Mikuni Slide Valve Carb on Spitfire

[jdsledder]

I just installed a VM 30 Mikuni Slide Valve carb on my 1980 Spitifire. I used the carb settings from a 1982 John Deere Snowfire. I can't get the engine to start, not even a "pop". I install the old butterfly carb and it starts and runs. I installed a new needle and seat in the slide valve carb, and just recently installed crank seals in the engine. The float bowl has fuel in it. The pilot jet is a new #30, the main jet is new #160. I have cleaned the carb several times. I obtained the carb settings for the 1982 Snowfire from an online service manual. The plugs are dry after I try to start the engine. Are my carb settings that far off?? Any thoughts would be appreciated - Thanks

[400brian]

If the plugs are dry, it doesn't sound good. I'm wondering if the enrichener is adjusted correctly.
Raise the slide, shoot some premix in, lower the slide, and it should fire.

[SpitfireKing]

I always use a base setting of about 3/4 to 1 full turn out on the mix screw and the idle about 1and 1/2 out...this always gets me started. Do you have the new choke in correctly? Maybe it's not in the right spot and giving you any pull? I'm with Brian....pop off the air box and give it a squirt of pre-mix with the slide open////sometiem they just won't pull until they have fired.

[jdsledder]

I figured out the problem with the Mikuni slide valve carb on my spitfire. The Mikuni VM30 slide valve carb has the vent tubes cast into the body of the carb. The vent exit from float bowl to the outside is thru a very small hole on the top of the inlet to the carb body. The hole is located on the RH side of the carb body. This hole was plugged with dirt, this caused the carb to supply the wrong amount of fuel to the motor. This hole is very small and can very easily get plugged with dirt or ice. You can follow the float bowl vent path by the casting marks on the outside body of the carb to help locate the vent exit. I cleaned the carb several times even blowing air into the vent passages, but there are two vents in the carb float bowl area and they are connected together, therefore when I was blowing air in one of them it would just come out the other vent and not blow out the vent exit hole. After this experience I am always going to make sure the vent path to the outside of the carb is open after a carb rebuild/cleaning.