1973 Commando 850 troubles

texasSlick · Dec 16, 2019

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

Piero:

Please be more clear.

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

Slick

Giannantonio · Dec 16, 2019

texasSlick said:
Piero:

Please be more clear.

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

Slick

Yes

gortnipper · Dec 16, 2019

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.

maylar · Dec 17, 2019

Do a leakdown test.

pierodn · Dec 17, 2019

maylar said:
Do a leakdown test.

Let us know how you do the test.
Ciao
Piero

maylar · Dec 17, 2019

pierodn said:
Let us know how you do the test.
Ciao
Piero

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.

Giannantonio · Dec 17, 2019

I did it....over 120

pierodn · Dec 18, 2019

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.

Thank you.
Piero

htown16 · Dec 18, 2019

I've had trouble doing leakdown tests on motorcycles. Engine wants to spin over and open a valve.

MexicoMike · Dec 18, 2019

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.

maylar · Dec 19, 2019

htown16 said:
I've had trouble doing leakdown tests on motorcycles. Engine wants to spin over and open a valve.

Yup... gotta hold the rotor nut with a wrench.

Super Seven · Sep 13, 2020

pierodn said:
Yes, if is this the case it would mean a I. E.failure.
Ciao
Piero

Switching the coils needs to be done, as previously stated.

1973 Commando 850 troubles

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