Hi all, I have a 93 F2 with about 40k miles. Bikes been running okay for the last 3 years that I've owned it, but recently I've been having some problems I thought were carb related.

When I get up to high rpm (7-8k) in 6th gear, I can twist the throttle all day, but the bike won't pick up. Seems to me like its not getting enough fuel. Also when cruising at high speed/rpm (highway driving) if I pull the clutch in sometimes the bike goes flat and stalls (instead of dropping to proper idle, it just dies). POp start it and it always starts right back up.

Anyway, Got the carbs out, and followed the great write up on this forum to try to clean it. Keep in mind this is my first time ever messing with any carb. I have aftermarket exhuast and air filter that was on the bike when I got it, so I imagine its jetted.

I cleaned the floats, float pins and needles. I didn't touch the pilot screws because I wasn't sure what exactly to do with them lol. I removed the main jet and pilot jet, sprayed them out real good with carb cleaner. I didn't mess with the jet needles or sliders.

Anyway now that its back together its a pain to get the bike to run. Need to hold the throttle open to get it to start, and even that is unreliable. The only thing I can think I may have goofed on is reinstaling the throttle cables. I'm not 100% sure they were adjusted right, however when I twisted the throttle I could see the butterflies move, so I assume thats alright?

Any thoughts or suggestions would be appreciated. I'm at a point where I'm ready to bite the bullet and take it to a shop (however none of my vehicles have been to a mechanic in years, so I'm sort of reluctant.) I also just did a bunch of work to it this summer, chopped the rear end, new danmoto digital gauges, old cruiser chrome headlight and turns, cleaned up passenger pegs, new tires and brakes, so I'm sort of anxious to get it running properly, and this thing is killing me.

So please, let me know if theres something I may have missed, or anything I can troubleshoot or check. Thanks all, and stay safe out there!

 

If you do a clean, you really need to do a sync.

Beyond that, did you use new gaskets, etc.?
Even a tiny leak can affect performance.
On that note, dbl-check vacuum lines and/or hoses.
Are the carbs properly mounted? No leaks around the boots?
Did you tighten all of the hose-clamps on the boots?
Have the needles been gently seated and then backed out the proper rotations?

There is also the possibility that the carbs were never the issue.
Sometimes incipient r/r failure will masquerade as a fuel problem.

The bikes old enough, you should do a complete over-haul/maintenance/inspection
of the wiring harness and all of the connectors/wire-runs.

Hope this helps, Ern

 

I got a chance to do more troubleshooting after charging the battery. I was able to get the bike to start pretty easily, but once it warmed up in about 2-3 mins it would drop rpm and stall. After that no start no matter what you do, until you give it 15 minutes or so to cool down, and then it starts up again....


I considered attempting a sync, but I was afraid of getting in over my head and creating more problems then I already had.

I reused the gaskets, but they all appeared in good shape, no cracking or dry rotting. I did come across the vacuum line that goes from intake right where the carbs mount to I believe the gas tank? However it was cracked and hanging, not connected to anything for at least a couple years. I didn;t have the right diameter emissions hose, so I just capped it for now. Tried running it without the cap, same problems. Boots all got tightened but I guess I could spray the area with carb cleaner to check for vac leaks.

Which needles are you referring to? The jets/screw things? I ran them in to "snug" but didn't back them out at all... IS this my problem?
I'm running a gsx-r r/r, no charging issues.

When I did the work with the headlight/digital cluster/tails and turns, I had the whole main harness apart. Everything looked clean and intact, no signs of any damage ot wear at any points.


Thanks for the detailed reply, maybe the needles are my problem? Please pardon my ignorance of carbs, but fuel induction experience consists of sbc and jeep tbi/tpi/4.0 stuff. Basically an advanced carb without the need for manual tun9ing, but wihtout all the sensor/technology crap on todays motors... But I would learn to love more about carbs

 

You half-cleaned the carbs if you did not remove every component and soak/scrub it down - needles are especially important here. You could have a piece of trash stuck in a jet and it would prevent a needle from seating, then you'd get all kinds of running problems. NEVER half-clean a carb. You either go all the way with it or don't touch it at all.

 

What parts didn't I clean? Also which needles, the jets? Or under the diaphrams?

 

Do a search in the how-to general forum.
There are several very good pictorials of carb clean/over-haul.
There are also a couple of excellent you-tubes.

Ern

 

I know this is an old thread but my 90 cbr1000f is doing the same exact thing after cleaning the carbs. Did you ever find a solution?

 

Welcome to the forum Ricky,

Did you balance the carbs after cleaning? It's a must do.


Cheers, SB

 

I did not. I noticed while I had them off they weren't perfectly in sync by holding wide open and just eyeballing it. But i didn't think it would stop it from running since it was running before hand and I didn't mess with the mixture screws, I just figured I would sync them once I got it back together, but I think I'm going to have to bench sync them first. The reason I cleaned them is it was running rough at low RPM and when just cruising along around 3k it would jump like I was playing with the throttle until I got above 4k. Now after the cleaning it runs great, so much smoother than before but only while it's cool. As it warms it gets worse and worse until it finally dies. I can keep it running by playing with the throttle but if it dies it will NOT start back without letting it cool completely. I don't have much experience with bikes but have been a fabricator and mechanic for a while, and from my experience this is the tell tale signs of bad coil packs or ignition module. So, after triple checking everything I had done with the carbs I replaced both coil packs, wires, plugs, and resistor boots only to change nothing. Thanks for the welcome and the quick reply. I'll bench sync them tonight and go from there.

 

Ok, so I bench synced the carbs, and had a friend of a friend sync them with his tool (carb tune pro I think). Fires right up and runs incredible, so smooth through the rpms, until it warms up. Then it wants to idle a little rough around 1800rpm or lower, not like it has a cylinder down, just rough like a single misfire every few revolutions. Also has a hard time taking off, misfires worse when I start to let out the clutch as it starts to pull, I have to rev it to at least 3k to get moving. As long as I keep it from idling down and dying it runs sooooo much better then it did, so smooth. If it is shut off or dies once it's warm, sometimes it'll start right back as long as I hit the starter within a few seconds of it dying, if it sets for at least about 30-45 seconds it WILL NOT start back until cooling down., Almost like the kill switch is engaged, it won't even try to start, just turns and turns. Using the choke or throttle makes no difference, new plugs, wires, and coil packs, getting fire to spark plugs, getting fuel to carbs. Just a thought that's been banging around in my head, the bike has Vance Hines exhaust and k&n filter but factory 122 jets, do you guys think it's possible that the previous owner, (to compensate for dirty carbs and higher flowing intake, exhaust) could've increased fuel with mixture screws and now that the carbs are clean and flowing better they're flooding the engine? The harder i twist the throttle the better it runs. Also, every time I pull the plugs, there's a sort of yellow film or haze on them, I have cleaned them every time I've noticed it, never seems to make a difference though. I'm completely stumped, this is my only DD so any and all help is GREATLY appreciated. Thanks in advance.