Quick Carb Question

PANDEMIC · 01-19-2019, 10:44 AM

I just received my Mikuni VM26 carburetor and have jets in hand, the temps outside are around 40°F to about 10°F could get colder but for now, let's go with that. Elevation ranges from 617' to 951' above sea level. what would be a good starting point for the jets on the Rhino 250?

I know lots of guys are running 30 pilot and 110 main with clip in the middle for the needle. but what temps is that setup for and what elevation?

I am learning everything I can from you guys on this site and can't thank you guys enough.

Megadan · 01-19-2019, 11:11 AM

Quote:

Originally Posted by PANDEMIC

I just received my Mikuni VM26 carburetor and have jets in hand, the temps outside are around 40°F to about 10°F could get colder but for now, let's go with that. Elevation ranges from 617' to 951' above sea level. what would be a good starting point for the jets on the Rhino 250?

I know lots of guys are running 30 pilot and 110 main with clip in the middle for the needle. but what temps is that setup for and what elevation?

I am learning everything I can from you guys on this site and can't thank you guys enough.

A good rule of thumb with main jetting changes is what I like to call the 25/2500 rule. For every 25 degrees Fahrenheit, or 2500ft of elevation, the jetting should be adusted half a step. Example with mikuni Jetting: If my ideal main jet size at 1000ft on a 70 degree day is a 115, and the average temps are now 45 degrees, ideally the main jet will now be a 117.5. Now lets say at the same time those temps dropped to 45 degrees I also magically ended up riding at 3500ft when those temps dropped. My main jet would stay the same because the relative air density is actually the same - the colder thinner higher altitude air is as dense as the warmer lower altitude air.

Now, technically the pilot jet should follow the same rule of thumb, but often changing just one of the jets is usually enough to compensate. I use the idle mixture setting as an analog for when the pilot jet may be the one in need of a size change. If it starts to go beyond 2 turns out or less than 1 turn out, I will change the pilot jet half a step at a time until I can keep that idle mixture between 1 and 2 turns

A 27.5 or 30 pilot would be a good starting point for those temps. I would say move the needle clip down a notch. Main jet would really come down to if it has intake and exhaust on it. I know that on a nice warm 70-80 degree average temp on a Hawk 250 with an intake and exhaust at around 1000ft, a 25 pilot and 115 main work rather well. Hopefully that helps.

PANDEMIC · 01-19-2019, 08:26 PM

any way we can save this to help others

http://www.takegawa.co.jp/files/03-05-0462.pdf

Megadan · 01-19-2019, 08:39 PM

I would gladly do that, but some of that data doesn't apply to the Mikuni that you and others have on their bikes. Things like the idle mixture screw on that Genuine Mikuni VM26 is an air screw - adjusting how much air is let it at idle. THe Mikuni you have is a fuel screw. Same job, but adjusts the fuel. Since they control opposite ends of the spectrum, their adjustments are also opposite. That genuine VM26 also uses different jet types from the ones we put on our bikes.

PANDEMIC · 01-25-2019, 09:06 AM

Megadan I need some help.

So on another note, I warmed up the ATV in my garage. Set the idle to 1440-1500 it bounces some. Drove it to my uncles 1 mile away when I arrived the engine stalled as soon as I came to full stop. I started it back up and it was surging from 1140 to 1320. Its cold out 17° F will the wind chill feels like -3° F. I didn't even think about the go pro for the ride next time.

PANDEMIC · 01-25-2019, 09:09 AM

Carb is the Mikuni VM26 it has the stock 40 slow and a 110 main jet with clip in the middle of the needle.

Now I do have a strobe and a light bar on during the drive could it be a low battery issue or not enough fuel issue? If I open the throttle just a tad surging stops rpm's raise and away I go?

**JerryHawk250** · 01-25-2019, 11:37 AM

Quote:

Originally Posted by PANDEMIC

Carb is the Mikuni VM26 it has the stock 40 slow and a 110 main jet with clip in the middle of the needle.

Now I do have a strobe and a light bar on during the drive could it be a low battery issue or not enough fuel issue? If I open the throttle just a tad surging stops rpm's raise and away I go?

40 may be to big. Try dropping down to a 30 or 27.5. Did you try adjusting the idle mixture to see if that helped?

Megadan · 01-25-2019, 12:41 PM

Assuming the jets are true to mikuni sizing that 40 should be quite a bit too big. With genuine mikuni jets, the sizes Jerry has named are going to be much more appropriate.

Weldangrind · 01-25-2019, 02:06 PM

Pandemic, I have trouble believing that it would even start with a 40, if it's a Mikuni. I suspect it's a Keihin clone. Please show us a pic of the carb.

**JerryHawk250** · 01-25-2019, 02:27 PM

Quote:

Originally Posted by Weldangrind

Pandemic, I have trouble believing that it would even start with a 40, if it's a Mikuni. I suspect it's a Keihin clone. Please show us a pic of the carb.

That would make sense and would be about the right size jet.

PANDEMIC · 01-25-2019, 10:26 PM

It was the clone carb from amazon it has 40 stamped into it. so drop it down to a 30. But wouldn't the -11*F make the 30 to lean no?

PANDEMIC · 01-25-2019, 10:27 PM

Link to carb https://www.amazon.com/gp/aw/d/B07CN...mob_b_pd_title

Weldangrind · 01-28-2019, 11:06 AM

No, a 30 would be just about right in cold temperatures, depending on your elevation. If you're near sea level, you'd likely be closer at 27.5. BTW, that's definitely the Mikuni carb I've used several times. Each one I've purchased had a 20 slow jet, so that 40 is puzzling.

PANDEMIC · 01-28-2019, 09:18 PM

Thats funny the amazon reviews said the same thing some of us are getting 40s in them. Lol 30 is in the mail

j0nny216 · 02-16-2019, 06:22 PM

Where did you order them from? We bought the exact same carbs as you and also have 40s. The spare parts kit it came with doesn't even have a number on it so that could probably go in the trash...haha

We will probably go with 22.5 and 25s since we are around 3500 ft running 105 main jets.

Another question (not trying to hijack)- if we are riding when its 40 degrees should we actually be running 115s (main)?

01-19-2019, 10:44 AM	#1
PANDEMIC Join Date: Feb 2018 Location: WI Posts: 213	Quick Carb Question I just received my Mikuni VM26 carburetor and have jets in hand, the temps outside are around 40°F to about 10°F could get colder but for now, let's go with that. Elevation ranges from 617' to 951' above sea level. what would be a good starting point for the jets on the Rhino 250? I know lots of guys are running 30 pilot and 110 main with clip in the middle for the needle. but what temps is that setup for and what elevation? I am learning everything I can from you guys on this site and can't thank you guys enough.
	1

01-19-2019, 08:39 PM	#4
Megadan Join Date: Apr 2017 Location: Omaha, NE Posts: 8,100	I would gladly do that, but some of that data doesn't apply to the Mikuni that you and others have on their bikes. Things like the idle mixture screw on that Genuine Mikuni VM26 is an air screw - adjusting how much air is let it at idle. THe Mikuni you have is a fuel screw. Same job, but adjusts the fuel. Since they control opposite ends of the spectrum, their adjustments are also opposite. That genuine VM26 also uses different jet types from the ones we put on our bikes. __________________ 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

01-25-2019, 09:09 AM	#6
PANDEMIC Join Date: Feb 2018 Location: WI Posts: 213	Carb is the Mikuni VM26 it has the stock 40 slow and a 110 main jet with clip in the middle of the needle. Now I do have a strobe and a light bar on during the drive could it be a low battery issue or not enough fuel issue? If I open the throttle just a tad surging stops rpm's raise and away I go? Last edited by PANDEMIC; 01-25-2019 at 11:15 AM.
	0

01-25-2019, 12:41 PM	#8
Megadan Join Date: Apr 2017 Location: Omaha, NE Posts: 8,100	Assuming the jets are true to mikuni sizing that 40 should be quite a bit too big. With genuine mikuni jets, the sizes Jerry has named are going to be much more appropriate. __________________ 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
	0

01-25-2019, 02:06 PM	#9
Weldangrind Join Date: Mar 2009 Location: Sardis, BC, Canada Posts: 25,977	Pandemic, I have trouble believing that it would even start with a 40, if it's a Mikuni. I suspect it's a Keihin clone. Please show us a pic of the carb. __________________ Weldangrind "I figure I'm well-prepared for coping with a bike that comes from the factory with unresolved issues and that rewards the self-reliant owner." - Buccaneer
	1

01-19-2019, 08:26 PM	#3
PANDEMIC Join Date: Feb 2018 Location: WI Posts: 213	any way we can save this to help others http://www.takegawa.co.jp/files/03-05-0462.pdf
	0

01-25-2019, 09:06 AM	#5
PANDEMIC Join Date: Feb 2018 Location: WI Posts: 213	Megadan I need some help. So on another note, I warmed up the ATV in my garage. Set the idle to 1440-1500 it bounces some. Drove it to my uncles 1 mile away when I arrived the engine stalled as soon as I came to full stop. I started it back up and it was surging from 1140 to 1320. Its cold out 17° F will the wind chill feels like -3° F. I didn't even think about the go pro for the ride next time.
	0

01-25-2019, 10:26 PM	#11
PANDEMIC Join Date: Feb 2018 Location: WI Posts: 213	It was the clone carb from amazon it has 40 stamped into it. so drop it down to a 30. But wouldn't the -11*F make the 30 to lean no?
	0

01-25-2019, 10:27 PM	#12
PANDEMIC Join Date: Feb 2018 Location: WI Posts: 213	Link to carb https://www.amazon.com/gp/aw/d/B07CN...mob_b_pd_title
	1

01-28-2019, 11:06 AM	#13
Weldangrind Join Date: Mar 2009 Location: Sardis, BC, Canada Posts: 25,977	No, a 30 would be just about right in cold temperatures, depending on your elevation. If you're near sea level, you'd likely be closer at 27.5. BTW, that's definitely the Mikuni carb I've used several times. Each one I've purchased had a 20 slow jet, so that 40 is puzzling. __________________ Weldangrind "I figure I'm well-prepared for coping with a bike that comes from the factory with unresolved issues and that rewards the self-reliant owner." - Buccaneer
	1

01-28-2019, 09:18 PM	#14
PANDEMIC Join Date: Feb 2018 Location: WI Posts: 213	Thats funny the amazon reviews said the same thing some of us are getting 40s in them. Lol 30 is in the mail
	0

02-16-2019, 06:22 PM	#15
j0nny216 Join Date: Jan 2019 Location: Middle Of Nowhere, Idaho Posts: 31	Where did you order them from? We bought the exact same carbs as you and also have 40s. The spare parts kit it came with doesn't even have a number on it so that could probably go in the trash...haha We will probably go with 22.5 and 25s since we are around 3500 ft running 105 main jets. Another question (not trying to hijack)- if we are riding when its 40 degrees should we actually be running 115s (main)?
	0