Hey guys, first post here, been lurking for a while. Ive got a 91 CBR600f2, that inherited when my bro in law past 6 months ago. Its been sitting for almost a year, and I decided to get it running yesterday. I pulled the carbs and cleaned them (pulled the jets, needle, floats, ect). Still wouldn't start and run right so I checked the spark and it was weak and the plugs looked fouled. The local bike shop wanted 10.50 a piece for them! So I cleaned them and put them back in. Also got some fresh preimum and put it in the tank (poured the bad gas in my work beater) It acutallys runs now... but is still having issues. It starts on the choke quickly, and I can rev the **** out of it on choke, but The only way to get it off the choke is to take it above 3k or so, turn the choke off, and not let it drop below 3k. It also seems to be running very rich.

So whats the next step? Bad carb boots maybe? Kinda seems like a vaccumn leak to me.

BTW, Im a mechanic, so you dont need to talk down or dumb stuff up for me

 

Vacuum leak will show irregular/surging idle, have you verified that the idle screw has been set and not backed all the way out?

Try turning the idle screw in until it gets to a point that it will keep the motor running, and from there back it down slowly to 1400 rpm.

If that fails, you may want to clean the carbs (using carb cleaner and compressed air) again in case you missed any plugged jets or dirty needles. While you're in there, check the needle slide diaphragms for any cracks/tears.

If it had been sitting for a year without any fuel stabilizer there is a good chance that the fuel went bad and left varnish in the carbs.

Be careful you do not flood the motor by revving the motor with the choke on, that will cause very rich conditions and probably why the plugs looked fouled.

If you're a mechanic you should have access to a compression test gauge, run a check on all 4 cylinders and report back your numbers.

Also verify that the battery is putting out 14v and holds a charge, and that the charging system is functioning.

I'm sorry to hear about your brother, we'll get this bike running.

 

I did clean the carbs with comp air and carb cleaner, verfied all the jets were nice and clean, and cleaned out the bowls. I could have missed something, but I really doubt it. Ive pulled apart a few carbs in my day, and these are so simple! Do you know what these bikes pull for vaccum if in good shape? I could throw a gauge on it, if its real low that might show a leak... The boots were not in the best shape when I had the carbs of, so Im leaning towards them being the leak, if it is leaking. How many other vaccum lines are there on the bike? I just see the one going to the tank. I did mess with the idle adjustment alot, didnt really seam to make a diffrence. I may go mess with a little more today...

Thanks for the condolences on my bro, me and him were less then a month apart in age. Hard deal. This bike was one of the few things he had that was nice, and was really important to him. I want to build this bike up to what he wanted as I can afford it, a tribute I guess. Its going to be white pearl with bronze rims by next season. He past at 23 years old, of a heart attack. No drugs, roids... nothing. Live it up while you can guys. You can drop at any time.

 

Im really leaning towards the bike having a vacuum leak, does that make sense?

 

Check the rate of fuel flow from the gas tank to the carbs by disconnecting the fuel line from the carbs and opening the petcock.

You may be getting only a trickle of fuel from the petcock at idle and when you open the throttle the increase in vacuum may draw enough fuel to keep it running.

Bad gas may have caused the vacuum diaphragm in the petcock to seize up, or it could simply be jarred out of place which can happen and is not uncommon for these bikes.

 

Actually, I already checked that . Its getting lots of fuel.

 

Then you may be right with the vacuum leak.

When you pulled the carbs did you inspect the rubber boots that are between the carbs and head?

If you're a mechanic I don't need to tell you how to check for vacuum leak (spraying propane or carb cleaner in the area of suspected leakage)... Give that a shot

(on the topic of vacuum, is there a tube connected on one end to the nipple just under the #1 cylinders carb [on the block] and the other end connected to the petcock?)

 

they were in pretty bad shape, dry rotted. The petcock vac line is hooked up, I believe that's the only vac line on the motor? I was going to try the carb cleaner trick on it yesterday, but it was to dang windy.

If I do need new boots, are these really expensive from the dealer? Anyone have a part#? I was thinking of making my own from some fuel filler hose. That would at least tell me if it was the problem untill I could get new ones. Hell, I still dont have a endosrment, plates or a helmet for the thing yet...

 

I just replaced my boots, $11.40 CAD each.

Worth it to just replace them.

 

Local or on-line? My local bike shop wanted 10.50 for ONE plug, So the would probably want 50 a piece for the boots!!!

Dont happen to have a part #do ya?