Topic: Compression question

[namesEric]

My third cylinder is getting spark, but not firing. I ran a compression test on my bike and got consistent numbers. However, I didn't hold the throttle open when testing and the choke wasn't completely open. Also, the bike wasn't at riding temp.

I'm assuming the numbers aren't going to work for truly testing the compression to the factory specs, but the fact that they are all the same is a good sign there isn't any valve issues; right?

[TwoTired]

If they are all reading the same, but one cylinder is behaving differently from others, it's not a compression issue, I'd say.

[tlbranth]

If you're getting a spark, remove #3 plug and put a tiny amount of gas in the cylinder. Replace the plug and see if it fires. If it does, check #3 carb for fuel level.

[namesEric]

If they are all reading the same, but one cylinder is behaving differently from others, it's not a compression issue, I'd say.

Great, next step: rebuild carbs.

[namesEric]

If you're getting a spark, remove #3 plug and put a tiny amount of gas in the cylinder. Replace the plug and see if it fires. If it does, check #3 carb for fuel level.

Thanks Terry! That is a nice tip to have. However, I think it's getting too much fuel and flooding, rather than not enough. There is fuel coming out of the cylinder/exhaust. I'm going to take the carbs off and see if a jet came loose on the third carb or maybe the air is getting blocked somewhere? I don't know. I'm just glad the compression is good.

[TwoTired]

If raw fuel is indeed coming out the exhaust, do check the oil sump for gas contamination.

[namesEric]

If raw fuel is indeed coming out the exhaust, do check the oil sump for gas contamination.

I changed the oil over the weekend and it didn't appear to have any fuel in it. I may do another oil change for good measure once I get the carbs rebuilt.

[namesEric]

The pilot jet came out on the third carb. It was flooding the cylinder and preventing it from firing.