1973 Commando 850 troubles

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pierodn said:
Changed carbs with other from well running bike.
The right cylinder doesnt work the same.
Changed coils, spark plugs, I. E.
It doesnt work.
Cuso
Piero
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Piero:

Please be more clear.

After you changed carbs, coils, plugs, and E.I., the left cylinder is still incandescent?

Slick
 
Disconnect both fuel lines and do a 30 second test with both peacocks to see if one flows better than the other.

Also check both fuel lines, and any filters.

If you are only using one petcock to provide fuel to run the motor, try both.
 
pierodn said:
Let us know how you do the test.
Ciao
Piero
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It's done with a tool made for that purpose. You turn the engine by hand until one cylinder is near top dead center and both valves are closed. Then apply air pressure through the spark plug hole with a compressor and the leaktest tool. If there are any leaks you will hear air escaping and the gauge will tell you how bad it is. I suspect that the exhaust valve on your non-running cylinder is leaking, and if it is you will hear air hissing in the exhaust pipe.

This is an example of the tool -

https://www.ebay.com/p/8018342597?i...C6eHf84IocQqTxkixc9qyTwZHEhVkqThoCPQEQAvD_BwE

Any automotive parts store should have them, perhaps for rent.
 
maylar said:
It's done with a tool made for that purpose. You turn the engine by hand until one cylinder is near top dead center and both valves are closed. Then apply air pressure through the spark plug hole with a compressor and the leaktest tool. If there are any leaks you will hear air escaping and the gauge will tell you how bad it is. I suspect that the exhaust valve on your non-running cylinder is leaking, and if it is you will hear air hissing in the exhaust pipe.

This is an example of the tool -

https://www.ebay.com/p/8018342597?i...C6eHf84IocQqTxkixc9qyTwZHEhVkqThoCPQEQAvD_BwE

Any automotive parts store should have them, perhaps for rent.
Click to expand...
Thank you.
Piero
 
I've had trouble doing leakdown tests on motorcycles. Engine wants to spin over and open a valve.
 
Yeah, even on car engines, if you don't get the piston precisely at TDC, the air pressure will just shove the piston down. It's best to lock the piston in position somehow - on the bike I'd put it in gear on the center stand and lock the rear brake - either mechanically or have a helper sit on the bike/apply the rear brake.
 
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