Mikuni Carb Help

[jpswift1]

I've been trying to get a 400 JLO going in my ST/400 that I picked up. The machine has been sitting for some time so I decided it would be a good idea to put all new fuel and fuel lines in it. I hooked up a temporary fuel tank and put a new filter on to see if I could get it to fire. When I poured some mixed gas down the cylinders and sprayed some starting fluid in the carb it fired right up, but then died right out. I also got quite a workout from pulling it over......the engine was rebuilt and it has A LOT of compression. Anyways, I could not get it to stay running, even though fuel was running to the carb. It is the stock carb that came on the engine, a Mikuni 28 or 30mm I believe....the one with the small mouth opening. I took the carb apart, sprayed carb cleaner in it, and sprayed compressed air through all the little ports and openings. When I put it back on it still wouldn't run. Does anyone know what there needs to be done to thoroughly clean the carburetor correctly so it gets it 100% clean and operational? Am I forgetting to do something here..........it seems like the carb was clean when I took it apart, and it was almost like new inside when I put it back together. Any help would be appreciated. Thanks.

[frabbit]

JP, it's either the diaphram of the jets (my opinion only). I don't think it's the jets. Diapham could be warped or have pin holes. Guess is warped. I'll make some calls and get back. mike

[Shorty73]

i could give you a smoking deal on a new carb, it has about 1 hr on it, i put it on a 440 kohler, now i'm switching it out with a 4 stroke, send me private message if interested thanks

[russriders]

hi have u take the main jet out and clean it u have to look thought the magnify glass see it clean

[Don]

Hey, JP;

If you disassemble the carb completely and either let it soak in carb cleaner overnight or spray through all the passages real well with carb cleaner then blow them all out with compressed air, it will usually work. Pay special attention to the main & idle jets. Good Luck!

[racerone3]

with the carb on the engine, and the temporary gravity feed tank hooked up, pull the main jet out of the float bowl and see if fuel runs out. if not you have a float or needle sticking. if fuel is running, clamp the fuel line shut with some vice grips and clean the jet again real good... thats all i can think of.

[micmac]

You can also take a fine flexable wire like a guitar string and probe the holes to clean any of the gunk out. On my mikunis I had to do this twice even after soaking and blowing with compressed air.