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Mikuni VM26 (and some tips on carb tuning in general)

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Re: Mikuni VM26 (and some tips on carb tuning in general)

Postby Amahoser » 23 May 2012 00:14

I haven't pushed it that much on my yx160 but so far I have seen an indicated 70mph. It seemed to have much more. I am running a 39 rear and stock front sprocket. I haven't taken it on the freeway yet as I am uncomfortable with the suspension for now. Working on that next! Moto Scoot dynod the yx160 and the stage 3 both at 14HP so I assume the power should be about the same.

I haven't adjusted or calibrated my Speedo so I know it reads high but I figure the bike should be good for at least 70+mph in it's current form.

Jose Soriano
Madass 125
Genuine Rattler 110
63 Vespa GL
Aprilia Shiver 750
MZ Baghira 660 Black Panther
Kawasaki Concours
Honda XR400
Harley Nightster

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Re: Mikuni VM26 (and some tips on carb tuning in general)

Postby pjrey » 07 Jun 2012 16:58

ok, now i notice gas is all over my left pantleg when i get done riding...

the hose that is aiming right at it is the top overlow? hose coming off the right side of the carb (if looking at it with the air intake facing you directly)
what is that hose for? i know the bottom hose is an overflow (if the floats are set incorrectly).. but what is the top hose for and why is it spraying gas on mee??

thanks again!!!
p
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Re: Mikuni VM26 (and some tips on carb tuning in general)

Postby MattM » 07 Jun 2012 17:11

The VM26-606 manual simply says vent hose. It is very high up on the carb, at the same level the fuel enters.
What fails that makes fuel vent there? I do not know.

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Re: Mikuni VM26 (and some tips on carb tuning in general)

Postby pjrey » 07 Jun 2012 19:31

ok.. bucking has stopped when i move the clip position to middle (plug readings still totally white)
moved it down one clip mark (2nd up from the bottom)... and bucking came back at 1/2 throttle.. check plugs again after a chop block (WOT in 4th, hit kill switch pulled in clutch)
stopped, and removed plug.. totally totally white!

today i sprayed starter fluid around intake area, maniforlds.. head.. all over the place, NO change in idle at all...
weird thing was, is i sprayed some in the air intake.. just a dab, to see what would happen, and the bike sounded like it was going to die.. (didnt rev up like i thought it should)
i didnt spray much.. just a tiny squirt.. tried it again, further away, and even a littler amount.. sounded like it was going to die..

but anyhow, it didnt rev, or sound like it was going to die when i sprayed it anywhere else....

this has got me STUMPPPPED!!
a 190 main.. and white plugs.. hmmm

found another nice little article here for anyone interested:
http://www.3cyl.com/mraxl/manuals/carbtune/carbtune.htm
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Re: Mikuni VM26 (and some tips on carb tuning in general)

Postby Amahoser » 07 Jun 2012 19:59

If your plug is white with a plug chop, you need a bigger main jet. Thats pretty much the only way to tell... unless you get a wideband. But just running with varying throttle positions and then pulling the plug wont tell you WHAT is lean.

You might need a larger jet than what I need. If it was my bike, and considering all the trouble you have had, I would check everything out first. Make sure compression is good, timing is good, ignition system and electrical is good, valves are good, etc. Once all that is sorted and known good, I would clean the carb, check and clean the fuel filter and fuel valve and then tackle the main jet, Full Throttle plug chops only and ignore everything else. Once I have the main jet sorted, I would then do the idle mixture and idle speed. Then I would check mid throttle. I know you have done all this already but I would personally do it all again.

At this point, I really think there is something else going on with your motor. A stage 3 kit should scream. Sounds like your motor is putting out about the same power as a stock 125.

BTW, if I pull MY plug after a normal run, I sometimes get a white plug. But if I pull the plug after a WOT run, it is a nice coffee color. I know my MID is a bit lean so I am still tuning but am doing it slowly.

Troubleshooting has to be slow and methodical. I personally have skipped something easy because I rushed through it. There really isn't much on a simple engine to check but it needs to be all there.

Also, you might have killed your motor (rings) by running lean for so long. You really do need a compression check.

Might be worth it to take it to a shop and see what thy say.

Jose Soriano
Madass 125
Genuine Rattler 110
63 Vespa GL
Aprilia Shiver 750
MZ Baghira 660 Black Panther
Kawasaki Concours
Honda XR400
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Re: Mikuni VM26 (and some tips on carb tuning in general)

Postby pjrey » 07 Jun 2012 20:11

hello jose!
and thanks again for all your help!

i bought a compression tester, but threading was wrong size (oopsies)
timing i think is good? i see the T on the flywheel match up with 9 oclock marking and the big 0 on the cam sprocket... ?but what if the cam sprocket was put on with the cams in the incorrect position? how do i know what/where they should be?? i cant just trust the cam/flywheel combo can i?
the guys out in california may have put the stock head back on.. that is what i am wondering... is there any way to tell? not pistons and cylinder, but cam/head/valves?
stock versus/142cc big bore kit?

electrical i think is good... ?
i noticed the stuttering was gone now in middle clip position... but speed was loww.. 52-54...
lowered it, and i got 55-56 but stuttering came back. hmmmmm
checked for air leaks today.. with starter fluid and WD-40
(like i said, when i sprayed a test spray into the air filter of starter fluid (just a tiny bit) bike sounded like it wsa going to die.. did not rev up at all.. so i thought, what good will this test do me??.. but i did it anyhow.. sprayed it everywhere after the carb... no change in RPM, up or down.. so?...

the bike just doesnt sound good when running WOT..
sounds flat
also sounds like it wants to almost stutter at max speeds.. like it is not getting enough fuel..

there is no one in my town, or the next 120 miles who knows more than me.. scary.. i know!!
i would LOVE to take it to someone!! tempted to drive it to wisconsin and let andy and bill figure it out

i did the plug chop today, WOT for 4 miles! white plug (now i didnt hacksaw the threads.. but just reading from the visible part... TOTALLY white)

i wonder about the head.. both if they put a stock head on.. if timing is slightly off...

thanks again jose for posting! really appreciate your input and help!

p
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Re: Mikuni VM26 (and some tips on carb tuning in general)

Postby pjrey » 13 Jun 2012 19:29

just put in a main jet 200...
wide open throttle for 7 miles.. killed the engine with kill switch, plug all white. should i go up to 220?
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Re: Mikuni VM26 (and some tips on carb tuning in general)

Postby cometulm » 13 Jun 2012 21:33

I run a 210 Main and am in Salt Lake so about 5000 to 8500 feet is where I am riding. The 210 is perfect at the city altitude. My setup is 2010 Madass with 155 Z/185R & Asspipe...
Rides:
    - Sachs Madass 2010 155 Z/185 R "coMet"
    - Harley Davidson - 1200 Custom Iron "Red"
    - Honda - 1973 CT90
    - Land Rover Sport HSE - 2008 4.4 V8
    - Ford - 1997 Custom Camper Van - Triton V8
    - Ford - 1965 Shelby Cobra 427
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Re: Mikuni VM26 (and some tips on carb tuning in general)

Postby pjrey » 13 Jun 2012 21:40

im at 500 ft sea level
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Re: Mikuni VM26 (and some tips on carb tuning in general)

Postby Sambones » 30 May 2013 15:54

I've had the same problems with plug chops coming out too light so I put bigger and bigger main jets in there. Right now I have a 22.5 pilot and 220 main with the needle clip in the middle. It runs pretty good but will die if I snap it from idle to full throttle.

I read this whole thing a few times before I bought the VM26 so I got a 32.5 pilot and a few smaller main jets when I ordered it. I started out with the big pilot, idled pretty rough so I ordered some smaller sizes but wound up putting the original 22.5 back in and it runs a lot better at slower speeds now.

I bought a bunch more main jets and worked my way up to a 230 and still couldnt get a decent looking plug chop but it was obviously too rich so I put the 220 back in and I think its still too big. I'm going to try some smaller mains but I guess I'm gonna have to just go by what makes it run the best because every plug chop I've ever done came out white or really light.

I will say no matter what combo of jets I use, the bike has always started easier and ran better than with the generic PWK carb I had before and if I take the plug out any time other than a WOT chop, it's always a light beige color.
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'06 50cc Auto (barely ran)
OOR 140cc - VM26 - OOR Twin Exhaust
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Re: Mikuni VM26 (and some tips on carb tuning in general)

Postby ijain314 » 16 Sep 2014 08:27

After reading about this post regarding the VM26...Im thinking about ordering one for my 2010 MA 125. I did a search on this forum and found that a member recommended http://tboltusa.com.
I did a search on there for VM26. Which one is the right one for our bikes? I just want to verify before I make the purchase. I need a new air intake system because the stock hoses that went up to the air box split. I figured this would be a good time to upgrade the crab too. Here is a link of my search results:
Than you for the help.

http://tboltusa.com/store/advanced_sear ... 26&x=0&y=0

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Re: Mikuni VM26 (and some tips on carb tuning in general)

Postby DirtyZ » 18 Sep 2014 11:22

The crf50 kit should work. However, it may be a bit large on an otherwise stock 125.

Edit: email Vince @ tbolt and ask which carb kit they use on the 141cc lifan kit. That should be the same one you need.
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Re: Mikuni VM26 (and some tips on carb tuning in general)

Postby ijain314 » 18 Sep 2014 22:44

I sent an email to them to see if that is the right one. How do I get in contact with vince? where do others buy their carbs from? Just looking for a total package type deal.

Thank you.
DirtyZ wrote:The crf50 kit should work. However, it may be a bit large on an otherwise stock 125.

Edit: email Vince @ tbolt and ask which carb kit they use on the 141cc lifan kit. That should be the same one you need.

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Re: Mikuni VM26 (and some tips on carb tuning in general)

Postby Greg » 19 Sep 2014 02:36

As stated and linked to in the original post I bought mine from Honda Trail Bikes who T-Bolt USA likely buys theirs from as well.

You will probably want a longer throttle cable and a fairly good selection of jets as well.

http://www.hvccycle.net/mikuni-pilot-jet-m28-1001/
http://www.hvccycle.net/mikuni-large-he ... large-hex/
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Re: Mikuni VM26 (and some tips on carb tuning in general)

Postby mrjohn544 » 16 Oct 2015 14:52

So I have been reading a lot of the forums, trying to figure out my problems. I have a 50, converted to 75 from what I can tell. I assume to carb came in the kit, but I cannot find d I found for a 75cc conversion. I have removed the Mikuni carb, but cannot see what model it is.... there is a serial #, but it doesn't look like model #. The Jets are 56/15.
So my question... how can I find out the model of the carb to order parts,,,,gaskets, o rings, jets.. ?
Where can I buy jets? Motoscoot site sucks and limited parts
Anyone have similar issues with bogging? I'm running rich.
Even went to a local scooter repair who is familiar with madass, he was an ass saying I'm stupid if I wanna pay him 95 an hour to look.. guess he doesn't want the work..
Any help helps.. thanks

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