Jetting - Starting Point?

[CarnageZ28]

Just picked up a Blaster on a trade. 99 Blaster, 03' Motor - for a 1991 RM125 that is blownI:I

The thing is kind of beat, not maintained, but fires up right away, and luckily I got it before they rode it much with the 03' engine (That has a fresh topend).

The quad has the stock carb on it. Mods are: FMF Fatty & Silencer, K&N Filter, may have reeds/porting but I doubt it.

Was still running the stock jetting! It is fine at idle/down low, but breaks up in the mid-range - top-end. I mean, it is DYING for fuel. I dont want to run it without jetting it properly. So what would be a good starting point on this one?

I was thinking of getting a 260-270-280 main jet. You guys think it should fall in this range? I've jetted carbs before, just trying to get a feeling for how far I should bump it up with this Blaster for said mods/knowing that it is so lean it is breaking up (Similar feeling to when it starts to sputter when you forget to turn the fuel on)

And I will be running with the airbox lid on (Possibly taking the stupid snorkel off though) This is going to be my girlfriends quad. She'll ride it like a vag for a while ... I just want it to run smooth. Not concerned with trying to make any more power out of this one!

 

[cirame1]

i would atleast drill holes in your airbox lid and start at about a 270 and work up. im running a 280 with airbox lid off and an fmf full exhaust.

 

[b_russell_82]

I've got about the same as you with air box lid on and I'm running a 270.. the only dirrerence is I'm bored .40 but I don't think that will matter that much.

 

[ron89]

hmm i would pop off the air box lid and start at like 300 main and work your way down ..

 

[CarnageZ28]

Thanks Guys! I guess I will get main jets from 270-300.

Im a little hesitant to drill the airbox lid... I've always just ran the box's with the lids on on all of my bikes/quads.

I'd consider it though???

 

[CarnageZ28]

Have a 290 in it now. Lid on - Contemplating getting a airbox cover/fabricating one as I have a very similar material.

 

[ron89]

hmm did u try and pull the lid off and take it for a ride cause a 290 would be a little rich with out the lid off ..

 

[cirame1]

I would try running it with the lid off i got a big dif. when running it off ive always had it on and i drilled holes in my airbox and i didnt even run it and i just took it off and it feels like its breathing way better and it doesnt seem like anything is gonna get in there unless i go through some deep water... as long as you have an airfilter on y not??

 

[CarnageZ28]

I might try that. I only worry because the plug doesnt read rich when it starts to lose steam and die off in 5th and 6th at WOT ... It actually looks slighjtly lean. But read rich as WOT in 1st or 2nd. I thnk there is some issue where its not getting enough fuel, misadjusted floats or clogged fuel filter.

I will be trying the airbox thing as well though.

Thanks all.