that we perhaps have'nt thought of. Got a buddys 283 chevy engine in a 40 Deluxe coupe. Engine history is unknown but pulls hard. Has 58 Fuellie/PP heads and a Duntov 097 solid stick, Mallory elec dist and Eddy performer and brand new Holley 600 vac sec mounted on a 1/4" bakelite spacer. The car drives real good under power and cruise but the issue we have is that once warm, it idles and then likes to quit at the lights with the car stopped. It appears to be more pronounced once the engine has warmed up. We cant get the timing mark where we want it and we only have 2-3 deg of dist rotation either way beyond which point it runs like crap either side of this range. Not sure if the std damper has slipped on the hub and giving bullshit readings. We cant see the timing mark on the damper with the timing lite. Checked idle vaccum when warm - cant get more than 10" of vaccum, regardless of A/F mixture or timing adjustments. To date we have : i. checked carb, its spotless inside, has no vac leaks, floats correct ii. checked intake, no vac leaks PERIOD iii. swapped out distributors...no dice, same deal. ballast resistor is new. iv. swapped out coils, have great spark, same result v. checked firing order, all good. vi. plugs medium tan colour, not fouled. vii. If anyone have any ideas, it'd be much appreciated !! Rat
sounds like a vac leak showing up when the engine is warmed up. I'd be checking for a leak....I've had good luck using a propane/butane torch (un-lit) 'waving' it around intake/carb base and all fittings, etc. If the RPM's change with added 'fuel' you have a vac leak. good luck.
maybe a stretched timing chain...making timing sloppy? Try 'rocking' the crank by hand while watching the dist. rotor to see how many degrees the crank moves before the dist. rotor turns...
Sounds like you have been very thorough, but there are a couple of things that seem a little strange to me. I think 10" of vacuum is pretty low, even with the 097 cam. Disappearing Timing mark could be a couple of things. As you said, the outer ring could have slipped. Or you could have a mismatch between timing cover tab and damper. There were at least 2 tab locations and the damper has to be correct for the cover used. (You don't have to change either the cover or the timing mark, but you do have to locate true TDC and remark either the damper or the cover) I also have never had a SBC that was + or - 3 degrees sensitive. (Not to the degree you stated) Other things to check Vacuum cold vs hot (will tell you if it is a temp related issue) Get a timing mark on the damper where you can see it with the timing light. (Actual location doesn't matter for this.) Start the engine, watch the timing mark as you accelerate, it should advance. Let the throttle snap shut and see if the mark retards beyond the initial idle location. You can double check this by snapping the throttle open and shut. This will tell you if the timing chain is stretched. The timing should not retard lower than it was at idle. You didn't say if you are running vacuum advance or not. I would have suspected a leaky vacuum advance diaphragm but since you changed the distributor this is unlikely. Don't forget to disconnect and plug the vacuum advance hose when setting the timing. Don't ask me why I caution you on this. I once had a situation where the centrifugal advance was sticking and the vacuum advance was leaking (intermittently). Chased this for a while. Please let us know what you find when you get it fixed. It's not that hard. SUCK, SQUEEZE, BANG, BLOW! What could go wrong? ;Q
Don't guess or assume anything on your timing marks. Use a piston stop and fine true TDC and assure the pointer is lined up to TDC.
First thing I'd do is be able to get a TRUE timing reading. Fix the things that are keeping you from doing that, then attack your other issue.
Like this! Are you checking full manifold vacuum or from an off-idle port on the carb? Make sure it's full manifold vacuum from someplace below the throttle plates. The more vacuum at idle the better for driveability and idle quality. A warmed up camshaft tends to drop idle vacuum. There's a couple ways to help compensate for the low vacuum. You can increase initial timing a bit as long as you don't end up with too much total timing. Also, do you have a vacuum advance on the distributor? Does it work properly? I fit does, is it connected to a full manifold vacuum source or is it connected to an off-idle vacuum port? If it's hooked up to off-idle vacuum you might try switching it to manifold vacuum. This alone could give you a couple more inches of vacuum by advancing the timing a bit at idle.
alos with that low vacuum amount depending on if vacuum advanced is used, and how much is in the vac can, you may be dithering in and out with the vacuum advance, can you plug it? if so how if any does it affect it?
First are the timing cover and the balancer compatible. A mix of early and late will not have the mark in the right place. Late timing will lower vacuum reading. The low vacuum may have the power valve opening. When cold being rich is not that much of a problem but warmed up rich would degrade the idle.
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