[Sin7]

Quick question. Based on this diagram what would you say my timing is on my 283 sbc with 2 barrel carb ? As you can see, when I shoot it with a timing light the mark is past the timing tab itself so I can’t tell what the timing is. Each arrow shows the location of the harmonic balancer timing mark in relation to the timing tab.



Is each mark 2 degrees? Just want to make sure the timing is within spec. I’ve noticed a slight stumble when accelerating, but disappears at about 20mph… Timing or carb?

Thanks in advance for any help you guys can provide. In the meantime i'll continue to search the web for answers.

[68NovaSS]

Yes each mark is 2 degrees. But in your drawing, what is "Off"? Also, your mark at idle is drawn as WAY ATDC, retarded, and at rpm, even further. I think you drew it upside down. As you rev, the timing will advance, move further from zero, BTDC. You know to time it with the vacuum advance disconnected from the distributor and plugged? Set it at about 12 deg BTDC as a starting point, then adjust it from there when it's up and running. A modified SBC likes initial timing, some as much as 16 or 18 degrees., up to about 36 total, as long as it doesn't detonate or "ping". Watch this video and see how the timing moves.

[Sin7]

Thanks for the quick reply. I actually watched that video you suggested a few times. In fact that video is what actually sparked me to check mine.

I marked "off" because that's where the harmonic balancer timing mark landed the last time i shut the engine off. Here's a picture and video i just took of both idle timing and increased RPM timing that shows how the timing mark climbs way ATDC like you indicated.



Idle Timing



As I increased RPM's

[Sin7]

sorry for the poor quality. I had to hold the timing light with my teeth

[Custom10]

You have a nice vintage looking mill there, original dampener? You might want to consider checking for true TDC and then make a timing tape so you/we need not guess.


http://www.crankshaftcoalition.com/w...op_dead_center

http://www.crankshaftcoalition.com/w..._a_timing_tape

[Sin7]

Originally Posted by Custom10

You have a nice vintage looking mill there, original dampener? You might want to consider checking for true TDC and then make a timing tape so you/we need not guess.


http://www.crankshaftcoalition.com/w...op_dead_center

http://www.crankshaftcoalition.com/w..._a_timing_tape

Thanks for those links . Looks like i have a little project on my hand now this weekend and yes it's all original.

[68NovaSS]

My mistake, looking at our drawing, I was upside down in my thinking of what the arrows indicated, sorry.