Timing Question

[6T7GTA]

'67 FB, 289, Holley 600, mild CompCam, headers. Set timing approx.12-15, runs like crap(especially under load and higher rpm's), set timing around 30, runs great. Question is "has the timing chain slipped a tooth or so"? Any insights?

 

[LMan]

are you using a vac advance?

 

[6T7GTA]

Yes, vac. advance

 

[slapper]

What does the total timing come in at?

 

[6T7GTA]

Hard to tell since the marks are worn off after mid-30's.

 

[302 coupe]

when you set the initial timing(@idle), did you disconnect the vacuum advance? If not, you probably got a bad number. Probably want about 12-14 initial(with vacuum disconnected), then 34 total by about 2800 rpms with vacuum connected.

 

[6T7GTA]

yes, vac advance was disconnected.

 

[67GTA-FB429]

you can try to time it using a vacuum gauge. hook up the gauge and when you get the steadiest number...you are there.

 

[LMan]

Something to look at is a vac leak. That can make the motor run poorly at low RPMs as you have a weakened idle signal, while getting better higher up as the increased air velocity overcomes the leak source.

I would do all the usual tricks for vac-leak checking to rule this out.

 

[jesserose17]

Have you checked the dwell?

 

[Max Power]

Distributor a tooth off?

 

[D.Hearne]

Balancer may have slipped also.

 

[6T7GTA]

Thanks for all the good advice of things to try! I will give them a try!