Hawk 250 carb tuning problems, please help

[Ariel Red Hunter]

Originally Posted by SeanM76

Ok here's where I am now:

Woke up this morning to a puddle of gas on the floor under the bike.
Took it all apart again. She is now at 110 jet, no washers on the pin at all, idle screw is 1.75 turns out. High end is maybe a hair off but I'm getting full throttle for the most part now. Starting the bike is harder than stock though. She wants to stall out like crazy. For the first two minutes I have to hold the throttle open a bit (the thumb screw adjustment for idle I have all the way in when starting as well).

The only place she bogs now is between 25% and 35% throttle and only in first gear (which makes no sense to me, why doesn't it do it there no matter what gear it's in?). Any tips on getting rid of that one little big spot? It bogs there once maybe twice, then continues on like it didn't happen. Just seem to have to get it past that spot.

There are only two reasons to have gas on the floor, assuming the fuel hose doesn't leak. Either the needle seat and valve is not shutting the gas toitally off, or float height set too high. Trying to tune the carburetor is a total waste of time and money until you have those/that issue resolved. You have to have a baseline to work from, so find the issue with the gas leaking out on the floor...ARH

[SeanM76]

I think the leaking gas problem is taken care of.

A: I never turn the gas valve off. It's down constantly.
B. When I took the carb apart to change the jet I think the rubber gasket was off a bit when I put it back together (it doesn't stay in its channel very well). When I put it back together this morning after changing the jet again I took a little extra time putting it back together to try and make sure it was in the right spot better.

I have the valve closed at work right now but tonight I'm going to leave it open again just to see if everything holds. I'm pretty sure even with the valve left open it shiuldnt leak if everything else is copacetic.

[Megadan]

Just my 2 cents, but it is a good idea to always close the fuel valve when parking. Aside from the potential fire hazard of a gas puddle on the ground, there is also the risk of engine damage. Say the float valve doesnt seat, and the overflow doesnt do its job.. that gas will head into the cylinder. Best case scenario, you get a crankcase filled with gas. Worst case, a cylinder full of gas, which can result in a bent rod.

In other news, I decided to snap a picture of my stock pilot. Jet is stamped K40A. I can only assume the K is to designate Keihin, so a Keihin size 40 which is a sensible size for a 200 to 250cc engine. For you guys with a 20 stamped pilot, does it have any other markings?

[JerryHawk250]

Originally Posted by Megadan

In other news, I decided to snap a picture of my stock pilot. Jet is stamped K40A. I can only assume the K is to designate Keihin, so a Keihin size 40 which is a sensible size for a 200 to 250cc engine. For you guys with a 20 stamped pilot, does it have any other markings?

I'll check mine when I change out the main jet. After cutting open the end of my exhaust I'm running a little lean now.

[Stealthy]

I did the Makuni swap yesterday. Went well and learned a lot about how carbs work. Now that it's done, it is bogging a bit around 50% throttle, and is noticeable mostly when driving in 1st gear. It sounds like I will need to shim it to correct the bogging, right? Also, on the original post they talked about a mixture screw, which is different than the idle adjust screw. Where is that on the Makuni and doesbit possibly need tinkered with?

[nickdowny]

The mixture screw is on the bottom of the carb close to the engine.

[Megadan]

Originally Posted by Stealthy

I did the Makuni swap yesterday. Went well and learned a lot about how carbs work. Now that it's done, it is bogging a bit around 50% throttle, and is noticeable mostly when driving in 1st gear. It sounds like I will need to shim it to correct the bogging, right? Also, on the original post they talked about a mixture screw, which is different than the idle adjust screw. Where is that on the Makuni and doesbit possibly need tinkered with?

There is no need to shim the Mikuni clones as they come with 5 adjustment notches. Generally they ship with the needle set in the richest position - the 5th notch, aka the very bottom notch. You actually want to lean it out by putting it in the 4th or 3rd (center).

Inversely, the pilot and main jets are too lean for our bikes and also should be changed for larger ones. Depending on your elevation, air temp, and mods, the Pilot should be a 25, 27.5, or 30. Main jet will be anywhere from a 105 to a 120 depending on the same factor.

As nickdowny stated, the idle mixture screw is on the bottom of the carb, between the bowl and flange/engine side.

[Stealthy]

Hm, I'm going to have to look closer for the notches. I don't recall seeing them when I had the new carb apart the other day. I have a 110 main installed, ill have to double check the Pilot needle. I also saw your post about not using cheap amazon main kits, which I may need to re-evaluate because that's what I have.

Since I'm so close to tuned my plan for now is to:

1. Move the Pilot needle to a different notch. Then check performance
2. Check size of the pilot needle, order a set and change if needed. Then check
3. Try different mains, of a higher quality to make sure a 110 is really a 110
4. Come back to the forums and cry for help Lol

If at any point I get it right, I'll post what I did and leave that baby alone.

Do I need to mess with the mixture screw? I'm reluctant to introduce another variable unless I need to.

[Megadan]

Do one thing at a time. FYI, its just a needle, not a pilot needle. The needle jet and needle meter fuel supplied via the main jet

[Jokerisawsome]

I got my stock 2020 hawk 250 RPS, I just put a 30mm nibbi carburetor on and got it to run just right after a couple jet changes, im at 307m altitude, but it got real hot. The guys on the Facebook group are telling me the nibbi is to much carb for a stock hawk for someome with 0 knowledge on carburetor calibration. But I'm a verry quick study and got it right in 3 trys. But it's running hot so I guess it's not right.please she'd some of your knowledge on me. I believe the last jets I ended up with was a 125 main, and 25 pilot. I was told to go up to a 30 pilot to fix the heating up problem, but I believe I had already had that or a 35 and it was spitting and shuddering in 1st gear and idle.

[Jokerisawsome]

Would cutting out my cat in the exhaust help keep the heat down?

[Megadan]

Originally Posted by Jokerisawsome

I got my stock 2020 hawk 250 RPS, I just put a 30mm nibbi carburetor on and got it to run just right after a couple jet changes, im at 307m altitude, but it got real hot. The guys on the Facebook group are telling me the nibbi is to much carb for a stock hawk for someome with 0 knowledge on carburetor calibration. But I'm a verry quick study and got it right in 3 trys. But it's running hot so I guess it's not right.please she'd some of your knowledge on me. I believe the last jets I ended up with was a 125 main, and 25 pilot. I was told to go up to a 30 pilot to fix the heating up problem, but I believe I had already had that or a 35 and it was spitting and shuddering in 1st gear and idle.

If you are going to paraphrase me, at least do it properly. (I am the guy from the Facebook Group) I said that the PE30 is too much carburetor for a stock Hawk 250 with zero mods, and that it is not a good idea for a person with zero carb tuning experience to try and get one dialed in either. When I stated to adjust the needle to the second clip and you had no idea what that meant, or how to do it, speaks loud enough for itself in that regard.

I have many years of carburetor setup and tuning experience on motorcycles and atv's from all over the world, and even I spent quite a while getting my PE30 dialed in on a bike with a full exhaust and ported head. I had to figure it out from scratch too as I was the first person to ever even install a PE30 on a Hawk. Before me, nobody even considered it.

Plus, at the end of the day, I can only make suggestions. If you don't know how to recognize the changes and/or identify the circuit that needs adjustment based on throttle position and/or behavior, you aren't going to get very far and spend countless hours with a bike that doesn't run right, or worse gets damaged.

Also, listening to most of those jokers on the Facebook groups won't get you anywhere. The vast majority of those guys are just as clueless as you, but they sound like they know something because they repeat what somebody else repeated from another person that repeated it, etc. Most of them will recommend a different main jet for an idle or low throttle position run issue, and that's just incorrect on many many levels.

[Megadan]

So, before we go any further, you say it spits and sputters at idle and in first gear....

The gears don't matter, they are irrelevant.
It spits and sputters just at idle? no throttle? Or only when you apply throttle?
What is the idle mixture screw set to? Do you even know where or what the idle mixture screw is or does?

If it spits and sputters with the throttle, at what throttle position? Between just open and 1/8th? Up to 1/4 throttle? 1/4 to 1/2, 1/2 to 3/4?

Guess what, we aren't even in main jet territory yet. See how little the main jet matters here? It BARELY does anything until a bit before 3/4 throttle and mainly affects 3/4 to wide open. Everything before half throttle is the pilot jet and needle/needle jet.

Idle is mainly affected by the idle air mixture screw, and the setting of that screw is affected by the pilot jet size. BUT, the pilot jet size is more determined by the A/F ratio of the light throttle range mostly up to 1/8th, and about half of it from 1/8th to 1/4.

The Needle the Nibbi PE30 comes with is a hair on the rich side in terms of diameter, so in order to prevent a slightly rich condition at transition around 1/8th to 1/4 throttle, setting the needle at the second notch delays the taper just enough to prevent a rich spike.

Last but not least, all of these adjustments NEED to be determined by how the bike behaves when hot. Adjusting the idle mixture, or determining jet sizing, at any other point is a waste of time.

if you are going to try and setup the idle mixture while stationary, it is a really good idea to point a fan at the motor so that it helps to prevent overheating.

Now, with ALL of that said, I still stand by my suggestion for you. Get a Mikuni clone, jet that, and enjoy riding your bike. Trust me, the PE30 isn't going to grant you any extra power over a VM26, especially with a stock exhaust and unported head. They are just too restrictive. Keep the PE30 for later down the line when/if you decide to start modding more.