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Old 08-20-2011, 10:18 PM
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Issue with erratic timing

My idle is acting odd when I rev things up. Initial is set at 21*, all in at 36* by 3000rpms. No vac advance. Idle is 1050rpms.

When I rev the engine timing advances a little, then retards back, then advances more as I keep giving her more gas. Sometimes coming back down after reving up, the timing sticks around 30* at idle until I blip the throttle or move the distributor back and forth.

I was worried my cheap harbor freight timing light was to blame so I got a nice craftsman timing light recommended for checking timing over 2000rpms. No difference.

My first thought is a bad cam button allowing the solid roller to walk slightly, moving the distributor. Then when rpms go back down it stays forward sometimes. Before I tear the front cover off, do you have any other ideas of what could cause this?

I'm going to try locking out the timing first. If it still retards when locked that should indicate cam walk, right? I'm also thinking the distro gear could be bad? It's a cheap Skip White HEI unit with a melonized gear which should go well with my Lunati VooDoo solid roller.

Not sure what other info you need. 383 SBC 11:1, Airwolf 220 heads, Dart SHP block with forged crank, rods and pistons. Air Gap dual plane and PowerJection III fuel Injection. Cam is about .600" lift and 250* 0.050". MSD 6AL.

Thanks!

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Old 08-20-2011, 10:26 PM
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Cheap HEI's are made with Cheap parts. Swap a good quality ignition module and see if the timing stays steady.
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Old 08-21-2011, 05:37 AM
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Quote:
Originally Posted by FmrStrtracer
Cheap HEI's are made with Cheap parts. Swap a good quality ignition module and see if the timing stays steady.
I agree. Sounds like advance mechanism is hanging up. Can you borrow a decent distributor from somebody and try it?
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Old 08-21-2011, 05:58 AM
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I can get a streetfire MSD HEI from Pep Boys and return it if it's not the problem.

Other than that I'd have to order a new distro from Jegs or Summit.

I changed the weights, springs etc.. I also put in a machine bolt to limit mechanical advance. I'll double check to see if the bottom of the bolt is touching something causing a hang up.

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Old 08-21-2011, 07:38 AM
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IMO if you lock out the mech. adv. in distro., disconnect vac. adv. and certain its not moving, the only other things it can be are cam walk, cam/distro. gear play, distro. shaft end play(up & down), distro. shaft bearing slop(side to side), timing chain slop, or balancer/balancer ring moving around.
Before you remove distro. see if you can twist mech assy back and forth with it locked out with a zip tie or just by grabbing the part that doesn't move with the advance portion if you know what I mean. It may not be easy to do, but it may tell you something. If it moves up & down too much it has too much end play. If it twists back and forth more than a few degrees you have to figure out why.
Try turning the balancer bolt/crankshaft back and forth a little at a time while watching the distro. mech. assy.. Should move almost in concert.
If it does suspect your balancer/distro mech adv.
If it doesn't, try turning the crankshaft back and forth while holding/applying twisting pressure to the distro mech assy. May be easier said than done on a Chevy, but it may be able to tell you something from the feel of it. For instance if you can move the crank a little without feeling anything in the distro. it could be timing chain slop. If you can feel the distro turn a little then stop it could be cam walk. If you feel it twist it back and forth freely it could be gear slop.IMO
FWIW
ssmonty

Last edited by ssmonty; 08-21-2011 at 07:47 AM.
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Old 08-21-2011, 10:43 AM
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Might be too light of a spring (s) on the advance weight's not alowing them to return back in all the way. I use the medium, some use 1 med. and 1 light.

Also be sure that the weights move freely in and out by lubricating the pads they ride on and the post's they mount over. Lube very lightly as you don't want oil or grease flying around in the dist.
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