75 Norton MK111 REvs Limited to 4000 RPM

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Marinok

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Oct 7, 2013
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I have a 75 850 MK111 which has the Boyer Igtion, Top end was rebuilt and new rings installed. After a break in period, I find that the engine will not rev past 4000 rpms. It acts like it hits a rev limiter and vibrates. Thoughts
 
Marinok said:
I find that the engine will not rev past 4000 rpms. It acts like it hits a rev limiter and vibrates.
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Amal chokes left on (choke cable set slack at the lever)?
 
Ignition timing not set correctly, or timing is not advancing as revs rise.

Check with a strobe the timing, and that it advances with an increase in revs.
 
Seems like your cam chain timing is out by 1 pin. The 4,000RPM limit is a symptom of this.
 
It's easier to pull the timing cover to check cam-chain indexing than to pull apart whole motor for known cam wear issue. Pull oil filter and rip apart to inspect for cam lobe bits ,pull sump plug for inspection.
 
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