fill the float bowls and it is being starved.

Any insight or personal experience would be appreciated.

 

[Blue85]

Well the surging sounds like a lean condition, although you describe it as too rich under other conditions. If it is rich enough to misfire and surge from richness, it should be blowing black smoke most of the time while it's doing it. If the fuel pump is not delivering enough, then the problem will get worse as the rpms get higher. Does this carb have mechanical or vacuum secondaries? It's possible that the primaries are jetted OK, but the secondaries are coming in too soon or are jetted too lean. What can you adjust externally?

The poor man's A/F meter is looking at the spark plugs. If you can get them clean and then try to drive only under the conditions in question (I know - easier said than done), they can tell you if you are lean or rich.

 

[Ahays000]

The carb has an idle screw, a cold start (fast idle screw) and 2 air/fuel mix adjusters, one for each side of the carb.

I have tried 2 different fuel pumps both produce same results

I just swapped in new plugs and the old ones looked to be fairly clean, no excess of gas or gunk on the electrodes

As for the jets and metering rods I have absolutely no idea, however I was told they were left stock from the edelbrock factory.

Think it would be a good idea to rig in a fuel pressure gauge so that I can see what its doing?