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Old 11-13-2002, 10:35 AM
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Post Timing problem - Help

I'm at my witts end, and I stumbled across this site. Most of the other message boards I've found everyone's running EFI and doesn't know jack about timing... so I'm here to ask you guys some questions.

Edit: This info would proably help:
I have a 1979 Chevy 4x4 Truck with a 350 engine, Edelbrock Performer Cam, Intake, and 600cfm Carb, HEI ignition, Headers and dual 2.5" exhaust.

The truck's been running funny lately so I went and hit it with a timing light again and it's fine at idle, 10-12 deg. BTDC advanced w/ the vacuum advance disconnected & plugged. But, as soon as I rev the engine, the timing retards back to between TDC and 4deg ATDC! I don't like the idea of revving it higher than 2500 rpms or so while my head's in the engine bay so I don't rev it higher than that w/ the light, but it's definatley hurting my performance and gas mileage. When driving the power seems to come back in about 2500 or so, which is, I assume, when whatever's wrong w/ the timing system corrects itself partially and comes back.

Also, when I hook the vacuum advance up and time it, I still get my 10-12 deg. BTDC advance but when I blip the throttle I get an immideate +10-12deg of advance, but at about 1500 rpms or so It still comes back to right about 0 degrees. Also, when I rev it to about 1200-1300 rpms and hold it steady the timing is bouncing all around...... advance fluctuating between 8 and 20 degrees advanced randomly. It also goes way retarted when I give the engine a quick rev to 2000 and let off, the timing falls way back and the engine idles like crap for a few seconds before advancing back up and smoothing out.

So, I've replaced out the ENTIRE HEI ignition system piece by piece, all the way from the distributor down to the plugs........ New Module, new coil, new cap, new rotor, new advance weights & springs (put in every possible combo), new wires, etc. It helped the problem, but by no means fixed it. It still retards back between 1000 and 2000 rpms and then climbs back up again, and still idles realy rough for a few seconds after a quick rev, but it did improve the condition somewhat.

Could it be the timing chain?

Another thing to note, is it seemed to have completely fixed it after I changed the distributor out yesterday, but the timing springs I put in were slightly heavier than I desired for my advance curve so I put in lighter springs, and after that is when I really seemed to notice it, but when I put the old springs back in it made no difference.

Please help! I'm THIS close to sending this thing down a boat ramp in neutral.


[ November 13, 2002: Message edited by: MTMike ]</p>

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Old 11-13-2002, 01:07 PM
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Well spank my *** and call me stupid.....

The truck is fine, the ignition timing is fine. I just forgot to remove the vacuum advance when I checked it that last time. I just went out removed it this time and checked everything over again and all is well.

The distributor did fix the problem after all.

Time to go have a few beers

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