Hi there

I own a 1993 CBR 900RR Fireblade, and this is my situation. Sorry its a little long but as I know, the more information the better the diagnosis.

I was having trouble with my second gear change for a while as well as my headlight bulbs tended to blow when on a ride. So then I took her to the mechanic for a gearbox overhaul. As well as the gearbox fix, he synced the carbs (he only synced them, he did not clean them) After forking out a couple of g's, the bike ran beautifully. Once I drove her home I swiched her off, but then she wouldnt start again. I gathered the dumbasses didnt put the battery on the charger while they worked on her so I ran a couple of charging cycles and the battery is good as new.

I figured with the bulbs blowing my rectifier was shot as well, which could in turn have chewed up my stator. I replaced them both and everything was cool. I didnt have a chance to ride her for a while after that but after work I gave her a few revvs in the garage and everything seemed perfect. This went on for about 2 weeks.

Then one day I started her and she sounded like a v-twin. I rode her down the road as I suspected the cabs might have been a bit clogged and attemped to blow them clean, but no change. I got new plugs as well as carb cleaner. I was told by the dealer that I was using the incorrect fuel so I drained the fuel and put in the correct fuel with the carb cleaner. She fired up beautifully first time and ran like a MotoGP bike. All of her flat spots have dissapeared and I was grinning from ear to ear.

About an hour later I took her for a spin. She ran wonderfully for about 5 kilometers but then I noticed that she started to misfire a little, especially when I coasted in gear I hear a small popping sound out the exhast. When I got home, she was starting to get as sluggish as before. Her first gear pull away is horrible with her almost dying on me. Only once the revvs climb above 4k then she pulls ok but there is still that misfire lag.

Everything is cool with the charging system, she starts fine after the ride, and battery holds charge well. I suspect that it could be gunk the carbs but Im not sure what as I thought the carb cleaner in the fuel should have cleaned the fuel delivery system. Her idle is a little nervous no matter where she lays between 1k and 2k.

If anyone has ideas to fix this problem, please lend a hand as I cannot trust the mechanic on this one, cuz I never had a problem like this before I took her to him.

Thanks in advance!!

 

I dont know what fuel options you have where you are but 87-94 octane gas will be fine for that bike.

As for it running like ****........it sounds like it might be a fuel flow problem of some sort. Mine did that where it was sparatic and it turned out to be the petcock diaphram, but I believe you have a fuel pump on that model (mine was a 99) so I doubt that specific problem will be your case but it could be a shorted fuel pump if you were having electrical issues at one time.
Could be a vacum leak as well. Did he nick a hose or forget to put one back on? A vacume leak tends to be an issue until it's fixed and not off/on but you never know. It's worth checking.

 

Hi gixxereater

Thanks for the info, I wil definately check it out. I didnt think of the vacuum pipes.

The kinda fuel we run on the coast in South Africa is 95 octane unleaded. I was using the 95 octane Lead-Replacement fuel but I was intructed not to use that by the dealer as it is a "dirty" fuel. My exhaust system is totally coated in thick carbon. I changed to the unleaded and added a carb cleaner fuel additive to clean my intake system. Basically it was an octane booster to burn out the crap. I dont understand why she ran beautifully for a short while with new plugs, fuel and booster, then she turned over an ugly leaf and is chuggy with misfires. I thought the cleaner was supposed to fix or prevent that.

This only started once I used the carb cleaner. I think it could also be something clogged in my carbs as the booster was cleaning my carbs.

Thanks again gixxereater, I will definately check your pointers out and hopefully my baby will be eating up gixxers here in S.A. soon enough.

 

Pull the plugs again. Check the color of them. if they are anything other than golden brown there is fuel/air issue. If darker than golden brown (as you've pointed out) then they are fouled and can't burn off the excess carbon build up. If they are much lighter than golden brown (whiteish) then something is running lean.

Also, pull the bowls off the carbs and clean the main and pilot jets. Check the bowls to see if the gas has left deposits on the bottoms (inside) of the bowls).

 

Yep, you are right on the button. The plugs were as black as the night. The build up must have been that bad that even the new cleaner fuel and carb cleaner could not burn the crap off. Now my jets are messed up as well. The thing is that those plugs have only seen about 20 kilomenters (12.4 miles) of riding so they still should have looked like new.

Guess the previous owner didnt look after her as he said and sold her once he new he was gonna fork out a lot of money to fix her up. He didnt warn me at all.

Thanks everyone for your help. I know exactly whats wrong with my baby now.

Cheers

 

Hey there fellow bikers

Would just like to thank everyone who helped with the great info. After running carb cleaner through my system and listening to a noob (wannabe expert) at the bike shop who told me to switch fuels and totally screwed my carbs. Plus the ******* who had her before totally skrewed the air fuel mixtre when he installed the DynoJet and she was running so rich, she soiled her plugs within a week of riding and started that v-twin sound that all in line 4 riders hate to hear coming from their engines.

I stripped the carbs, installed a fuel filter(why the hell was this not installed earlier), flushed out the other fuel, cleaned every possible part of the carbs (Needles, Jets, disphrams), correctly set my air/fuel mixture, installed new plugs and put in the lower octane fuel back in and she is running like a brand new bike again. As I have personal experience, the CBR900RR Firebalde runs best on lower octane fuels. Higher octane fuels cause it to bog down heavily on the first gear once warm (or maybe its just my bike), that knowledge cost me two ignition coils and you can imagine how frustrating that must have been to see her react exactly the same with the new coils on. Lower octane fuels definately burn much better in the 900RR.

Thanks everyone for your input and maybe I'll be seeing fellow South African members in the mountains this weekend.

Cheers