RZ250R WITH 350 TOP END - MAIN JET SIZE

[foley.michael]

Hi All. I desperately need to sort out the main jet. Goes hard in the low and mid ranges to 8000rpm then dies if at full throttle

The bike has a 350cc top end and standard exhaust chambers.

Yamaha Ident for Model Index, Model Code, Color Code and Frame No. are:
MTC = 3RT1; FRAME NO. = 1XH0004156; MODEL NAME = RZ250; MY = 1989; USA = YES; COL 1 = W; COL 2 = FWB

The standard carbs on the machine are Mikuni VM26 SS roundslide, I intend to run the sandard air box and filter but have installed new pod filters for convenience until I sort sout the jetting.

I have purchased and used a KEYSTER Carb Repair and Parts Kit (KY-0295) for RZ250R - Pilot jet replaced at standard #25. I have not dropped back to the std Main Jet supplied at #155.

I have researched the KEYSTER Carb kit for the RZ 350 - kit is KY-0620N. Main Jet supplied for the RZ350 are #128; 3132; #138 and a Pilot Jet at #38.

I have bought fresh Main Jets and have progressively reduced from #230 when I acquired the bike to:
1st - #220 and 2nd - #200.

Its still running rich at #200 at full throttle.

Has anyone out there correctly jetted for the 350cc barrels, terrain just above sea level and climate tropical?

Could you please advise - I want to get this right but not nip it up by jumping to a very lean main jet mixture.

Thanks
Happy

[hablair]

Are you still using the 250 exhausts ?
If so you will need a set to suit a 350, what you are describing sounds like that is your issue
The second point is that keyster kits are not as good as one would wish

[two-stroke-brit]

I think the 250 exhausts had washer type choke in them, seem to remember a member documenting the removal.

[tacky1]

I have to agree. The keyster kits are pretty bad. I had one in my 350 and I ended up getting oem needles and emulsion tubes and jets and it fixed my jetting woes!

[RZtuner]

Number 1 rule jetting a two-stroke "Give the engine what it needs" not what someone on the internet recommends. Start rich and work down on the MJ. Only use genuine Mikuni jets and needles so you know what you have. Dump the keyster stuff and pods, start with the OEM airbox and stock 350 settings as a starting point.