hi everyone. i have a 2000cbr 600 f4. its been running great the past few weeks. till one day on my way to work it started to drop some cylinders, then evenutually it died. I had it sit for a few hours at work and it started up just fine and i took my chances and rode it home. but after 15 mins it started to drop some cylinders again and I had to walk the bike home. I didnt get the time to work on it till a few weeks later.I had the idea i had either a fuel issue or maybe the coil packs. ( im no master mechanic )

i cleaned the carbs, changed the plugs, i didnt know how to test the strenght of the coil packs, but i did check for spark... so after all that i thought maybe the bike would run.

i could not get it to run. only cylinder 1 would fire.
i went ahead and did a compression test. i think the spec is 178psi (correct me if im wrong) and i got:
cylinder 1- 140
cylinder 2- 169
cylinder 3- 140
cylinder 4- 169

since my bike is already apart, should i look into this?
i figured since no. 1 only has 140 psi, and its the only one running that maybe the rest should fire. also, does anyone else think its so odd that the pressures are so consistent? ( again, im no master mechanic
so any help or advice would be great )

 

From the description of it dying, I'd say look into your fuel system. When your bike runs out of gas, the cylinders will drop off individually as each carb's float bowl runs out. For some reason, it sounds like you have fuel starvation, such as a plugged filter, petcock screen plugged, fuel pump faulty, plugged tank vent line, fuel line delaminated internally...ect

Compression PSI will change depending on your elevation. So its hard to say what your bike should be.

As for the test itself. Did you do a dry compression or a wet compression. It makes a pretty big difference. But the main thing to look for when doing a compression test is to see that all cylinders are within 10 percent of each other. Your readings are not, and could be a wear issue. I doubt it has anything do to with your running issue though. But I would test it again, but make sure its done wet and that should even out your compression ratios. If it doesnt, you may have some excessive wear.

If it were your coil packs, they usually fail in the higher rpms.

I would start with taking your float bowls off, or release the drain screw (if equiped) and see how much gas is in each bowl. If there isn't any, or very little, that is probably your problem.

 

I agree..... sounds fuel related to me too. While the compression numbers might be a little low, it's more than enough for it to run perfectly (now if it was 30 psi that would be a different story). Plus something else to note, if you were cranking it and it wouldn't start, there's a good chance you got what's called 'cylinder washdown', where the cylinder walls get coated with fuel (since it didn't burn), and it more or less cleans the film of oil from the cylinder wall, which will result in lower compression (we've actually had cars not start because of this). So that could be why your numbers are a little wacky