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I have been dealing with a timing issue (I think anyway) for about 6 weeks now. At an idle the engine fluctuates 200 rpm and up to 4 degrees of timing at the crank. I have researched this on here for a while and have tried many of the ideas recommended. Here is the background:

The motor is a stock 67 350, with stock intake, Qjet and distributor. I replaced the points with a Crane electronic unit about 5 years ago. This past spring, I sent the carb to Lars in Colorado for cleaning and tuning. It had several issues that he repaired and when I re-installed it, I noticed the idle issue. I initially found a leaking vacuum advance canister so I replaced it with a VC1765 (B26) as recommended by Lars. It helped a little because the old canister couldn't hold a vacuum, but it still wasn't right. After searching the forum, I replaced the mechanical adv springs with a heavy set from Mr. Gasket -the problem still happens. With the vacuum advance canister unplugged and the vacuum port plugged, the motor idles at a rock steady 500 RPM and the timing never moves.

The timing is set at 18* initial, 36* total at 2500 rpm. The vacuum guage reads 20 inches at 500 rpm. The vacuum advance canister is plumbed to the stock location at the base of the carb and is putting in it's 8*, I can see it with the timing light.

Is this the correct vacuum advance canister for this motor? What else should I look at? Thanks!

Tom
 

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Check the v at idle, no VA...and make sure (if manifold vac) the VA is all in at or just above the idle vac.
Also check at what rpms the curve comes of ..should be at least a couple 100 rpms above the idle.
Make sure the butterflys are nearly closed and at idle it is running on the idle curuit and not on the main jets....If the mixture screws and idle speed screw are within factory specs then it should be on the idle circuit.
 

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Discussion Starter #3
Steps,

The VA is all in at idle, I have checked that. I haven't checked where the curve comes off, what would that indicate? I am wondering if the distributor needs to be rebuilt. Is there anything related to the advance systems that can wear out? I will also look at the carb. Thanks for your reply!

Tom
 

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I haven't checked where the curve comes off,
Drop heavy springs in, dont change anything else, disconnect VA....this will hold them in at idle and will tell u what the intial is....and will not move till 500/1000 rpms above idle
Then lighten increase idle speed about 150/200 rpms, and lighten up springs till the idle timing can just be seen to increase....that is light as you can go.

Dizzys wear...shaft bushes...it is the shaft that wears more than the bearings
The small bushs the weights turn on
The shim tollerance above the bottom gear.
Rotor burn
Cap pin burn.
Note: when doing shaft/bushes NEVER reem the bushes to size..they are sintered bushes and reeming the surface blocks the sintered surface and prevents lubrication
 

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I have been dealing with a timing issue (I think anyway) for about 6 weeks now. At an idle the engine fluctuates 200 rpm and up to 4 degrees of timing at the crank.
How much end play (up-and-down) do you have in the distributor mainshaft? If the gap between the shim pack above the drive gear and the bottom of the housing isn't set up properly (.010"-.015" is fine), excessive play will result in unstable timing as the helical driven gear moves up and down against the helical cam gear.

:beers:
 
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