Mikuni VM 26 question

Hillbilly-06 · 01-26-2019, 09:47 AM

Hello, I have spent some time searching and reading threads here, for as much info as I can get on the Mikuni VM26-30mm carb. My brother got it for me to help get my bike started (Hawk 250) and running after it had been sitting a couple years. I didn't take the jets out too see what size they are, but I did pull the bowl off and just look quickly to see if it was stamped where I can read it. One is stamped 100, and the other is turned in where all I can see is a number 2, not sure what th other digit is without taking it out, so I left it in and put it on the bike. It took a while to get it started, but When I did, I tuned the air mix screw on the bottom after it warmed up to get my smooth idle. I was impressed at how smooth it was actually, but as I walked away for a second, just to listen to it run, it began to run away with the idle all by itself, to a fast idle. I didn't touch anything, and havent been back out there to mess around with it, yet. I waned to ask here before tinkering too much, if maybe this is a float issue? It won't die out, and will recover if I throttle it a few times, BUT after it settles back to idle, it again will speed up on its own to a fast idle witought touching anything at all. I havent messed with anything else, I am not really all that mechanically inclined with bikes, but it will run and ride great except for that problem with the idle running away from me. Any suggestions? and yes I searched the threads for days, but didn't see much on this issue that could solve it yet, so any ideas would help out, Thanks.

BBOWL10 · 01-26-2019, 10:50 AM

The Mikuni that I bought was a Chinese copy and had a 40 size pilot jet (the small one). You need to pull that one out and check it. The number should be on the side of the jet. If it’s anything bigger than a 25 you need to order a couple of smaller jets if your Hawk is relatively stock. As far as carburetor adjustments you have to have everything warmed up before you start adjusting it and do one small adjustment at a time. A cold bike will run totally different than a bike that is at operating temperature
For the main jet I would run at least a 110 if not a little more.

http://www.jetsrus.com/

Megadan · 01-26-2019, 11:09 AM

It doesn't hurt to check the float height, but more than likely the idle mixture still needs a little adjusting. That increase in idle speed is a subtle symptom that the idle mixture is still a little lean. One way to know for sure would be to apply the choke and see if the condition changes.

If the carb is new or has been sitting a while it would be a good idea to start from scratch after taking the jets out (good change to verify the pilot jet size) and then actually cleaning the carburetor and using an air nozzle to blow out all of the carb passages. These cheaper aftermarket carbs are sometimes known to have metal particulate that can clog jets and passages, especially the idle passage. This will also give you a chance to check and set the float height.

As a side note, these Mikuni carbs tend to come with a too lean pilot. Yours is likely a 20, which I have found in most instances to be too small and require around 2 1/2 turns out from seated on the idle mixture. I would recommend around a 25 pilot jet. For the main jet, if the bike is completely stock, I would increase the main to a 105.

Main jet is an N100.604
Pilot jet is a VM28/486

I always recommend Genuine mikuni jets.

Hillbilly-06 · 01-26-2019, 11:42 AM

I may take another look at it soon, just got to have the time to sit down with it again. I don't have any of those little paper float measuring devices around, but I do have a small metal ruler that can measure smaller than I can read, if that helps, I just need a reference to where to measure it and what it should be, if anyone knows off hand that would be awesome.
As for it being lean, I will surely look at that first and foremost, and count how many turns out it is before I even start it up again. I thought about that when it happened, but I wanted to ask before I touched too many different things at one time. Thanks for the help so far, I will keep it up to date as I tinker with it.

Hillbilly-06 · 01-26-2019, 02:02 PM

i took another look at the fine tuning just now...
the air screw was 2 turns out exactly, so i added 1/4 turn to it and cranked it. once i got it warmed up and the choke off, it seems to idle now like it should. i havent driven it today yet, but the throttle response seems good, return to idle seems good, and it isnt running off at fast idle now, not yet anyway, and i let it run a few minutes. thanks for the help so far... if anything changes, i'll let you know, so far it seems good.

01-26-2019, 09:47 AM	#1
Hillbilly-06 Join Date: Jan 2019 Posts: 11	Mikuni VM 26 question Hello, I have spent some time searching and reading threads here, for as much info as I can get on the Mikuni VM26-30mm carb. My brother got it for me to help get my bike started (Hawk 250) and running after it had been sitting a couple years. I didn't take the jets out too see what size they are, but I did pull the bowl off and just look quickly to see if it was stamped where I can read it. One is stamped 100, and the other is turned in where all I can see is a number 2, not sure what th other digit is without taking it out, so I left it in and put it on the bike. It took a while to get it started, but When I did, I tuned the air mix screw on the bottom after it warmed up to get my smooth idle. I was impressed at how smooth it was actually, but as I walked away for a second, just to listen to it run, it began to run away with the idle all by itself, to a fast idle. I didn't touch anything, and havent been back out there to mess around with it, yet. I waned to ask here before tinkering too much, if maybe this is a float issue? It won't die out, and will recover if I throttle it a few times, BUT after it settles back to idle, it again will speed up on its own to a fast idle witought touching anything at all. I havent messed with anything else, I am not really all that mechanically inclined with bikes, but it will run and ride great except for that problem with the idle running away from me. Any suggestions? and yes I searched the threads for days, but didn't see much on this issue that could solve it yet, so any ideas would help out, Thanks.
	0

01-26-2019, 10:50 AM	#2
BBOWL10 Join Date: Nov 2018 Location: Gastonia, NC Posts: 102	The Mikuni that I bought was a Chinese copy and had a 40 size pilot jet (the small one). You need to pull that one out and check it. The number should be on the side of the jet. If it’s anything bigger than a 25 you need to order a couple of smaller jets if your Hawk is relatively stock. As far as carburetor adjustments you have to have everything warmed up before you start adjusting it and do one small adjustment at a time. A cold bike will run totally different than a bike that is at operating temperature For the main jet I would run at least a 110 if not a little more. http://www.jetsrus.com/ __________________ 2017 Kawasaki Versys 650 - Seat Concepts Seat, Moto Werk Foot Peg Lowering Blocks and Highway Pegs, MadStad Windshield, SW Motech Rear Rack, Givi Handguards and Rear Fender Hugger, Polaris Series Regulator Mod, Denali Sound Bomb Air Horn, SHAD Luggage 2018 RPS Hawk 250 - CRF230 Exhaust, Mikuni Clone Carb, LED Headlight and Tail Light, Pod Air Filter, Generic Hand Guards, Volt Meter/USB Port, Grip Puppy Grip Covers, 45 Tooth Rear Sprocket, Shinko 244 Tires with IRC HD Tubes, AGM/SLA Battery
	1

01-26-2019, 11:09 AM	#3
Megadan Join Date: Apr 2017 Location: Omaha, NE Posts: 8,100	It doesn't hurt to check the float height, but more than likely the idle mixture still needs a little adjusting. That increase in idle speed is a subtle symptom that the idle mixture is still a little lean. One way to know for sure would be to apply the choke and see if the condition changes. If the carb is new or has been sitting a while it would be a good idea to start from scratch after taking the jets out (good change to verify the pilot jet size) and then actually cleaning the carburetor and using an air nozzle to blow out all of the carb passages. These cheaper aftermarket carbs are sometimes known to have metal particulate that can clog jets and passages, especially the idle passage. This will also give you a chance to check and set the float height. As a side note, these Mikuni carbs tend to come with a too lean pilot. Yours is likely a 20, which I have found in most instances to be too small and require around 2 1/2 turns out from seated on the idle mixture. I would recommend around a 25 pilot jet. For the main jet, if the bike is completely stock, I would increase the main to a 105. Main jet is an N100.604 Pilot jet is a VM28/486 I always recommend Genuine mikuni jets. __________________ Hawk Information and Resource guide: http://www.chinariders.net/showthread.php?t=20331 2018 Hawk 250 - Full Mod list here. http://www.chinariders.net/showpost....62&postcount=1 2024 Royal Enfield Shotgun 650 https://chinariders.net/showthread.php?t=34124
	1

01-26-2019, 11:42 AM	#4
Hillbilly-06 Join Date: Jan 2019 Posts: 11	I may take another look at it soon, just got to have the time to sit down with it again. I don't have any of those little paper float measuring devices around, but I do have a small metal ruler that can measure smaller than I can read, if that helps, I just need a reference to where to measure it and what it should be, if anyone knows off hand that would be awesome. As for it being lean, I will surely look at that first and foremost, and count how many turns out it is before I even start it up again. I thought about that when it happened, but I wanted to ask before I touched too many different things at one time. Thanks for the help so far, I will keep it up to date as I tinker with it.
	0

01-26-2019, 02:02 PM	#5
Hillbilly-06 Join Date: Jan 2019 Posts: 11	i took another look at the fine tuning just now... the air screw was 2 turns out exactly, so i added 1/4 turn to it and cranked it. once i got it warmed up and the choke off, it seems to idle now like it should. i havent driven it today yet, but the throttle response seems good, return to idle seems good, and it isnt running off at fast idle now, not yet anyway, and i let it run a few minutes. thanks for the help so far... if anything changes, i'll let you know, so far it seems good.
	0