Recurving a Distributor
Posting Guru
Joined: Jul 2010
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From: Marysville, WA
IMO, that ProComp distributor is not the best quality. It may have a bad curve in it, but you need a timing light preferrably with a tach built in to see what the curve is, or if it has other problems.
I agree that if there are carb issues, get the rebuild done to cut out one variable. Then, like I asked, disconnect the vacuum advance, get initial timing reading at idle and at 2500rpm. If you want to see the curve, slowly screw in the idle screw and take readings at 1000, 1200, 1500, etc.
Once you have the readings, you can plot the curve. Should be a nice arc all in around 2500rpm.
I agree that if there are carb issues, get the rebuild done to cut out one variable. Then, like I asked, disconnect the vacuum advance, get initial timing reading at idle and at 2500rpm. If you want to see the curve, slowly screw in the idle screw and take readings at 1000, 1200, 1500, etc.
Once you have the readings, you can plot the curve. Should be a nice arc all in around 2500rpm.
FTE Legend
Joined: Jul 2010
Posts: 32,875
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From: Northeast, OK
It is the mechanical, aka centrifugal, that we are testing or recurving. I don't have a light with a tach, but I have an ignition scope which shows RPM. We'll get there.
Posting Guru
Joined: Jul 2010
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From: Marysville, WA
If you disable mechanical advance, even with vacuum advance, you will have no curve. No advance.
Rercurving applies to the mechanical advance. Vacuum advance works in conjunction with mechanical, but not vice versa.
Perform the check like I spelled out above, plot the curve and then go from there. Plotting the curve will tell you if the curve needs to be changed. Also, if the curve is not a nice arc, then there may be worn parts, broken springs, sticking weights, etc.
Rercurving applies to the mechanical advance. Vacuum advance works in conjunction with mechanical, but not vice versa.
Perform the check like I spelled out above, plot the curve and then go from there. Plotting the curve will tell you if the curve needs to be changed. Also, if the curve is not a nice arc, then there may be worn parts, broken springs, sticking weights, etc.
pedant
Joined: Jan 2008
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From: EXTREME southwest CT
An old school type Auto Electric shop should have a distributor machine like a 'Sun'.
This will allow you to swap weights, stops and springs right there and save a lot of trial and error.
FTE Legend
Joined: Jul 2010
Posts: 32,875
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From: Northeast, OK
Not knowing how much cam he has, although it sounds like a fair bit of overlap, I'm guessing he can use quite a bit of advance.Bruno - These are aluminum heads? What combustion chamber size? Or, what is your compression ratio supposed to be?
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Postmaster
Joined: Nov 2009
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From: Broken Arrow , OK
They are after market iron heads. The have 64cc combustion chamber(I know I should have went with a "0" deck heighth). The pistons are like a 14cc dish. When the machinist and I figured out the compression ratio it came out to about 9.1:1.
Bill Vose said to throw the heaviest springs in the kit at it. Also I dont know if I mentioned it or not. I read a thread where a guy was working a new unit like mine and it was rough on the inside as far as the weights and moving parts went . The guy recomended that everything needed to be deburred and sanded in order to get everything operating smoothly.
I figure we will see what its like when we get in there.
Bill Vose said to throw the heaviest springs in the kit at it. Also I dont know if I mentioned it or not. I read a thread where a guy was working a new unit like mine and it was rough on the inside as far as the weights and moving parts went . The guy recomended that everything needed to be deburred and sanded in order to get everything operating smoothly.
I figure we will see what its like when we get in there.
FTE Legend
Joined: Jul 2010
Posts: 32,875
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From: Northeast, OK
Ok, iron heads and 9.1:1 compression means we need to keep the advance a bit shorter (meaning less advance) than with aluminum heads or 8.5 CR. But, I'm not sure I understand why Bill said to put the heaviest springs in. That means your advance will come in more slowly than with lighter springs. In any event, we need to have a target for X degrees of total advance by Y RPM. Then we will install springs and stops to get to that point. Somehow we need someone to give us a target.
Jim? Don? Bill?
Jim? Don? Bill?
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Posting Guru
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From: Marysville, WA
I pretty much gave you a target back in post #11. To reiterate, 12 degrees initial, all in(34 degrees) around 2500rpm. In addition, as fast advance as the motor can take without pinging.
And until you plot what you have, we don't know where to go from here.
Exactly my point of not the best quality from ProComp. I don't care how "new" a low quality part is. Maybe the weights are sticking. And the reason(IMO) why MSD, Mallory, etc. are worth it.
And until you plot what you have, we don't know where to go from here.
I read a thread where a guy was working a new unit like mine and it was rough on the inside as far as the weights and moving parts went . The guy recomended that everything needed to be deburred and sanded in order to get everything operating smoothly.
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
I pretty much gave you a target back in post #11. To reiterate, 12 degrees initial, all in(34 degrees) around 2500rpm. In addition, as fast advance as the motor can take without pinging.
And until you plot what you have, we don't know where to go from here.
Exactly my point of not the best quality from ProComp. I don't care how "new" a low quality part is. Maybe the weights are sticking. And the reason(IMO) why MSD, Mallory, etc. are worth it.
And until you plot what you have, we don't know where to go from here.
Exactly my point of not the best quality from ProComp. I don't care how "new" a low quality part is. Maybe the weights are sticking. And the reason(IMO) why MSD, Mallory, etc. are worth it.
We'll check the internals of the dizzy out, plot what it gives with the stock config, and go from there - when I get back unless Bruno finds someone with a Sun machine instead.
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