Hard acceleration stumble

[equinoxlb]

Hi. I recently picked up an -89 FZR 1000. Very happy with the bike in general after valve clearance adjustment. However, during hard acceleration in both 2nd and 3rd gear the bike stumbles for a split second and then continues to pull hard (haven't tried through 4th and 5th yet, it's not a pleasant feeling at those speeds). It's like it looses power completely for a very short moment. This happens fairly high into the rpm range. When I looked around at different bikes one guy with an -87 model said his did the same in 3rd gear. Is this a known problem with these bikes? Could it perhaps be ignition related? Any tips would be appreciated.

[rotortech]

equinoxlb,

I suggest that you check for air leaks at the boots that join the airbox to the carbs and at the carb adapters that connect the carbs to the engine. Sometimes the airbox works its way loose on one or more of the rubber boots and will open up with vibration. The adapters that connect the carbs to the engine are also rubber and will crack with age.

Check the airbox to carb tubes by visually inspecting the area and making sure they are all the way down on the carb inlets and that the clamps are tight. With the bike idling you can check for leaks by spraying starter fluid on these adapters. If the idle jumps up a little, you know you have a leak. Keep at it until you can isolate the problem, then fix it.

Could it be electrical? Yes. You could have some wire that is shorting briefly at just the right rpm - for instance the wire that provides 12 V power to the coils. These are hard to find since they happen only at speed.

Check for air leaks first since it is a common problem.

[equinoxlb]

Thanks, will try that.

[McFizzer]

It doesn't happen in 1st? Is the bike jetted at all? And what mods if any..

What rpm does this happen? Is the exup valve serviced and cables properly tightened?

[equinoxlb]

It doesn't happen in 1st? Is the bike jetted at all? And what mods if any..

What rpm does this happen? Is the exup valve serviced and cables properly tightened?

No, it doesn't. Pulls fine through 1st gear. Happens around 7-8 k and no, the bike is not jetted. Only mod is a viper slip-on (as far as I know). According to the previous owner the carbs were synced by a local shop shortly before I bought it but I have not checked that myself yet. Yes, I have seviced and adjusted the exup cables and the valve is moving freely.
It is a very pronounced split second power loss that makes you fall forward on the bike, that's why I was thinking electrical (sudden loss of spark). Guess I need to start from the airbox and work through everything to eliminate potential error sources. Doesn't to it at half throttle either.

[apsolus]

does sound electrical. might be a good time to replace spark plugs if you havent already.

[reelrazor]

Bad spark plug (possibly cracked) or a bad plug cap/wire.

[equinoxlb]

Finaly got around to work on the bike. Cleaned the carbs (didn't look like that was necessary though), replaced the carb boots and made sure they were tight as hell. Took it out for a drive an the problem appears to be gone. Thanks for the input.

[yamaha_george]

Finaly got around to work on the bike. Cleaned the carbs (didn't look like that was necessary though), replaced the carb boots and made sure they were tight as hell. Took it out for a drive an the problem appears to be gone. Thanks for the input.

Well I am glad that worked out OK but please put your location in your personal profile please ALL 1k's are NOT the same world wide and it helps us to help you if we know what model market area you are in
Thnx
Y-Geo.