Carb problem

[Lit Hawk]

So on my hawk I was having sputtering problems at top speeds. Finally gave in and bought a Mikuni clone carb and a 117.5 main jet. When I installed I was having same problems so I switched to a 115 main, same thing now But got better when my mixture screw was closed. So I went down to a 110 runs really good I can hit 75 on freeway only problem is, my mixture screw is closed. Can anybody please help on why my bike would run best with the mixture screw closed all the way. I think I might have got a bad carb. I’ve done airbox mod, k&n filter, decat the muffler. All before I got my new carb. I do have a leak at my pipe coming out the engin because a bent flange. I was able to straighten it a bit and make it better, but it does still leak slightly when tested with soapy water. I haven’t gone down to a 105 main yet but I think it will be the same thing. I’ve tried everything and always the same bike runs best with mixture screw closed. I know this isn’t right, so does anyone have some suggestions or thoughts. TIA

[Tashka]

what is the pilot jet youre running? the fuel air screw only adjusts idle fuel mixture

[Lit Hawk]

Originally Posted by Tashka

what is the pilot jet youre running? the fuel air screw only adjusts idle fuel mixture

It’s still stock fro when I bought it amazon says 20,6 hole pilot. I got a 110 main inthere now screw screwed in all the way, runs good

[JerryHawk250]

Originally Posted by Lit Hawk

It’s still stock fro when I bought it amazon says 20,6 hole pilot. I got a 110 main inthere now screw screwed in all the way, runs good

That doesn't sound right. Shouldn't even idle. Something is definitely not right. Did you pull the mixture screw out to see if it has a tip on it?

[ChrisWNY]

Are you referring to the fuel/air screw on the very bottom of your carb (toward the engine side of the carb) or the one on the side that can be adjusted with a Phillips head screwdriver? Regardless, your engine shouldn't idle if either of those screws are turned clockwise all the way in. Ideally your BOTTOM fuel/air screw should be 1.5-2 turns out from bottom, and the side idle adjustment screw should also be backed out a couple of turns but YMMV depending on weather conditions, etc.

Where did you buy your carb? Can you post the link (Amazon, eBay, etc.)? Sometimes debris can get into a new carb and clog a jet so it might be worth grabbing a sewing needle to poke into those jets and using brake cleaner to fully clean out your carb.

[Weldangrind]

Lit Hawk, what elevation are you at?

[Lit Hawk]

https://www.amazon.com/Mikuni-Carbur...ref=mp_s_a_1_2

Here’s the link to the carb I bought. I’m at 50 feet above sea level. It’s definitly the mixture screw and not the idle screw. I’ve had it a 1.5,2,3 turns out all run ok but when I try to tune the carb idle goes up to highest revs when screw is all the way in. It rides fine except after I’ve ridden it for about 20 min it’ll stall at a light when I go to take off. It’ll also sometimes die when I’ve been riding at top speed and release throttle it’ll shut off. I didn’t know you could pull out the mixture screw and check if tips broken so I’ll check that tonight. If it is broke can I get a replacement?

[Tashka]

Are you still running stock spark plug?

[Lit Hawk]

No I got an iridium spark plug. I checked the mixture screw right now and it looks good. I went down to a 105 and it’s still the same. I can turn the screw in all the way and it sound at it’s best. Took it around and could hit 68 top speed no freeway. I’m stumped I’d like to leave it alone but damn it’s bothering me that something’s not right. Oh yeah and it did shut down on me right now after hitting top speed and releasing throttle. Should I try to return the carb and say it’s faulty?

[Ariel Red Hunter]

Originally Posted by Lit Hawk

No I got an iridium spark plug. I checked the mixture screw right now and it looks good. I went down to a 105 and it’s still the same. I can turn the screw in all the way and it sound at it’s best. Took it around and could hit 68 top speed no freeway. I’m stumped I’d like to leave it alone but damn it’s bothering me that something’s not right. Oh yeah and it did shut down on me right now after hitting top speed and releasing throttle. Should I try to return the carb and say it’s faulty?

It's possible that it's faulty, but the odds are like 5 to 1 it's the mechanic who's faulty....ARH

[Lit Hawk]

Originally Posted by Ariel Red Hunter

It's possible that it's faulty, but the odds are like 5 to 1 it's the mechanic who's faulty....ARH

Whyyyy youuu!!
What are your thoughts ARH? Maybe tightened the screw too tight and broke it? It looked good when I removed it. Would an over tightenedmixture screw cause this. I got no luck at all with carbs
Only thing I can find online that would cause this is too big a main jet, but I’m already down to a 105 and it’s the same thing.

[kirkallen143]

I know you said, "highest revs when mixture screw is closed," but in tuning the carb you want smoothness in your idle, not just highest revs.
If I were you, I would set the mixture screw at maybe 1 to 1 1/2 turns out from fully seated and ride it. The stalling at a stop I believe is because of your "closed" mixture screw. Do you have the spring, washer and o-ring on your mixture screw, and in that order? If not, it will cause weird things to happen when setting up the carburetor.
https://www.bing.com/images/search?v...+mixture+screw
Also, make sure there is no trash in the pilot circuit on the carb as said before.
How about the float level? Too high of a level and it will be rich as described, check that. The float should be pretty much level with the base of the carb with its tang just touching the top of spring loaded needle while in its seat. You do this visually by turning the carb upside down and the float bowl off to check.
https://www.bing.com/images/search?v...uni+carburetor

Only other thing that I can think of is a worn main jet needle and seat. It will do the same as you describe, but this is a new carb. I all out of ideas, but have you tried the original carb on it? If you do, don't forget it will need to be mod'd since you have "uncorked" your engine. You know, pull plug on mixture screw so to set, raise needle with a couple of washers, etc...

Kirk

[Ariel Red Hunter]

Originally Posted by Lit Hawk

Whyyyy youuu!!
What are your thoughts ARH? Maybe tightened the screw too tight and broke it? It looked good when I removed it. Would an over tightenedmixture screw cause this. I got no luck at all with carbs
Only thing I can find online that would cause this is too big a main jet, but I’m already down to a 105 and it’s the same thing.

Well, maybe I can help you with this a little, and I'm going to ask you "dumb" questions. First one, you realize that there are TWO idle screws, right? The one on the side of the carb controls the idle speed. The other one is the idle mixture screw, and is located at the carb body/float bowl interface. I set these at 1 1/2 turns out from a GENTLY bottomed out screw. Yes, screwing it in too tight will distort the tip to where it will drive you more crazy than you already are, trying to get repeatable results. Also put the needle clip in the middle slot on the needle. You also KNOW that the pilot jet 100% controls all fuel flow up to 1/4 throttle, right? So what I do, and others do this differently, is change pilot jets until I get a strong 1400 - 1500 rpm idle. A strong idle to me means once you have the machine moving with the clutch fully engaged it will carry you along with the throttle off, it will carry you along a firm level dirt road without stalling. It should accelerate strongly up to 1/4 throttle, but don't cheat. Make sure of the idle quality before you "gas it up". OK, so now it runs like jack the bear up to 1/4 throttle. Next, I go to the main jet. Reading spark plugs is an art learned from a lot of practise. There is an easier way. What I call the roll off-roll on method. Be sure the bike is well warmed up, go to the nearest low traffic 55 mph road you can find. Then run the bike up in high gear wide open to 50-55 mph, now roll the throttle back just a little, 1/8th turn. If you feel a mini power surge, the main jet is too lean, if it is doggy or wimpy, it is too rich. You may not be sure the first time you do this, so repeat this little test several times, you'll see, it becomes clear to you. Once you have the right main jet in it, now you can eliminate mid-range flat spots with the needle clip position. The lower the needle clip goes on the needle, the richer it is. The higher you put the needle clip, the leaner it is....ARH

[Lit Hawk]

Here’s the new mixture screw that I bought fix the Mikuni carb from amazon I linked earlier. Makes adjusting so much better only comes in blue,ships from states only thing is spring o ring and washer came in wrong order so make sure you put in correct order before installing thanks kirkallen143 for the diagram in earlier post. Enjoy

https://www.ebay.com/itm/Air-Fuel-Mi...item285ef36a5e

[Riggs]

Thanks for the info. That will help many of us.