74 GT750 running rich...float height?

[BillyMadison]

Hello. My name is Bill. I live in NJ and just finished putting together a 74 GT750. It has a rebuilt engine including crank and seals. The carbs have been stripped and passages verified with carb cleaner and compressed air. The problem I'm having is the bike is running very rich at all throttle positions. It's very blubbery with lazy response. Fuel mists out of the carb throat when it's running. I have the stock jetting. Genuine mikuni 47.5 pilots, and the float height is set to 27.6mmper the manual. I'm running the bike on a container of fuel since I don't have the fuel tank installed yet, and when I pinch the supply hose to restrict fuel flow the bike runs fantastic. Very snappy, very clean, like a 2 stroke should. Spark plugs are black and sooty also. I tried increasing the float height to 30mm as a test but it didn't do much. It's definitely rich I just don't know why. Also, the mix screws are turned out 3/4 from seated per the manual. Any advice is welcome and thank you very much. Sorry for the long post.

[PaulD738]

Have a look to see if the choke plungers are seating correctly before you go any further

[BillyMadison]

Have a look to see if the choke plungers are seating correctly before you go any further

I will check that thank you. I didn't think of that.

[BillyMadison]

I have a small hand held vacuum pump I can use to apply vacuum to the brass rod in the float chamber that picks up fuel to the starter circuit. If it leaks, I'll know. I'll try that tonight after work.

[teazer]

Have a look to see if the choke plungers are seating correctly before you go any further

I had that issue on one of mine. The "rubber" seal on the end was hard as the hobs of hell. I found replacements at MikesXS.com which worked well. It's also possible that they are just stuck and need to be cleaned or springs need replacing. Easy to fix..

[BillyMadison]

Well just tested the start circuit with vacuum and pressure. Holds both. Not sure what to do at this point. I feel like it's something stupid I'm missing. The 47.5 pilots I'm using are from a VM series carb with 4 bleed holes. I know these aren't the correct Jets and I have the correct ones coming, but I can't see that causing the issue I'm having. At least not this extreme.

[BillyMadison]

Pressure tested the floats and found them not sealing between the seat and the carb bodies. Replaced the fiber washers and also put in the correct bs30 series Jets (#47.5). Runs better but still very rich. I'm at a loss.

[PaulD738]

The vacuum & pressure test doesn’t always work on the choke system as it exerts a lot of pressure which isn’t there normally. Don’t forget the float valve has to seal with the weight of a float bowl full of fuel! I would physically remove the valves from the carb bodies and check both the rubber tip on the valve and also the brass seat. It only takes a tiny deformity or grain of crap for the thing to leak. I would also check the spring loaded plunger is moving freely.

[teazer]

The correct slow jets should make a sizeable difference.

Did you check the fuel level? Not the float level. The fuel level. It's easy to do if the carbs are off the bike.

Did you also clean out the exhaust baffles? If they are clogged, it will make a difference.

[BillyMadison]

The correct slow jets should make a sizeable difference.

Did you check the fuel level? Not the float level. The fuel level. It's easy to do if the carbs are off the bike.

Did you also clean out the exhaust baffles? If they are clogged, it will make a difference.

It has a brand new Delkevic exhaust. I ended up figuring out the problem. Once I got the floats to hold pressure and stop leaking, I fired up the bike and it still didn't run right like I stated in my previous post. Well I checked the exhaust temps and cyl 1 was stone cold. Pulled the plug and found it fouled out. Cleaned it and started the bike again. Runs damn near perfect, although I'll still be putting in the correct pilots when they arrive. I'll be taking it for a ride this weekend. So to summarize, the leaking floats was the actual problem, just don't forget to make sure it's firing on all cylinders lol. Thanks is everyone for the suggestions and reading my long winded posts.