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Ps did you add some oil for a wet compression test, only 10 to 15cc of normal engine oil needed.

If you have a compressor or inflated car wheel and tyre and the kit, you can do a leak down test but ordinary compression tests are fine.

Over.....
 

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Pps, idle mixture screw, what is that set to now, and, the screw assembled properly as per CMSNL.com exploded view, ie screw needle, spring, washer, o ring, then fit into carb body.

Hope you were carefull when stripping carbs as that tiny o ring can stick/stay down the small hole, and be a devil to get out particularly if it "rotates". It can get jammed down in the hole if you don't know about it or are careless....
 

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1980 Honda CM400T
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Discussion Starter · #23 ·
Tapping definitely noticeable on the test ride. I probably increased the valve lash a tad too much. 77 mile test ride today shows mpg around 30. Still need to pull the plugs.

exhaust is in good shape until after the H-pipe, then the out pipes are in rough shape. Not sure how they’re really supposed to look but the following pictures demonstrate.

Automotive tire Liquid Plant Rim Automotive wheel system

Wheel Tire Automotive tire Bicycle part Rim


tachometer cable is brand new, the one that came on the bike was broken

I’ll check carb sync and plugs. Thanks again.
 

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1980 Honda CM400T
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Discussion Starter · #24 ·
Ps did you add some oil for a wet compression test, only 10 to 15cc of normal engine oil needed.

If you have a compressor or inflated car wheel and tyre and the kit, you can do a leak down test but ordinary compression tests are fine.

Over.....
Affirm; wet compression test was performed.

Pps, idle mixture screw, what is that set to now, and, the screw assembled properly as per CMSNL.com exploded view, ie screw needle, spring, washer, o ring, then fit into carb body.

Hope you were carefull when stripping carbs as that tiny o ring can stick/stay down the small hole, and be a devil to get out particularly if it "rotates". It can get jammed down in the hole if you don't know about it or are careless....
and yes, luckily I’d done some decent research prior to idle mixture screw installation. Ensured all old O-rings/washers came out and the new ones went in the correct order.

Thanks again.
 

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That exhaust end is breaking up and will be noisey...get an other one or repair that one. Expect it to be broken inside....or better still get a two into one, much lighter and better I feel. Motad.
 

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1980 Honda CM400T
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Discussion Starter · #26 ·
Pulled carbs to check float height, dead on at 15.5. Examine the air cut valves in some better light and they were definitely worn, had some cuts in them. Ordered new ones to replace. Hoping they will be the culprit. New plugs I installed a few days ago are just as black as the ones before. Mpg continues to be less than desirable.
 

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Float level looks a bit high to me. If 'air cut' valve refers to the slide, then it is possible the diaphragm 'rubber' has hardened or stiffened over time and is no longer responsive. It may delay the return of the slide to the closed position.
I never used the term air cut valve, as to me they are the 'slide' that opens in response to vacuum, allowing the adjustment of the fuel:air mixture as the needle occludes the jet passage less and less as the slide is pulled up by vacuum. Supposed to keep the mixture relatively stable as the airflow increases.
If the diaphragm is stiff, it will restrict airflow and cause an over-rich mixture that is sort of uncorrectable. Individual diaphragms are available to allow replacement without need to replace the whole assembly.
If you didn't know: Keihin CV carburetor diaphram installation page for JBM Industries
I have no interest, just saw the above. May need some for my old machine.
tom
 
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