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Carb Question

796 views 11 replies 4 participants last post by  frickenbored 
#1 ·
Ive got a 1988 k5 blazer with a built 350 engine. Last summer I bought a holley 750 carb with vacuum secondaries and electric choke and i spent forever finally getting it tuned to where I thought it ran right. The truck started on the first or second crank everytime and it idled at around 900 rpm. It took off and drove perfectly never backfiring or choking. Untill I really got into it, if i floored the truck from a stop then at about 60 mph the engine would start sputtering because it was running out of fuel, if i took my foot off the gas for a few seconds the bowls would fill up and i could slam the gas back down, and i also feel like the truck could be making more power at all rpms.

The truck used to be tbi so it has an in tank factory style fuel pump that puts out about 15 psi that I have regulated to 6 psi. I don't know the exact specs of the cam but I do know it is on the wild side with a pretty rough "race car" sounding idle and the compression is a little higher than factory at 10.5:1. And the th400 trans has a 3800 stall converter in it, a bit high i know but fun when your getting into the throttle. And if it matters I have 4.56 axle ratios.

My question is whats the best way to fix this high speed/rpm sputtering. I also have a holley 670 street avenger with large jetting (90 something). Would the street avenger be a better choice for this engine because its supposed to be a performance carb. I was also thinking about a 650 or 750 double pumper but I don't know if that will be too much for this engine. Or am I looking at this all wrong and ignoring the fact that I might need a higher volume fuel pump?

Any help or suggestions would be great.
 
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#6 ·
Augusto said:
bad pump or clogged fuel filter, leave the carbs alone until you find the problem.

for the 350 engine on the street, the 670 should be more than enough, happiness is a small carb on the streets.

Well the pump is brand new but I am using all the original fuel lines running down the frame rail and the original 1988 inline fuel filter is still there. I'm going to get rid of that filter and replace it with some tubing or hose since I have a pretty good filter right before the carb.

This truck is mainly used for mud bogging not street driving.
 
#12 ·
yea I'm going to get rid of the old factory in-line filter and maybe change out the filter going into the carb with a better one.

the 670 is a street avenger (wish it was a truck avenger) i'm going to put that one on the truck this summer and see if theres a difference.

does anyone know if the 670 street avenger is an internal or external vacuum carb? I'm trying to buy an electric choke kit for it but I'm not sure how to tell the vacuum source. I'm guessing internal vacuum.
 
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