mikuni sudco VM34 jetting (again)

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alan hodge said:
i think before i throw a whole bunch mo money at this machine i will try the B6 plugs
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Buying new plugs is more money. As long as the engine runs, try your change and see if the plugs clean up. I have not bought plugs since the early 80's. People give their dirty plugs to me and I run them in my engine and they come out clean after a dyno run or a few miles on the highway.
If you change the cutaway and are successful, the plugs will clean up easily after 5-10 miles back road ride and one burst of speed....
The goal is to keep the combustion over 900 degF (at all speeds and throttle settings). Under 900 the plugs get black.
Get the temperature up at your light cruise speed.
Borrow a leaner slide if you can.
 
gotcha is the ebay slide the one? somebody got one for sale? thanks for all you'uns do in this ongoing commando college course
 
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I don't know exactly what you have RH or LH and I don't have any specific parts list with parts #. If I wa$ going to $pend money, I certainly would do my re$earch. If you are in fact running a 2-1/2 then going up to 3 will lean it out at light cruise and raise the temp.
 
idle adjustment screw is on left side the jet/slide #s were given me by sudco guy directly
 
I have the same problem. If you are riding stoplight to stoplight you're gonna dirty your plugs. Id try finding a place you can ride at 60+ for awhile then chop the plug. See where you're at.

You have a Left Hand slide if your idle adjustment is on the left of the carb.
 
dynodave said:
I don't know exactly what you have RH or LH and I don't have any specific parts list with parts #. If I wa$ going to $pend money, I certainly would do my re$earch. If you are in fact running a 2-1/2 then going up to 3 will lean it out at light cruise and raise the temp.
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"if you are in fact running a 2-1/2"
This is a good point, if you really are thinking about changing the throttle valve make sure you know which one you have now.
I have never looked to see if they stamp the valve with size info? but it can be measured.

mikuni sudco VM34 jetting (again)


mikuni sudco VM34 jetting (again)
 
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thanks CW for the graphic. The slides are stamped on the bottom/throat side.

NPeteN said:
If you are riding stoplight to stoplight you're gonna dirty your plugs.
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Not if you fix/tune your carb!

Alan
Take the slide out grab a file/sand paper on a flat plate and shape the front taper into a 2-3/4 try it, then make it into a 3....try it, make it into a 3-1/4- try it...then a 3-1/2 try it. Then buy/make the one that was the best... Or just stop modifying once you think you are there.
This is not rocket science, if it is best at 2-1/2 (I'd bet a beer it is not), you only need to buy one slide... and you may have learned something.
I've had guys doing this over 15 years ago...almost all the time with success.
 
My plugs stay same colour most all the time , got tired of looking .... my bike not Alan’s though ....
 
gonna ride bike 65 miles sunday morning out in country as is and will jump on this as soon as I get back....thanks
 
Craig said:
My plugs stay same colour most all the time , got tired of looking .... my bike not Alan’s though ....
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While I don't actually run any single carb system on any of my bikes at this time, I do respect the Mic's as an excellent touring system(when tuned). I certainly recommend them if a guy can leave the ricky racer complex behind...to me a commando is primarily a touring/commuter bike.
I have a 34VM, 36 keihin CV, 38VM, 38mm amal MKII, and 40mm amal MKIII and have a few different size manifolds to accommodate them. One day I would like to try the 40mm amal MKII and then the Drouin/38mm pumper Keihin (sportster) on the 74 920.:)
 
ok so I got a #3 slide and put it in and rode 45 miles this morning at 45-55 mph bike ran great looked at plugs they are now chocolate brown instead of black.so I must be on right track will monkey with it some more later on but ok, not loading up, for now
 
alan hodge said:
seattle did you keep clip in same needle groove
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I usually keep the clip in the middle groove. Go ahead and try one groove richer just to see what will happen.
The size of the needle jet will influence the mixture JUST OFF IDLE...and beyond. Moving the needle up or down will only come into play when the taper on the needle reaches the needle jet, approx 3/16 throttle and more..
The diameter of the parallel section of the needle varies from needle to needle, it is a shame Mikuni didn't use a standard diameter needle for all the VM carburetors because it would take a lot a variables out of the tuning.
 
alan hodge said:
this the type?
https://www.ebay.com/itm/Mikuni-Slide-Idle-Left-3-VM34-110-3-0-VM-59-3102-VM34-110-3-0-003-102/323843004206?_trkparms=aid=555018&algo=PL.SIM&ao=1&asc=60042&meid=cbb9421a4d3d4818b114818609c9e981&pid=100005&rk=1&rkt=12&sd=333270972635&itm=323843004206&pmt=1&noa=0&pg=2047675&_trksid=p2047675.c100005.m1851
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Be careful buying a slide...they are right and left handed depending on which side the throttle adjuster screw is on. Be VERY certain that it is the correct one. I prefer having a left hand carburetor so I can hold the throttle with the right hand and adjust the idle with the left hand. MAP will supply a right hand carb unless you ask for a left.
 
http://www.mikuni.com/pdf/vmmanual.pdf
1. Chart on page 15 shows slide cutaway effect on fuel delivery

2.
seattle##gs said:
Go ahead and try one groove richer just to see what will happen.
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3. ? I was going to suggest the exact opposite! You are after all looking to lean things up mid (throttle) range to get a cleaner plug!

4. Noticed your comments on the dunstall muffler thread. I hope you realize you are trying to adjust to a moving target?
 
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