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Old 11-29-2010, 06:31 PM
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Transmission, Carb, or Engine????

OK. Here's what ive got.

78 Dodge Custom 150
6.6L 400cu. in. Motor
-Hughes Whiplash Cam .518 lift 229/242 duration 102 installed centerline
-MSD StreetFire Ignition
-440source Pro Billet Distributor(Mechanical Advance)
-Single Plane Edelbrock TM-6 Manifold
-Holley 750 Vac. Sec w/ 1" spacer
Torqueflite 727 3spd Auto


Here is my problem. I get the truck up to cruising speeds and let off the gas hard and the truck starts hesitating on deceleration. I dont know if hesitation is the right way to describe the condition but it stutters... its not a smooth transition from cruise to idle. Only happens under load. Runs awesome in park. Now my question is, what is causing this to happen? The tranny got some water in it from drip in radiator cooler. So i flushed it the best i could, added trans tune by seafoam, and it shifts fine. Is it tranny?
Then I get to thinking. My initial timing is set to 28*. at 3000 rpm its at about 63*. I have the initial timing so high cuz of low comp. Could that be it? Do I need to Limit mechanical advance?
Then i think some more. Im getting 10hg vacuum at idle. Carb has a 65 powervalve. Could that be the problem. I know its A problem but does it cause this condition?
Maybe I should Stop Thinking, and ask and listen. Any info would be greatly appreciated. Thanks, Chris

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Old 11-29-2010, 06:51 PM
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Usually you advance timing due to high compression. With low compression you would want less timing. But i'm not sure if that would cause your problems or not.
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Old 11-29-2010, 07:02 PM
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I advanced the timing because its a low compression motor with a helluva cam. Low comp motors like a lot of initial timing when using a rumpity cam. If i put it at 12* initial i get like 6 in of vac.
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Old 11-29-2010, 09:32 PM
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ahh, i didnt notice the cam.
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Old 11-29-2010, 09:41 PM
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You need to recurve the distributor so that you can get you 20+ initial but not more than 40 total by limiting the mechanical avance. Keep running it at that high total you have now and it will destroy itself. Doesn't matter whether it has low comp or high comp, niether will tolerate excessive total timing for long.

If the compression is really low enough this may be an instance where you want to lock the mechanical straight at something between 36-40 all the time, no curve at all.
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Old 11-30-2010, 01:54 AM
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it may be fuel 'pullover' I had a rochester qjet that used to do that. it would suck fuel out of the carb by manifold vacuum instead of the vac created by the venturi effect.. with my glasspacks it would sound like a .38 calibre hand gun if I snapped the throttle shut quick


I'm not sure if it's related, but a single plane intake seems like a lot intake for your cam. I'm not familiar with judging a cam by it's centerline.. but .518 lift with only a 229 (I'm assuming at .050) seems like it wants a tall dualplane? I'm running a 214/224 @ .040 in my 350 with .442/.465 lift and it's super mild I couldn't imagine wanting to run a single plane?
i would think something along the lines of an Edelbrock Performer RPM would be a better choice? or whatever brand you happen to like..
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Old 11-30-2010, 04:35 PM
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thanks for the replies
i will start with the distributor and see what happens. what compression is low enough cuz im running at like 8 to 1... maybe less. It would probably be easier to lock in the distributor advance cuz i bought the distributor from 440source.com and it didnt come with anything to adjust it. About the intake, ive been thinking about a dual plane but i had this one laying around so i just slapped it on there. And it doesnt sound like a .38 but it shutters like a motor does when it hits a rev limiter.
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