My GZ250 gets funky in fifth...

[Cordell_Love]

So this is my first bike and I've been ridin for about two weeks. I love my lil GZ250 but I have a problem. The bike runs great except when I shift it into 5th, then bike lunges or lurches rhythmically every 5 to 10 seconds. You can hear the engine revving up before it lunges too. It only lunges in 5th and only if the throttle is open. Weird huh? Thanks to everybody for any and all advice on the problem.

[Sarris]

Try a new spark plug and clean or replace the air filter. If those are OK, try some carb cleaner in the gas tank. If your bike was purchased used, these items may need to be addressed.

Another thing to check is for a vacuum leak, possibly a disconnected or cracked hose. Specifically check the one connected from the carb to the back side of the fuel petcock. Hopefully one of these suggestions will fix your problem. Keep us posted.

:2tup:

[jonathan180iq]

Does this only happen under hard throttle?

If so, you may also want to check for a possible clutch adjustment.
Along those same lines, drain your oil and replace with motorcycle oil, just to be safe. Wierd things happen to some people when they use automotive oil with friction inhibitors.

Combine what Sarris mentioned with what I've said and you pretty much covers everything in the "simple-fix" category.

I'm gonna wager $3.57 that it's a disconnected vaccum hose somewhere. Of all the hoses that connect to the carb, only 2 of them are clamped on.

[Easy Rider]

Originally Posted by jonathan180iq

I'm gonna wager $3.57 that it's a disconnected vaccum hose somewhere. Of all the hoses that connect to the carb, only 2 of them are clamped on.

I'll up the bid to $3.60!

Sounds to me like it is "lugging".

Cordell: At what speed do you usually shift into 5th gear? :??:
And how old is your bike......how many miles?

[Cordell_Love]

thanks for the help...i'll run down the simple fix list tomorrow. the bike's a 2007 and its got 8500 miles...lugging sounds like the right word for the experience...more throttle increase the luggin however the bike does it anytime i open it up in 5th...

[Easy Rider]

Originally Posted by Cordell_Love

thanks for the help...i'll run down the simple fix list tomorrow. the bike's a 2007 and its got 8500 miles...lugging sounds like the right word for the experience...more throttle increase the luggin however the bike does it anytime i open it up in 5th...

OK, two things: A single piston bike is known as a "thumper" for a reason.....and that reason is most noticeable in high gear, under a load. It thumps.

So, if you shift into 5th at any speed below about 40 mph, it will sound a bit different. If you do it around 30 , it will FEEL different too. If you shift into 5th below 30, you are risking engine damage.

What you are hearing/feeling MIGHT be perfectly normal. At 8,500 you are probably due for some routine maintenance too. Check your manual.

[Cordell_Love]

hmmm, so that thumpin could be natural, weird, cuz it feels so jerky...I follow the shifting schedule found in the manual pretty closely, meaning I don't shift into 5th below 37 mph...i checked the air filter and hoses and didn't find anything, now i gotta figure out how to get those spark plugs out...

[music man]

Just in case you didn't know its only got one spark plug.

[5th_bike]

Originally Posted by Cordell_Love

now i gotta figure out how to get those spark plugs out...

Take saddle off, get toolkit, get tank off, take left cap off cylinder, pop cap, use spark plug tool with something bar to unscrew spark plug.
To replace spark plug, carefully turn in with fingers, when stuck give it an extra 1/4 turn (not totally sure - look it up please) with the tool.

[Cordell_Love]

ummm, yeah, of course i know that it has only 1 spark plug...or not...thanks for the advice!