2019 Hawk 250 jetting settings and question

[bmw111]

2019 Hawk 250 -- stock other than changing to a PZ30 Keihin from eBay.

Main jet: 110
Pilot Jet: 45
Needle: 4th notch from top
Idle Mixture Screw: 1.5 turns out
Altitude: 1000 ft

Starts up with little to no choke (finally!) and settles into a reasonable idle. No more stalling, sputtering, and warming up for 20 minutes. Feels much fatter throughout the rev range. Definitely more pick up from 50 to top speed.

Only issue I have is that once the bike is warmed up -- which doesn't take long now -- and I am riding anywhere from 10 mph up, it stutters or surges (not really a stumble) at around 1/8 steady throttle. Feels almost like a fuel injection model that is hyper sensitive and hunts between throttle on and throttle off.

Any ideas?

[Megadan]

That 1/8th light steady throttle point is exactly the point where pilot jet sizes show their strengths or weakensses.

That is also the point where the needle starts to add fuel, so if the pilot jet is not too big, then lowering the needle to the third slot should lean out that point just enough to stop that surge feeling that you are getting.

Since the needle adjustment is a lot easier and faster to do, I would try that first. If it still does it, then try a 40 or 42 pilot jet.

If I were a betting man, I would wager on the needle adjustment just going off of a 110 main AND a 45 pilot on a stock bike. That's definitely on the heavy side.

[CaptainKP]

Originally Posted by Megadan

That 1/8th light steady throttle point is exactly the point where pilot jet sizes show their strengths or weakensses.

That is also the point where the needle starts to add fuel, so if the pilot jet is not too big, then lowering the needle to the third slot should lean out that point just enough to stop that surge feeling that you are getting.

Since the needle adjustment is a lot easier and faster to do, I would try that first. If it still does it, then try a 40 or 42 pilot jet.

If I were a betting man, I would wager on the needle adjustment just going off of a 110 main AND a 45 pilot on a stock bike. That's definitely on the heavy side.

I really wish jet sizes had a standard.. I get so confused when I read 40/42 pilot and im over here with my 27.5 and then realize it was labeled 42 because difficult carbs/jets have different sizing numbers

[Digger]

Stock carb? If so, do a internet search for pz30 carb tuning. Very detailed and will answer all your questions.
Good luck.

[bmw111]

Originally Posted by Megadan

Since the needle adjustment is a lot easier and faster to do, I would try that first. If it still does it, then try a 40 or 42 pilot jet.

Thanks, that's where I'll start.

[Megadan]

Originally Posted by CaptainKP

I really wish jet sizes had a standard.. I get so confused when I read 40/42 pilot and im over here with my 27.5 and then realize it was labeled 42 because difficult carbs/jets have different sizing numbers

I only speak in official jet numbers. If you have a carb using Keihin jets, I use Keihin jet sizes. If you have a Mikuni, then it's mikuni sizes. Doesn't get more official than that. Chinese jet sizes don't count in my opinion for the reason you stated.

[bmw111]

Wanted to give an update on the setting change. Lowering the needle to the third slot (as Megadan suggested) fixed the issue. Thanks!


Feels much, much better now. I'm always amazed at how a properly tuned carb makes a bike feel so much better.


It's nice to be able to do that on these bikes, compared to all the technological wizardry we have to deal with on modern bikes. Snatchy fuel injection gets real old.