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I set my non vacuum advance idle timing to 18 and 34 at 3500 RPM. idle mix screws are set to MAX vacuum which is 15 in Park 11 in Drive. Drives fine this way. but ive been having idle issues. Anything under 850-900 idle RPMs in Drive and it will be ok sometimes but most of the time it will start to die and stall out. This is in Drive or Reverse with foot on brake. In Park it idles fine. I seem to need the in drive idle at around 900 to be stable which is just too high IMO.
After doing some reading on larger Cams and the timing I decided to play with the advance. I moved it to 25 at idle and its still at 34 at 3500RPM.
Well that seems to solve my idle issues. Its able to idle at 680 RPM in Drive and about 800 in Park with this timing.
question is, am I on the right path here. Any Cons to leaving the timing like this? Should I lower it back down to 18 and use the vacuum advance on the Manifold port to advance the idle timing instead of how im doing it now?
Oh and starts fine Hot at this timing, no overheating.
You need to see at what RPM your distributor advance stops. There is about 20* of mechanical advance built into an HEi distributor, so what ever your initial is set to you need to ad 20 to it and that should be your total. Apparently your not raising the RPM's high enough to see what your total actually is. I would set it at 16/18 initial and hook your vacuum advance to manifold vacuum. The vacuum advance can needs to be mechanically limited to 10*. I'm afraid with your current settings your going to run into detonation at the upper RPM's and cruise.
You need to see at what RPM your distributor advance stops. There is about 20* of mechanical advance built into an HEi distributor, so what ever your initial is set to you need to ad 20 to it and that should be your total. Apparently your not raising the RPM's high enough to see what your total actually is. I would set it at 16/18 initial and hook your vacuum advance to manifold vacuum. The vacuum advance can needs to be mechanically limited to 10*. I'm afraid with your current settings your going to run into detonation at the upper RPM's and cruise.
Trying that now. Lowered it to 18 initial and I hooked up the vacuum to manifold and now I'm at 45 with the vacuum on the manifold so I have 27 worth of vacuum advance. Sounds highIhigh togto me.
I got it up to 3500 rpm I have to imagine that is enough to stop the advance. It stopped at 34 with no vacuum. So I'd say I have 16 mechanical which is close to the 17 I heard the Accel hei has in it.
So it sounds like I need an adjustable vaccum advance set that to about 10 and see if that fixes the idle issue.
Last edited by glamaina; July 20th, 2020 at 06:39 PM.
You can make a mechanical stop for the vac advance. Ken71 has posted several pics of his, i made one too. Its a little trial and error but if you have 27* of advance and you stopped it halfway its about 13.5* so if you add a little adjustability to your stop you can probably get 10-15* for a range.
moroso also sells one that achieves the sameish thing.
You can make a mechanical stop for the vac advance. Ken71 has posted several pics of his, i made one too. Its a little trial and error but if you have 27* of advance and you stopped it halfway its about 13.5* so if you add a little adjustability to your stop you can probably get 10-15* for a range.
moroso also sells one that achieves the sameish thing.
I was looking for some adjustable advances and seems only crane cams makes one that comes with a mechanical stop plate. All the others are just cans that you can adjust the timing of the vacuum with an Allen wrench but can't adjust the overall advance. So that seems like the same concept as fabricating a stop yourself. I'll look into that.
Right now I reduced the initial to 14 with the advance on manifold I'm at 34 idle. At 3500 rpm I'm at 52 total timing with vacuum advance. I'll keep an ear out for knocking. But seems stable at idle.
This is the adjustable stop that I made based on information that Schurkey posted. It's a 24º advance canister off a 78-79 403 HEI distributor and I originally just slipped a round bushing over the end of the shaft to limit its travel in the slot. That reduced the travel by 1/3, so it provided 16º advance (24º x 2/3 = 16º). I wanted to reduce it even further so I made the adjustable stop.
Last edited by Fun71; July 21st, 2020 at 10:07 AM.
This is the adjustable stop that I made based on information that Schurkey posted. It's a 24º advance canister off a 78-79 403 HEI distributor and I originally just slipped a round bushing over the end of the shaft to limit its travel in the slot. That reduced the travel by 1/3, so it provided 16º advance (24º x 2/3 = 16º). I wanted to reduce it even further so I made the adjustable stop.
awesome thanks ive been endlessly searching threads to try to find these pics. looks like a simple mod. Im going to take it on the highway and see if there is any detonation with my current config before I bother doing this though.
I assure you your timing is not stopping at 3500. There is probably another 3-5* if you increase it as normally and HEI has around 20* built in. With that said your probably ok with the 18*. Adjustable vacuum cans only adjust for rate based on vacuum available thats why a mechanical stop is required.
July 20th, 2020, 03:28 PM
