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Motorcycle Repair/ct70h honda 1971 engine noise


Bill; I have ct70 1971 manual clutch. we have done much work on it including piston n rings, valve job, hitachi stator assembly,
cleaned the carb. with new jets etc. I use gn4 10-40w oil in crank and clean gas. the problem is two fold. upon start up and warm up the engine doesn't sound like normal idle combustion. it jumps around a bit as if it wants to almost shut off. I adjusted air mixture in carb and rechecked points. at TDC points are closed opening ideal at the F mark.
Also, when kicking motor over one hears a toy squeak at times
which appears to be coming from the head. what is that? by toy squeak I mean like one steps on a shower baby ducky type noise.

Mark, the noise around your cylinder head area could be a leaking head gasket or the camchain could be off the guide roller.

Hopefully, the oil pump is working properly and lubricating everything as normal. Piston clearances should have been setup around 1.5 to 2 thousandths of an inch. Check your compression to see that your rings are seating and valves are closing tightly. Compression readings with wide open throttle should be around 150-175 psi. If you got the cam timing off a tooth, then the compression will be reduced and the engine won't idle correctly. Air leaks at the intake manifold will cause idling issues. Check o-rings and gaskets on the intake/carb side. Idle mixture screw should be responsive to changes in and out.

Points should be closed until the F mark alignment, then open at that time. They should not be closed at TDC (T mark). Make sure you are rotating the flywheel/rotor the correct direction... counter clockwise.

Sometimes a dry engine seal will squeal against the shaft that it is trying to seal, but it is rare.

Bill Silver

Motorcycle Repair

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Bill Silver


Need help with vintage Hondas from the 1960s? I am an expert with 250-305cc bikes in particular and most all of the other pre-91 models, in general. I do NOT claim to have a great deal of experience on Gold Wings, Cruisers, ATC/ATVs and dirt bikes.


I have owned/ridden/maintained Honda motorcycles for 35 years. I have written five books on Honda repairs and collecting. I was a service manager for two Honda shops back in the 1980s.

VJMC (Vintage Japanese Motorcycle Club) of North America

VJMC newsletter, as editor for two years and as contributing editor currently.

3 years auto shop in high school, teacher's aide in Automotive Technology in Jr. College, Diesel mechanic course in college, self-taught mechanic and automotive writer.

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