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 Oh no!! Lean cylinder!!!! 
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Joined: Sun Dec 21, 2008 10:50 am
Posts: 67
Location: Atlanta
Post Oh no!! Lean cylinder!!!!
So I am dealing with two issues:
1- Backfiring on deceleration/engine braking
2- Engine stalls or does not produce power at low RPM. (need to rev up to 1500-1800 RPM before I can load)

So addressing 1, I took the exhaust manifolds down to inspect/replace the gaskets. And guess what!!! Nbr 2, 3 and 4 cylinders produce a nice black coat of black deposits on the interior of the manifolds, but nbr 1 is white/light gray clean. not a single trace of carbon!!!

Carburetor problem? Any idea where to start? If there was a leak affecting only one cylinder, where could it be?

Many thanks,
Jerome

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Jerome
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Sun Jul 16, 2017 7:34 pm
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Joined: Mon Aug 10, 2009 11:13 pm
Posts: 1264
Location: Coeur d'Alene, ID
Post Re: Oh no!! Lean cylinder!!!!
Check your valve adjustments.

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Sun Jul 16, 2017 8:15 pm
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Joined: Thu Oct 06, 2011 4:25 pm
Posts: 720
Location: Mount Vernon WA USA
Post Re: Oh no!! Lean cylinder!!!!
Unlikely to be a carb problem - its really a one barrel carb supplying two cylinders.

I'd check the intake manifold and it's gasket. Could be loose or a crack? Valve adjustment as well - eliminate the easy items first.


Sun Jul 16, 2017 9:13 pm
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Joined: Sun Dec 21, 2008 10:50 am
Posts: 67
Location: Atlanta
Post Re: Oh no!! Lean cylinder!!!!
Valve adjustment just done. Perfect. Didn't need to touch any of them!! Bad valve?

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Jerome
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Sun Jul 16, 2017 9:46 pm
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Joined: Mon Apr 12, 2004 9:36 pm
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Post Re: Oh no!! Lean cylinder!!!!
It's helpful to do a compression test on each one to narrow the guessing down, and it's easy.

How do the plugs look in those cyl's? Anything weird looking inside the dist. cap?

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Sun Jul 16, 2017 10:16 pm
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Joined: Sun Dec 21, 2008 10:50 am
Posts: 67
Location: Atlanta
Post Re: Oh no!! Lean cylinder!!!!
I pulled the plugs and they look all about the same... kind of nice color.
Here is a pic:

https://drive.google.com/open?id=0B6pvS ... TViMzFuOHc

Isn't the brake vacuum and distributor vacuum sourced from the front cylinder manifold? Could I have a leak or just too much vacuum lost in the distributor?

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Jerome
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Sun Jul 16, 2017 11:17 pm
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Joined: Wed Jan 18, 2012 9:07 am
Posts: 218
Location: Vienna, Austria
Post Re: Oh no!! Lean cylinder!!!!
if you close the vacuum connector on the front manifold you loose brake power support, but you will learn if that is the culprit.
Also check the rubber hose connecting both intake manifolds

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Tue Jul 18, 2017 12:44 am
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Joined: Thu Oct 06, 2011 4:25 pm
Posts: 720
Location: Mount Vernon WA USA
Post Re: Oh no!! Lean cylinder!!!!
Perhaps it's caused by a leak at the connection of the exhaust to the cylinder head? That would also explain the backfiring as well...


Tue Jul 18, 2017 6:26 am
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Joined: Sun Dec 21, 2008 10:50 am
Posts: 67
Location: Atlanta
Post Re: Oh no!! Lean cylinder!!!!
I replaced the exhaust gaskets... So if that was the problem I will know soon.

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Tue Jul 18, 2017 11:07 am
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Joined: Fri May 12, 2006 9:41 pm
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Location: Mount Pleasant, Tx.
Post Re: Oh no!! Lean cylinder!!!!
No power at low RPM, fuel cut out solenoid on effected cylinder.

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Wed Jul 19, 2017 7:39 pm
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Joined: Sun Dec 21, 2008 10:50 am
Posts: 67
Location: Atlanta
Post Solved most of problem!
Ok, trying to fix the lean condition on the first cylinder, I fixed by 90% my low rpm power problems. The engine almost does not stall anymore on loading it at low RPM. It was a bad setting of the idle mixture screws.

I followed the Pinz manual procedures instead of an old post on this forum, and it worked much better. I have a lot of banging and backfiring from the exhaust, which makes sense since I have now increased the fuel in mixture and I know my flex joints are not in good shape.

The Pinz manual recomends to open the idle mixture screws and close the carb butterflies as much as possible while maintaining a healthy idle. (about 850 to 900 RPM?)

And I always thought it was an ignition problem, since the symptoms were the same as wet distributor!

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Jerome
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Thu Jul 20, 2017 7:31 am
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Joined: Sun Dec 21, 2008 10:50 am
Posts: 67
Location: Atlanta
Post Re: Oh no!! Lean cylinder!!!!
OK, so engine runs kind of OK with idle screws at about 3 turns open, too much, definitely too rich, but that's the only way to get it to run loaded at low RPMs.
I opened the wind tunnel and took the manifolds out, changed the gaskets, on both sides, added some thin layer of gasket maker... no chance of leaks. Changed the hose between the manifolds, and finally, removed a squirrel nest from the top of cylinder 4.
I do suspect about the possibility of a leak on cylinder 1, on the bottom of intake manifold gasket. We'll see in the future what color I get out of that manifold.
So since no leaks were found on the top side, I am now leaning towards a fault in my acceleration pump jets.. or maybe on the pumps and the carb valves? Not sure...

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Jerome
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Sun Sep 24, 2017 3:39 pm
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