Hawk 250 Carb

[thehawk]

Hello,

So I got the mikuni VM26 carberator from Amazon. But I cant find any video's or guides on how to actually change it out. I found some on rejetting the current card, but nothing showing how to change it. Can I just put it in place? or do I got to do others tuff to it? The Amazon site said it was a direct replacement so I want to do that and see how it goes. Has anyone done this and can you provide guidance?
Thanks

[thehawk]

I forgot to mention in my first post that I am hoping to get away with not changing out the jets. Will that break the bike? or just make it a little slower?

[Joshlaird]

Changing jets is pretty easy once you get into it and get to know what’s what. Just take it apart and research parts and you’ll see where each thing is on your carb and get familiar with it. It doesn’t take any special tools or anything. There’s no telling what jets are in that new carb. If they are the same as what you currently have then there’s no point in changing it. What are you changing it for? If you’re looking for better performance you’re going to need to rejet it. And no better time than before it’s on the bike!

[thehawk]

Hello,
I'm changing out the carb because I killed the old one and cant seem to get it cleaned properly enough to run. I'm not very mechanical, hence the hawk sitting there for a while and the gas going bad in it.

Anyways, I changed the carb out. Didn't do anything but swap the carb to the new one (I did look at the jets, they were 100 and 20). It could be me, but it sounds different, no, not just running, but a lot better.

I havnt taken it for a test ride yet because I need to adjust the idle i'm sure. Was going to try and adjust idle but cant remember if the choke lever is supposed to be all the way up, or all the way down? It runs with the lever pushed all the way down, but if you bring it to the up position, it dies.

[Megadan]

Originally Posted by thehawk

Hello,
I'm changing out the carb because I killed the old one and cant seem to get it cleaned properly enough to run. I'm not very mechanical, hence the hawk sitting there for a while and the gas going bad in it.

Anyways, I changed the carb out. Didn't do anything but swap the carb to the new one (I did look at the jets, they were 100 and 20). It could be me, but it sounds different, no, not just running, but a lot better.

I havnt taken it for a test ride yet because I need to adjust the idle i'm sure. Was going to try and adjust idle but cant remember if the choke lever is supposed to be all the way up, or all the way down? It runs with the lever pushed all the way down, but if you bring it to the up position, it dies.

The jet numbers will be different because they are jets from a different brand (Mikuni) v the stock carb (keihin).

In my experience, the 20 pilot is too small for anybody living below denver altitude. A 25 pilot (Jet model VM28/486) is a much better match to an unmodified Hawk. Match that with a 105 main jet (Model N100.604) and you should have a great starting setup for a standard Hawk.

The Mikuni clone choke operates in the opposite direction of the stock carb, so with the stock carb, all the way up is choke fully on, down is off. The Mikuni clone = Up is off, all the way down is on. The reason your bike dies at idle with the choke off (fully open) is that you don't have enough fuel. The idle mixture on that 20 pilot will need to be at least 2 turns out (usually more) in order to idle properly.

[Megadan]

None of these carbs come jetted properly for these bikes. The stock one is too lean, and so is that Mikuni. The reason so many of us use/used the Mikuni clones was because we could change the pilot and main jets, and they are just much easier to get the jetting dialed in through the full throttle range.

Changing jets is the reality of owning a carbureted bike. It is super easy to do so don't be afraid of it, and with so many members here with your bike and that carburetor, it is very likely we can get your jetting close to perfect right off the bat.

As far as installing/removing. In this thread you will find two videos that show it well enough you should be able to get it done.
http://chinariders.net/showthread.php?t=23853

[thehawk]

Megadan, thanks for your reply.

I watched the videos, what is the idle mixture screw for and do I need to play with it? Also, is the choke lever supposed to be in the upper position or pushed down? I know middle is half way.

[Megadan]

Originally Posted by thehawk

Megadan, thanks for your reply.

I watched the videos, what is the idle mixture screw for and do I need to play with it? Also, is the choke lever supposed to be in the upper position or pushed down? I know middle is half way.

Ok, so to clarify, there are two different idle adjustments on the carb. On the side of the carb (right side) is the idle speed adjustment screw. On the bottom of the carb, between the two rear bowl screws you will see another screw with a flat head slot, that is the idle mixture screw. This adjusts the ratio of air and fuel of the motor at idle by increasing or decreasing the amount of fuel it lets in (also called a fuel screw). You will need to adjust this, yes.

This will directly affect how well your bike idles and how easy it is to start. Traditionally you would first screw it all the way in gently until it just stops. Dont screw down hard on it. Once it seats, back it off 1 1/2 turns. This is a standard starting point to tune the mixture with. From there, with the bike fully up to temp, you would turn this screw in or out a quarter turn at a time to adjust the mixture until you have achieved the highest and most stable idle you can. The pilot jet directly affects this circuit (they are connected). So if you change pilot jet sizes, the mixture needs to also be adjusted. A leaner pilot requires the screw to be turned out more, a larger requires less. Ideally you want the mixture to be no more than 2 turns out, but no less than 1 turn out. The 20 pilot jet needs approximately 2 turns out or a little more on a stock bike, so I would start with that. As I said before, I would recommend upgrading the pilot to a 25 as it is more properly sized for the Hawk, and requires less than 2 turns out to achieve a good idle.

As I said, that 100 main jet is also too small. If you are going to stick with the 20 pilot, then a 110 main jet would be a good idea. If you do change the pilot jet, then a 105 main works better. If you live right at sea level a 110 may work better.

If you do buy jets, then do yourself a favor and don't buy the cheap jets from Amazon. Spend the extra money on genuine jets, or at least high quality aftermarket items.

Main jets: https://jetsrus.com/a_jets_by_carbur...arge_round.htm

Pilot Jets: https://jetsrus.com/a_jets_by_carbur...-486_pilot.htm

[Joshlaird]

Megadan the man! Everything I know about this carburetor and the pumper carb I mainly learned from you. Heck most the stuff I know about these Chinese bikes is from you. Thanks for all the great info.

[thehawk]

I took the bike out for a few miles (3 miles), it rode nice, but, I have concerns about the choke.

I have the choke leaver pushed all the way down. I think this means that the damper is pushed all the way open. I do not know if this means the choke is on, or off. Nothing changed as the temperature rose and came up to operating temperature. It remained down the whole time. lifting the leaver (I think this is closing the internal damper) killed the bike. neither giving it more gas or less would let the bike continue to run, it just died pretty quick. This happened while cold and after I got it warmed up. Pushing the leaver down allowed the bike to start right up.


Is this operating correctly? or incorrectly? Is it ok to drive like this or will continued operation damage the bike? I ask this because I know previously I had to start in one manner and then switch the choke over as it warmed up. But right now I have no ideal if this is operating with the choke on or off.

[Megadan]

Originally Posted by thehawk

I took the bike out for a few miles (3 miles), it rode nice, but, I have concerns about the choke.

I have the choke leaver pushed all the way down. I think this means that the damper is pushed all the way open. I do not know if this means the choke is on, or off. Nothing changed as the temperature rose and came up to operating temperature. It remained down the whole time. lifting the leaver (I think this is closing the internal damper) killed the bike. neither giving it more gas or less would let the bike continue to run, it just died pretty quick. This happened while cold and after I got it warmed up. Pushing the leaver down allowed the bike to start right up.


Is this operating correctly? or incorrectly? Is it ok to drive like this or will continued operation damage the bike? I ask this because I know previously I had to start in one manner and then switch the choke over as it warmed up. But right now I have no ideal if this is operating with the choke on or off.

Do yourself a favor and remove the intake pipe and verify which position is which for yourself. It will help you make a mental note of it. All the way down should be fully open (choke off, butterfly parallel t airflow).

Closing the choke on a bike that is warmed up is a quick way to stall it out by giving it too much fuel.

[thehawk]

Dan,

The valve is held completely open (maximum airflow allowed through) with the lever pushed down. Just to confirm that's the position I'm wanting it to be for actual riding around town?

[OneLeggedRider]

Originally Posted by thehawk

Dan,

The valve is held completely open (maximum airflow allowed through) with the lever pushed down. Just to confirm that's the position I'm wanting it to be for actual riding around town?

Yes, that means the choke is off and that's the position it should be in for riding. I think you should look up some articles and videos about small engine basics and repair. If not maintaining a China bike is going to be very difficult for you.