Mis-Matched balancer/timing pointer

[ACEFOOTER]

Trying to help out a freind who has a 75 C10 pick up with a GM 350 crate motor in it. His initial concern was deiseling after shut off, but while checking "the basiscs" I found the timing set at 50+ degrees advance. Set to top dead center and pulled cap & rotor, pointed to #1 on the cap. The vaccuum advance was frozon solid and mechanicle sticky. I replaced the vacuum pod and lubed the mechanicle weights, set initial at 10, checked and have good off idle mechanicle advance to 22 degrees, and total with vacuum @ 40. Problem is it felt severly retarded, would barely accelarate and too much throttle would back fire. I traded with a known good carb and no difference. This timing pointer is seen at a 45 angle from the drivers side where my 78 350 is seen from straight down center of the cover. I beleive the origional installer mis matched an early balancer (it's blue rather than crate motor black) and a late cover/pointer. Question is does anyone know how many "degrees of timing" there are between the old style pointer and new style pointer so I could use my adjustable light to "cheat" the intial setting? Thanks Ace

[David Pozzi]

There are three timing mark locations.
1 Chev SB up through 1968, timing mark lines up with crank keyway
2. Chev SB from 1969 up, timing mark is 9 deg retarded on damper. Timing mark on block moved toward water pump for better visibility.
3. There is a van and motorhome version that may have been used in some pickups or other vehicles. The timing tab is behind the water pump. Unfortunately I don't have a deg difference for this balancer.

Backfiring is definately retarded. I have a motorhome that got timed over 20 deg retarded and it backfired at 3000 rpm's or so. They set the timing without disconnecting the brown lead. It has throttlebody injection.

You can put on your own mark.
You need a piston stop, I made one by knocking the insides out of a spark plug, then threading in a bolt around 3/8" dia. You may be able to borrow one or look for a spark plug extender and thread a bolt into that. I had to put a nut on the end of the bolt and grind it down enough to get it in the hole, the plain bolt would not hit the piston. Make sure you disconnect the battery when you do this and remove the stop as soon as you are done. Be very careful not to damage the piston.

Screwe this stop into the #1 plug hole making sure the piston is down in the bore. Hand turn the engine one way, make a mark on the balancer where the timing tab says TDC. Turn the crank the other way till it stops and make a second mark. Measure half-way between the two marks and that is TDC.

[ACEFOOTER]

Dave, Thank you so much for your response, it was an easy fix for the problem. Due to the fact thay I completely cleaned and re-aranged my shop last month, I did not have one single old spark plug (Threw away the full diaper wipe container of them I have been saving for the past 15 years, what do I need used spark plugs for? ) I found an old compression tester fitting that I tapped the end to accept a 1/4 bolt and made a piston stop. Thanks for the "Dis-Connect the battery" safety warning as well, Murphy and I go way back ;) Truck runs great now, no deiseling, good advance the throttle still sticks a little above idle at times but it is a Holly rebuilt Q-jet. I have heard the Edlebrock Q-jet is a good replacment so thats what I recommended. I of coarse forgot to use the adjustable T-light to check the difference in degrees, but Dave's way to determine TDC based on any pointer location is very quick and easy. Thanks again!!
Ace

[David Pozzi]

Glad it worked out!

Check the choke unloader vac pot on the pass side front.
I disconnect the vac hose, push the link into the unloader, then cover the hose nipple on it with my finger. Then release the link and it should only move out a quarter of it's travel. If it returns fully, the vac can has a leak in the diaphragm and it can be easily changed. I do lots of Q jet maintenence on our fleet of pickups on our farm.

There is a screw on some of the links, depending on the year, it adjusts the amount of choke pull-off. When cold the engine will tell you what it wants if you nudge the choke blade open or closed from it's normal setting.
Make sure all that choke linkage is clean or it can stick.
David

[ACEFOOTER]

Some one prior to me ever seeing this rig had removed the vacuum choke and fabricated a lever and cable to make it a manual choke. I shudder to think of what else has been modified on this carb as it didn't have as much linkage as my 78 Q-Jet. The truck has gone home and I hope to avoid any more carb repairs/adjustments on it. Thanks again Dave!!!