Leaking Carbs 79XS1100 Special

[jkoeringMN]

Hey guys,
I have a 1979 XS1100 Special. I have a bogging problem which I have traced back to leaky carbs. I have found gas in the oil and gas out the airbox. I know the petcocks are good. I have cleaned the carbs multiple times, thoroughly.

Specific things I have done:
Carb Floats - I have tested them for leaks and they are NOT leaking
Float Valve - The needle is not deformed and makes a good seal on the valve seat.
Bowl Gasket - The float has clear play and is NOT getting caught on the gasket

On the bench, with the bowls off, I have manually pushed up on the valve and can confirm that it easily shuts off the fuel flow. However, when I fully assemble the carb, the float does not turn off the valve. It subsequently hemorrhages fuel out of the "main nozzle".

I have adjusted the float level tang to an extreme just to test and it makes no difference. I have also adjusted the minimum float level tang (whatever the other tang is called) to prevent the max travel of said tang, again just for testing. These tests have had zero change.

Could the float be sticking on the bowl somewhere? If so, where. Are there other things I can check to diagnose the problem and get a solution.

[rpgoerlich]

On the 79SF I had, I swapped the brass float with the plastic ones from Mikes. Ran fine except when I got on it or ran low on fuel, they would drop and hang up against the float bowl. I ended up modifying the top end of the float so it would swing clear.

[Aches n Pains]

One carb or all carbs? When you took the carbs apart, did you keep the seats and needles together for each carb?

Sounds to me like you need to swap out the float needle seats and float needles. If you force the float up with the bowl off you can get a seal but the float by itself will not seal. Lots of guys like to run the needles with the Viton tips if you can find them.

As a first try you might take a thin piece of Scotchbrite on the end of a Q tip stick. Push it down into the seat and twist it around to really clean the seat. Scotchbrite the needle as well to try to establish a new seat.

Georgefix kits would do the job. Not sure if you can get him to sell you just the seats and needles.
http://cgi.ebay.com/4-YAMAHA-1978-XS...sories&vxp=mtr

Haven't used this guy before but he's selling just the gasket, seat, and needles.
http://cgi.ebay.com/Yamaha-XS400-XS7...sories&vxp=mtr

Fuel in your oil suggests that the carbs are tilted a little forward. If you are running pods you might want to make a bracket that positions the carbs just slightly down at the rear. That way they drain to the rear is they should leak. Better than the alternative.

Good luck,

Aches n Pains

[mack]

float heights

Check to ensure your float heights are correct. Valves could be working fine but not closing where they should be.

[Gallaecus]

check to see if there are any burrs on the tang. or a rough spot the would cause the float to hang up on the float needle, or on the float pin? or anything else that would stop the float from moving freely...

[GLoweVA]

You might want to check to see if your floats will "float".
If they aren't floating, then they aren't going to rise up and shut off the flow.
I've got an 80G and I got the plastic floats, but I guess the 79's had brass ones. one of them might have a pin hole leak and then won't float.
Maybe try a simple test. get a glass/cup of gas, drop the float in there and see if it floats. That might tell you a whole lot.

Just my 2 cents, hope it helps.

[natemoen]

A mch better and faster test for the brass floats is to boil some water, put it in something you do not care about and can take the heat and then dunk the floats in the really hot water. If there are holes in the float you will see bubbles coming from the hole.

[GARTHXS]

A trick I learned is when you have the carbs buttoned up turn them to normal orientation and blow on the fuel lines. If they leak You will be able to tell right away

[Kevin11]

Hey gents-
I'm the OP's roommate, and am doing the work on the carbs. Thanks for all the replies!

A couple notes, in response to some questions/suggestions you guys have made:
-Carbs #2 and #4 are the only ones that are leaking
-All original valves/parts are with their original carb
-The needles are clean, polished, and not visibly deformed, as are the valve seat
-I've done the "blow" test Garth suggested above, and also bench-tested with gas, manually pushing up on the float to close the valve, and it works great
-Floats are air-tight (no leaks)
-All tangs have been polished (overkill? maybe!) with no visible deformities
-The carbs, when installed from intake boots and airbox, do tilt forward just a little, so that looks normal to me
-We are using inline fuel filters

The thing that bugs me is that this more or less, came out of nowhere... Are there specific places on the floats where it may hit the bowl and bind up?

Thanks again guys!

[Aches n Pains]

Looks to me like you're into the "it just takes three" zone. It always seems to take three complete carb cleanings before things work right.

I'm still a little concerned about the forward lean of the carbs. Check the oil to be sure they're not leaking into the engine.

[BigRed]

Any chance you're getting a leak around the seat? I'm not sure about the '79 carbs, but on mine, there's an o-ring around the seat that can leak.

I had the same problem that you're having... for me it was that the floats were set too high, and couldn't float high enough to make a seal before the fuel dumped out my air filters. I was confused because the leaking carb would change. I didn't figure that out until I did a wet-check on the fuel level in the bowls, and saw that they were all too high.

Along the same line, do you have the floats in up-side-down? I don't mean that as an insult... I've done it. Working on the carbs up-side down, I installed the floats right-side up (into the up-side-down carbs). Not my greatest moment.

[Kevin11]

@Aches: Rule of three...I swear, I've opened the bowls and pulled, cleaned, checked, tweaked, etc. something at least 12 times. Gas has for sure made its way into the engine...oil's been changed, and will be changed again before we give it another shot with the carbs on the bike.

The orientation of the carb rack (i.e., slight forward tilt) appears to be correct, when it's fully mounted between the airbox and intake boots.

@BigRed: I'm 100% sure I have the floats in the correct orientation (right-side-up).

I've "played around" with the float height settings, even setting them to an extreme, where they'd shut off at the slightest upward motion of the floats...but to no avail. #2 and #4 would still leak, and leak quickly, as if nothing was even slowing the flow of fuel.

I've done a bench-test of the float valves using gas, and they stop fuel from flowing (manually raising the float while the bowl is off). I've done "the blow test", which the valves also function and halts the flow of air. I'd buy new float valves, but I just don't feel like that's where the issue lies. I'd look around for some different floats (plastic, or replacement brass), but those don't seem to be the issue either...what am I missing?!

[GLoweVA]

I've done a bench-test of the float valves using gas, and they stop fuel from flowing (manually raising the float while the bowl is off).

So, have you've tried the bench test with the bowls on?
This should fill the bowls up and the float should float and the valve should seat. If it doesn't, then try tapping on the carbs to 'free' a stuck float.

Is it leaking down the throat of the carb. ie. level getting to high and coming out the emulsion tube?
Just asking because I had an issue once where the 'T' between carbs 1 & 2 leaked.

[Kevin11]

So, have you've tried the bench test with the bowls on?

Yep, I've done the bench test with the bowls on and off. Bowls off, when I can manually activate the float, it stops. Bowls on, the fuel comes out the "main nozzle" on the intake/airbox side of the carb throat (as opposed to the emulsion tube).

Is there a surface inside the bowl on which the float can get stuck that I'm just not seeing?

Honestly, I appreciate all your guys' help!

[jkoeringMN]

Just as a minor update to the thread:

We tried swapping a working carb's parts (float, float valve, needle) with the one of the leaking carbs. Putting the materials from the working carb into the leaking carb produced the same result. Fuel still pours out of the main nozzle.

This is confusing the hell out of us both. We've cleaned and cleaned and cleaned, we've put working parts into the leaking carbs...nothing has solved this problem. So needless to say we are both getting kind of frustrated. Any ideas?