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Discussion Starter #1
I have a Gen1 383 with Dart SHP 200 Aluminum heads, Comp 274 Extreme cam, Performer RPM intake.

I'm getting #5 running hot/lean, about 125 degrees F hotter than my other cylinders when running a temperature gun on the header. I get mild fluctuations in the vacuum at idle and it's a little rough (not related to cam).

I've done the carb spray check for a vacuum leak. No difference. Compression checks all came back in the same range.

Anything else you could recommend checking for a hot/lean cylinder? thanks!
 

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Discussion Starter #4
Compression close within 5psi on all cylinders. Just reset valve lash last fall when I installed new rockers. I'll look again at the valve lash, but wouldn't an exhaust valve not closing cause the left bank to run rich? i don't see any difference in the exhaust between the two, right bank is steady 12.5 at idle.
 

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I have a Gen1 383 with Dart SHP 200 Aluminum heads, Comp 274 Extreme cam, Performer RPM intake.

I'm getting #5 running hot/lean, about 125 degrees F hotter than my other cylinders when running a temperature gun on the header. I get mild fluctuations in the vacuum at idle and it's a little rough (not related to cam).

I've done the carb spray check for a vacuum leak. No difference. Compression checks all came back in the same range.

Anything else you could recommend checking for a hot/lean cylinder? thanks!
Timing too retarded maybe ? Gas burning in header maybe ? Maybe try increasing the timing at idle 5 or 10 deg. and see what happens ? maybe that cylinder will clean up ?
 

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Valve in liftr not operating properly, not keeping valve set correctly.

I had a friend's chevelle years ago, brand new rebuilt engine my pal installed, would read good compression on test, fire it up, number 8 went away. Lifter for the intake on th number 8 was pumping past valve settng, holding intake valve open when oil pressure was raised when engine ran. Replaced brand new lifter, problem solved.

Recheck valve settings first, E-O, I-C method only.
 

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Intake gasket leak on that cylinder??????????????
 

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Discussion Starter #9
Lifters were just replaced <500 miles ago, my first thought was Intake Gasket leak. Seems to be conflicting installation, some say to use Gasgacinch sealant, some say to use RTV. I didn't use RTV on the intake side, in fact the gaskets I use already had a bead meant to seal them.

 

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Where does the vacuum for the power booster come from? #5 runner?
 

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Actually, the sealer on the intake manifold gaskets, you have the end sealing covered, RTV works in place of the rubber end seals.

That stuff around every intake port and water port is a compound used not only on gaskets, but as a gasket for metal to metal junctions, metal to rubber, etc.

The motorcycle industry uses a sealer that is the same as the beads, called Three-Bond, and is anything from 4, 1104, 1194, and other levels of sealer. They use it between engine cases that have no gasket but the T-B compound, on gaskets, and just about anything except exhaust heat areas. Motorcycle manufacturers have it as well, Honda Bond, and the number, Kawasaki Bond, Yama-Bond, Suzuki seal, and on.

I use it to seal rubber intake manifolds on bike engines, to the aluminum head flanges,

I don't know what it is called in the automotive industry, but it is great stuff, and different colors on different gasket sets.

Key is to get the surfaces clean, clean, CLEAN, and install, let set up for a couple of hours before use. Cleans up easily with acetone or lacquer thinner, and it stays a touch wet.
 

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Did you recheck the valve lash and how much do you run the motor or how long has it sat up. And if it sat up or wasn't run very much. Bc if you set the valve lash and then the motor sat for a period of time with the spring pressure on the lifters its possible even if it was done 500 miles ago that it could be bad. Over winter when my motors are not being run I loosen the rockers so there is no pressure on my lifters just for this reason. And I've seen brand new comp cam roller lifters be stuck now as soon as we called them about it they made it good on there end. They set another set no questions asked
 

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an intake leak would also be pulling oil mist from the galley. So #5 plug would look sooty.
 

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I have never liked the Edelbrock gaskets. Get a set of Fel Pro performance ones. You should not need to use anything with them other than a little rtv around the water passages. I have seen guys use rtv around the intake ports and the stuff is so slippery that the gasket moves and causes a leak.

This is way out there but I think #5 and #7 cylinders are the two that are prone to cross-firing ? Are the wires going to those two cylinders well separated and where they cross they do so at a 90 degree angle ? Like I said that is way out there but you never know.
 

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Discussion Starter #17
thanks everyone, i'll review the following this week-end:

- spark plug cross over (new MSD wires on and new separators but it's an easy check)
- pull the plug check it
- check booster for leak by plugging port
- re-measure temps
- check timing
- let cooldown
- re-check valve lash

I think the gasket is fine, given that most people don't recommend sealing them with RTV, and all the other cylinders are fine.
 
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