Hello there, first post to this forum. I recently bought a 93 CBR 600F2 not running. After doing some research i eventually got it to run with some wiring help, i noticed fuel leaking from carb bowls also, so i did a carb rebuild on them. After rebuilding the Carbs it ran once and now every time i try to start it it backfires on me. i did some research on this forum about this, and i think it seams to be the carbs need sync'd, but that is a new world to me. Any suggestions or comments will help.
Thank You
ry_burner

 

Sure your firing order is correct ?

 

yeah sure the firing order is right double checked that, im curious if the timing is off but it gets the timing straight from the computer, not sure what changes the timing but that is another thing i might check.
Thank you so much for the suggestions.
ry_burner

 

RB,

I wouldn't worry about syncing the carbs yet. If they are out of sync then the engine should still run, maybe just a bit rough. If the engine is not starting but is turning over ok, then I would just check a few basic things...

- Are you sure you are getting a spark at all four plugs?
- Do you know if you have good compression in all cylinders?
- Do all the boots on the carbs look good, no cracks where vacuum can be lost?
- Are the floats working fine in the carbs and not sticking to cause fuel flow issues?
- Is the air filter in good shape to allow good air flow?
- Have you taken the valve cover off the engine to check the valve timing is ok?

These are the first things that spring to mind.

 

good idea check the spark plugs for good spark, will do a compression test also. the boots are good and flexable remarkably, havent checked the valve timing yet, but not to familiar with that so id rather not go in the engine if i didnt have to. Like i say tho it started before fine and after the carb rebuild it started once and now wont start again.
Does the throttle valve adjust the carb synchronization? The left 2 are open more the the right 2 at idle throttle it looks like.

 

There are some small screws that control the butterfly valves at idle and they are what you adjust for the carb sync. You'll need some kind of vacuum guage to actually do a sync and the F2 manual will explain the rest. Simple enough if you have a screwdriver long enough to reach the right screws.

Don't take this the wrong way but just wanted to check you have the choke on and the engine switch in the 'on' position for starting? Simple things that can get overlooked. Is the bike in neutral? That should eliminate any issues with faulty side stand switches.

How is the condition of the battery? I've had batteries that will turn the engine over but it just wouldn't fire up. Almost enough juice but not quite left in them I guess. Have you checked the charge?

 

I was also going to mention the choke, but to ask if you knew for sure if the circuit was opening and closing appropriately, as you engage/disengage the lever. Is there a moderate to heavy fuel smell, when you start the bike?

 

Alright you guys are freaking awesome, the battery is brand new, had the fuel tank off, so i put a little gas in the tube and blew int he tube forcing fuel in the carbs a few times about 1/4 cup maybe altogether. put the choke on full and started turning it over, accelerated the throttle and it backfired, so i didnt do the throttle again, let the choke in half way and it wanted to start so i let it out a little again, noth9ing so i pushed in half way and she started up, rough though, but she started. when she was started i tried the throttle again and right away it died, it started again, and the same with the throttle. so i went to the store and got some 91 octane fuel put the tank on and put 2 gallons in it,,and now she wont start again, even after messing with the choke again. so the choke was my original problem but now it seems to be something else. i heard the F2 petcock is bad and the F3 is recommended. Any ideas?
Thank You
RY_BURNER

 

Ok after doing more research i think my petcock is bad, it is vacuum, and the way i understood it, the gas will only come out when there is vacuum coming from the intake. anyways when i take my tank off the petcock leaks like a siv, i struggle to find the "sweet spot" on the off position, just to get it to stop, otherwise it acts like it is wide open and it comes poring out.

 

I could understand your petcock being the problem if it was stuck closed and no fuel was flowing, but if it is stuck open then it shouldn't be a problem unless your float's aren't doing their job and controling the flow of fuel through the carbs.

I think you have a fuel/air flow problem through the carbs. You said that this all happened pretty soon after you rebuilt them and I think that might be a clue. Try running the old Sea Foam through them or taking them apart and cleaning them out again