Graham Jarvis Mikuni carb mods and jetting specs

[GlennE]

Well, I'm going to rock the boat on the Keihin love.

My buddy has a 300 that is getting some work done and he let me borrow his 36mm Keihin.  I thought I would try it just to compare with my Mikuni on my 18 250 XC-W with SX head and CDI.  Ive been very happy with the Mikuni but I thought it was worth the time to compare.

I ran settings really close to my previous (3) 300s.  5-7k and 60 degrees 

#7 slide, NECJ #2, 152 main, and 38 pilot,

Ran really well.  Maybe a touch more snap/aggressiveness but actually seemed to loose low end torque and lugging vs the Mikuni.  I was thinking that was where I would see the gain but lost out.  Overall felt very similar to my Mikuni setup (410, S-1, 42-75#1, 30) but I like the Mikuni better.  

I checked the plug and looked a little too dark brown for my taste.  A little more spooge as well.  Might try a 40 pilot and NEDJ #1 (half clip leaner) next ride.  I also have an N2ZJ I could try as well.

Can probably borrow it for few weeks so may see if I can get it closer.  Might dyno it as well, but right now, I prefer the Mikuni.

Edited May 3, 2020 by GlennE

[mog]

28 minutes ago, GlennE said:

Well, I'm going to rock the boat on the Keihin love.

My buddy has a 300 that is getting some work done and he let me borrow his 36mm Keihin.  I thought I would try it just to compare with my Mikuni on my 18 250 XC-W with SX head and CDI.  Ive been very happy with the Mikuni but I thought it was worth the time to compare.

I ran settings really close to my previous (3) 300s.  5-7k and 60 degrees 

#7 slide, NECJ #2, 152 main, and 38 pilot,

Ran really well.  Maybe a touch more snap/aggressiveness but actually seemed to loose low end torque and lugging vs the Mikuni.  I was thinking that was where I would see the gain but lost out.  Overall felt very similar to my Mikuni setup (410, S-1, 42-75#1, 30) but I like the Mikuni better.  

I checked the plug and looked a little too dark brown for my taste.  A little more spooge as well.  Might try a 40 pilot and NEDJ #1 (half clip leaner) next ride.  I also have an N2ZJ I could try as well.

Can probably borrow it for few weeks so may see if I can get it closer.  Might dyno it as well, but right now, I prefer the Mikuni.

I think that needle might work better with a 6.5 slide ,it's lacking torque as it's lean there imo 

[RMK800]

On 4/27/2020 at 6:03 PM, ThumpX said:

LooooL. I know what this thread is about. I’ve been contributing in helping others and also learning like others have some 85+ pages back. LooooL. 
I think you May have missed my point though. And it’s not just a Mikuni thread. It’s a carb thread and we all have compared the Mikuni to other carbs. The Keihin with Stic metering block is wo th our a doubt a better carb in every way. And don’t knock something until ya tried it is my Moto. ?

Nah, it is not just a carb thread.   This is a thread specifically for the Mikuni and how the Graham Jarvis mods can make it better.    It’s a Mikuni thread, but hey if you STIC guys want to clutter this up, so be it.  

[Armbarn sailor]

6 hours ago, RMK800 said:

Nah, it is not just a carb thread.   This is a thread specifically for the Mikuni and how the Graham Jarvis mods can make it better.    It’s a Mikuni thread, but hey if you STIC guys want to clutter this up, so be it.  

Its not clutter. After the first post it was clutter if it were to be called clutter at all. First post details work to be done....you do the work and its better, but its not a good carb for singletrack. Great carb for moto.

[SmokeX]

1 hour ago, hondaman331 said:

Its not clutter. After the first post it was clutter if it were to be called clutter at all. First post details work to be done....you do the work and its better, but its not a good carb for singletrack. Great carb for moto.

Yep. That is a totally true statement!!

and how do we know that HondaMan? Cause we’ve been around the block a few times with both carbs. I want the best carb on my bike for trail riding. And that’s why the Keihin with Stic metering block and JD red needle is in my bike. 
 

this thread started out with guys wanting their bike to run good and to figure out the Mikuni. We accomplished that 70 pages ago lol. If anyone wants to get their Mik right just read the first several pages. Done. as it turned out some of have discovered something really killer in a Carburator and want to share it with others while some want to deny the truth in it for what ever reason claiming we are off topic. What a joke.  
 

[Armbarn sailor]

3 minutes ago, ThumpX said:

Yep. That is a totally true statement!!

and how do we know that HondaMan? Cause we’ve been around the block a few times with both carbs. I want the best carb on my bike for trail riding. And that’s why the Keihin with Stic metering block and JD red needle is in my bike. 
 

this thread started out with guys wanting their bike to run good and to figure out the Mikuni. We accomplished that 70 pages ago lol. If anyone wants to get their Mik right just read the first several pages. Done. as it turned out some of have discovered something really killer in a Carburator and want to share it with others while some want to deny the truth in it for what ever reason claiming we are off topic. What a joke.  
 

Just the keihin itself is an improvement. I havent touched either of the 300s air screws even in 70 pages. Just pop in occasionally to see if people were still trying. Got a mikuni with jd kit for sale if anyone wants one....

[shudog]

8 hours ago, RMK800 said:

Nah, it is not just a carb thread.   This is a thread specifically for the Mikuni and how the Graham Jarvis mods can make it better.    It’s a Mikuni thread, but hey if you STIC guys want to clutter this up, so be it.  

I made the exact same point several months ago

[SmokeX]

And it was shot down !!

looool. ???

[Armbarn sailor]

3 hours ago, shudog said:

I made the exact same point several months ago

You dont get to 88 pages sorting out a carb.... heads, fuel, cdi's....all those were covered too. Its a do-it-all thread.

[SmokeX]

LooooL. ?

[GlennE]

7 hours ago, hondaman331 said:

Its not clutter. After the first post it was clutter if it were to be called clutter at all. First post details work to be done....you do the work and its better, but its not a good carb for singletrack. Great carb for moto.

Totally disagree.  For my rocky alpine single track terrain and 5-9k the carb works great.  So far I like it better than the Keihin, but will continue to attempt to get the Keihin to work better than the Mikuni as my buddy let me borrow it for a few weeks to test with.  

After all the horror stories I had heard about the Mikuni on the CR250, I thought it would be a nightmare, but I find it works great.  I also like that you can change the needle jet for even more tuning options.  

[shudog]

1 hour ago, GlennE said:

Totally disagree.  For my rocky alpine single track terrain and 5-9k the carb works great.  So far I like it better than the Keihin, but will continue to attempt to get the Keihin to work better than the Mikuni as my buddy let me borrow it for a few weeks to test with.  

After all the horror stories I had heard about the Mikuni on the CR250, I thought it would be a nightmare, but I find it works great.  I also like that you can change the needle jet for even more tuning options.  

I'm in same boat.  Did almost 200 miles of single track in Michigan this past weekend.  Bike never stalled on downhills, had tons of grunt in tight single track lugging taller gears, great over-rev...   elevation was consistent the entire trip but temps ranged from 30's in morning to 70's in afternoon.  Checked my plug color and it was good.  I'm a happy camper with Mikuni.  Let my buddies ride it who put Keihins on their bikes or have TPI and everyone felt it ran great.

[RMK800]

On 4/27/2020 at 4:59 PM, QDRHRSE said:

I think you misunderstand. This is a thread about the Mikuni carb that comes on the newer KTMs and Husqvarnas. My point is that if I was smart I wouldn't have bought another carb. I fully admit that my bike already makes more power than I can use. You can get the Mikuni to work perfectly for very little money. I completely understand when people complain that after spending 9-10K the bike should run right to begin with but because of the regulatory environment we have here in the US that's not possible. There should be a Keihin conversion/STIC thread elsewhere. So my underlying point is that without spending a lot of money and/or pulling your carb off your new bike you can get it run great in about an hour for less than $10....$20-25 if you buy the jet block gasket....or a hair under $100 if you opt for the JD kit which is advisable if tuning isn't your bag. I'm lucky that I can afford a bunch of bikes and buy shit that I just feel like trying out for them. I'm very fortunate and I'm grateful for that. Most people are not as impulsive as I am. I would be so much better off if I took my own advice.  

Edited May 6, 2020 by RMK800

[ffryno13]

I have a 2018 TC 250. I have done the GJ mods. I saw a post with the dimensions of the slide cut out but I can’t find it now. 
 

also why is the jetting spec so different from the 2018 ktm 250xc? 
 

anyone have good jetting specs for sea level for the tc250? 

[RMK800]

25 minutes ago, ffryno13 said:

I have a 2018 TC 250. I have done the GJ mods. I saw a post with the dimensions of the slide cut out but I can’t find it now. 
 

also why is the jetting spec so different from the 2018 ktm 250xc? 
 

anyone have good jetting specs for sea level for the tc250? 

I used a chain saw round file from Home Depot.  It really doesn’t  take much, be careful and don’t go too deep. I would not go any deeper then this picture.

They changed the needle jet between the years.

most have been going with the S-1 That was in the 19 bikes.

i would try the following at seal level.

Main Jet:440

needle: 42-75 clip 1.  All the ktm needles, most all have ran them on the top clip.

Pilot Jet:27.5 or 25 with the S-1.

look through the thread, there is definitely some riders that have posted seal level settings. It will be close to what I posted there.

Edited May 9, 2020 by RMK800

[Oregon Comrade]

On 4/27/2020 at 7:43 AM, QDRHRSE said:

Even though I drank the Coolaid  and bought a Keihin with the STIC metering block I haven't got it yet. My 300 is still stock and with a mix of Jarvis mods and Jarvis/book jetting mine is running great. We just rode Kernville yesterday which probably has a range of 3000-7500 feet and my Mikuni ran great. No spooge and made good power all day in a range of elevations and temperatures. We did some very technical riding and the one thing that I didn't have to worry about was how my bike was running. I have to admit that buying a $737 carb was totally unnecessary. My 2019 300 has enough power stock to do things that I am not capable of as a rider and I'm very skilled. I wish that I could just settle on stuff. I still have a full exhaust and vforce reeds to install with the new carb....none of it necessary. Since this is a Mikuni thread I want to just say that I've set up 3 Mikunis in 2 seasons and they do not require replacing or the JD jet kit. With that being said the JD kit works so well that you can install it and your bike will run excellent w/o the Jarvis mods but will run even better with the mods too. My buddy just bought a 2018 TX 300 which had the JD kit installed and it ran really well but it improved even more with the Jarvis mods.

 

I have no idea if the STIC really works. I like to try stuff so I bought one. I did a lot research. As it turns out the cheapest way to buy one is to order it direct from the manufacturer @ http://www.sticsupertorque.com/ . It was $737 OTD shipped to my house w/JD jet kit. Its almost the same price to buy the carb direct from JD w/STIC specific jet kit, which JD will do for you, and then get the STIC from the manufacturer. I got to talk to the guy who invented the STIC which was pretty cool. He's a little kooky but nice just the same. The other thing I like about this whole conversion is that, other than the carb, its all made in America. JD & STIC are here, your money stays in the USA, and gets paid to American workers. More than ever we really need to take a stand and stop buying Chinese. In fact, this may be way off topic and crazy sounding, but if the COVID-19 isn't impacting you please spend as much money as you can. We need to keep the economy rolling. 

Great input...out of curiosity, have you jetted a bike with a high-comp head and landed on a setting that worked well?

[QDRHRSE]

Yes/No. I have 2 bikes that I did the Jarvis Mods  to. My 250 has the RK head and it runs awesome following the 2019 KTM jetting specs.  My 300 did run great before the Keihin/STIC swap but it has the standard XC head. On the 300 I think my settings were close, but a hair leaner, than book specs. I think that I ran the pilot 1 size smaller and the clip 1 step leaner than the manual [after the Jarvis mods].

[Oregon Comrade]

14 minutes ago, QDRHRSE said:

Yes/No. I have 2 bikes that I did the Jarvis Mods  to. My 250 has the RK head and it runs awesome following the 2019 KTM jetting specs.  My 300 did run great before the Keihin/STIC swap but it has the standard XC head. On the 300 I think my settings were close, but a hair leaner, than book specs. I think that I ran the pilot 1 size smaller and the clip 1 step leaner than the manual [after the Jarvis mods].

I have a 250 with RK also...do you have link to the 19 jetting specs?

[QDRHRSE]

This should get you close. Here’s a pic:

 

 

Edited May 11, 2020 by QDRHRSE

[Oregon Comrade]

On 5/11/2020 at 2:18 PM, QDRHRSE said:

This should get you close. Here’s a pic:

 

 

Any idea what the differences is between the TMX38 (80) vs the TMX38 (85)?  My TE250 has the (80).....same needle although it looks like the MJ and IJ for the same elevation and temp is quite a bit leaner on my TE vs the 250 XC shown...

Thanks