Hi guys, I have a strange problem with my bike I've been trying to figure out for months. Bike is a 93 cbrf2 with a little over 40k miles. Carbs were JUST cleaned, clean air filter, plugs changed 2 years ago. Motor burns a little oil but has generally run well since I've had it.

Anyway here's the problem, bike starts and idles fine, however after 20-30 minutes of riding it will start to sputter at low rpm/idle and will die if you don't keep on the gas. Once it does die it is IMPOSSIBLE to restart until it cools all the way down. Even more strange is if you keep on it and keep it running, it apparently leaks some oily substance. I was never able to replicate this leak, I only saw after it did stall that oil was sprayed back over the length of the bike (from the air movement.) Even after cooling it down and restarting, I can't see any leaks, no drips, etc.

The last time I tried to take it out I only rode about fifteen minutes and it stalled just as I arrived at my buddies house. No leaking.

My only possible thought is that there is a crack in the block somewhere, and as it heats up and expands it starts to lose compression. If you keep on it it it keeps getting hotter and eventually the crack is large enough to let oil escape. I've let it idle for 15-20 minutes and could never replicate the problem with it just sitting there. I know it's a shot in the dark but I don't know what else to think. I'm willing to try pulling and rebuilding the motor but I wouldn't even know where to begin.

Has anyone experienced anything close to this or have any other thoughts on what to check? It's getting warm and I'm dying to ride and trying to avoid another monthly payment haha. Thanks in advance everyone!

 

Check the regulator/rectifier (r/r). You're listing almost classic symptoms.
When the r/r begins to fail, it heats up and chokes the current to the ignition.
Lose spark, lose power. After it cools down, it will work fine for a while.
Then heats up, lose power...

The leak thing is the odd note. It may not be related.

I would check the r/r, first.
Is it (or the connectors/wiring), looking melted/bubbly, etc.?
If so that's probably causing your power issue.

If/and, after that keep the bike clean and monitor for the return of the "mystery" leak.
Check before and after a ride, looking for signs,

Be cautious (for a bit) about using it as a "dependable" transportation option.
Start to relax after 2-3 rides, if you haven't seen anything.
Might just have been something on the road.

Hope this helps, Ern

 

Check your vacume operated fuel petcock.

 

Thanks for the advice on the r/r. Inn actually running the gsxr one as was recommended by this forum. Is there any way to probe it with a meter to see if it is functioning properly? or would it only malfunction when hot?

 

And is there any chance you have a vacuum diagram for the petcock? All my vacuum lines under there are a mess

 

Scratch that I just found the thread with the r/r troubleshooting info. I'm picking up a new battery now then I'll start poking around

 

Petcockvacuum line is connected to the left side of the motor. Wiring to my gsxr r/r looks fine, so inn going to cut the wires and measure resistance tonight (pain in the butt). I'm just wondering if the resistance for the gsxr unit should be the same as for the factory one (as per the fsm here
https://cbrforum.com/forum/f2-tech-93/charging-issues-troubleshooting-testing-91252/

 

Okay here's a long overdue update. Finally got my replacement cheapo (for now) r/r in from China and installed it today. Had the bike idling in my backyard while I was doing some yard work, and it ran fine for about 20 minutes. I finally heard it stall out. Went over, cracked the throttle about halfway, and wouldn't you know it starts right up! Only problem is about a minute later idle drops out and it dies. However at half throttle it will start right up again. Also if you give it a little gas once you start it, it will stay running fine (which it did not like to do before.) So I'm confident my rr was bad, and that problem is now fixed! I'm guessing my running issue is carb related?

I did have my carbs cleaned last summer (I was in the middle of a frame swap on my jeep so no time to learn how to do it myself haha). However I brought them in to the guy without the bike, so I'm thinking now it's probably just a matter of carb tuning and possibly jetting? This is assuming he did a good job cleaning them also.

Oh and another thing worth mentioning I just thought of, around last summer I cleaned up all the wiring harness from the frame and ended up running it in front of the airbox. I also had to take off the snorkels to accomplish this. I wonder if the wires are restricting airflow? If so could it be enough to mess up the tuning enough to make it not run? If I made some sort of ram air set up, would it help? I imagine that would require more carb tuning as well?

Thanks everyone, I never would have thought about that r/r as a problem

 

I think your idling problem is more of a tuning issue then a jet change. If it pulls hard in all rpms, your jetting is right. You said you took the carbs to someone to have them cleaned off the bike, without the bike, theres not a good way to set your idle screws. You can set them at the recommended base, but thats about it. Sounds kinda like its set a little off. Get the bike to operating temp and then adjust the pilot screws on all four carbs for proper idle and see if that helps. I wouldnt worry too much about the wires in the front, as I've ran mine similar when I threw the rr front end on. Also, are you riding with the fairings on? If not there is an airbox mod that should be done to prevent surging and whatnot at cruising