High Altitude Carb Tuning

Pfordy · 01-19-2020, 11:42 PM

Hi everyone!

I recently bought a Taotao Tbr7. I installed a Mikuni Carb and have tried a 100-120 main jet with no luck of being able to run it without having it half choked. I tried moving the jet needle up and down a click and played with the fuel mixture screw on the back. I've also adjusted the valves and changed the spark plug.

I live in Cedar City, UT (5,846ft above sea level) and it's been mid 30-40s out. The bike always starts easy on half or full choke in the cold, runs great once its warm. It does bog a little at full throttle, but not much.

I've read a ton in here about tuning the carb, but nothing for higher altitudes. Any advice or help is much appreciated!

Thanks

**JerryHawk250** · 01-20-2020, 05:58 AM

What size pilot jet?

OneLeggedRider · 01-20-2020, 08:49 AM

The trouble is your pilot jet. And you've got a few factors to consider here. High elevation does require smaller jets, but you're trying to run it in temps that are just a few degrees above freezing which requires a bigger pilot. And the TBR7 airbox is more restrictive than the Hawk's which has to be factored in as well.

The pilot jet that came with your Mikuni is unmarked mass produced garbage that we can only guess is a 20. Remove it and throw it in any direction as far as you can. Now order a pilot jet kit from Amazon for $7..

I would start with a baseline of a 22 pilot, 105 main, needle clip center position, and 1.5 turns out on the fuel mixture screw. If you can get it to run without being choked (after it's warmed up) then start tuning the mixture screw. If it won't run un-choked go to the 23 pilot, and keep going up from there until it will run without the choke. Then just follow standard carb tuning procedure which has been spelled out several times in this forum and can be found using the advanced search function. Easy peezy lemon squeezy.

Pfordy · 01-20-2020, 02:42 PM

Awesome thanks!! I ordered some pilot jets last week and they should be here soon! I'll update then

I also put on a harbor freight 3800 box on the back! Here's a pic, more to come!!

Thanks again everyone!

Savageman69 · 01-20-2020, 11:24 PM

I live about 2000 meters above sea level and run a 105 main with needle set in the middle. Runs perfect. Starts great and very responsive.

mtbjunkie · 08-10-2020, 05:23 PM

Pfordy, I'm guessing that you figured out your winning combinations since this thread died? I'm at 7200' elevation and still trying to figure out a good combo with all other stock parts on the TT250. Just wondering what you ended up sticking with?

Goob · 08-11-2020, 09:40 AM

Maybe apples to oranges, but I have the Mikuni VM26 flange mount on my Orion RXB150 and ended up with a 27.5 Pilot. Can't remember what main I have right now. I am in Denver, so similar altitude. This engine has about 14 hp, vs, 18 for most 250's, so maybe not far off tuning wise.

Took it up to the mountains at 8500+ and it still started and idled fine, and ran fantastic on steep rocky trails in 1st and 2nd gear, but would bog some when I was cruising in 3rd gear on smooth flat stretches of dirt road. I would just blip the throttle and it would clear up. If I kept it at that altitude I think I would just need one size smaller main to be good.

Tlume · 08-13-2020, 09:20 AM

Pfordy, what did u end up with? I have a tt250, live at 6200 and go between 4200 and 9000 and am having trouble knowing what to do. I have played a little with the clip on the pin as well as just started to play with the fuel pilot screw (after cutting a slot across it for a flat head screwdriver).

Goob, u have a tt. Any suggestions?

01-19-2020, 11:42 PM	#1
Pfordy Join Date: Jan 2020 Location: Cedar City, UT Posts: 11	High Altitude Carb Tuning Hi everyone! I recently bought a Taotao Tbr7. I installed a Mikuni Carb and have tried a 100-120 main jet with no luck of being able to run it without having it half choked. I tried moving the jet needle up and down a click and played with the fuel mixture screw on the back. I've also adjusted the valves and changed the spark plug. I live in Cedar City, UT (5,846ft above sea level) and it's been mid 30-40s out. The bike always starts easy on half or full choke in the cold, runs great once its warm. It does bog a little at full throttle, but not much. I've read a ton in here about tuning the carb, but nothing for higher altitudes. Any advice or help is much appreciated! Thanks __________________ -- 2020 Taotao tbr7
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01-20-2020, 05:58 AM	#2
JerryHawk250 Moderator Join Date: Oct 2016 Location: Houma, La. Posts: 11,574	What size pilot jet? __________________ 2023 Lifan Lycan 250 Chopper 2023 Venom Evader 2022 Lifan KPX250 2020 Kawasaki Vulcan S 2004 Honda ST 1300 2016 Black Hawk 250 (sold) Keihin PE30 carb,125 main,38 slow.Pod filter,ported & decked head 10:1 CR,Direct Ignition Coil,15/40Sprockets,NGK DPR8EIX-9,De-Cat,Dual Oil Cooler,Digital Cluster 2016 Cazador180 XL 2014 Coolster150 JerryHawk250.com My YouTube Channel
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01-20-2020, 08:49 AM	#3
OneLeggedRider Join Date: Nov 2018 Location: Stockport, Oh. Posts: 1,442	The trouble is your pilot jet. And you've got a few factors to consider here. High elevation does require smaller jets, but you're trying to run it in temps that are just a few degrees above freezing which requires a bigger pilot. And the TBR7 airbox is more restrictive than the Hawk's which has to be factored in as well. The pilot jet that came with your Mikuni is unmarked mass produced garbage that we can only guess is a 20. Remove it and throw it in any direction as far as you can. Now order a pilot jet kit from Amazon for $7.. I would start with a baseline of a 22 pilot, 105 main, needle clip center position, and 1.5 turns out on the fuel mixture screw. If you can get it to run without being choked (after it's warmed up) then start tuning the mixture screw. If it won't run un-choked go to the 23 pilot, and keep going up from there until it will run without the choke. Then just follow standard carb tuning procedure which has been spelled out several times in this forum and can be found using the advanced search function. Easy peezy lemon squeezy. __________________ ~ Don't poke the bear ~ M.M.I. Dean's List graduate class of '95 and Specialty welder 2020 Ice Bear Terifecta 150cc Trike 2011 Honda Foreman 500ES 4x4 2001 Polaris Scrambler 400
	3

08-11-2020, 09:40 AM	#7
Goob Join Date: Nov 2019 Posts: 353	Maybe apples to oranges, but.... Maybe apples to oranges, but I have the Mikuni VM26 flange mount on my Orion RXB150 and ended up with a 27.5 Pilot. Can't remember what main I have right now. I am in Denver, so similar altitude. This engine has about 14 hp, vs, 18 for most 250's, so maybe not far off tuning wise. Took it up to the mountains at 8500+ and it still started and idled fine, and ran fantastic on steep rocky trails in 1st and 2nd gear, but would bog some when I was cruising in 3rd gear on smooth flat stretches of dirt road. I would just blip the throttle and it would clear up. If I kept it at that altitude I think I would just need one size smaller main to be good. __________________ CSC TT250 Orion RXB 150XL
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01-20-2020, 11:24 PM	#5
Savageman69 Join Date: Dec 2019 Posts: 54	I live about 2000 meters above sea level and run a 105 main with needle set in the middle. Runs perfect. Starts great and very responsive.
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08-10-2020, 05:23 PM	#6
mtbjunkie Join Date: Aug 2020 Posts: 2	Pfordy, I'm guessing that you figured out your winning combinations since this thread died? I'm at 7200' elevation and still trying to figure out a good combo with all other stock parts on the TT250. Just wondering what you ended up sticking with?
	0

08-13-2020, 09:20 AM	#8
Tlume Join Date: Jul 2020 Location: SLC, Utah Posts: 6	Pfordy, what did u end up with? I have a tt250, live at 6200 and go between 4200 and 9000 and am having trouble knowing what to do. I have played a little with the clip on the pin as well as just started to play with the fuel pilot screw (after cutting a slot across it for a flat head screwdriver). Goob, u have a tt. Any suggestions?
	0