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oldbluetruck #1127348 Thu Oct 01 2015 07:49 PM
Joined: Sep 2001
Posts: 31,811
Bubba - Curmudgeon

In case you have not seen the mind-bogglingly-simple technique for tuning timing & carburetor with a vacuum gauge, here is an abbreviated run-down.

1. Disconnect the rubber line from the vacuum wiper motor to the port/fitting/tube on the intake manifold (at the intake manifold).
2. Connect a rubber line/tube from the vacuum gauge to the vacuum fitting on the intake manifold.
3. Start the engine and warm it up.
4. Set the idle RPM to around 450-500 RPM (or, by ear, if do not have a tachometer).
5. Adjust the timing by rotating the distributor slowly in both directions, to obtain maximum vacuum. At max vacuum, tighten the bolt on the distributor.
6. Re-adjust the idle speed, if necessary.
7. Adjust the mixture screw on the carburetor to obtain maximum vacuum.
8. If you want to continue, repeat steps 4-7.
9. Disconnect the vacuum gauge hose at the manifold and quickly reconnect the vacuum hose to the wiper motor.
10. Go for a test ride.

Good luck.

Tim []
1954 3106 Carryall Suburban [] - part of the family for 49 years
1954 3104 5-window pickup w/Hydra-Matic [] - part of the family for 15 years
- If you have to stomp on your foot-pedal starter, either you, or your starter, or your engine, has a problem.
- The 216 and early 235 engines are not "splash oilers" - this is a splash oiler. []
oldbluetruck #1127393 Thu Oct 01 2015 11:17 PM
Joined: Mar 2010
Posts: 10,720
Renaissance Man
Great post Tim!
I especially like step #8. A lot of people (me included) often forget to do that.
If your idle was on the high side after you reach maximum vacuum, the mechanical advance in the distributor could have begun to kick in, monkeying up the process. This could be the case for both mixture, and timing adjustments.

oldbluetruck #1131816 Thu Oct 29 2015 03:00 AM
Joined: Jan 2013
Posts: 1,474
Tim, is it me or is it hard to find all your good tech advice on your web site? For example, your tuning steps above. Maybe you just put it all here?

Yeah, well, that's just like, you know , your opinion, man - The Dude

1948 Chevy 3600 - goal Original restoration, Current Stage 1 - Disassembly and getting body in primer
1954 GMC 3100 goal Hot Rod, Current Stage 1 - Get body in primer
1931 Ford Model A 5 window Coupe - Old Skool Hot Rod
1945 Ford 2N Tractor - Runs great
1964 Ford 2000 Tractor - Use it every week
1974 Stingray Corvette

oldbluetruck #1131944 Thu Oct 29 2015 10:52 PM
Joined: Jan 2002
Posts: 2,405
Thanks to all. Good advice. I took the timing light back and used my vacuum gauge.

Thanks Tim. As always

-there is nothing stronger than the heart of a volunteer-
oldbluetruck #1241348 Mon Oct 30 2017 06:24 PM
Joined: Jun 2008
Posts: 1,769
Where is the mixture screw on a Rochester B carb?

1950 Chevy 1/2 ton (all original)
1951 Chevy 1/2 ton (future streetrod)
1941 Chevy coupe
1938 Chevy coupe streetrod
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