My OT farm truck is running a 250 6 cylinder from a 74-ish Nova. When I bought it, PO had installed the motor with stock intake, rebuilt 1bbl carb, and split header with a 2 into 1 exhaust setup (yeah, kinda goofy). I'm having trouble getting it to where I think its 'right' PO had timing set wrong, hold down screw for the points was stripped and it wouldn't hold dwell, etc. It always felt 'cold' and didn't take throttle well. I got all that fixed, including a heat plate kit from Tom Langdon, plumbed into the temp sender location in the head, and a threaded bung in the top of the Tstat housing. The plate gets pretty warm, and I'm running a 195 'stat. My outboard plugs look great, almost a little lean, but the center plugs (3,4) are really black. The truck runs with decent power, revs ok, but doesn't feel very torquey. (truck is a 3/4 ton gmc w/4.10 gears, just for reference). Eventually it may go into an older pickup if I can find the right candidate Would like to make the best of what I have before going all in on an engine build, especially considering this is a low compression motor that's not going to take well to a lot of cam and carburetion. Thanks...
Have you checked the advance weights in the distributor to make sure they're free and not sticking? Does the vacuum advance diaphram hold vacuum and actually move the breaker plate? If the spark advance isn't coming in like it should, it will have a sluggish feel. Due to the design of the engine / intake, the center cylinders will run richer than the outer ones, but they should'nt be that rich. Are the center cylinders getting a weak spark compared to the rest? Double check the cap, wires and plugs for the center cylinders to make sure there's no problem there. Those two wires aren't crossed are they?
I've checked the vacuum and mech advance, and both seem to work as they should. I'm wondering if the balancer has slipped though - it likes a lot of timing and when its set according to the timing marks, feels really retarded. I've been slowly advancing it more and listening/looking for detonation on the plugs. Nothing yet. Plugs, cap, rotor are new but haven't checked wires - good idea. What about running a couple hotter plugs on the center cylinders? might try that tomorrow.
You mentioned the dizzy was in wrong maybe the cam was installed retarded by a tooth or two? Or it may have the wrong balancer.
Swapped in two fresh plugs in the center and its running smoother, but still feels down on power. I'm going to get new plug wires next and play with timing a little more. Dist was in correct, but the point hold down screw was stripped and gap kept changing. Funny, with a real wide gap - like .035, it had more power but missed a lot at idle and didin't rev well. I've set it at .018 and its smooth overall, revs easier, but not as 'peaky' power-wise
1. Check your top dead center and the mark on your balancer. 2. worst case is that the timing gears have worn and are retarding the timing. (you will notice a growl from the front cover after revving the engine) 3. My "70 Nova ran very strong after I streached the power valve spring. 4. fix your distributor, every time the vacuum pulls the plate the points change. 5. My Nova ran like **** when I first got it. I changed the coil, put in an oversize screw to hold the points from moving, replaced the advance springs in the distributor, reset the spring in the carb and replaced the balancer, cap, rotor and wires...it ran very strong with no hesitation. The spark plugs were dark gray on the center two and the other four were light gray.
The best improvement I made to my 250 nova engine was installing a hei dist, long reach plugs with a .060 gap, timing at 12 degrees, the car pulled like a v8, it was great on hills. Also I would go to a better carb from Langdon's, he is so reasonable on his prices. good luck
Wide point gap advances the timing, and that's probably the answer. Set it by ear, when it idles fastest, lock the dist. down and test drive it. It might have to be retarded a tad, sixes don't like a lot of advance. Tighten the manifold bolts, the black center plugs sounds like a vacuum leak at the ends.
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