I have read most of the timing threads on this forum and others and have a pretty good understanding of the components of timing and how they work. I recently installed a GM 350/290 hp crate engine in my 79 vette. My problem is I can't get the engine to idle at the recommended 12 degrees of initial timing. The engine immediately stalls when placed into drive and/or the A/C is turned on. If I increase the initial timing up to 25 degrees the engine idles smoothly at 650 rpms with the A/C on and in drive. As suggested in many of the threads the vacuum advance line from the canister on the distributor is connected to a manifold vacuum port. With the 25 degrees of initial vacuum and 12 degrees from the vacuum advance, I am idling rpm with 35 degrees total vacuum. With another 24 degrees of centrifugal degrees of vacuum at 2,500 rpm, total vacuum could be as high as 61 degrees at highway speed. I have driven the car and the engine does not ping. How can this be? I have checked the timing tab and it is located in the right location for an 8" balancer. I have checked the balancer and the timing mark is located 10 degrees left of the key hole. Does anyone have any ideas why I can't set the timing at the recommended 12 degrees? Any ideas or thoughts would be greatly appreciated.

 

are you going by the tach in the car or are you using a remote tach wired to the dizzy?

if going by the car's tach you maybe off on that tach.

disconnect the vacuum advance can set timing at 12 at 3k then connect vacuum can back up and you should have 26 at idle.


but first make sure your car is really idling at what you think it is. if your tach in the car is a few hundred off then instead of idling at 650 what your thinking its maybe really 300. and when placed in drive or accesories placed on its putting more load on the RPM's and the motor can't spin that low.

 

Do not set the timing at 12 at 3K as suggested above - that is incorrect, and will give you a completely faulty timing setting.

Start with the basics and work your way up:

Get yourself a TDC indicator from Summit or Jeg's (or use the method outlined in my TDC paper - e-mail me for a copy) and verify TDC on your balancer and timing tab. Once done, set your timing to 36 degrees total as outlined in my timing paper. Once you have it set to 36 total, make note of the resutling initial and see where it is - it should be in the 12-18 range. Finally, obtain a correctly matched vacuum advance control unit and limit it to 12 degrees as outlined in my vacuum advance paper and run it off manifold vacuum. Once done, your engine will run correctly.

If you get stumped, e-mail me and I will send you my phone number so you can call me for a technical run-through.

Lars
V8FastCars@msn.com

 

Lars, Thanks for responding, recommending a process to follow, and offering a technical run-through of the process. I will begin tomorrow on finding TDC and then use the process you suggested. I will let you know how it works out. Thanks, again.

 

I'll be in my workshop from Fri-Sun this week doing tuning and engine swaps all weekend. Let me know if you need to chat and I'll get you set up. But do your homework first with TDC verification and some work.

Lars