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lean front cylinder... help!

Moderators: Curt!, Pa

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41WLD45

Posts: 10

Joined: Tue Feb 08, 2011 4:11 am

Post Thu Nov 24, 2011 4:16 am

lean front cylinder... help!

My '46 U has started running very lean on the front cylinder. The plug colour is totally different to the rear. The rear is nice and dark with soot around the edges, the front is clean with no deposits and almost pinkish colour electrode. A cold compression test came up at 70psi. There's no noticeable signs of leaks from the head gasket area and no visible cracks. She's running on both cylinders but not smoothly, lots of popping and banging.
My first guess was inlet manifold. I tried spraying carb cleaner around the inlet to see if it drew it in and started to race but it made no difference.
Anything else that I've missed? My thoughts are a leak on the inlet at the front manifold nut. If it is the inlet do I need new parts or just a clean and reassemble? Do you use a sealant?

Many thanks, Steve
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Jerry Wieland

Posts: 606

Joined: Mon Nov 01, 1999 1:01 am

Location: Menomonie, Wisconsin, USA

Post Thu Nov 24, 2011 9:59 am

Re: lean front cylinder... help!

Spraying carb cleaner does not always detect a leak. I would pressure test to about 6psi and use soap and water. Sure sounds like an intake leak. Jerry
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Pa

Site Admin

Posts: 4478

Joined: Sun Mar 12, 2000 1:01 am

Location: Ohio USA

Post Thu Nov 24, 2011 10:00 am

Re: lean front cylinder... help!

Replace seals with Peek seals. Available from two different vendors on this forum. Search "Peek" ...you will find the vendors. Pa
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41WLD45

Posts: 10

Joined: Tue Feb 08, 2011 4:11 am

Post Thu Nov 24, 2011 12:19 pm

Re: lean front cylinder... help!

Much appreciated Jerry and Pa.

I've found the Peek seals, thanks for that tip.

Steve
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wilko

Posts: 159

Joined: Fri Jan 15, 2010 7:36 pm

Post Thu Nov 24, 2011 5:39 pm

Re: lean front cylinder... help!

Tight tappets?
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41WLD45

Posts: 10

Joined: Tue Feb 08, 2011 4:11 am

Post Fri Nov 25, 2011 9:18 am

Re: lean front cylinder... help!

I'm going to check the tappets as the bike is new to me and they're on my to-do list but if they were tight enough to let air in wouldn't it loose compression?
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Cotten

User avatar

Posts: 2659

Joined: Thu Sep 30, 1999 12:01 am

Location: Central Illinois, USA

Post Sat Nov 26, 2011 5:53 am

Re: lean front cylinder... help!

41WLD45!

Please follow Jerry's advice, but use from 12 to 15 psi max:
http://virtualindian.org/11techleaktest/html

Beware that you must have an un-blemished manifold for Moldthreads's seals to fit properly.

Good luck!

....Cotten

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