Power Loss

[Clockwork]

Hello Fellow GZ250 enthusiasts.

I am wondering if somebody can help me diagnose a problem with my Bike. When ever I am driving, after about 15 minutes (presumably the time it takes the Engine to heat up) the bike looses a lot of it's power. This is most noticeable at high speeds. It happened today (First time taking it above 60kph/37mph in a long time), After driving along at 80kph/50mph for 10-15 minutes, the engine makes a noise that is hard to describe. It is sort of like the sound of fine grained sandpaper being used, or like air being sucked through a crack. With this sound also comes the power loss. The bike slowly looses speed. When this happens, the bike can only maintain 70kph/43mph in 5th gear and can't get above 60kph/37mph in 4th. This problem persists until I turn off the bike and let it cool down. Once cool, the bike returns to normal and the power comes back.

My thought is that there might be an air leak between the carb and the head which gets worse with heat. Perhaps it is messing up the vacuum, so not as much fuel is being drawn into the carb. Does this sound possible? Any other thoughts?

Thanks

Clockwork

[Easy Rider]

Originally Posted by Clockwork

My thought is that there might be an air leak between the carb and the head which gets worse with heat. Perhaps it is messing up the vacuum, so not as much fuel is being drawn into the carb. Does this sound possible?

Yes, highly likely I would say.
Could even be between the carb and the air box.....or the head gasket.
Does the GZ have rubber "boots" on both sides of the carb ?? On one bike, they were so loose that I could twist the carb around with my bare hands; I think it was the GZ.
Check those boots......but don't over torque them; you can split the rubber if you do.

[Clockwork]

Yes it has rubber boots on either side of the Carb. To the touch, they seem tight, however I noticed 3 small cracks 3mm or 1/10 of an inch long where the boot meets the head. I don't know how deep they are though, so they might not be the problem. I have to take my bike in for a safety tomorrow anyways (Lucky it happened close to when I had an appointment booked). Any Idea how much labor I should expect if I ask the garage to have a look at the problem for me?

[mrlmd1]

Can you gob or glue something on there temporarily or cover it up with tape and see if closing off that crack stops the possible air leak and stops your problem? It's been a while since I had my GZ and I don't remember what that looks like.

[Viirin]

I'd say you nailed the problem already but just in case i'd drain the airbox as well - sometimes there's a mixture of oil and water that builds up there that can interfere with the air going through the filter - I had a similar problem on motorways when the bike got hot but it led to to total power loss, not partial - anyway there's a tube and plug at the bottom of the bike that you can twist with a pliers to see if anything comes out - couldn't hurt and takes about 40 seconds

Vii

[Sarris]

Check your oil, as the GZ will experience a power loss if it overheats.

[Clockwork]

I will try the glue and the airbox drain. Hopefully it isn't the oil, I had it replaced less than 500 miles ago.

Thanks everyone for your Help!

[blaine]

Originally Posted by Clockwork

I noticed 3 small cracks 3mm or 1/10 of an inch long where the boot meets the head. I don't know how deep they are though, so they might not be the problem.

Spray some W-D 40 on the cracks,if your idle speeds up you found your leak and your problem.Good luck.
:cool: :2tup:

[Clockwork]

So I took my bike into to get it safetied (it passed), but the garage wasn't able to determine the problem. They took it for a drive, but I don't think they were out long enough for the bike to heat up and the problem to occur. Their suggestion was to bring it by when the problem was happening. I drained the airbox and there was no liquid in it. Also, I sprayed WD-40 on the little cracks on the boot connecting the carb to the head, and the engine stayed constant.

I am going to take the spark-plug out to see if that can tell me anything. Does anybody have any other suggestions of what might be going on?

[Viirin]

damn it - thought the airbox was surely the problem - if i get a second guess id say the carb (which is the cause of most of the GZ problems) - maybe a lazy carb clean is in order - you can spay some straight into the carb from the airbox (if the bike is running the carb cleaner will smother it and the bike will cut out - means your spraying in the right place) - the second part is some fuel additive (berrymans b12 or something) to the tank and run it through - after that i'm afraid i'm out of ideas man but i'm sure someone one here will be able to solve the problem - best of luck man