Question about stock hawk 250 vs
 

So stock the hawk 250 should be topping out around 50 bogging out and stuttering a bit when past half throttle? Also when starting cold especially sub 50 degrees have to hold the throttle for almost 5 minutes before it will idle and then start riding die at first stop sign?

Im assuming i know the answer already (carb) but I would like to get opinions on which upgrades are most important to performance and which to upgrade first and in what order. Once I have the new carb what jet size do I put in with everything else stock except maybe airbox, 110? <---- for example..

I want to keep this as inexpensive as possible. Makuni carb, 110 jet, airbox mod, baffle out of stock exhaust.. Sound reasonable??

I do not want to change the sprocket sizes but if its a must to cruise at around 55 let me know. I would like to get the quickest cheapest way to cruising at around 55. Right now when going uphill i try to give more throttle and it starts bogging.. Thanks guys.!

I ran a Mikuni on my Hawk from day one. What jet sizes depends a bit on your elevation, but at a minimum, a 25 pilot and 105 main with the needle in the 4th notch from the top.

Or, you can tune the stock carb. If you google hawk 250 carb you are bound to find a few vids and posts about what is needed.

The reason you bike feels like it falls on its face and wont idle until its hot is because these bikes come with a too lean idle mixture setting, lean needle height, and too lean main jet. Unless you live above 4000ft, then it would be just about right lol

You can sort of fix it by going to a larger main jet, and shimming the needle higher. That's the cheapest way. The better way (in my opinion) is to buy a Mikuni, because jets are easier to find, and you really need to change the pilot jet as well. And one more thing. If you buy a Mikuni carb, only buy genuine Mikuni jets. The knockoffs are not made accurately enough....ARH :doh:

I'm still running the stock carb and runs perfect. When I was stock I ran a 110 main, shimmed the needle with two thin washers and idle mixture screw out 1 1/2 turns. Now even with all the mods I have only had to change the main jet out to a 120. No problems with cold starts. Only time I have used the choke is when it was below 50. My stock carb pilot is marked as a K40A.

Same here. 120 main and 1.5 turns out if I am not mistaken. Runs like a champ. Over 60mph pretty easily.

Ive watched the motocheez and cackles carb tune videos about 10 times a piece and have read all the threads with this info so i was pretty sure i just didnt know if anything had been updated..

Anyways thanks for the responses. Where would i get this main jet for stock carb and could I just drill the one i have out?

You actually have two choices for the main jet. The main jet used in the Mikuni is dimensionally the same as the Keihin jet that comes in it, with the exception being a very minute difference in the threads. Most guys that tune the stock carb just tend to use a Mikuni Jet since it is such a well known quantity.

That option would be the Jet number N100.604, https://www.jetsrus.com/a_jets_by_ca...arge_round.htm

The other option is a Keihin Jet 99101-393. https://www.jetsrus.com/a_jets_by_ca...und_28-xxx.htm

You certainly can drill out a main jet, but a numbered drill bit index is expensive. If you happen to already have access to one, use Google to convert a numbered drill bit to a decimal. Once you have that, use Google again to convert that decimal number (which is in inches) to millimetres. Mikuni jets are in mm, so that's a good way to reference your drill sizes.

For example, a #60 drill bit is 0.04" or 1.0076mm (which is normally the smallest bit in a numbered index). That's basically the size of main jet that comes in a new Mikuni. If you drilled the jet out to with a #57 bit, you would end up at 1.0922mm, which is awfully close to a 110 jet. A #56 bit takes you to 1.1811mm, which is a rather large jump. That's the point where you'd want to just buy a 112 or a 115. BTW, it's tricky to drill stuff that's so small without breaking the bit.

You can also drill out the slow jet, but that requires a drill bit index that ranges from #61 to #80. You need a pin vise to control those bits, since they're not much larger than a coarse hair. Beware that bits in that range are not normally correctly sized in the index, unless you pay big dollars. I use a vernier caliper to confirm the bit size before drilling. Learned that lesson the hard way.

I also still run the stock carb. Similar to the others, my mixture is set to 1 3/4 out, and I've shimmed the needle with two thin washers.

On the main, I've been even more half-assed. I was planning on either buying a larger one, drilling out the diameter, or just getting a Mikuni. But . . .since I had it apart, I just decided to pound an awl into the main jet and open up the diameter. Lo and behold - it's just about perfect for around here. I get a clean response all the way through the gears, and I top out in the low 60s with the 17/50 setup I run.

I am certainly not recommending that as a standard tuning technique, but it ended up in the "if it ain't broke, don't fix it" category for me. But it does correlate with the others who have stayed with the stock option near sea level elevations - a larger main, shimming the needle, and opening up the mixture setting should get you to a much better place than the default EPA settings that it ships with.

Awesome !^^^^

Couldn't help but jump in...
I'm staying with the stock carburetor, also. I just got through drilling out my pilot to 0.018" (#77 drill bit), and the stock pilot dia. seemed a lot smaller (do not know how small the K40A is actually, that was the smallest bit I had).

Funny, I have not even started the engine yet (still assembling), but from research on here, I am trying to get ahead for a properly running engine. To start, I drilled the main jet to 0.042" (same orifice dia. as a keihin 110 jet), shimmed needle w/ two washers, will do the air box mod w/ KN filter, removed catalytic converter, and mod'd stock muffler (extra holes in baffle plates, includes grinding the inside header weld).

Here at sea level in Texas, say on 200cc to 400cc single cylinder engines (non-racing) I've had good luck on drilled pilot sizes varying between 0.018" to 0.022", and the usual 1 to 2 turns out on the mixture screw (depending on temps/humidity).

We'll see how it goes, but I'll start another thread about my settings at a later date (hopefully soon)...

Kirk
ps.(forgot to note I have the 2018 Hawk 250)