having hard time with the thumper cam

[69heavychevy]

i was wondering if anyone here was running a thumper cam, #12-600-4 to be exact. i just got thorugh installing one in my truck but having trouble with the timing. i seem to have to retarded quite a bit to get it to even run right. if anyone is running this came what do they have their timing set to. im also open to any suggestions. oh yea i have a performer rpm, edelbrock 600cfm, headers, and 993 heads. thanks in advanced!

[69heavychevy]

anybody??

[shortbed70]

could be one tooth off on dizzy.

[69heavychevy]

finally got it to run ok, have set at around 3 degress, any higher n i pretty much have to back out the idle screw completely. will mess with it some more 2morow

[vectorit]

Sounds 180 out.
Pop the #1 spark plug, and tap the starter till you hear compressed air rush out. turn the motor by hand (helps if you pull all plugs) with your balancer, till the TDC mark it on 0 with the tab.
Then pop the dizzy cap, your rotor should be pointed at the #1 plug terminal.
If it's not, then pull the dizzy out and rotate to its correct position.

Sounds silly, but it's a common mistake.

Thats my first guess.

Good luck!

[69heavychevy]

yea sounds silly, but i was wondering the same thing. when #1 cylinder is at tdc, is the marking on the cam gear supposed to be at 12 o'clock or 6 o'lock. ive seen both listed on different manuals

[cdowns]

Originally Posted by 69heavychevy

yea sounds silly, but i was wondering the same thing. when #1 cylinder is at tdc, is the marking on the cam gear supposed to be at 12 o'clock or 6 o'lock. ive seen both listed on different manuals

most timing sets the cam is at 6 the crank at 12//for dizzy TDC must be on the compression stroke

[faribran]

... depends on how your distributor wires are placed on your dist. cap...
important thing is... does the rotor point close to the wire to #1 plug?

[faribran]

did u use a standard timing set? or one of the "multiple choice" ones?

[69heavychevy]

standard timing set, n rotor was pointing towards the #1 cylinder.

[68Stepbed]

Have you talked with CompCams about it? They have a tech help line. They designed the cam, so they might be able to help you more.

[71c10bbsuper]

sounds like you have things right you should need about 10 degress btdc
if it is trying to idle to high with that i would be looking for a vacumn leak
the mark on the cam does not matter if it at 12 oclock or 6 oclock as long as
your rotor is pointing at #1 spark plug terminal when engine is at tdc on the compression stroke

[69heavychevy]

interesting, i guess thats why u see the cam marking set at diff points depending what manuals u use. anyways i messed with her some more today n it seems to like it around 8 degrees btdc.

[scott's69]

I had to fight spark knock when I nailed the throttle and running on when I switched it off. I went back and forth with the timing. Just find the sweet spot and dont worry about "manuals and instructions". The techs at Comp can help ya if ya need to. Good luck.