lean conditions and rich conditions....

[na96ek]

Well, first off I have a 06' Vento Zip R3i... currently running an athena sport 70cc kit and an Athena Hyper race 70cc pipe... Malossi multivar with 2.7g rollers, and malossi white clutch springs and malossi yellow torque spring.

I am looking into an aftermarket carburetor at the moment but trying to tune with the stock carb at the moment. So far I have installed an 82.5 MJ which seems to work good on the top end at WOT, I have also upjetted from a 22.5 to a 27.5 Pilot Jet... Overall it runs very well from a stop to top speed when going WOT but the only thing that concerns me is that I have a lean condition when i am partial throttle and the pipe gets on the powerband, the bike wants to acccelerate due to scavenging effect of exhaust but cannot supply fuel through the MJ, this is the reason I upjetted the PJ a good amount but it didnt seem to help much. It runs extremely lean though, so bad that the engine makes terrible rattling sounds, (could be detonation or soft sieze?) until I either let off or give it 100% throttle to use the MJ.. i tried raising the needle and it didnt do much either and made my take offs terrible flooding the engine with fuel and taking awhile to clear up. I am starting to think the only way would be to use a different needle profile... but at that point i might as well just upgrade my carb...

Also when i go WOT for a few seconds and get up over 45mph or so and then let off and let the engine decelerate with 0% throttle, the engine will run very lean, the idle will be high and it will hesitate ( I know the sound of a lean engine by experience)... What i dont know is what is controlling the fuel when I am at 10000 rpms and im not on the gas? is it the pilot jet? Thats why i upjetted it and it still does it, maybe i need to go even larger? I am determined to get this thing in a somewhat decent state of tune with the stock carb, i know its been done before.

[90GTVert]

It sounds like you pretty much already know what you need to do. I don't know where to get needles for a stock carb, most just replace the carb with something larger and that has parts available. You can sand the needle down to thin it out. I've put needles in a drill and spun them while holding sandpaper on the needle to thin it out evenly. If you go too far though, there goes your needle. The aluminum kit makes me really think a different carb is a good idea. If it's running lean anywhere it could only be a matter of time before you end up with a hole in the piston. You might wanna try rolling off the throttle a little instead of just cutting it for now. I killed my Airsal aluminum kit letting out of the throttle and coasting and it holed the piston. The right needle and part throttle settings should help with that part as well, but yeah when you close the throttle the same things that deliver fuel at idle are trying to deliver fuel at 10,000RPM or whatever.

If you aren't already, use premium fuel. It will help some with that detonation you're hearing.

[reveeen]

I'd be tempted to back the timing off a bit:

www.spmotostore.com/product_p/t9909180.htm

[na96ek]

yes im guessing retarding the timing a few degrees would help, as would having the proper a/f ratio at all load/rpms... im guess its just time to upgrade my carb... any suggestions? Im thinking a 19mm dellorto....

coming from EFI tuning on hondas, im really tempted to buy a small engine EFI kit... hmmmm , anyone on here tried one on a 70cc 2stroke scoot with sucess?

[na96ek]

tried one as in an aftermarket kit setup on a scoot that was sold with a carburetor... I realize some scoots are made with EFI as factory stuff

[90GTVert]

If you go with a carb, I'd consider 19-21mm DellOrto PHBG.

jmkjr72 converted his Zuma to EFI. Starts talking about it HERE in his build thread.

[reveeen]

I'd give the EFI a bit of a rest until the parts start becoming more common (and more reasonable in price).

[dr1445]

there's a lot of info on the forum regarding the dellorto, 2 strokes kinda like flatsides, but the only 19mm flatside readily available is the oko. there seems to be a lot of mixed reviews on the oko. might be worth some study and sometimes they can be found used on ebay at an attractive price, worthy of experimentation.

[2strokd]

I think poor casting causes the mix reviews on the oko? Im sure some work better than others.?

[dr1445]

i was going to try an oko 28mm on my bultaco build this winter but i found a mikuni 28mm flatside from a suzuki rm80 at a good price. i read that about poor castings but they have been at it a while now and maybe the new ones are better. sounds like a good reason to avoid an ebay oko, but treatland has them new at a low price.

[lshigham]

Apr 29, 2012 22:54:28 GMT -5 2strokd said:

I think poor casting causes the mix reviews on the oko? Im sure some work better than others.?

The OKO's are the best copies of Kehin carbs, Koso's, despite being about twice the price are in fact terrible.

[dr1445]

but the koso's have a better polish job!