[MgB]

Hi, I've done tons of searching online but having a hard time finding a specific measurement for the correct float height.

I find either 6-7mm, or 8.7mm +- 1mm.

Can anyone clear that up, the bike is leaking fuel even from the slight angle of being on the kickstand.

I see theres a tsb for 17 250/300's regarding carb angle and looping overflow. But I don't think it applies to the 150?

Thanks

 

[augiedoggie]

Dribbling can be caused by worn inlet needle or incorrect float setting. If needle has any metallic coloration or wear on elastomer tip replace it. You can set float slightly lower to try to stop dribbling but a worn needle will dribble at any float setting.

 

[Axzon]

Float height is set in same way on most/all carburetors. If your float needle is good (and the small pin that has a spring movement works well), if the seat for the float needle is good (can get pitted with age and use) and the float tang (that pushes on the needle) is good and has no damage, then the process is straight forward:

 

[IDTrav]

Ahhhh the dreaded Mikuni tuning challenges!!! Toss it and get a Smartcarb Jk that's what I did and never looked back.

Robbed from another forum but lots of guys were happy with these modifications to the carb. Not the same jetting for the 150 but a few tricks to prevent overflow and get that bike running proper!

Graham Jarvis Mikuni jetting specs and modifications:

I eluded to these mods and jetting specs in another thread so I thought I would post these in a separate thread. I found these pictures and description on KTMTalk.com forums (not the awful Facebook group). They are from a member named "AfricaOffroad". He says these modifications and jetting specs came from another factory Husky rider he knows in South Africa who got them from Graham Jarvis's mechanic. He has posts as far back as 2008 from the Roof of Africa hard enduro race (Lesotho - 5000ft) so I am guessing he really does know someone who got this info from said source. Additionally, I have read somewhere along the way that when Jarvis or Johnny Walker come to ride/race in the USA, they bring 3 things with them from their UK race bikes: Suspension, Head, and Carb. Install those 3 things on a stock bike in the USA and go to town.

Any text in italic text is a direct quote from "AfricaOffroad" and pulled from lots of different posts from different threads. My Liberal Arts degree taught me that plagiarism is wrong. My later earned Mechanical Engineering degree taught me a lot more interesting things 🙂

Here are the jetting specs:



Left column is sea level +
Lesotho jetting would be for 5000 ft +

You want about 1 to 1 and a quarter turns on the air screw with the jetting spec I gave at sea level

Here are the float bowl modifications:





Description of these mods, "The drain bolt holes connect to the outer holes in the bowl. The drain plug has a groove filed in it to act as a feed. This all ensures a good fuel feed to the main jet, similarly for the plastic splash guard.

Brass pipe is bent up slightly and partially crimped closed. Helps eliminate wasteful spillage from the bowl.

Good friend of mine is a factory sponsored Husky rider.
He got these mods straight from Jarvis' mechanic.
He did the work for me."

"I wasn’t happy with my buddy squeezing my overflow tube like that but happy to report it does work. Note it is also bent slightly upwards"

Here are mods to the splash guard:



Here are the notch mods to the slide:





"Note regarding the slide notch, only the small notch gets made bigger."

"All the mods were done with hand tools."

"Try it, every person I know who has used this set up raves about it.
Two very good riders previously running a Lectron and Keihn have reverted back to their Mikunis with these settings"

Quotes from James Dean of JDJetting.com (A great resource on that forum and why its worth going though the hoops to join it)

"Remember that the 2017 KTM 250 has a needle jet size #R-8 and it's smaller than the #S-4 needle jet of the 2018-19, so some of the differences in needle settings are coming from this. Explained: 2.79mm (R-8) vs 2.82mm (S-4), making the 2017 leaner by .03mm overall on the needle."

"Maybe the float level has been lowered too much. Try 8.5mm instead, and then a #35 pilot jet, taking 1 step at a time."

I am unsure if the 2017 Husky vs. 2018/2019 Husky are similar needle jet changes.

Another telling post from KTMTalk member "towerjack" about his Mikuni experience and these mods:

"My son bought a new left-over 18 300XC mid September. Brought it to my shop and was leaking from carb before ever being ridden. Tore it apart and found a broken o-ring under the float needle seat. Took the bike for a first ride and it ran terrible, just as described in this thread. Read entire 70-plus pages here and started in on it.

Checked reeds and could see daylight like crazy, replaced with VForce4. Did notch in slide mod and went to work on the taper on air box side. Drilled feeder holes in the bowl drain plug, enlarged the holes in the splash guard and bent the overflow pipe and crimped it.

Installed 43-75 needle, first clip - 25 pj - 440 main - 1-5/8 on AS - 8.8mm float height - closed plug gap gown to .019
Above work took about 2-1/2 hr.

Rode bike over to a harvested bean field and rode easy for 15 min. to warm it up good, then adjusted AS and idle. Turned the smoker loose and no worries mate. Runs as well as my '12 300XC that is mildly ported, 225 comp. and aftermarket head, .040 deck height and 36mm Keihin. Running 110 Turbo Blue with 40:1 Amsoil Dominator. Rode for 2 hrs. in a gravel pit pulling hills over weekend and performance never changed. Maybe we got lucky and got a Mik with no mfg. flaws, but after the mods I've got no complaints."

Overall thoughts:

I have not personally performed these mods to my Mikuni carb. But I have read a lot of posts at KTMTalk.com from people I respect there and they really like these mods to the Mikuni against a Keihin or Metering Rod carb.

Additionally another guy suggests using the following needles from an RM125: 16 or 17/62 Suzuki needles.

If you looking to improve your Mikuni for very little money versus buying a metering rod carb, give these a shot and report back here.

I hope this helps some folks. Took a fair amount of time to dig all this info up.

 

[Axzon]

Add an after market gasket and seal kit to the shopping list for the Mikuni.

 

[IDTrav]

Add an after market gasket and seal kit to the shopping list for the Mikuni.

YES!!! Forgot that and one of the most important thing you will ever do to that Mikuni. JD jet block kit is what you want - $20.

 

[Axzon]

Anything and everything can be sorted. What is needed is will, knowledge, experience and money. But in a world filled with kids who want to be the next champion there is not enough dads who have all that to take them there. And it is really sad that a company like KTM allows a carbi like the late model Mikuni's to be a roadblock that can destroy a riders confidence and chances.

We have only ever used KTM bikes in our 13 years on the track. All have been 2 stroke ones from the first aircooled 50cc to the current 150sx. We have only had Keihin carbies on our bikes. (Can't remember what carbies the small 50/65 bikes had. But they were whatever KTM had fitted on them and we never had any issues) The most I have ever had to do was to change jets and adjust the circlip on the needle. And never has our carbies ever been the reason for us not winning or the bike not making it to the finish line.

As result of the masses of posts and articles regarding the shortcomings/faults of the Mikuni carbies we will never race with one. Never! I do not care if some guru has found the magic bullet that gets a poorly performing Mikuni to work. The first thing we do when getting a new (for us) bike is to check it over, replace the oil and coolant. And empty the tank so we can fill it with our fuel mix. Then it is time for a test ride. If I had to spend hours sorting and testing the carbi I would look elsewhere for another brand of bike.

And that is what is currently happening in New Zealand. Yamaha is becoming the 2 stroke bike kids are starting out on and when looking at the full gates the KTM's are slowly becoming less and less. (KTM's other arm: Husqvarna was a few years ago starting to grab some of the market. But here the Husky has almost totally disappeared now. There are a few GasGas racing. But they can be counted on one hand)

Why are KTM not listening? Instead of sorting their flagship bike (KTM) they go and buy a third bike company (GasGas). KTM is building factories in India, China and Brazil. If you ask me they have lost focus. Today it is only about making money, not about being the best. Watch the quality drop and market share become smaller.