Having problems

[joneseyjnr200...]

Hey, i'm having problems with my 1991 gpz 500. Today on the way to work the revs kept dropping randomly, say from 6000 to 4000 then back to 6000, as though i was shutting the throttle then opening it, jerking me about, also at slow speeds, and when moving off, i had to give it alot of revs to stop it cutting out.

I live 5 minutes away from work so i thought i'd chance it back to my house. Same story on the way back, but it backfired this time, which its never done since i owned it.

Anybody any ideas what this could be? I'm fairly new to bikes and no mechanic, but i'm willing to sort this myself if i can.

Comments much appreciated guys, cheers.

[tutton]

Would get a better repsonce in the workshop section
PM a moderator to move it for you.
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Past: '05 Peugeot XPS '99 Aprillia RS125 '94 FZR600R
Current: '02 ZX636 A1P '51 CCM R30

[stinkwheel]

From what you describe, it could be the spark momentarily cutting out or possibly the engine "searching" for fuel/air.

One issue I've had in the past is a blocked fuel tank breather. Try running it with the fuel cap open and see if the problem is still there.

An issue I've heard of other people having is with water in the fuel tank. If you open the drain screw at the base of the carb and collect what runs out in some sort of container, any water contamination in the fuel should be obvious.

A further issue I've had is with an intermittant contact on the ignition switch causing the engine to cut out. A liberal spray of WD40 into the switch and a good wiggle about sometimes sorts this out.

There is also a possability with a 1991 model that some of the magnets in the alternator may have dropped off, damaging the mechanism that produces the spark. This is a known issue with pre-'94 models. If this has happened, there is a fair chance the engine is beyond economic repair. Spares are available but generally work out costing more than a second hand engine.

You would check for this by draining the oil, removing the left hand engine cover and inspecting the rotor and magnets for signs of damage (which would usually be pretty catastrophic and obvious).

Likewise the sidestand switch can cause problems with cutting out. Might be worthwhile temporarily bridging across the contacts of the connector for this switch with a paper clip or similar to eliminate it from your list.

A blocked air filter can cause odd symptoms on those bikes.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[joneseyjnr200...]

Thanks, soon as i can get in my garage for a while i'll try these things and let you know how it goes, just incase it's still playing up.

Cheers.