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Discussion Starter · #1 ·
How high is too high, I wonder?
Trying to work out some bugs today, I took a compression reading (just cause it was warm and I've gotten in the habit of checking every so often)...

L:180 R:170

As we are all aware, ideal compression for the 350 is 170psi. So the right is in spec. The left however is 10 over. Honda's shop manual says if the compression is over 170 "wall and/or piston probably have carbon deposits." How critical is this?
I'm inclined to think not enough to warrant pulling it part...

Funny thing is, I've always gotten this reading since I started working on the bike as a non-runner about 6 months ago. I had it, covered and sitting outside, for 2 years prior to working on it. I don't know the last time it ran before that but I suspect it was quite awhile, years even.
I have checked the compression with another tester, values were the same, so I know the gauge is calibrated properly.
 

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Sensei
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Your left side is probably just carboned up as you stated, However, it could have been rebuilt with not enough clearance, ring gap, or similar...How many miles on the engine?... Does it seem to run/produce power OK?...How do the plugs look?.....
 

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Discussion Starter · #3 ·
Right, of course.
It has 9,300mi on the odometer.
Seems to perform well. Pulls away well, accelerates well... Haven't done extensive road testing yet, but it doesn't bog down under any condition I've had it in yet. Most of my troubles were/are carb related, I believe. Idling problems, a too lean mixture, I suspect over heating... Carburetors were thoroughly cleaned, but of course upon re-inspection, the slow jets were completely plugged.
Cleaning them out took care of the idle problem. Very steady idle now. Still some bugs, but I'll spend more time poking at it before I start asking questions...
But assuming carbon deposits, I would be ok to leave it alone for now?
 

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Discussion Starter · #4 ·
66Sprint said:
could have been rebuilt with not enough clearance, ring gap, or similar.
Do you think it's worth pulling to check?
 

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Sensei
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Not if it's running OK now....... Maybe next winter....LOL....
 

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Discussion Starter · #6 ·
66Sprint said:
Not if it's running OK now....... Maybe next winter....LOL....
Yeah, I guess worrying about this is silly. Diagnostic tests and their indications are interesting, though...

Thanks.
 

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Someone on this forum mentioned putting in a teaspoon of water- very slowly- into the carb to make it pop the carbon out? Something about how water does not compress, and so it forces the carbon off? Any validity to this? I also have a 180 reading, on the left cylinder of my 360, and wondered if it was worth doing, instead of taking apart a perfectly good engine ;)
 

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I suggest working on this problem all Spring, Summer, and Fall. Use regular full throttle runs to red line in as many gears as you can and still have a license.
TomC in Ohio Looking forward to Spring and seeing 10,000 rpm again.
 

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You could always try running some seafoam through it mixed with gasoline.. Maybe from a temporary tank while keeping the RPMs up...

Just a thought, as it's a very good carbon remover..


GB :mrgreen:
 

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Discussion Starter · #10 ·
TomC said:
I suggest working on this problem all Spring, Summer, and Fall. Use regular full throttle runs to red line in as many gears as you can and still have a license.
TomC in Ohio Looking forward to Spring and seeing 10,000 rpm again.
Ha ha!
A sound suggestion. I'll get to work ASAP.
 

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That actually is a sound suggestion. In theory it works to remove carbon deposits..

The Seafoam will probably help as well...

GB :mrgreen:
 

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Discussion Starter · #12 ·
Bird76Mojo said:
That actually is a sound suggestion. In theory it works to remove carbon deposits..
The Seafoam will probably help as well...
For sure. I understand... it's just funny. A problem whose solution requires (at least in part) riding the bike often doesn't seem like so much of a problem... or at least it is a welcome one.
I didn't mean to discount your suggestion, either.
I have some Seafoam in fact, and I wanted to ask your opinion about it. Some people seem to think that using an additive this way on an older engine can cause problems somehow (presumably by melting away old seals, gaskets... I donno?)
Has anything like this ever been a concern to you? I suppose if some component of the engine is that fragile, it's only a matter of time anyway...
 

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My belief when it comes to Seafoam is that it's no miracle worker. Although it does do a good job at removing carbon deposits if used correctly. I don't see it becoming a problem on the gaskets and/or seals. I NEVER pour it into the crankcase like some people do. If I wanted to thin out my oil with a solvent then I'd just dump fuel into the engine. Not much difference if you ask me.. However, I do use it in the fuel system and have used it in my truck engines by pouring it into the vacuum system (upper intake) right before an oil change.

I think it makes the most sense, especially in your case, to use it in the fuel only. It's definitely worth a try. I can't see where it'd hurt to give it a shot. If you have any doubts on its effectiveness, then shine a light into the plug holes or borrow a boroscope and look at the tops of the pistons. Then run the Seafoam and have another look. I have before on my old daily beater Ford Ranger and the piston tops were clean as a whistle after the treatment.. YRMV...

I wouldn't run a full tank of fuel with it added though. Just a test tank type of arrangement maybe.. Or run a 1/4 of a tank with the correct ratio of Seafoam added, and run it to redline several times, like previously suggested. Then top off the tank with premium for the trip home.. ;)


P.S. I didn't think you discounted my suggestion.. :D



GB :mrgreen:
 
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