Topic: 550 carb overflow, Niagra put to shame

[jvandyke]

Just finished rebuilding a friend's carbs, complete teardown and rebuild, back on bike and gas ran right through them (at least 3/4) pulled them (yes I know, I should have benched tested before install), checked needles and seats, they all pass the blow test, easily holding back what I can blow into the gas lines, double checked float height, all 22mm, this is part of the reason for the rebuild; gas pouring through the carbs although I'm 95% sure this is first time rebuild for these carbs since '75.  All 0-rings were rock hard.  Not sure where to go from here, I will check overflow tubes for cracks, make sure floats actually float I guess....what else?

[OldGreyBeast]

2 of my carbs do that any time the bowls run dry.  I have to slowly feed gas into them and tap on the bowl/body lightly with a screwdriver, add a little more gas, tap again, etc.  I've replaced the floats and the pins but those 2 carbs do it regardless.  The floats have just a tiny bit of resistance before they'll start floating.

If you do that does gas still pour out,or does it eventually stop and hold properly?

[jvandyke]

I can try tapping and such to get them to shut off but just now I used a tube in place of the drain screw and verified on the bench that that one at least just keeps on flowing so I readjusted it to a bit over spec; 23 or mm, which to me means it will shut off a bit quicker and re-tested, it didn't overflow, according to the clear tube next to the carb body.  I think I just go through and reset all the float heights and bench test and play until I get consistent shut off, it's no fun fitting carbs over and over for testing.  My manual shows checking the float height with the carb at 90 degrees, but when flat my floats are light enough they don't seem to compress the needle spring at all so not sure it matters. 

[jvandyke]

Okay well I'm not sure what did it but after resetting all float levels to maybe 23, just a tad out of spec, they stopped dumping (yes, bench tested this time!) reinstalled and she seems to run great.

[Flyin900]

When refitting the fuel needle it is important to ensure it moves smoothly in the brass seat bore too. The side of the brass seat can also be gummed up with old gas varnish.
So if as you noted the fuel needle isn’t smooth in its motion in the brass seat, that will also cause hang up float issues and flooding.

[Stev-o]

2 of my carbs do that any time the bowls run dry.

My 550F is same way, one carb will overflow when first started but then will be ok after a few minutes

[dave500]

are they the early type one or the later PD carbs?the PD carbs can develop a split in the over flow pipe,ive seen a few,some have split the entire length and others about 10/12 or so down from the top.

[sixthwisconsin]

I've had much better luck using the clear tube method for setting float height. I set if for about 2mm below the bowl seam.

Here is a link but there are many.

http://forums.sohc4.net/index.php?topic=151263.0

[Deltarider]

I've had much better luck using the clear tube method for setting float height. I set if for about 2mm below the bowl seam.

I've tested this clear tube method and I found it quite a hassle with the risk of jumping too early to conclusions. Also you have to manufacture a tube that will fit (thread!) first. My method is simple, fool proof and works well on all oldstyle carbs. As a bonus you will have cleaned the bowls from any debris in the process, which is recommended to do anyway, say once a year. http://forums.sohc4.net/index.php/topic,185754.msg2151647.html#msg2151647
Oh... and I never had to readjust the float heights in 46 years, so as long as previous owners have not touched them...