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Discussion Starter #1
My buddy came over yesterday, and we went through the valve train in the 68 again. Zero lash, plus a half turn. Now, the motor sounds more roller rocker-ey, which I am fine with.
The question is this.....During my last few attempts to diagnose ignition issues before I left for Kuwait, I blocked off the vacuum advance at the distributor. When I took the car out for a test drive last night, I left the vacuum advance blocked off. Under a load, the car was back firing now out the exhaust a bit. It seems reasonable to me, that it was due to the distributor being plugged. Do you concur?
 

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The vacuum advance pulls more timing when there is basically no load or some vacuum. Most people that do not use vacuum advance are doing it to stabilize their timing. You would be less likely to backfire from timing with it plugged if your timing is right. A lot of people set their timing at idle never knowing what their total timing is. It could be that when you set your total timing that at idle it will fall out of a range that works. In that case that is where a recurve of the mechanic advance. It could even be that the mechanical advance is hanging up, spark plugs/wires ,or bad valve seal. I have seen a engine that backfired and missed from having the #7 and #8 plug wires ran too close together for too far of a distance.
 

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Discussion Starter #3
Well, I just took it for a drive again, and I'm thinking it could be a mis-adjusted rocker arm, or more likely I wiped a lobe. I'll go through the valve train again after I get back from NY, and see what I can see...
 

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For the small block Ford and Cleveland lifters, I never go past zero lash plus a quarter turn. The small block Chevy can handle a half turn, but the Fords seem to have troubles with it...not always, but some.
 

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Discussion Starter #5
Well, I will say this. The first Edelbrock cam I put in the car that failed, has much shared responsibility. The machine shop, the parts guy, ME.....The second time all I did was replace the heads, with the "right" springs! It ain't rocket science..Exhaust opens, adjust intake. Roll engine over until intake almost closed, and adjust exhaust. Repeat. It only does pops under a load, around 25--3500 rpm, other wise it runs great.
If I find a wiped lobe on this car again, I am going to have a conniption!
 
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