Zongshen Gearbox Problems, And Revving Problems,

[hardcorehoon]

g'day, i just brought a 2008 zongshen 250 dirt bike for 250 dollars, knowing their was something wrong with the gearbox but was unsure, just wont go into gear, so got it home, had a look, was still idleing perfect and what not, all i did was check if the fly wheel nut had came off or something, but no it wasnt that, now, the bike rev's high as soon as i start it, no problem with choke on when its cold, just when it gets warm, stalls with choke (as normal,) but without choke, revs high, anyone help with my problems please ???

[MICRider]

If the throttle cable is free and you didn't have the top cap and slider out I'm guessing maybe a vacuum leak on the intake boot?

[hardcorehoon]

i did have the top cap and slider out, i thought i had it in right, but maybe not, i took it out again just before, and their seemed to be scratches on it, from rubbing, that werent their before, could this be my problem ?

[MICRider]

You probably have it rotated 180 degrees, the little pin has to line up with the notch or it will keep the slider from going all the way down... That's probably what's causing the high revs.

[katoranger]

As for the won't go into gear. Check the clutch adjustment and also dirty old oil will cause shifting problems.

[Weldangrind]

Welcome!

X2 on both comments. Choose either 15W40 non-energy conserving oil (like Rotella) or four stroke motorcycle oil; 10W40 in cold weather and 20W50 in hot weather. That might make the transmission behave.

I got a kick out of your screen name.

[hardcorehoon]

hmm, so what notch ? it has 2, one that goes pretty much all the way up the slider, with a little sort of circle at the top of it, and one at the bottom of the slider, what one lines up with the idle screw pin ? and the little nob bit on the other side ? and also, the with the gears, the guy i brought it off said it just stopped, its stuck in nuetral, it will click up and sound like it went into gear, yet still nothing, i put clean oil in the day i got it, 10W40, due to i live in tazzie lol, so next to test is the clutch ?, thanks for all your help guys

[katoranger]

The short notch should line up to the idle screw. The long one with the little pin.

[hardcorehoon]

hmm i tryed that, and it seems to be making a little worn notch were the idleing pin sits, that was'nt their before, and ive tryed ajusting the idle screw and nothing ?, very new to these sorts of bikes, also their is a tube with what looks like an over sized fuel filter coming out the top of the engine, with nothing on it ? blows lots of air out, but unsure were its meant to be going ? once again, thanks for all your help guys

[FastDoc]

The tube is the crankcase breather. It is functioning normally.

The slide needs to be very free moving up and down in the bore of the carb. If it is not something is wrong. You may have to take it off the bike to get a good look at it, not sure on a Zong.

[Weldangrind]

With a round slide carb, there is a small ramp at the bottom of the slider on one side. The ramp mates with the idle screw, and that's how the screw increases the idle.

The other side of the slider has a groove that runs the entire length, and it mates with the small pin in the bore.

[hardcorehoon]

hmm it seems to be down pretty much all the way, until i give it a rev, then sorta of gets stuck on the way back down, how much of a gap if any should their be between the slider and were the pin goes in ? if i look through one side of the carb (choke side) its higher than the other side,

[Weldangrind]

The slider is angled at the bottom, so it will definitely be higher on the inlet (choke) side. If it's getting stuck when you open the throttle, there is some imperfection in either the bore or the slider. Remove the slider and inspect it carefully for rough edges.

[Bobby-V]

I had the same problem on my 250. I just swapped out the carb and it made a world of difference. I tried everything from carb cleaner and toying with the idle screw when it was at running temp.

It seemed no matter what I tried it didn't want to settle in. The only thing I didn't try (bravery issue more than anything) was a complete carb tear down.

[Weldangrind]

Originally Posted by Bobby-V

I had the same problem on my 250. I just swapped out the carb and it made a world of difference. I tried everything from carb cleaner and toying with the idle screw when it was at running temp.

It seemed no matter what I tried it didn't want to settle in. The only thing I didn't try (bravery issue more than anything) was a complete carb tear down.

You now have the opportunity to gain some bravery. Take your old carb apart and remove the slow jet and main jet, and you'll get a sense of how that works together.