Tuning and jetting hawk 250

[Megadan]

Originally Posted by Jeff Richardson

Good stuff MD and ARH!!!
Mikuni came with the needle clip at 3rd slot so I left it. 115 main and 25 pilot. Ran great but can't say I have a strong idle though. 1,500rpm is close to dying. I set little below 2,000. Top end felt good managed 58mph @6,000rpm or so. I'm heavy rider at 260lbs. Should I go up a size on both pilot and main? Or do anything with needle clip? Thanks!

You need to dial in the idle mixture. The actual idle speed of these engines is stated as 1500rpm + or - 100rpm (1400-1600). If it won't stay fairly steady in that range, it is either slightly loading up with fuel, or slightly starving for fuel, and so the rpm's are hunting to try and equalize.

The best way to do this is with the bike running and fully up to temp (point a strong fan at the motor to help stop it overheating). The tricky part is the mixture screws location makes it very difficult to turn while mounted on the bike. There are tools out there made for doing it, but even the cheap ones are 20 bucks.

So, short of tuning it on the bike, the next best thing you can do is to adjust it by removing the carb enough to access the mixture screw. Start with 1 1/2 turns out. I found that to be pretty darn close on my bike with a 25 pilot jet. I think I ended up between 1 1/2 and 1 3/4 turns out before I switched out for a 27.5 pilot due to the 25 being just a tiny bit lean for part throttle.

Regardless of the method, from that 1 1/2 turns out, move it a quarter turn at a time until you find a position that will allow it to idle fairly steady around 1500rpm. If you still find it hunting a little bit, then try 1/8th turns.

As far as the main jet goes, the easiest way to know if you should go up or down is a WOT plug chop on a clean plug. I personally found the 115 to be the most ideal size, but bordering a little more on the lean side than I like, so I upped to a 117.5 which is a tad on the rich side of things in hot weather, so it works out well. Ideally, I should take the time to drill out a 115 main somewhere between the two for maximum performance.

My needle setting is in the 3rd position for warmer weather, and 4th for colder on the 117.5 main. I left it in the 4th notch on the 115.

I am basically the same weight as you are, and 6'4 with big wide shoulders - effecftively a sail on top of my bike, and I can get it to 70mph on most days, and 65mph on any day, though it will be pegged if there is a head wind lol. Get some miles on that motor and it will slowly start to open up a bit more as well. Around 800 to 1000 miles is when my Hawk could consistently hit speeds above 65.

[Jeff Richardson]

Last night rode with same setup and it rode pretty good for some reason after a while the idle would hold 4000rpm at a dead stop which pissed me off didn't have a screwdriver handly. Rookie mistake. Just now I switched out jets to 27.5 and 117.5 warmed up idle was holding 1,500rpm can't ride though started raining. Not sure the pilot was a bit loose this time I tightened better didn't want to overtorque. Not sure if that was it. Will test tomorrow and try fine tuning from there.

[Jeff Richardson]

Did manage to take it out for short ride the throttle response was good throughout but that idle is riding up at 3,500rpm. Also idle screw on side wouldn't adjust it down. Lower needle and/or work on idle mixture screw?

[Jeff Richardson]

Maybe the floats? Gotta be too much fuel in the bowl or something. Checked for vacuum leaks didn't find any.

[Megadan]

Is the idle climbing that high from 1500rpm, or is it just sitting at 3500-4000 when you let off the throttle? That is a extremely high RPM, even for a lean condition. I almost wonder if the throttle slide isn't hanging up.

[JerryHawk250]

Originally Posted by Megadan

Is the idle climbing that high from 1500rpm, or is it just sitting at 3500-4000 when you let off the throttle? That is a extremely high RPM, even for a lean condition. I almost wonder if the throttle slide isn't hanging up.

I'm thinking the same thing. Check to see if there is a little slack in the cable or that the cable is all the way in at the carb.

[Jeff Richardson]

Haha that was definitely it at the top of the carb the spacer that the cable slides through was up and out.
Now throttle drops when coming to stop almost too much I need to rev a bit so doesn't die. Back to adjusting mixture screw. Thanks for pointing out something I would've and did miss repeatedly!

[Megadan]

Originally Posted by Jeff Richardson

Haha that was definitely it at the top of the carb the spacer that the cable slides through was up and out.
Now throttle drops when coming to stop almost too much I need to rev a bit so doesn't die. Back to adjusting mixture screw. Thanks for pointing out something I would've and did miss repeatedly!

Or you would have unwittingly fixed on your own when you pulled the carb again to try and do something else lol.

[Jeff Richardson]

So ended up 25 pilot, 127.5 main and 3rd notch.
The idling issues were a due to many outside factors with valve clearance probably also playing a role.

[Megadan]

Originally Posted by Jeff Richardson

So ended up 25 pilot, 127.5 main and 3rd notch.
The idling issues were a due to many outside factors with valve clearance probably also playing a role.

127.5? I am assuming that's 117.5 with a typo lol. Either that, or you have the most powerful Hawk ever made lol.

[Jeff Richardson]

Haha megadan don't underestimate the power of pure determination. I have a turbo and NOS system ready just say the word. 😉

But you're correct, sir, pilot 25, main 117.5 and needle at third notch for mikuni vm26. My bike is very happy. I can do better but the clicking and clacking makes me more cautious. I'm pissed I never tried the valve clearances it was a very easy fix. SMH

[CaptainKP]

Originally Posted by Megadan

Jetting recommendations with an airbox mod and stock exhaust on the Mikuni clone at your altitude.

Main Jet, 110
Pilot jet 25 (recommend also buying a 27.5)
Needle set at 4th notch from the top/1 down from center.
Idle mixture, start 1 1/2 turns out from lightly seated.

This will get you very close, but obviously fine tuning may be needed to get your bike ideally jetted.

I couldn't get my stock carb to idle at correct RPMs even after a couple valve adjustments so I ordered the Mikuni clone and followed these specs. Only thing I'm missing is the pilot jet that is still processing.

But, holy cow what a difference. After gas got into the bowl it immediately idled and I've set the idle speed pretty low (i'm guessing by sound as I dont have anything to measure with)

Still waiting for paperwork so I can actually take it out of the neighborhood but very pleased. Also replaced the stock shifter with the one everyone recommends and very pleased with it.

[Megadan]

Originally Posted by CaptainKP

I couldn't get my stock carb to idle at correct RPMs even after a couple valve adjustments so I ordered the Mikuni clone and followed these specs. Only thing I'm missing is the pilot jet that is still processing.

But, holy cow what a difference. After gas got into the bowl it immediately idled and I've set the idle speed pretty low (i'm guessing by sound as I dont have anything to measure with)

Still waiting for paperwork so I can actually take it out of the neighborhood but very pleased. Also replaced the stock shifter with the one everyone recommends and very pleased with it.

Yep, yet some people think the Mikuni is a waste of money, and they complain that mean people made fun of them.

Glad it worked out well for you.

[CaptainKP]

So, a little update and additional question.. I got the pilot jets in today to replace and pulled out the stock one and to my surprise it was labeled 42...

I ordered a 25 and 27.5 and put the 27.5

How the hell would going from a 42 to 27.5 make sense? Now I'm questioning every sound I hear as it idles

[NzBrakelathes]

Originally Posted by CaptainKP

So, a little update and additional question.. I got the pilot jets in today to replace and pulled out the stock one and to my surprise it was labeled 42...

I ordered a 25 and 27.5 and put the 27.5

How the hell would going from a 42 to 27.5 make sense? Now I'm questioning every sound I hear as it idles

Are you mixing Mikuni and Keihin numbers or jets??