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Old 09-22-2007, 09:50 PM   #1
MadseasoN
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Carbon Buildup on Piston - Normal?

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Old 09-22-2007, 11:00 PM   #2
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Are you burning any oil? The deposits look a little oily in the picture. If you are, it could be leaking past the intake valve guide seals. If not, I would suspect (if your carb isn't flooding or jetted too rich) that extra oil cooler may be cooling your engine a little too well and not letting your cylinder/oil get up to normal operating temps, therefore not able burn off the carbon deposits. I've raced the out of XR-70's in the early 80's in extreme conditions, never needed an external oil cooler. I've reamed the **** out of those bores, too. Typical Honda, they last forever!
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Old 09-23-2007, 12:01 AM   #3
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yup looks like oil to me. smoke on deceleration(rings)? if its not oily and it is actually carbon, your stock exhaust may be choking that huge carb and race head. Measure the od of the pipe just past the head, let me know what it is, I may have some exhaust you can try out.
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Old 09-23-2007, 12:04 AM   #4
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Quote:
Originally Posted by josh302 View Post
yup looks like oil to me. smoke on deceleration(rings)? if its not oily and it is actually carbon, your stock exhaust may be choking that huge carb and race head. Measure the od of the pipe just past the head, let me know what it is, I may have some exhaust you can try out.
I haven't noticed any smoke. I'm using the stock exhaust. I have a new aftermarket exhaust for a fiddy that I can trade you (a DID Chino knockoff). It's still in the box and won't fit the 70 without heavy mods.
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Old 09-23-2007, 01:41 AM   #5
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Quote:
Originally Posted by denhou1974 View Post
I haven't noticed any smoke. I'm using the stock exhaust. I have a new aftermarket exhaust for a fiddy that I can trade you (a DID Chino knockoff). It's still in the box and won't fit the 70 without heavy mods.
Looks normal. Only piston engine I ever saw that didnt look that way after a while was an ls1 (434 ci.) that was tuned very well and was run mostly on race gas(12.5+:1 comp)

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Old 09-23-2007, 02:17 AM   #6
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Looks normal. Only piston engine I ever saw that didnt look that way after a while was an ls1 (434 ci.) that was tuned very well and was run mostly on race gas(12.5+:1 comp)
nah that's not normal to oily looking.
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Old 09-23-2007, 10:14 AM   #7
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Come to think of it... I think I took that pic after spraying solvent on the head so that may be solvent, not oil.
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Old 09-23-2007, 12:03 PM   #8
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then it's pretty normal. the piston isn't going to be super clean i'm sure you know. just make sure your jetting is spot on. Now nasty was my ttr90 piston when i got it out after I had been running the heck out of it with bad rings.
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Old 09-24-2007, 12:55 PM   #9
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where the spark plugs black and wet? easiest way to find out if it was oil or carbon buildup.
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Old 09-24-2007, 01:02 PM   #10
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You probably need a rear shock.
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Old 09-24-2007, 01:09 PM   #11
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You probably need a rear shock.
Not anymore.
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Old 09-24-2007, 01:11 PM   #12
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Not anymore.
Well then... I want to try that thing out for a couple of laps during practice.
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Old 09-24-2007, 01:44 PM   #13
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can we get a pic of the spark plug if it hasn't been sprayed with solvent? The plug color will say a lot. . .
Have you done a compression test? Piston to Cylinder clearance?
That bike has come a long way Dennis, keep up the good work.
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Old 09-24-2007, 01:58 PM   #14
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Quote:
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can we get a pic of the spark plug if it hasn't been sprayed with solvent? The plug color will say a lot. . .
Have you done a compression test? Piston to Cylinder clearance?
That bike has come a long way Dennis, keep up the good work.
Thanks. I'll post a pic of the plug when I get home.
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Old 09-28-2007, 02:27 PM   #15
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Looks completely normal to me....

Remember horizontally mounted cylinder engines will burn more oil then conventional upright cylinder engines...

Look at the spark plug, is it grey and ashy looking? if so, its burning oil....if its just oily looking, you may have a TAD of oil draining past the valve seals...

It really just looks jetted a little rich too me....Carbon has a lot to do with the type of fuel you run also... I would leave it alone, rich is good for air cooled engines....

Its basically a briggs n stratton engine there, I wouldn't over analyze it...

BTW I had a 1970 Honda Trail 70 dirtbike, it was street legal and tagged up until 92'. It had 3200 miles on it, it topped out at 40 mph.....LOL never rebuilt. I did have to go through the carb every few months though.....
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Old 10-02-2007, 10:19 AM   #16
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Quote:
Originally Posted by ZXALAN View Post
Looks completely normal to me....

Remember horizontally mounted cylinder engines will burn more oil then conventional upright cylinder engines...

Look at the spark plug, is it grey and ashy looking? if so, its burning oil....if its just oily looking, you may have a TAD of oil draining past the valve seals...

It really just looks jetted a little rich too me....Carbon has a lot to do with the type of fuel you run also... I would leave it alone, rich is good for air cooled engines....

Its basically a briggs n stratton engine there, I wouldn't over analyze it...

BTW I had a 1970 Honda Trail 70 dirtbike, it was street legal and tagged up until 92'. It had 3200 miles on it, it topped out at 40 mph.....LOL never rebuilt. I did have to go through the carb every few months though.....

Thanks!
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