Rebuilding Petcocks & Carbs

[sail4free]

Carbs Leaking

I guess it'll either get done right now . . . or later ) Is there a good source for float needles/seats for this '79 XS Special?
JIM P.

Here's that pic Tylet sent -- just noticed the bank is setting in a tub. He says gas if flowing from the one filtered vent and the two openings inside the red circles. As long as the tub is level side-to-side, is that an okay way to "bench test" the floats/fill needles/seats?



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JIM P.
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[IanDMacDonald]

Here's that pic Tylet sent -- just noticed the bank is setting in a tub. He says gas if flowing from the one filtered vent and the two openings inside the red circles. As long as the tub is level side-to-side, is that an okay way to "bench test" the floats/fill needles/seats?



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JIM P.
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The best way to test them is to hook them up to a surface similar in plane as the bike, then run fuel to the carbs. If they're leaking, you already know your issue.

Source? Georgefix.

[sail4free]

Thanks!

The best way to test them is to hook them up to a surface similar in plane as the bike, then run fuel to the carbs. If they're leaking, you already know your issue.

Source? Georgefix.

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Good point -- looks like they're a little low (in the tray) towards the engine and high to the rear? A co-worker pointed out, too, that just one needle/seat could be leaking and both carbs would overflow because of the shared vent. Thanks for your input on this. I remember one post which pointed out that on a level surface with the bike on the centerstand, if the front tire was touching (and a needle/seat doesn't shut off the flow), gas can dribble down into the crankcase through an open valve. With a 2x4 laying flat *under* the front wheel, the gas would flow out the rear (drip off air pods, run out airbox, etc.).
JIM P.
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[sail4free]

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Good point -- looks like they're a little low (in the tray) towards the engine and high to the rear? A co-worker pointed out, too, that just one needle/seat could be leaking and both carbs would overflow because of the shared vent.
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My email back to Tyler includes Ian's comment and:
You might try plumbing the fuel just to #3 and then just to #4 (temporarily remove the shared vent) to see if only one needle/seat is leaking? Others have reported the float/needle/seat working fine until they put the bowl back on and then the float would hang up on the bowl somehow -- preventing the float from going all the way up. Sometimes the bowl gasket has to be trimmed flush on the inside to keep the float from catching on that gasket as well. Sometimes a little tap/tap/tap on the bowl with a soft hammer will knock the float loose and let it rise up too. These floats *do* tend to stick (not rise up all the way) on initial fill. Once filled and in use, they tend to find their *center* better and not be such a PIA.
JIM P.
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[natemoen]

you have your carbs hooked up wrong. The hose the is circled is a air vent. That is why you are getting fuel coming out of the areas in the little red circles. Fuel only gets connected to the lower Tee's on the carbs. Upper Tee's are air vents.

[jetmechmarty]

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Is there a good source for float needles/seats for this '79 XS Special?
JIM P.
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Jets R Us sells genuine Mikuni needles & seats.

http://www.jetsrus.com/needle_valve_float_bowl_gasket/needle_valve_and_float_bowl_gasket_yamaha_street.htm

[sail4free]

you have your carbs hooked up wrong. The hose the is circled is a air vent. That is why you are getting fuel coming out of the areas in the little red circles. Fuel only gets connected to the lower Tee's on the carbs. Upper Tee's are air vents.

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Possible -- I guess -- but I don't think the plumbing is wrong? Don't let that inline filter fool you . . . that's just a way of "capping" the vent with no airbox to run it to . . . plus the left pair (plumbed the same way) doesn't leak? It's hard to see in the pics but I'm pretty sure (?) the fuel supply is connected to the lower of the two pairs of barbs?
JIM P.
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[sail4free]

Jets R Us sells genuine Mikuni needles & seats.

http://www.jetsrus.com/needle_valve_...aha_street.htm

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At Jets R Us, they list *two* needle valve assemblies for the '79 XS1100 Special. This one:

http://www.jetsrus.com/individual_parts/007_976k_su.html

Or this one:

http://www.jetsrus.com/individual_parts/KL_18_4652.html

Safe to assume the slightly more expensive one is the genuine Mikuni?
JIM P.
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[DiverRay]

Before you spend money on the needles & seats, make SURE the float isn't hanging on the side of the carb body!
Easy way is to mount the carb bank on a 2X6 with a "C" clamp so you can move it around, and still mount it upright in a vise.
Then remove the float bowls from the two carbs that are leaking. Once out, check BOTH SIDES of the floats and make sure they do not interfere with the bowls or gasket.
Next, mount carbs upside down in vise, and check for leaks by putting a remote tank about 2 feet above the carbs, and allow gas to flow into the leaky pair. The floats should keep ANY gas from flowing! You can see where the gas is getting in if it is.
IF that works, needle and seats are good. On to the floats.
Disconnect remote tank, and mount carbs right side up. Now slowly install one bowl at a time, watching to see if it drags on the floats. If it does, you can adjust the float in just slightly so it clears the bowl.
Good luck! If one side is good, it's probably a float hanging up.

[sail4free]

Awesome!

Before you spend money on the needles & seats, make SURE the float isn't hanging on the side of the carb body!
Easy way is to mount the carb bank on a 2X6 with a "C" clamp so you can move it around, and still mount it upright in a vise.
Then remove the float bowls from the two carbs that are leaking. Once out, check BOTH SIDES of the floats and make sure they do not interfere with the bowls or gasket.
Next, mount carbs upside down in vise, and check for leaks by putting a remote tank about 2 feet above the carbs, and allow gas to flow into the leaky pair. The floats should keep ANY gas from flowing! You can see where the gas is getting in if it is.
IF that works, needle and seats are good. On to the floats.
Disconnect remote tank, and mount carbs right side up. Now slowly install one bowl at a time, watching to see if it drags on the floats. If it does, you can adjust the float in just slightly so it clears the bowl.
Good luck! If one side is good, it's probably a float hanging up.

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Thanks -- Ray -- for the good intel. Just reading your post right now but this was the conversation Tyler & I had last night.
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Got this back from IanDMacDonald:
"The best way to test them is to hook them up to a surface similar in plane as the bike, then run fuel to the carbs. If they're leaking, you already know your issue."
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ME: "Good point -- looks like they may be low towards the engine and high to the rear? [I'm thinking that on the bike they are closer to level front to back?) A co-worker pointed out, too, that just one needle/seat could be leaking and both carbs will overflow because of the shared vent."
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ME: "You might try plumbing the fuel just to #3 and just to #4 (temporarily remove the shared vent) just to see if only one needle/seat is leaking? Others have reported the float/needle/seat working fine until they put the bowl back on and then the float would hang up on the bowl somehow -- preventing the float from going all the way up. Sometimes the bowl gasket has to be trimmed flush on the inside to keep the float from catching on that gasket as well. Sometimes a little tap/tap/tap on the bowl with a soft hammer will knock the float loose and let it rise up too. These floats *do* tend to stick (not rise up all the way) on initial fill. Once filled and in use, they tend to find their *center* better and not be such a PIA."
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TYLER: "Alright. I'll look at it. It did look like it was only leaking through the 3 and 4 carbs. So it COULD just be one float that is jammed.

The first time I tried it was on the bike, so perfectly level and it leaked. I quickly removed them to avoid gas in the oil and tried again and making some adjustments in that container. I tilted them vertical while allowing the fuel to flow and it didn't help. I'll see if I can narrow it down to one stuck float and try to free it up."
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ME: "Kewl -- the tap/tap/tap is with fuel ON -- getting close -- I can feel it! )
I'm assuming you kept the needles/seats paired up as you went?
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TYLER: "Alright I'll give it a shot. Some of the needles and seats may be mix and matched because there were a few really badly gunked up. So I picked the best of the litter between your bike carbs and the replacement carbs. I picked the least worn needles, so they should seat regardless of the seat. I just wish they had used a rubber tip needle. They seat so much better."
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TYLER: "Great success! Tapping trick worked. Started right up. Idled perfectly. Good throttle response and dropped to idle quickly. I can still run a carb sync, but I think the bench sync got it really close based on how well it ran.

Awesome!"
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[sail4free]

TYLER: Some of the needles and seats may be mix and matched because there were a few really badly gunked up. So I picked the best of the litter between your bike carbs and the replacement carbs. I picked the least worn needles, so they should seat regardless of the seat.

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Aren't the needles made from harder metal (?chrome steel?) than the brass seats? If so, the seats are the part doing the bulk of the wear over time with all the vibration, etc. By the time any wear is visible on the float needle, the seats must be toast. Then again, the assemblies (float needle + seat) are so cheap, it's not a significant expense to replace them.
JIM P.
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[DiverRay]

Then again, the assemblies (float needle + seat) are so cheap, it's not a significant expense to replace them.

Yeah, but they WILL go for 100K miles with just a little care!
Make SURE the mechanic does the carb sync. Ask ekim about the difference between close and right.

[IanDMacDonald]

Is he stating that he's not going to sync them because the bench sync is "close" enough? Make sure they are synced with a manometer. And, they'll have to be synced over & over fine-tuning the idle mixture. In-fact, you'll find over time time your sync will be off, and will need to be maintained. A sync is not a one-time event, never to be done again.

[sail4free]

Yeah, but they WILL go for 100K miles with just a little care!
Make SURE the mechanic does the carb sync. Ask ekim about the difference between close and right.

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I had the same reaction to what he said. Delivered $100 to him today; $80 and another hour or two (@$25 per) to go rebuilding the petcocks. He'll find out this week if he's moving out of state. I suspect he's looking to wrap up as best we can due to this pending move.
JIM P.
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[sail4free]

Is he stating that he's not going to sync them because the bench sync is "close" enough? Make sure they are synced with a manometer. And, they'll have to be synced over & over fine-tuning the idle mixture. In-fact, you'll find over time time your sync will be off, and will need to be maintained. A sync is not a one-time event, never to be done again.

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I had the same response to what he wrote. I dunno' if he has a manometer but he *does* have the four-vacuum-gauge thing. How often do these require a running sync? With it running, I should be able to ride it home (a few blocks) even though I've yet to go through the brakes *and* new tires are a given before we ride it much of anywhere. Perhaps this is as good a time as any for me to reclaim my ride and learn how to do the sync my own self? Can you link to a step-by-step and a good source for the manometer? We have a few new brands in the fire and may need to throttle back on this bike rebuild a bit -- depending on how things go in the next week or so He might even loan me his gauges if that can get us close enough?
JIM P.
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