Help with two-stroke tuning

[Skunk]

It could be running very very rich. Sounds like the symptons of very rich jetting. Could be hundreds of other things though.

I'll stick with the carb at present. Rich you think. I'll drop the needle first and see if there's any improvement. If there is I'll get some smaller main jets. I don't think this carb has any choice in needle jet size but at the throttle % I'm using it shouldn't be on the main jet.

[Ixion]

Not something simple and silly, like the needle being loose and not rasing when the slide lifts. But I'm also wondering about that carb, cos under no load even revving hard it's probably only got the slide open a bit. So maybe main jet is too large once the needles well up.

[Skunk]

Not something simple and silly, like the needle being loose and not rasing when the slide lifts. But I'm also wondering about that carb, cos under no load even revving hard it's probably only got the slide open a bit. So maybe main jet is too large once the needles well up.

My understanding is that the main jet is the jetting above 75% throttle. The needle and needle jet do 20% to 75% throttle. That would mean you could be right... I need a smaller main jet, as it only dies under load (wider open throttle).

I've checked the needle. It won't move. (Strange clamp system - haven't seen one like it in my limited experience)

[Skunk]

The needle is a 5DH2 and the slide cutout is a 2.5, for those who have Mikuni charts.
The slide cutout should probably be smaller (ideally) but I have no option.

[Mr. Peanut]

Are you sure its not a back pressure/porting problem? RGVs/TZRs have powervalves, which even when open restrict flow.

[Ixion]

I suspect it is , partly. Prolly one of those things where there's no one single thing actually WRONG, just a bunch of things that don't get along. Insufficient back pressure will mean a wider throttle opening will be needed to generate enough power to get under way. If the carb is too rich , that means even more throttle needed and so on.

[Skunk]

It's an early TZR chamber (1kt '86-'88 model). I didn't think they had the powervalve.

I'll be checking the richness tomorrow.

[Mr. Peanut]

Yeah they got a powervalve.

[Skunk]

Expert advise is that it's lean. Confirmed by covering half the carb to increase the air velocity and it goes better. Theory is that the 100cc is not sucking as much air as the "125" the carb would normally be on, so it's not pulling the fuel into the air correctly.
I'm going to drill the main jet and see what happens.

Edit: Seems better. Need open space to run it now.

[Ivan]

hope it works

[Sparky]

You can raise the needle by moving the circlip that holds it in place. you have to remove the throttlecable and spring, under that is a "thingy" with 2 scewrs, remove that to take the needle out. there are 3 grooves in the needle so take your pick.
Maybe worth trying?? got and exploded view picture of carb if you need it


PS you can always pull the choke up to increase the fuel and see if that makes it better or worse

[Skunk]

You can raise the needle by moving the circlip that holds it in place. you have to remove the throttlecable and spring, under that is a "thingy" with 2 scewrs, remove that to take the needle out. there are 3 grooves in the needle so take your pick.
Maybe worth trying?? got and exploded view picture of carb if you need it


PS you can always pull the choke up to increase the fuel and see if that makes it better or worse

Choke helps at an idle but as the slide lifts its effects are negated. I've drilled the main jet and raised the needle to full rich. Still looking for a test road.

[k14]

Expert advise is that it's lean.

Hmm, well glad you didn't listen to me then

Hope you get it sorted.

[Skunk]

Mate, it doesn't mean they're right! I'll find out when it's going properly. I did listen, and I tried.

I'm betting that if anyone was here they'd know straight away. Reading someone describe it is never easy.

[k14]

Yeah glad nothing bad happened on listening to my advice. On reading it again lean does make sense. Revs easy but makes no power is the sign of lean jetting. Found a "closed road" for testing yet?