Gas Leaks In Right Cylinder

690 Views 5 Replies 3 Participants Last post by 66Sprint, Apr 7, 2019

Tim1965

Discussion Starter · Apr 7, 2019

I left the petcock on my cm400t for a few days and found that though it was leaning left on kickstand gas had filled the opposit cylinder and I had to remove plug to let out the gas cause of pressure buildup so that it would turnover and start..
My first thought is float needle isn't seated or intake valve isn't seething. I recently adjusted valves gaps too proper specs.
Any other possibilities I might have overlooked?

Thanks

Save

1 - 6 of 6 Posts

66Sprint

· #2 · Apr 7, 2019 (Edited)

I hope you changed your oil and filter before starting the engine.........
On these bikes, you MUST turn off the petcock any time the engine isn't running...PERIOD!
Failure to do so results in at least an oil and filter change, or you risk catastrophic engine damage from improper lubrication caused by fuel-thinned oil.....

Save

Tim1965

Discussion Starter · #3 · Apr 7, 2019

No I did not. But it ran fine all day and will change oil tomorrow. However, what causes such a leak of gas into the cylinder, gravity? I assumed a sticking valve or float needle not seating properly.

Save

J-T

· #4 · Apr 7, 2019

The float valves provide an imperfect seal. It is common for some fuel to seep past and overfill the carbs allowing fuel to flow down the carb throat, past an open intake valve, and into the cylinder. Some of this fuel will get past the rings, into the crankcase, and dilute the oil. It takes only a small amount of fuel and a short time to trash the engine.

Save

Tim1965

Discussion Starter · #5 · Apr 7, 2019

Gotcha. Appreciate the insight. Will definitely change oil tomorrow.

Save

66Sprint

· #6 · Apr 7, 2019 (Edited)

Tim1965 said:
No I did not. But it ran fine all day and will change oil tomorrow. However, what causes such a leak of gas into the cylinder, gravity? I assumed a sticking valve or float needle not seating properly.

Yes, gravity is the force getting fuel from the tank to the carb..... However, the shut-off needle and seat coupled with a properly adjusted float are primarily responsible for keeping the bowl full enough to run the bike, but not so full as to overflow and flood the engine....(Your shut-off needle and seat may be damaged, or you may have a bad/misadjusted float)...... Your secondary defense is the overflow tube (yours may be clogged)..... Failing those, Excess fuel or flooding of the cylinder will occur next, usually allowing fuel seepage past the rings where it enters the oil sump/supply and reduces the viscosity of the lubricant endangering ALL of the engine's moving parts......
The results are seldom pretty.....Damage may have already started and is not self-healing and tends to get worse with use......On the 175's I have seen an aluminum bearing block get galled and actually cause the steel camshaft to be eaten almost halfway away...Needless to say, it didn't run well at that juncture.......
ALWAYS shut off the petcock mitigating this possibility.....

Here's a link to a damaged camshaft topic which has a picture of typical damage after just a brief running time with less than adequate oiling....I shudder to think about "run all day".....

124564-cl175-cam-damaged.html

See less See more

Save

1 - 6 of 6 Posts

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.

Top Contributors this Month