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[T3] Timing, backfire, compression, carbs.


72 Sqbk, 1600, dual Weber 34 Icts, distrib off a 76 Bus (not my choosing)

So I did the timing thing last weekend. Very enlightening. I got an advance
measuring gun which proved extremely helpful. According to the gun, my
ear-based timing that I did last week was WAY OUT THERE! 15 BTDC at idle.
Hoo boy. Managed to get the advance to 32 BTDC at 3500 rpms, hoses on, as
Jim said was right for my advance, and that brought the idle timing down to
0 but then it idled really hard.
When I set centrifugal (hoses off) speed to 7.5 BTDC, the advance at 3500
rpms was like 40. Hmmm.

Brought the advance to an agreeable middle point since I'm going to be
replacing it soon with a stock distributor instead of this one for the 76
Bus I have in my car now. A week or 2 more shouldn't do too much more
damage.

So one final look at the timing with the engine at 3500... out of nowhere
the engine cut and BANG a backfire, a puff of black out the right exhaust
(I was talked into a LeMans muffler last year...oh well). Uh oh. I let it
sit a while, and thought maybe something hapened with the hookup of the gun
and/or the tach but everything looked ok. Car started back up. No funny
sounds.Thought Maybe I should just quit for the day.

Later read about that series of events in Muir. Potential valve swallowed.
Yikes. Is there a visual way to check for this? Anyway, I thought a
compression check would tell me if I had no valve.

Did check two ways: Muir says turn engine over 6 times, says nothing about
throttle. Doing it this way got #1=95, #2=120, #3=110, #4=135
Bentley says turn engine over "a few moments"at full throttle. So I figured
about 4 turnovers. Results:  #1=125, #2 = 120, #3=140, #4  = 135

Finally, My new sparks are already coated in carbon! TOO TOO RICH! Weber
instructs are damn near useless. No precision to them whatsoever. Regarding
idle air screws "Turn them in until rpms fluctuate, then turn them out
until idle evens out" is all they say. This is caveman stuff. Isnt there a
slightly more precise way to measure mixture without buying a computer?

So todays questions are:
1)Why this backfire? Anyone have any thoughts?

2)Someone tell me what these compression figures mean.

3) Does anyone have access to Weber's # so I can call them for tech support
and/or some more accurate specs?

- Mike


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