Power Valve Selection
Cargo Master
Joined: Apr 2003
Posts: 2,389
Likes: 58
Ok, and you took it past 3000rpm and observed that it had stopped advancing at that point?
If backing off of the initial timing cured the ping, then the next step is to play with the advance curve. Add as much to the mechanical advance as you remove from initial and see how it drives.
Example, if you start with 12 initial, and 24 mechanical, try 10 initial and 26 mechanical. You will still have 36 total but the curve will be a little different and may be just what is needed.
You can also plot your advance curve, every hundred or couple hundred rpm note the amount of mechanical advance. That gives you something to compare with a new curve and lets you know just where it is at cruise.
And remember, don't even use the vacuum advance while you fine tune the mechanical curve. Disconnect it, plug it, and forget about it until you have the mechanical curve figured out.
If backing off of the initial timing cured the ping, then the next step is to play with the advance curve. Add as much to the mechanical advance as you remove from initial and see how it drives.
Example, if you start with 12 initial, and 24 mechanical, try 10 initial and 26 mechanical. You will still have 36 total but the curve will be a little different and may be just what is needed.
You can also plot your advance curve, every hundred or couple hundred rpm note the amount of mechanical advance. That gives you something to compare with a new curve and lets you know just where it is at cruise.
And remember, don't even use the vacuum advance while you fine tune the mechanical curve. Disconnect it, plug it, and forget about it until you have the mechanical curve figured out.
Postmaster
Joined: Oct 2010
Posts: 4,656
Likes: 4
From: Northern and Southern Cal
Sorry if I'm a dunce.
I must not be following.
I thought you got rid of the ping by bumping your timing and easing the curve already.
The only problem being you have to deal with a carb that is to big.
Logistics Pro
Joined: Mar 2005
Posts: 3,771
Likes: 80
From: tujunga, calif
I'm not sure what SAFE total max timing can be on a stock Y Block running on the crap fuel we have today. I play it safe and set mine to a total of 34 degrees, 10 initial and 24 mechanical. I doubt a few more degrees will set me back in the seat or set any new speed records. Just call me chicken LOL.
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Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
The only issue noted was ping at steady cruise around 50 or 60 mph, when engine vacuum is steady and high. None at full throttle acceleration or part throttle acceleration, no kickback with the starter, etc. Also had the vacuum advance fully pegged.
Ping or detonation is sometimes hard to detect. It was very light, but fairly constant. SO, probably what's happening, after jetting down to a reasonable air/fuel mixture, at cruise either the vacuum advance is adding too much, OR, it's years of carbon buildup lighting off and causing the ping. A rich fuel mixture will cover for timing that's too far advanced. I think it will be fine to utilize as much mechanical advance as it will take, but need to get the vacuum advance dialed in. There's no lean surge at cruise, but don't want any busted rings or holes in pistons either. I agree the fuel isn't so hot these days.
Ping or detonation is sometimes hard to detect. It was very light, but fairly constant. SO, probably what's happening, after jetting down to a reasonable air/fuel mixture, at cruise either the vacuum advance is adding too much, OR, it's years of carbon buildup lighting off and causing the ping. A rich fuel mixture will cover for timing that's too far advanced. I think it will be fine to utilize as much mechanical advance as it will take, but need to get the vacuum advance dialed in. There's no lean surge at cruise, but don't want any busted rings or holes in pistons either. I agree the fuel isn't so hot these days.
Cargo Master
Joined: Apr 2003
Posts: 2,389
Likes: 58
Since dialing back the initial cured the ping but made it more sluggish, then the dialed back initial with a little more mechanical may cure the ping and keep performance about the same. This is where plotting the advance curve really helps because you can see if the advance may be slightly lower at cruise, thus curing the ping and the same at 3000rpm, maintaining performance. You can also play around with the springs to change the rate of advance, which can also cure the ping, maybe have it advance more slowly from say 1200rpm to 2000rpm and more quickly from 2000rpm to 3000rpm.
Postmaster
Joined: Oct 2010
Posts: 4,656
Likes: 4
From: Northern and Southern Cal
Ok, so you backed the vacuum assisted advance off a little and that solved the light ping.
Your initial is 12 and you have 34-36 in by 3000.
And your throttle is better now?
Edit:
Sorry Charlie and Jim I was writing as you were also.
Obviously we're interested Ted
Your initial is 12 and you have 34-36 in by 3000.
And your throttle is better now?
Edit:
Sorry Charlie and Jim I was writing as you were also.
Obviously we're interested Ted
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Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Think it was a little bit of paranoia. It's better to make incremental changes, one thing at a time. Instead dialed the vacuum advance back three turns out of twelve and also took 4 deg. off the crank timing.
It did remove the ping but, noticeably more sluggish. We'll see how it runs with 12 or so deg back in the crank (or approx. 34-36 total mechanical) but keep the vacuum advance dialed back a bit. Again it might just be 20 years of cylinder sludge burning off, though the timing shouldn't affect that either way? Hm.
I could it run it up again to plot out the exact curve, but really don't care much for spinning fan blades at 3500 RPM in neutral. Suppose I could remove the fan belt for the test. (People have been seriously injured if a blade decides to let go.) Was just happy to see it done doin' it's thing before 3000 and obviously limited to around 24 deg or so. The old distributor didn't finish advancing till well over 4000 iirc.
It did remove the ping but, noticeably more sluggish. We'll see how it runs with 12 or so deg back in the crank (or approx. 34-36 total mechanical) but keep the vacuum advance dialed back a bit. Again it might just be 20 years of cylinder sludge burning off, though the timing shouldn't affect that either way? Hm.
I could it run it up again to plot out the exact curve, but really don't care much for spinning fan blades at 3500 RPM in neutral. Suppose I could remove the fan belt for the test. (People have been seriously injured if a blade decides to let go.) Was just happy to see it done doin' it's thing before 3000 and obviously limited to around 24 deg or so. The old distributor didn't finish advancing till well over 4000 iirc.
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Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Purchased pump nozzles on 26th, out of Mechanicsville, VA. They departed San Bernadino, CA this morning, so we're making steady progress here to Iowa.
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Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Checked that already. Not quite a stumble as I would describe it. But a quick snap of throttle - when under the hood engine in neutral, isn't quite instant. This may be a factor of an oversized carb?
Postmaster
Joined: Oct 2010
Posts: 4,656
Likes: 4
From: Northern and Southern Cal
Ok one more thing.
You mention circle track carb.
Does that carb have a 50 cc accelerator pump?
I was looking at 2300s on Speedways site and some come with 50cc pumps.
That's bigger than my 4bbl pumps.
Wonder if you could change that out for a smaller shot.
You mention circle track carb.
Does that carb have a 50 cc accelerator pump?
I was looking at 2300s on Speedways site and some come with 50cc pumps.
That's bigger than my 4bbl pumps.
Wonder if you could change that out for a smaller shot.
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Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Yeah, afaik it's a 50cc pump. It's actually a list 4412 and a good carb for mostly WOT, not so much for other uses. I'd be money ahead at some point to find a quality rebuild Autolite of around 350 cfm.
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Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Okay, the nozzles arrived the other day, finally. Replacement reminds me a little bit of the old Milton-Bradley board game called Operation. The idea here is to not drop screws or washers down the intake. The stock nozzle was a 28 as listed and installed a 25. The roads are snowy and salted so no test drives for a while. Started it up and let it warm up, verified float level and idle mixture to be sure. Pulling 20 in steady vac and idles nice.
It did noticeably stumble when engine is still cold, winging the throttle hard. Didn't do that before. It's maybe 35F. But, when engine warmed up a few minutes it's OK. Before tuning this carb hardly needed a choke to start in cold weather either, just a fast idle. With a manual choke it's sort of the same thing, so this may be normal?
It did noticeably stumble when engine is still cold, winging the throttle hard. Didn't do that before. It's maybe 35F. But, when engine warmed up a few minutes it's OK. Before tuning this carb hardly needed a choke to start in cold weather either, just a fast idle. With a manual choke it's sort of the same thing, so this may be normal?