Hawk 250 choke up or down ? How to tune ?

[tonycstech]

Am i an idiot or i read too much internet instead of relying on logic and my own knowledge ?
People say: tune carb with choke off.





When choke is off, flap that restricts air is wide open, allowing more air=more RPM.
When choke is ON, flap restricting air is closed. Air restricted=RPM low.
Tuning should be done when choke is ON, when flap is closed and air is restricted.



Can someone clarify to me, why no one seems to know which way choke is ON and which way its OFF ?


Also, i am completely unable to tune the carb no matter what i do
Adjusting air/fuel mix screw has little to no effect. Bottom it out, idle change is hardly noticeable.
Shimming needle by adding washers makes it worse.
Installed main jet 100. Well, i am not at this point yet. Bike wont RPM higher then 4K unless i open the choke allowing more air then all problems go away.


Is my carb crap or what ?
I cant ride with open choke, RMP is too high and it jumps up and down by nearly 500RPM


I spent almost a month fixing weld problems with this bike.
Designed and 3d printer my own chain guide and fixed rear wheel to shift back making chain tight just from idling vibration.
Today i finally got to the carburetor just to find out that its not working either.

[Wild Dog]

I think you have the concepts mixed. The function of the choke is not to give you more rpms.
The function of the choke is to restrict the air flow to enrich air to fuel mixture, to help cold start. Once the engine is warm you can put the choke off. You should NOT run the bike with the Choke ON.

The tuning must be done with the choke off

Originally Posted by tonycstech

Can someone clarify to me, why no one seems to know which way choke is ON and which way its OFF ?

What do you mean with this??? Who doesn't know?

If you check the handlebar of your motorcycle you will notice a choke lever on the left side.
If you move that lever to the left it will activate the choke, to right the choke will be off.

[Megadan]

All carburetor tuning needs to be done for the bike at operating temperature. Since this is the state that the bike will be performing a majority of its life, this is where the fueling needs to be optimized.

The chokes only function is to restrict airflow to increase the amount of fuel in relation to air when the engine is cold. Why? A cold engine poorly atomizes fuel and the ring gaps are at their widest and piston at its smallest and don't seal as well, reducing combustion efficiency. The air charge is also at its most dense due to a lack of heat transfer to the intake charge.

In EFI vehicles this is known as a cold start enrichment, but the function is the same. It allows the vehicle to start more easily when cold.

I think your confusion as to the choke position is due to the difference between the Keihin clones and the Mikuni clones. They actually have opposite choke positions.
Stock PZ30 carb
- Lever down = choke off (open)
- Lever Middle = half choke (partially closed)
- Lever Up = Full choke (fully closed)
Mikuni VM26 "30mm"
- Lever down = Full choke
- Lever Middle = half choke
- Lever Uo = Choke Off.

Point to reiterate - ALL carb tuning needs to be done with the engine hot and the choke fully off. Having the choke on restricts airflow and draws more fuel through causing a rich condition, and thus defeating tuning the carb. The chokes only purpose is to increase fuel relative to air when the bike is cold. Generally speaking you shouldn't need to or have the bike on full choke for more than a minute and/or if it is around 50 degrees or colder outside. After no more than a minute the bike should be able to sustain idle on half choke while warming up. If none of these apply, the idle mixture and/or slow/pilot jet is incorrectly sized for the conditions the bike is in.

My suggestion, if this is the stock carburetor and an unmodified bike set the carburetor as follows

Pilot - 40 (stock size)
Mixture - 1.5 turns from lightly seated
Needle - 1 shim
Main - 105.

If you have any modifications (intake or exhaust) this can change, but I know nothing about your bike so I am starting with a stock setup. From those settings you can adjust as needed based on altitude, air temp, etc.

In order to judge the state of tune make sure the bike is up to temp, go for a 10 minute ride if necessary - with the choke off - and then see how it idles and adjust the idle speed and idle mixture if needed in order to get a steady 1500rpm idle.

Originally Posted by Wild Dog

What do you mean with this??? Who doesn't know?

If you check the handlebar of your motorcycle you will notice a choke lever on the left side.
If you move that lever to the left it will activate the choke, to right the choke will be off.

The Hawk doesn't have a handlebar choke lever, it has a lever on the side of the carb.

[OneLeggedRider]

I admire you Dan, ever helpful with patience and understanding.

[Megadan]

Originally Posted by OneLeggedRider

I admire you Dan, ever helpful with patience and understanding.

Those with knowledge should share it to those without. I could easily just brush stuff like this off, roll my eyes, call him a newb, etc. That doesn't help him, me, or anybody in the future that might read this.

In the words of the man (my father) who taught me. Knowing what it is gives you operating knowledge. Knowing why gives you analytical knowledge. If you understand the reason for the function you can diagnose, adjust, adapt, or repair any potential issue.

Accurate information is the other half - which is why I try to provide as much as I can.

EFI has been around long enough that many younger guys have never even dealt with them (carbs or fuel tuning) in any way, and can seem like voodoo or witchcraft. While I enjoy the little ego boost of being viewed as some kind of wizard, I enjoy seeing the lightbulb moment of understanding when I show somebody else and they get it a lot more.

[NzBrakelathes]

Here’s a good first tune set I sell:
Correct parts to make things easier etc
https://rover.ebay.com/rover/0/0/0?m...2F303210680840

[Wild Dog]

Originally Posted by Megadan

The Hawk doesn't have a handlebar choke lever, it has a lever on the side of the carb.

The system i mean has a cable from that lever to the lever in the handlebar. I wonder why they didn't put that extra lever in the hawk.

[Megadan]

Originally Posted by Wild Dog

The system i mean has a cable from that lever to the lever in the handlebar. I wonder why they didn't put that extra lever in the hawk.

They probably didn't even think about it or it would add more cost than they wanted would be my two guesses. Trust me, I wish they had a choke on the handlebars because the carb position on the Hawk puts the lever well under the tank right behind the cylinder head and it makes it a pain to reach.

[China Rider 27]

Doesn't take much for everything but choke position to get into your head. The other day I increased a main jet with a new free flowing exhaust and reinstalled the carb and "through tight space manipulation issues accidentally bumped it to half choke." Warming it up it died anew few times and took it out for drive and it sputtered with throttle. While everything should have been a lean condition it was acting rich? Thought about it overnight, I must have accidentally bumped it to half choke. Sure enough next day I checked it and it was set on half choke! Great explanation Dan!

[OneLeggedRider]

And that's why I admire you. I came across this thread before you posted and ALMOST offered some knowledge but thought nah, if the OP is this far in the dark I'll be wasting my breath and time.

And there's a part of me that feels that it's your responsibility to use this great tool called the internet and find the answers you seek. I mean after all I spent thousands of dollars and years of my life at 2 separate colleges to gain my mechanical education. Just here recently (I'm ashamed to admit) I lost my cool with a few fellas on a fb group about a no spark issue on a Hawk because others were offering information and apparently they thought the "complicated" electrical system was demonically possessed and couldn't be fixed without a ouija board.

I even went further to rip a few members about misinformation concerning valve adjustment, carb tuning and forks. But Dan you're right on the money, give a man a fish and he'll eat for a day, teach a man to fish and he'll eat for a lifetime.

[Megadan]

Originally Posted by OneLeggedRider

. I came across this thread before you posted and ALMOST offered some knowledge but thought nah, if the OP is this far in the dark I'll be wasting my breath and time.

And there's a part of me that feels that it's your responsibility to use this great tool called the internet and find the answers you seek. I mean after all I spent thousands of dollars and years of my life at 2 separate colleges to gain my mechanical education.

I have these thoughts sometimes as well, but then I remember that while I am on here, I am a part of that internet.

Plus, to be fair there really isn't a lot of good "laymans terms" videos about carb tuning out there. Some guys have tried and do a good job of explaining what to do, but they either don't touch on the why's, or fail to dumb down the explanation for the average Joe who may not be fluent in tuning speak. There are a few good gems out there though, but you REALLY have to dig to find them.

[Megadan]

Originally Posted by China Rider 27

Doesn't take much for everything but choke position to get into your head. The other day I increased a main jet with a new free flowing exhaust and reinstalled the carb and "through tight space manipulation issues accidentally bumped it to half choke." Warming it up it died anew few times and took it out for drive and it sputtered with throttle. While everything should have been a lean condition it was acting rich? Thought about it overnight, I must have accidentally bumped it to half choke. Sure enough next day I checked it and it was set on half choke! Great explanation Dan!

I had that happen to me WHILE riding lol. I managed to hit a bump just hard enough that it managed to knock my carb into half choke, and then all of a sudden I couldn't go beyond half throttle or 4000 rpm. I pulled over and started checking electrical connections and all sorts of other stuff thinking of every possible issue other than my choke got turned on. Then I accidentally discovered it when I reached in to check my fuel filter (thinking it was clogged) that I saw the lever wasn't where it should be.

You know those moments where you feel a huge sigh of relief, but also like a huge idiot, all at the same time? That was one of mine.

[wedooit]

Originally Posted by OneLeggedRider

I admire you Dan, ever helpful with patience and understanding.

Dan once told me he enjoys helping others, and with his analytical approach has assisted and taught me on several issues. He can explain technical issues with ease. Sometimes I dive into a project without using the kiss method, and way overthink. Then I can get slapped by Frank and Dan.

[bogieboy]

Originally Posted by Megadan

I had that happen to me WHILE riding lol. I managed to hit a bump just hard enough that it managed to knock my carb into half choke, and then all of a sudden I couldn't go beyond half throttle or 4000 rpm. I pulled over and started checking electrical connections and all sorts of other stuff thinking of every possible issue other than my choke got turned on. Then I accidentally discovered it when I reached in to check my fuel filter (thinking it was clogged) that I saw the lever wasn't where it should be.

You know those moments where you feel a huge sigh of relief, but also like a huge idiot, all at the same time? That was one of mine.

this is why i took the detent off my choke on the Roketa, and have a spring on it, to return the choke to the open position... hold it up to start, hold to half choke for a minute to warm everything up, and then release and not worry about it getting changed...LOL