CBR600 f4 carb issue?

[andy777bmx]

Buggy was working great about two months ago. Tore everything apart to finish, paint and reassemble to be completely done. When everything was put back together the engine started having some troubles.

As of now, the engine wont start without opening the choke all the way and keeping it there. I fully warmed the engine up and whenever I put the choke back it dies, or if i give it gas, it dies. Two months ago, it would start right up even without opening the choke and ran fine.

Do you think the carbs are gummed up? It has only been sitting for two months and worked fine before. I ran some seafoam through it and will try it today and see if that will help.

Just wanted to get some opinions before I tear apart all the carbs and clean.

Thanks!

Andy

[Bugpac]

Sounds like an air leak to me, To much air not enough fuel, Could be the carbs for sure tho...

[dunerocket]

I bet the low speed jets are clogged. I've found a quick way to clean it is to blow some compressed air in through the bowl drain. Be sure to drain each bowl and only have the one that you are cleaning open. Otherwise take the carbs off, remove bowl and low speed jet and clean.

[dunerocket]

Oh and if mine sits for more than a week with fuel in the bowl it will do that. There is no pattern to which carb will clog, but at least one will.

[andy777bmx]

I'm thinking it's the jets as well. I'll see if the seafoam helped tomorrow but I doubt it did much.

So you are saying you can leave the carbs on and just clean one at a time? Do you just undo the screw, let drain and then blow air in it? What PSI about? Also do you need to re sync the carbs after doing this?

I'm hoping this will work so I don't have to pull everything apart. Might as well try it first. Thanks for the advice.

[dunerocket]

Yes, leave all the carbs on the engine. Normally the gas has already evaporated out of all the bowls so I don't have to worry about draining them.

I leave the compressor set at 90 psi. I open up one bowl drain and blow some air into it. I don't seal the air gun to the bowl, just line it up with the drain. Most of the air doesn't even go into the carb.

On my carbs there is a tube that connects each carb, some sort of overflow. I see that bob up and down as the air blows through. I have a CBR900RR, but my F3 was the same. I'm guessing your F4 is the same as well.

You only need to re-sync after taking the carbs apart. People say sync them after you take the carb assembly off the engine, but I haven't seen them move enough to matter.

[andy777bmx]

Tried the compressed air and it now idles without having the choke open which is good. When I give it gas it dies still. Does this sound like the main jets are clogged? If so I am assuming I need to open up the carbs and clean. Being that you have done this with an F3, any tips for the job? I found some links showing how it is done for different bike engines but not this one. Do you need to remove the carbs from the engine or is it possible to clean by just taking off the float chamber?

Thanks!

[nutz4sand]

Sounds like it would be smart to just take each carb apart to the bones to make sure its good.

You get one running lean and that cylinder will run hot. Not so big a deal on this VS a two smoke but still an issue.

[dunerocket]

When you give it gas, are you feathering it slowly or just gunning it?

Try letting it warm up for a minute. Using a spray bottle, mist some water onto the headers one at a time. See if one is not getting hot, it will be obvious. Sounds to me like one of the low speed circuits is still a bit clogged.

It may be possible to do it on the engine, but I wouldn't bother trying, too much work.

Tips:

The 3 screws that hold the bowl on are phillips head. I alway encoutered one screw per bowl that wouldn't come loose and wouldl round out the head. I cut a slot in it with a dremel and get it out with a slotted screw driver. I then replace all the screws with socket head cap screws.

Clean the seat for the fuel shut off. There is one per bowl.

Do one carb at a time. This way the jets will not get mixed up. That shouldn't matter, but it doesn't hurt.

I took the carbs apart once to replace some leaking o-rings on the fuel input. It was a major pain and I wouldn't do it unless it was absolutely necessary.

If you haven't synced the carbs, it wouldn't hurt to do it when you put them back on. Once you are happy that it runs properly, either buy or make a sync tool.

[andy777bmx]

I tried slowly giving it gas and also gunning it, same thing right over 2000 rpm.

UPDATE: I pulled the carbs apart today. You were right, one screw stripped so I used your dremel method and got it out and replaced them all with socket heads. Good tip! Everything was pretty clean except for the jets. Almost every jet had so much crap you couldn't see through it. Cleaned them out with compressed air and carb cleaner.

TIP: I found a tip online saying to throw the jets in boiling water and stir them around a little. That worked just about the best along with compressed air to get the major stuff out. The carb cleaner was good for getting the last little bit of stuff off.

Too late to start it up tonight so I'm going to try it tomorrow and let you guys know how it went. I'm thinking it should work a lot better now. I have a carb sync tool, never used it, but will give it a try. Looks pretty simple to use along with the bike manual.

Thanks again for the help...