250r surge

[resto250r]

I have an 84 250r atc, I just put a 34mm mikuni flatslide carb on it w/ 290main(large hex jets) and 50 slow. My problem is what u might call a surge or lunge @ low speed or off the throttle. My engine is .020 over w/ mild port work, fiber reeds, DG pipe an silencer, running @ 32:1. On the throttle and high speeds seem great. Does this sound like a low speed jet problem or am I still experiancing a air leak some where, I was having a dieseling prob before after driving but I have since pressure tested engine, replaced intake boot & gaskets. I drove it all day w/ no dieseling. Any ideas? Thanks guys!

[AZ250R]

I have an 84 250r atc, I just put a 34mm mikuni flatslide carb on it w/ 290main(large hex jets) and 50 slow. My problem is what u might call a surge or lunge @ low speed or off the throttle. My engine is .020 over w/ mild port work, fiber reeds, DG pipe an silencer, running @ 32:1. On the throttle and high speeds seem great. Does this sound like a low speed jet problem or am I still experiancing a air leak some where, I was having a dieseling prob before after driving but I have since pressure tested engine, replaced intake boot & gaskets. I drove it all day w/ no dieseling. Any ideas? Thanks guys!
I've got an 85 with a 38mm kuni and am running a 300 main, don't know what your 50 slow is, and think I'm @ the same elevation as you (Phoienix valeyish). So I'm kinda wondering if that 290 is too much for a smaller carb, but I'm no jetting expert. We'd have to compare the slide "needle" positions too. Let me know if ya need me to pull it off to look.

[resto250r]

I know mine is in the third from the top (middle). I was thinking I might need to lean it down but my plug looked good when I checked it maybe I'll check it again since I did some hard riding after that see if it leand any. Thanks

[resto250r]

just got around to pulling out the plug and it is on the dark side but the electrode is dry. what should I do try a 180 jet, or raise the clip on my needle.

[BIG BAD RED]

i would throw that 180 in there first and see where she puts you...then tune from there

[resto250r]

opps I said 180 jet I meant a 280 but I think we new what we meant(lean it on size)

[AZ250R]

opps I said 180 jet I meant a 280 but I think we new what we meant(lean it on size)
Heck, go down to a 260 to start. These Mukuni jet size differences are much more subttle than the rest.

[3Razors]

When using jets make sure you use only genuine Mikuni. The aftermarket jets don't have the close tolerances that mikuni uses, which can make things very difficult. I have some jetting specs for that application I will see if I can dig them up for ya.

[3Razors]

Here goes: This was a set-up for an 82 air cooler with a 36mm Mikuni flatside. Needle 5FP17, 4.0 slide, 389 Q2 needle jet, 35 slow, 300 main, air screw 1.5-2 turns out. For the main jet I would drop a really fat like 350 or bigger jet and make it run like crap on the top end and work my way down until it revs very clean. The liquid cooled R's are a different engine design the air cooled ones, so jetting specs do not cross over between the two.
Air cooled R's bore and stroke of 70.0 x 64.4 mm "oversquare"
Liquid R's are 66 x 72 mm and the port demension differ aswell.

[resto250r]

Thanks for the specs do u think that could be causing my surge?

[resto250r]

Here goes: This was a set-up for an 82 air cooler with a 36mm Mikuni flatside. Needle 5FP17, 4.0 slide, 389 Q2 needle jet, 35 slow, 300 main, air screw 1.5-2 turns out. For the main jet I would drop a really fat like 350 or bigger jet and make it run like crap on the top end and work my way down until it revs very clean. The liquid cooled R's are a different engine design the air cooled ones, so jetting specs do not cross over between the two.
Air cooled R's bore and stroke of 70.0 x 64.4 mm "oversquare"
Liquid R's are 66 x 72 mm and the port demension differ aswell.

Do u think I should bring my slow jet down I have a 50 in it now, I didn't even know that there was a needle jet so I'm not sure what mine is. Where could I find a set of jets that way I don't have to buy them all individually? Thanks

[3Razors]

When it's running at idle to low throttle use the choke and see if it runs better. If it does then your slow jet is too small. For the jets here in Arizona I would go to Jerry Hall at Halls Precision he's got just about everything and I'm almost positive that he could give you an even better jet recomendation than mine, since he's been doing those bikes since they started production in 1980. Or you could try www.carbparts.com

[resto250r]

where is halls precision?

[3Razors]

It's located in Glendale, (lucky you), on 51st and Luke I believe. Their ad is in the phone book under the motorcycle section.