Alright this is for a buddy of mine. His 350 SBC with a moderate cam, single plane intake, and pretty good heads(i dont know the specs of them) runs poorly when getting on the gas <2000 RPMS. Above 2000 RPMS while getting on the gas it is smooth and all power. Now I am not talking about a lack of torque, it just runs rough and misses out a little bit. What could the problem be, it has not always done this???
Thanks
Brady

 

ttt

 

Vacuum leak? Is this car computer controlled? If not, is the vacuum advance hooked up correctly to the distributor?

 

I'd check the valve lash. My rockers had loosened up and my car ran like crap at low RPM's but ran strong at higher RPM. I reset the valves and the problem was gone.

 

The setup he has is probably not a torque setup. Single plane manifold and good heads, assuming he has big port heads. That would create throttle response problems.

 

Just out of curiosity, what are his cam specs? (spec. lobe separation) He could have built a completely top end engine without any low end driveability... Single plane manifolds are not recommended for daily driven vehicles since the power band (with matched cam) usually lifts to about 2000-6500 RPM up from about 500-5500.

 

i dont know - he might not even now. it is not a lack of torque, it is missing out and running rough. it didnt always do this just started

 

Well, if you saw my head gasket post... I thought I had blown a head gasket, but it turned out to be the timing chain, the car idled very lopey and it stalled when I shifted sometimes, or just while idling... the top end was fine, just a VERY crappy idle.

How old is the engine is one question... if over about 80k miles it is possible that the timing chain could be too stretched, although most chains last a lot longer (158k for me).

You don't want that baby to break though, that's a fast track to a nice boat anchor.

I would suggest testing the compression (two low cylinders may be a blown head gasket) look at the oil for discoloration (grey and foamy is probably a head gasket) and check the valves for leaks, broken springs and bent valves... If you hear a clackity clackity from the timing chain cover than yank that thing ASAP.

 

I'd start by pulling the spark plugs to see whats going on in each cylinder. If it's carbed it may be just running rich or a fouled plug which cleans up with a good rev. Look at the easy stuff first, spark plugs, carb tuning, basic tune up stuff.

 

i was having that same problem with my 1987 Z28 305 and it turned out to be the furl pump and regulator. so look at that.