serious loss of power

my second build has been running beautifuly for 5 months. it now has no power at all, it lost all power in a small 15 minute trip into town. it will get up to speed on a flat road but as soon as the slightest hill comes along i slow down so much that if i dont pedal it will stall. havent changed anything on it exept the stock plug and lead when i 1st built it.... i am so confused as to what is going on with it. i tried running a little leaner. all that did was heat the engine up faster, so i tried running richer and it still has no power.

time for a new build or can u guys fix it?

ps its not compression .. she has plenty of that.

Check the exhaust pipe...It may be clogged.

Jim

checking that right now .. typing with greasy hands


Edit: clean and clear of clogs. i dont think i will buy gruubee again, my zbox engine is built so much better.

If it has compression, and is not running lean due to an air leak, (light or white plug) then check for binding rear wheel bearings, or other drive train issues.

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wheel and chains move freely (with clutch pulled in of course)tomorrow i will try swapping parts from the good bike 1 by 1

What does the plug look like?

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has a little blacky brown residue .. not really much

do you have any oily residue under the mag cover or under the clutch cover all of it will be where the crankshaft comes through the crankcase on either side? you might have a main crank seal leaking/going bad and oily poo with some black dust is a dead giveaway of a seal leaking. some engines are assembled with seals that are damaged when they are assembled they will run fine for awhile then get to running sorry and keep getting worse until you either trash out the engine from it running lean for hopefully find the problem before it gets that bad.
Norman

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You might have what Jim just discovered in my first motor over the weekend.
One of my crank bearing seals was placed on the inside of the motor; thus shielding it from any lubrication whatsoever. The crank barely moved and was heading for a seize up. Jim found melted rubber in my case around one crank bearing. The motor had very little miles on it, but it was too late by the time the seal melted away. The motor was losing power daily.

Where did you get your motor?

'BrettMavriK

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'BrettMavriK
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got it from a gasman resaler near fairy meadow (south of sydney) i stripped it bare just yesterday and cannot see a single thing wrong with it. put it back together and it still has no power. it will get up to speed on a flat but the 1st sign of a hill and it slows right down to a crawl. i have given up on it and am buying a new zbox engine. i dont think i will ever buy grubee again.