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Old 03-01-2006, 10:58 AM
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350 Chev timing, compression, vac

This is a Chevrolet 350 in a running drivable 33 Plymouth coupe.

Bought it as is and no way to trace the engine builder and specs.

Basic hotrod 350: Edelbrock dual plane and carb, headers, Accel electronic dist etc.. .Whats inside is anyones guess but I suspect a mild hotrod cam.

Problem? Just doesnt have the power it ought to. Compression checks low on all cylinders. 2-107, 4-115, 6-107, 8-110 - 1-120, 3-110, 5-120, 7-110
Fairly even but ought to be nearer 150?
Oil the cylinders and re-check gets the readings up around 5 lbs so I think rings are fine?

Vac reads very low at idle 5-8 but goes up quickly, smooth and stable when rev'd up.

I am grasping, but the low Vac could be a hotrod cam.... I am suspecting a jumped timing chain or improperly installed at buildup.

What do I check next or do I need to pull it and just see whats inside?

Anyone willing to comment or guess?????
Thanks
Craig

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Old 03-01-2006, 11:11 AM
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Does the cam "sound" radical or not. Does it have a rough idle, or lope as the engine idles. I wouldn't think the timing is jumped if the thing starts up, idles and runs well enough to check the things you have so far.
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Old 03-01-2006, 11:17 AM
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cam

From sound and having run all sorts of mild and wild cams I think this is just a step up from stock, very mild lope.

Have owned and drived the car since 1999 but it has just never "felt" right... and the low vac must be a clue.

Ive squirted carb spray around the gaskets and there is no idle rpm change.

Car runs down highway fine. Will back fire through carb when cold everyonce in awhile.

I guess I suspect cam, timing chain etc since they are the things.. I cant lay my eyes on...
Craig
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Old 03-01-2006, 11:26 AM
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I had a crappy cam recommended to me and it made my truck run the same
way, low vac until revved up and it doesn't lope due to a wide 114 deg. LSA.
The guys here told me the wide LSA was to make up for someone installing
that cam which has too much duration, to keep it from loping(intake reversion)
but the wide LSA kills vacuum, making a lean mixture and causing it to pop back through the carb.
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Old 03-01-2006, 11:31 PM
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If you're going to pull the timing cover and/or pull the cam to check it out you may just want to have a new cam ready to go in. Of course, you still have the low compression check numbers to consider.
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Old 03-02-2006, 12:36 AM
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Doc here,

Everything you have described is indicative of a jumped chain or incorrectly installed set of gears..

Low Compression, followed by low vacuum is the clue..

Pull the Dizzy cap, Pull the left valve cover, pull number 1 plug...Bring it up on #1 TDC, Compression, Both Intake and Exhaust dead closed..(not just sorta closed..dead closed with slack on the push rod) Look at your timing marks, They should be lined up on 0 ..If you can't Coordinate these three items, you have a jumped chain.

Next if they do, or do not line up check the dizzy, It should be dead on #1 plug tower..if not and the rest lines up, set it to #1..if all doesn't line up..chain and gear time.

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Old 07-18-2009, 11:02 PM
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I agree with the suggestions heard so-far, but-maybe the timing chain has not jumped a tooth but is stretched. You can check this easily by removing the distributor cap and turning the engine by hand in one direction until you see the rotor on the dist. start to rotate.With a piece of tape and a pen, or use the timing marks on the balancer,note the spot and then turn the engine in the opposite position until the rotor starts to move in the opposite direction. Note this position and compare the difference between the two marks.It's possible that the chain has stretched enough to cause this problem. If you can't turn the engine by hand then remove the spark plugs to make it easier to turn-just a suggestion- it's happened to me.
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Old 07-20-2009, 10:42 AM
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The last posting on this was in 2006. I sure hope this problem has been resolved by now!
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Old 07-20-2009, 03:47 PM
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When I read the post, it said it was over 100 days ago; oh well , better late than never. I'll pay closer attention next time. Thanks, Stan.
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Old 07-20-2009, 10:41 PM
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No big deal. It happens all the time...
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