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Old 09-26-2009, 05:54 PM
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Trouble with my new 383

Hi folks. This is my first technical post on this forum, and boy do I need some help....
My 383 complete re-build was broke in about 2 weeks ago. I followed the timing sticky exactly and everything was fine on the recommended numbers as far as I can tell. Great throttle response!
I could never get a good idle. It runs rough.
Timing scatters back and forth
dwell on the points goes from 30 to 36 during acceleration.
Then I went to adjust the carb. It had no response on either screw.
Vacuum OFF THE MANIFOLD is abnormally low, 11 inches at about 750rpm and also jittery. I don't think it can run the B26 vacuum can on the distributor as it is clattering at idle. Just off idle it stops.

I figured I may have 2 problems, carb. and distributor. Both rebuilt by LARS. So I sent them to him to check out.
Yesterday LARS said he tested extensively on the test stand and in his car and it is all correct.

he suggested the possibility that my timing light is defective due to the fact that it is physically impossible for the dwell to go up with RPM and because the timing is scattered. In addition that maybe there is a wiped lobe(s).

So with what I did today I now know that I do not have a cam problem. I took the manifold off and the hydraulic lifters all look brand new. Not a scratch where they ride the cam. I do think that my rockers needed adjustment though as they were not, well, all the same when I wiggle them.
I guess the carb doesn't respond on my car because something else is so out of whack.
So I am hoping that the timing and dwell are related to a bad light. To test I have an old fashioned timing light (no advance) and another dwell meter. I will compare data from both.
The vacuum may be due to the incorrect pre-load on the hydraulic lifters, I guess, as I do not believe I have any leaks or open ports. Even if I did that would not explain the jittery vacuum, only low vacuum. Maybe it is also the bad timing gun. The timing may be off too much and the valves are not open enough on the down stroke?

Unfortunately by the time I get the carb and Dist. back next week I have to go out of town. It won't be till October 10th that I can get back to it.
Any ideas would help
P.S. The plugs are black and sticky. Does this mean the rings are not broke in yet? Engine has only ran a couple hours.

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Old 09-26-2009, 06:05 PM
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First thing i would do is lose the points, Invest in a good ignition system like MSD or something, I put petronix in my vette and it ran great only cost little over $100. But you can get a good system from $100 up. Sounds like you might have a vacuum leak somewhere. Are the valves adjusted properly you sure?JMO....Cole
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Old 09-26-2009, 06:22 PM
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Quote:
Originally Posted by eloc431962
First thing i would do is lose the points, Invest in a good ignition system like MSD or something, I put petronix in my vette and it ran great only cost little over $100. But you can get a good system from $100 up. Sounds like you might have a vacuum leak somewhere. Are the valves adjusted properly you sure?JMO....Cole
It is the original distributor so I am trying to keep it. No, I do not believe the valves were adjusted correctly at this point. I will re do it in the next 2 weeks. Can some of my troubles be related to this? Vacuum?
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Old 09-26-2009, 06:26 PM
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Yes, Vacumm effects the running of a engine. I understand you want to keep it original if you put a petronix ignition in it you will be able to keep your distributer and run factory style plug wires and distributer cap no one would know but you. Cole
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Old 09-26-2009, 06:29 PM
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Heres a link to petronix take a look i have use this several times and it has always worked well on what ever engine it was in. http://www.cbsperformance.com/ignitor.shtml ....... You can get this at jegs/summit and other places also. Cole
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Old 09-26-2009, 06:39 PM
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I second the vote for the Pertronix swap. That is on the gotta-have list. I would also wonder what weights and springs are in the distributor and their condition, it could be the source of the jittery timing.
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Old 09-28-2009, 02:47 AM
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Quote:
Unfortunately by the time I get the carb and Dist. back next week I have to go out of town. It won't be till October 10th that I can get back to it.
Any ideas would help
Points per se are not the problem.

What may be the problem, is the God-only-knows how old and worn the points distributor is- and this will still be a problem even w/an electronic under-cap conversion if the original points plate and mechanical advance mechanism is to be used.

The distributor has supposedly been seen to already- if this is the case, it will run fine w/points. But if there's slop in the points plate or excessive clearances at the shaft/bushings, etc. the dwell can and will wander.

You didn't mention what cam is in it, or what carb for that matter, but if I was to take a WAG at it, I'd say it needed a lot more initial timing. Also, hook the vac. advance up to manifold (not ported) vacuum.
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Old 09-28-2009, 03:30 AM
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What cobalt said. The timing being scattered around tells you things are amiss. As I`ve said many of times before, the best place for points is the trash. I would never sacrafice reliability for originality.
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Old 09-28-2009, 03:50 AM
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Did you inspect the intake gaskets for being pinched all the way around each intake port?
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Old 09-28-2009, 04:27 PM
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This is true a distributer that ole could be just plain worn out, The plates are bad making it jump around, You can get a rebuild for it if thats what it is and still install something like petronix . Or go ahead and replace it with a update . there are a few options here yet. But as was said what is all been done to the motor whats in it? Cole
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Old 09-28-2009, 04:34 PM
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Quote:
Originally Posted by techinspector1
Did you inspect the intake gaskets for being pinched all the way around each intake port?
Yes I did. They were pinched. But it does seem that the passenger side are discolored on the bottom of 2 of 4 ports. Instead of nice and blue (Fel-Pro colored) They are oily or greasy and black on the bottom portion. To me that may mean a leak. But then again it is pinched. It doesn't matter because a new gasket will go on and I will be very careful. Well see what happens.
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Old 09-28-2009, 05:09 PM
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AH, You need to be vewy vewy careful when installing a intake. . Cole
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Old 09-29-2009, 04:51 AM
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Quote:
Originally Posted by eloc431962
This is true a distributer that ole could be just plain worn out, The plates are bad making it jump around, You can get a rebuild for it if thats what it is and still install something like petronix . Or go ahead and replace it with a update . there are a few options here yet. But as was said what is all been done to the motor whats in it? Cole
Car is a 8 327/350 hp Vette.
Engine is now a 383 completely rebuilt. The short block was done by what I believe to be an excellent shop. CR is 9.5/1 or slightly less.
Heads are original camel humps, rebuilt completely and slightly opened to if I remember correctly 2.02 / 1.6.
The carb is a Rochester from a 74 and distributor is original both rebuilt by LARS Grimsrud, known by many to be THE guy. People have their new carbs drop shipped to him to be adjusted. He tests then on a stand them throws them in a car and runs them. I sent him 2 carbs. This one he rebuilt and the other he said was junk and wouldn't touch it. He specifically said the timing was rock steady and if my dwell is going up, it is impossible physically and to check my equipment.
Stans Headers-2-1/2 going to Magnaflow mufflers.
original intake manifold

Cam is an Engle:

valve lift 480"
adv. duration 274"
cam lift 320"
.050 dur. 230
lobe center 110

I assume this cam should pull plenty of vacuum.
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