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SU float troubles

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spritenut

Luke Skywalker
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I am going nutz with the front float on an SU carb.
It leaks, so does the second float lid as does the third.
I have tried Gross jets, they always leak for me, I have 4 brand new float needles and seats, and I even replaced the bowl incase it was cracked.
Now it doesn't leak with the fuel pump clicking away and the car not running.
It doesn't leak with the car idling or at a fast idle.
But rev it up and the gas pours out of the overflow.
Float is set correct. I even shimmed the needle.
The replaced the needle, added the shim, adjusted the float, replaced the float lid (2 different lids) and alot of combos of new needles, lids, and a different bowl.
What is causing just one float to spray, not just drip, gas when the engine is reved up?
3000 is about max before it sprays gas, 4000 and it spits gas, 6000 and it shoots gas across the radiator.
I have never seen this before and I just can't figure it out.
Any ideas?
 
Man, you have just covered all the bases. Different needles and seats, different covers, different floats, what's left?

Put the good one up there and see if the prob moves with the float or is it the location?

That's all I can think of and not sure what I would do then.
 
Wow. In a word: no. The pump is a low pressure unit? Must be or it'd puke on the key before start. Excess vibration is the ONLY thing I can think of. Which SU's are we talking? If it's coming out the overflow tube it almost certainly has to be a needle/seat problem. Have you tried the "Viton" tipped valves? IIRC Gross-Jet has those, tho...

Have you checked the float actuating arm to be sure it isn't cracked or split? And the pin anchor staunchions for splits in the metal near their base... except you changed the lids... I'm grabbing at straws here, but have seen these things happen.
 
He has H2s doc.
 
Brass floats with the centre holes or "sidesaddle" plastic ones?
 
Should be the plastic ones Doc.
 
Frank
I'am only thinking out loud, have u checked your fuel pressure? using a electric pump or a manual I thought the early BE's used a manual pump since the problem is related to engine RPM?
 
But it's just ONE carb "flooding". Really strange if all is as stated.
 
No telling what pump frank is useing. I surely don't remember but I would bet it is correct pressure.

You know the intresting part about this is that Frank is usualy one with answers.
 
This won't be a pressure issue. This'll be one of those "Holy COW!!" things. Rev's = vibration... something is failing ONLY at some harmonic freq... a weird circumstance.
 
Could the float itself be damaged, punctured even? So it doesn't stop the flow when it should? The vibration at high revs could "provoke" a slow leak in the float itself and cause it to sink. Of course once sunk, you'd see it immediately.

Just brainstorming... not sure if this is helpful.
 
Could try wraping the float chamber in a rag and duct tapeing it, LOL.
 
Or re-route the overflow back to the tank, Jack?? hehehe /bcforum/images/%%GRAEMLIN_URL%%/grin.gif
But seriously, I think Doc. is on the right track due to the variable changes that have been eliminated, or, is fuel pressure increasing with the increase in RPM somehow, causing the needle to open? It does seem that the amount of overflow is RPM-related in its intensity, ergo more RPM, greater fuel pressure! This is an odd one that doesn't seem to add up!
 
You can try "lapping" the float needle into the seat with a little toothpaste.

The higher RPMs may make a needle that is "only just" seating, oscillate off the seat. This happened with one of my old bike carbs...never have seen it on SUs though /bcforum/images/%%GRAEMLIN_URL%%/confused.gif

May want to look at electrical current going to fuel pump too. Is voltage climbing as RPMs go up? (causing more fuel pressure, maybe?)

Weird problem....obviously I'm grasping for a reason here.

Let us know if you find the problem.
 
Here's what I did find on my SU leak.
First they are HS2s (1.25") on a 1275 in a 58 Sprite with a transistorized round 5 psi electric fuel pump.
The tab on the carb body that locks the float bowl in place is missing. Sheared off. I can watch the float bowl vibrate and tilt as the revs go up. So I think with the bowl tilting it's upsetting the fuel and/or the needle and seat.
I just didn't catch the missing locating tab on the carb body when I replaced the bowl or did I sheer it off then?
Either way, I have to replace the carb body and I am cleaning up a body now so I'll know more as soon as I replace it.
 
Hoo boy, did we nail that with the vibration thought. Maybe.

Guess Frank will let us know, hope his new body has good bearings.
 
United we stand!! /bcforum/images/%%GRAEMLIN_URL%%/grouphug.gif /bcforum/images/%%GRAEMLIN_URL%%/thumbsup.gif
 
Well 3 totally different carbs later and different new fuel hoses it still leaks. Only the front carb and no matter what I do it leaks and it leaks bad!
So I am going to turn all these SU carbs into next years beer cans and go with a Weber DCOE.
I had a whole 2 weeks of "originality" and that's about 13 days too much.
Other original things that MUST go are the whimpy shift knob and the giant steering wheel. Sure it's nice to be able to steer with your knees but geeze, my truck has a smaller wheel.
I QUIT!
 
Gesh, he sounds like me. Now Frank you know there is a reason. Have a beer and let the back of your brain think about it.
 
Frank
Did you try damping the vibration (ie: electric tape holding it to the body to stop the vibrations) to see if maybe just a new rubber alignment washer would help? Also- is the alignment washer bolt tight enough?
Bill
 
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