390 not running right

[bcsideshow]

Heres the scoop on my 1970 AMX:
1969 390 Rebuilt stock bore stock pistons balanced bottom end. Comp Cams 270H. R4B. Edelbrock 750. 70 (6291C) heads. with 3 angle valve job and comp cam spring and retainers. Roller tipped rockers. late model motorcraft ignition.

The only way I can get the car to run is by advancing the timing such that I can't see the mark on the damper with the timing light. When the car runs it is very hard to start when hot. Just turns over real hard. When I put the hammer down off the line it just cuts out and doesn't go. Runs at cruise speeds very good but put it to the floor and it starts popping out the exhaust.

Any thoughts? Timing, carb to big??????

Thanks,
Brian

[jeepsr4ever]

almost sounds like the timing chain is on wrong....but before we go down that road lets start the check list



plug wires right
good spark
carb gasket sealing
timing right


oh yeah welcome aboard! iu was in kenosha last year....great show :t:

[Dusty]

yeah plug wires in right order.........?

[bcsideshow]

I will double check the wires. I am pretty sure they are right. I have tried to find a vaccum leak and came up with nothing. I have changed cams on AMC v8's many a time and it is pretty idot proof. Line up the marks and your good to go but I am really thinking that is what it is.

THe Kenosha show was great!

[tufcj]

The only things I can think of is that the outer ring on the harmonic has slid. Did you check that the balancer was at 0 with the #1 piston at TDC? I've seen them slip as the rubber between the rings deteriorates with age. Once that happens, the mark is useless for timing. Hard start when hot is usually too much initial advance. Check to see that the centrifugal advance isn't sticking, and the springs are good. You are setting initial timing with the vacuum advance disconnected and plugged? Just some thoughts.

Bob
tufcj

[bcsideshow]

Hey guys. I want to just say you have a great sight and the fast response is awesome. It's nice to get some input from some knowledgable people. My wife just had twins and we already had one (3 girls) so finding the time to trouble shoot is very limited so it's great to have you guys to help with the brainstorming.

I did verify plug wires were on right and rotor was pointing to number one when timing mark was at TDC...I did not verify piston wsa at TDC. Maybe damper slipped. When I painted it I did notice rubber was cracked. I never would have thought of them slipping. I will check that this weekend. I am also going to pull the valve cover and check the location of the number one valves at TDC. I could throw an indicator on them if I need. I don't want to pull the timing cover unless I know for sure something is wrong. I distinctly remember checking those marks but I was having few beers.

THanks again!,
BRian