I know its a chevy but I need help

[Nathan123]

My buddy has a 78 chevy k20 with 9 inches of lift and 37's. It has a 350 out of an 84 k20, and has high compression pistons and a pretty rowdy cam in it. Stock quadrajet carb. It has a pretty bad misfire under load and looses a lot of power. It will idle fine and rev into the 5000 range just fine. But while driving, it will start to miss pretty bad especially around 2200 rpm. Also, while under load, at aroudn 4000 rpm the motor just starts to flutter and wont rev higher, almost like valve float, but when in park or neutral it revs much higher. We've changed the plug wires and put a new rotor in it. We also tested the pickup coil and its resistance was 768 ohms, which is fine. There is no egr setup on the motor. Anyone have any clue what could be bad? We really suspect ignition but could it be fuel?

 

[shane96ranger]

My buddy has a 78 chevy k20 with 9 inches of lift and 37's. It has a 350 out of an 84 k20, and has high compression pistons and a pretty rowdy cam in it. Stock quadrajet carb. It has a pretty bad misfire under load and looses a lot of power. It will idle fine and rev into the 5000 range just fine. But while driving, it will start to miss pretty bad especially around 2200 rpm. Also, while under load, at aroudn 4000 rpm the motor just starts to flutter and wont rev higher, almost like valve float, but when in park or neutral it revs much higher. We've changed the plug wires and put a new rotor in it. We also tested the pickup coil and its resistance was 768 ohms, which is fine. There is no egr setup on the motor. Anyone have any clue what could be bad? We really suspect ignition but could it be fuel?

Have you checked for vacuum leaks? This includes around the intake manifold.

 

[85_Ranger4x4]

Knocks or pings?

How much is "high compression"? What grade of fuel?

 

[Nathan123]

We didn't check the intake for a vacuum leak but all the hoses look good. When the missing is at its worst, it sounds kinda like the ticking of an exhaust leak. It's high enough compression that he can't run 87 but he can get away with 89. Its always had a really choppy idle that bounces the truck back and forth at a stop sign. He bought the motor and put it in he didn't build it so he doesn't know all that much about it, but it did run fine for over two years up until a month or so ago. Its always had a really choppy idle that bounces the truck back and forth at a stop sign.

 

[JC 97]

Check the distributer shaft for play.It could have a worn bushing.I had an old camaro that gave me symptoms like yours.Finally traced it to a wobble in the shaft.

 

[shane96ranger]

We didn't check the intake for a vacuum leak but all the hoses look good. When the missing is at its worst, it sounds kinda like the ticking of an exhaust leak. It's high enough compression that he can't run 87 but he can get away with 89. Its always had a really choppy idle that bounces the truck back and forth at a stop sign. He bought the motor and put it in he didn't build it so he doesn't know all that much about it, but it did run fine for over two years up until a month or so ago. Its always had a really choppy idle that bounces the truck back and forth at a stop sign.

My 85 Mustang used to run intermittent at certain RPM's, and the idle was high. We sprayed carb cleaner near the intake gasket, and it revved up. We just re-torqued it, and it ran fine again.

 

[Nathan123]

I have another friend that's gonna bring a new primary coil on Monday to rule out a weak coil, we'll definitely check the shaft for play. If it's bad is it worth re-bushing it or better to get a whole new dizzy? How much work is required to re-bush the shaft? A new one with coil is 160 bucks, but the guy doesn't want to spend that and not be sure that's whats wrong. I guess it wouldn't hurt to spray some ether around the intake just to make sure that isn't it either.

 

[Rose2300]

How much work is required to re-bush the shaft?

lol

 

[shane96ranger]

lol

I didn't catch that

 

[ap3x]

Cracked plug? Happened to me before and I was stumped. Felt like an idiot when I finally discovered the culprit.

 

[inuyasha2875]

have you checked the dizzy to see if it came loose

 

[84bluebronco2]

lol

Repped

 

[Rose2300]

Repped

 

[Nathan123]

Well, we couldnt swap out the accell super coil because we didnt have the screws that came with it and the stock screws were too short. But we did clean the little contact pad on the bottom of the stock coil. We finally put a timing light on it only to find that it has an aftermarket timing cover and the little pointer isnt there. Regardless, the hash mark on the balancer pulley wasn't any where in the little opening where the pointer should be so we retarded it until we could see the mark and then went by ear. It seems to not miss anymore, still isnt so great at high rpm. Also noticed he's missing two header bolts on the passenger side rear cylinder so thats the ticking sound under load. I think the timing just needs fine tuned a little more.