I just bought a 1999 cbr 600 f4 and it cranks but won't start. Got fuel, got fire, compression was off in one cylinder but the bike sat for 2 years, so maybe sticking valve?Carbs were recently jetted and worked over, and new fuel pump and relay. I kinda figured the guy before me was throwing parts at it, so this is where I'm at. Any suggestions? Bike only has 8600 miles on it.

 

If it was sitting for two years I would start at the carbs most likely its going to need a carb clean try using some starting fluid to see if you get any kind life out of it if you do even if its just for a sec you need a carb clean

 

I would check your sparkplugs again. Sometimes, these plugs will fire when out in the open, but not when in the bike under gas and compression. They are very finicky plugs and usually if they have ever been fouled, they need to be replaced.

Another thing to consider is to make sure the battery is fully charged. If the bike doesnt turn over fast enough, it will not start. Also, it needs a good battery to run. Motorcycles can not support their own electrical system like a car can.

Also, if the fuel is 2 years old, replace it. Drain the tank completely. Remove the carb bowls and see if there is any residue in the bowls. If there is. A carb cleaning will be in order. Gas that has sat for 2 years will be tarnished and more than likely have its share of water in it and its ability to fire will be severely reduced.

If it was me and I knew the guy before rejetted it. I would tear apart the carbs to make sure it was done correctly. I've seen a ton of DIY people that really don't have a clue as to what they are doing.

Its odd that the fuel pump and relay were replaced. The guy must have thought he had a fuel delivery problem. 8600 miles isnt that many miles to start seeing these problems. It makes me wonder if he was on the wrong track. I'd start looking at the electrical. A bad coil or faulty spark plug will act the same as running out of gas..

 

I checked for fuel delivery and have it. The gas tank was flushed and is clean, andI changed the plugs to the iridium ones it calls for.I've narrowed it down to the ignition system or compression. The problem being I don't have the right compression gauge set up for motorcycles. The schrader valve is at the top of the guage with a long hose adapter, so the combustion chamber is increased giving me a false reading. Also I'm having trouble with peak voltage reading at the coils. I'm supposed to have battery voltage a the the coils with key on, and I have it. But peak voltage is supposed to be 100 volts minumum when cranked,and when tested it, itdoesn't change from the battery voltage reading that it initially had. So by the book troubleshooting guide, it shows to replace the ignition control module. If that's it, is it common for something like that to go out on a bike with that few of miles? Anyways thanks for the help, and if you have anymore advice I could use it.

 

It might have been something the previous owner that could have damaged the ICM and caused it to fail prematurely.