Suzuki K10 w/Mikuni VM22 Low Speed Roughness

Pushrod Fifty /

My Suzi runs great but just off idle its rough, when I open the throttle it is flat or rough until it kicks and then takes off smoothly. New seals, gaskets and top end. Carb clean, needle clip in middle position, low speed screw 1 1/2 turns out. I tried adjusting it but not much better. Using Valvoline 2 stroke motorcycle oil, 25:1, its a cast iron jug. When the engine is cold its worse. Yes this is definately OT but there isnt much out there for 2 strokes and this bike is pretty rare, 80cc on a moped frame basically. Any ideas? The service manual states that the more open the low speed screw is turned, the leaner. Seems like it may be rich because its erratic.

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Re: Suzuki K10 w/Mikuni VM22 Low Speed Roughness

VM22 has an air mixture screw, so turning it in (clockwise) decreases the air and enriches it and turning it out increases air and leans it out. Is the VM22 the carb that came stock with that bike? If it were mine here's what I'd do, in order, checking progress as I go:

1. disassemble and clean out all passages of carb (ultrasonic ideally) and make note of idle jet size. test operation.

2. raise needle one setting. check operation.

3. order a size or two up on the idle jet and install. test operation with needle at original position and raised one setting. edit- idle jets have very small passages, and many mechanics i've talked to recommend just replacing the idle jet on older carbs that may have built-up varnish because they are hard to clean. so maybe buy a new one of the same size as well? up to you

4. report back (edited)

Re: Suzuki K10 w/Mikuni VM22 Low Speed Roughness

Pushrod Fifty /

Actually, its a VM 17-18, original. The manual was written for a later model bike. I cleaned it by soaking in Gunk carb soak and then spay, and using wire strands in all passages to clean. Jets came out bright brass and I poked all orifaces and saw clear light thru them.

My carb has a 70 main jet, 4J5 needle, and a 7.5 low speed pilot jet, from notes I took at dissassembly. The manual had the needle clip at 4th down from top out of total 5 positions. That was too rich. I raised it up to the 3rd, which is about middle, and it ran better, which is where it still is. At 2nd position, it just bogs. It has a #1 slider. I tried a #2 slider and it ran smoother and sounded awesome with more air intake but was too lean at 1/8 to 1/2 throttle.

I think it is rich just off idle and fine at 1/8 and above. It idles good even when cold.

Re: Suzuki K10 w/Mikuni VM22 Low Speed Roughness

Re: Suzuki K10 w/Mikuni VM22 Low Speed Roughness

what is the stock carb for that bike? vm22 sounds like it could be too large for the output on that cylinder.

Re: Suzuki K10 w/Mikuni VM22 Low Speed Roughness

Pushrod Fifty /

Correction- It is VM17-18.

Re: Suzuki K10 w/Mikuni VM22 Low Speed Roughness

Yeah that sounds more in line. In that case, the guides posted above should be a good starting point.

Re: Suzuki K10 w/Mikuni VM22 Low Speed Roughness

Pushrod Fifty /

The guide helps, but I would like to find what the float height should be for this carb. My manual lists a different carb, and .78" is impossible to set it at as specified because the tab hits the needle valve body. The needle and valve are perfect but I am getting leakage by the float needle. Yesterday I went to ride it and it was hydrolocked. I have a bad petcock, I tried to fix it by replacing the spring washer but it was leaking by. I found a new oem Suzuki petcock on partzilla. I will pull the carb and try to iron out the needle issue and bench test to be sure its not leaking. The excess gas passing by the needle may be the source of my problem with the hesitation.

Re: Suzuki K10 w/Mikuni VM22 Low Speed Roughness

Pushrod Fifty /

It turns out that I had a bad condenser after ironing out the carb issue. I brought one from NAPA and mounted it inside of the frame. After switching to a Standard brand condenser that I got on ebay, my bike runs great. I switched to Blendzall Green label castor oil. I have ran a couple of tankfulls of it so far and its awesome. The bike revs like mad and has lots of power across the rev range. I just got a gallon jug in the mail yesterday. I can't stay off this bike! (edited)

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