top of carb

Just took the hat off of carb 1 for the first time tonight, the diaphragm was wet with fuel, is that normal? I know I have a float issue so I was wondering if this was normal or a side effect from my floats being off? Also trying to do the clear tube float test, using 1/4 clear hose. What are some of you using as a "nipple" or fitting to keep the hose in the overflow hole? I tried to fabricate the end of a plastic ink pen and it fit nice until fuel went through it, lol, just curious about what you guys are using. They are mikuni carbs on a 550.

 

Just wondering but did you check to see if your needle and seats held pressure. That may be your issue instead of the floats. The diaphragm being wet I don't know if that's normal or not. I have seen it in a lot of carbs but usually when i take them apart its because there is a problem. i wouldn't worry about that just yet. Check the needle and seats and make sure they are holding pressure first and you should be able to clear up any float issues if they don't. If they do hold pressure a good way to check floats is to take the carbs and take the float bowls off. Hold the carbs upside down kind of sidewaysish and see if the floats are parallel while resting on not compressing the little spring pin on the needle. If they are parallel or close then the floats will be ok.

 

The floats look as you describe, and if I'm measuring right, are at the 21.5mm setting. I just put in new float valves and needles so I'm not sure if it threw the floats off, assuming they were right to begin with. How do you test the pressure on the needle and seats?

 

You need the carbs off to do this but you turn them upside down and take a hand pump like a mityvac that can do pressure and that has a gauge and just hook it to the fuel inlet and pump it up. It should hold about 4 or more psi. You can also check them by setting them up in a pad and keep them level. Hook a tank to them that you can gravity feed fuel into them and wait to see if any of the carbs leak. I hope I'm not making this too complicated.

 

Every time you replace the fuel needles and seats the fuel level needs to be checked. Dry measure first then wet level check. I don't know exactly what the 550 carb bowls look like but most I've see have a nipple to attach a hose of some diameter. Would a smaller hose work better, 1/8 or 3/16 ID works most of the time.
Fuel in the diaphrams is probably left over from the floats overfilling, don't wory to much about it until the float level is right.
There is not much presure on the needles, I will attach a hose to the fuel inlet and blow into it. Turning the carbs upsidedown and right side up to see if the needles seal. If you can't blow through it then fuel won't leak through.

 

I did the fuel thing and no leaks, other than my stupid clear tube not working right, but once all buttoned up I left them with fuel for a bit and no leaks. The other test sounds great but I don't have a hand pump I don't think. But I'll keep at it, I appreciate the info!

 

Your carbs should be ok if there was no fuel leaking. If all your floats looked good and none of the carbs leaked I would install them and try em out unless there was something else indicating a problem.

 

No, no NO. Please don't give incorrect advice based on automotive or other non-XJ experience.

If you didn't/don't set the float levels correctly you'll just have to pull the rack and do it right.

FLOAT LEVELS ARE CRITICAL TO HOW THE BIKE STARTS, RUNS AND IDLES.

You mount the rack on a stand (I carefully chunk mine in my bench vise) so that it's perfectly level side to side and front to back, and using fuel, you set the levels in the bowls by measuring with a clear tube, as macros10 was attempting to do. The correct adjustment is within a 3mm "window."

You can't just give up, slap it together and assume all will be fine because it's not leaking. IT WON'T BE.

Needle seats/valves do not need to be "pressure tested." The floats will work fine if CLEAN, not worn/broken, and properly adjusted.

I use a little plastic vacuum nipple I scrounged in the "HELP" rack at the auto parts to attach the tube to the carbs (or I might have "borrowed" it from my Mity-Vac kit.)

 

I am a Yamaha mechanic and I have quite a bit of carb experience as well as a lot of advice and teaching from a 30 year+ Yamaha motorcycle mechanic. It is not incorrect advice and the needle and seat valves do need to be pressure tested because if they can't hold a small amount of air pressure they wont hold the fuel weight either. He also said that he checked the float levels. My advice was not based on automotive or non-xj related experience. I have a 1982 xj750 maxim that had been sitting for 8 years before i got it. I did all of the carb work myself so my advice is from a bigger bike but the same concept. I am not trying to be disrespectful in any way I am just defending my self.