No Performance

[86GMC4x4]

I have a 86 GMC 4x4 with a 350 carb. engine and a TH400 3.08 gears. The issue is poor performance and no gas mileage (8-10).it also has a Q-jet carb and stock manifold, the carb. has had a kit installed and a brass float installed. Just did cap, rotor, plugs and wires, timing is set at 4 degrees.When throttle is punched down truck doesn't seem to respond, it will gradually pick up speed doesn't seem to bog just no quick response.Could this be a vacum problem causing the trans not to shift down allowing quick throttle response.The gas mileage has been poor since I have owned the truck, I have had 350's before that have been excellent performers but this one just doesn't seem to have it.Any info. would greatly be appreciated

Thanks

[Redneckchevy]

Well its not the engine its just thats its geard low....it was never ment to go super fast its ment for pulling and towing....if u wanna get some speed start looking at a tranny and rear end swap..

[Lt.Del]

3:08 is a relatively HIGH gear....good for high speeds on the interstate and such...not so good in city driving.

I'd get a cheap vacuum guage and see what you got.  I am not familiar w/ the 86 models, not sure if you have a transmission modulator (vacuum) or it may be electronic. I know that year is close (and 87) to lots of changes.  

I would readjust the carb just to rule that out or it may be the problem.

You are not gonna get much better that 10mpg for city driving...in fact that may be right on from city driving.  Highway driving may get you 14 -15 perhaps.

again, unfamiliar w/ 86 models but do you have a vacuum advance in your distributor?  Is it advancing...easy check....see if your vacuum keeps air. Manually advance. then place finger over where the line attaches see if it holds.  Take you timing light and look at the marks whils someone accelerates. See if marks move.

Just a few things to think of.

SgtDel

[Redneckchevy]

I own a 1986 and mine is geard low..that all i was thinking...