Clutch repaired, but carburetors- Uggggghhh!

[ThrottleJunky]

Hi guys and gals,

I took the clutch out of the bike, and used scotch brite pads and solvent to clean up the steel plates which the friction plates were completely stuck to. I got it all reassembled and was finally ready for my maiden voyage. The bike starts very nicely, and after warming it up for a few moments I was off. The clutch worked flawlessly. But, after no more than a minute or two, the bike started to run very poorly, and there was a fuel smell. After bringing it back to the shop, there was fuel just pouring out of the air box. Aaargggh!! Why? I have no idea if there is a problem with the floats, or needle and seat, or perhaps even the petcock, but this is really bothering me. I have had the carbs apart twice, and completely cleaned every single part. They are pristine. I am at a loss as to why this fuel is pouring into the airbox.

[DiverRay]

Check that the floats go up and down in a strait line. BE SURE THEY CANNOT GET COCKED!! I've had carbs that the pivot point wears and allows the float to catch on the inside of the float bowl. You can just tighten up the floats at the pins to stop that.
The needle and seats should be stopping the fuel. If the needles are clean, with NO VISIBLE RING, they should be good. If you have the later carbs, check the "O" ring that seals the seat. They should be replaced as they WILL leak.
I know that's not much, but it's all I can think of for now.

[thecamelman79]

I have had the carbs apart twice,

Ahh there's the problem! A good buddy once told me that all these Yamaha Carbs have a rule of three. in other words "they gotta come off the bike three time before you gettem right"

I am no carb guru and fuel in the air box just sounds weird. I mean that would be backwards of the air flow

I know I'm not being any help here, but I'd just wait for the carb Gurus to step up with some suggestion. (why did i even bother to post right?)

Although I would definatly check your float levels (3MM below the top of the bowls.) and check your needles for any deformaties.

Good luck!

[ThrottleJunky]

I happen to think that the petcock might be involved, too. I don't understand the system as well as I should, but something is causing massive amounts of fuel to back up into the airbox where it is pouring out the bottom. I am not opposed to completely removing and taking apart the carbs again, but I can assure all of you that they are pristinely clean. I took every single part off of them, and cleaned and soaked it. The bike's only got 20,000 miles, and the carbs weren't very dirty the first time I rebuilt them.

[mro]

If you’ve installed new needles and seats then most likely something is sticking open one or more of the needles.

It takes but a tiny bit of debris (rust spec or bit of rubber from the inside of an old fuel line) caught in the float needle for them to flood into the air box.

Easy to check the petcocks. With the line to the carbs disconnected and pet in the off position for specials or on position for the standards (motor not running) there should be no flow other than what is in the hose. The flow from the petcocks will not "over flow" the carbs if the needle and seat are good.

On one carb kit I used a few years ago, the float bowl gaskets needed to be trimmed so the float would not touch em, and like Ray said …………….

BTW
Have you ever cleaned out the fuel tank?

[SFSPECBIKER79]

carbs

clean them again and try fuel filters on each line into carbs. thats what i did, thought they were clean but crap from tank keeps foulin them out. after 1000 miles on mine now after last cleaning. and can see little particles in the filters now. might help to clean tank too. goodluck

[natemoen]

Those guys have you covered so far. They do bring up good questions! Is your tank rusty? Do you use online fuel filters?

[TopCatGr58]

Hey there Throttle,

Did you get new springs for your clutches, or did you just go back in with the old ones? There is a spec in the manual, and I think I posted it in the Extra Steel plate mod as well. The springs get sprung surprisingly quickly, like just a few years or so...I experienced it with the set I put in when I first rebuilt mine, part of why I went in with the extra steel plate a few years later.

The petcocks might be leaking, but if the carbs and floats/needles are doing their job, then the carbs won't leak, so you need to look at the carbs first. You have the 81 Standard....fyi....would be good to put this info in your SIGNATURE so it shows with every post, so folks wouldn't have to look your profile up to see it and will save you having to type/post it yourself.

Did you pull the seats out, and replace the Oring around them, they harden, shrink and can leak. Folks don't realise or know this when they are cleaning them, they put in new floats, but don't know about the O-ring under the seat.

The 81 should have the plastic floats, so they are very less likely to leak compared to the older brass types. Also, the 81 has the float bowl vent built into the intake throat of the carb, so it's not a matter of it being clogged again unlike the 78-79s, if the upper vent "T" tubes are clogged WILL cause them to flood/leak.

So...like others have posted, either junk getting into the carbs between the float needle and seats...you did put in new viton/rubber tipped needles didn't you? Or the floats are hanging up against the side of the bowls.

Once you get the leaky carbs fixed, then you can address the petcocks as necessary...but just take the hose off, turn it to OFF, if it doesn't leak, then they are good.

T.C.

[tinman905]

MAke yourself a rack that you can set the inlet of your carbs on so they are sitting level . Hook the gas up and you can see which carb is leaking. This is a good way to check fuel levels in each also.
You shouldn't be surprised that the bowl gaskets may need trimming like was stated already. The plastic floats can also stick on the sides of the bowls near the bottom .I have found this on many carbs I have delt with as many of us have.
Your float levels may also just be set too high(when upside down) . If you have 81 carbs get a clear hose (tube) and check your levels .

[James England]

Hi guys and gals,

I took the clutch out of the bike, and used scotch brite pads and solvent to clean up the steel plates which the friction plates were completely stuck to. I got it all reassembled and was finally ready for my maiden voyage. The bike starts very nicely, and after warming it up for a few moments I was off. The clutch worked flawlessly. But, after no more than a minute or two, the bike started to run very poorly, and there was a fuel smell. After bringing it back to the shop, there was fuel just pouring out of the air box. Aaargggh!! Why? I have no idea if there is a problem with the floats, or needle and seat, or perhaps even the petcock, but this is really bothering me. I have had the carbs apart twice, and completely cleaned every single part. They are pristine. I am at a loss as to why this fuel is pouring into the airbox.

It's 99% sure to be one of your float needle valve assemblies. The fuel overflows in the carb bowl, then goes back down the air intake rubber boot, into the airbox and out of the two holes in the bottom of the airbox.

I had a set of shoddily 'rebuilt' carbs (see previous posts) which did exactly that. One of the float needles was stuck.

[ThrottleJunky]

I'm betting it's a float needle getting stuck. I did not replace the o-rings in the seat, and should do that, too. One of the seats was a little bit out of round. I'm wondering if the needle is hanging up on it. It might behoove me just to buy a needle and seat kit, and replace all of them. I do need to check the float levels, too. I found that the left side petcock is leaking. My bike is an '80, not an '81, and I'll fix my sig. Thanks for all the feedback, and I'll let you know what I find.

PS- I used the same springs which I measured. They were well within spec. The clutch works flawlessly. I had intended to change the friction plates, but they were like new. I measured them with a caliper as well.

[ThrottleJunky]

I am going to get some inline fuel filters as the tank, though I washed the entire thing out, may have some debris in it. Should I add them right past the petcock? There are some very tiny dots of rust in the tank. I plan on doing the electrolysis treatment when I can get to it. The float needles all seemed to perform fine when I had the carb apart. It's quite disconcerting to find that they are leaking so badly into the airbox. I am wondering if my fresh oil is compromised. I really hate carburetors, and it's quite fitting that's where my main problems would lie. I'd rather disassemble an engine than deal with these godforsaken things. One last thing- why on earth would the petcocks not have a fricking "OFF" position? That is just stupid. Sure, they're supposed to be off when the bike is not running, but in the case of my left one, it's not working properly, and if a needle is stuck open, then I'm just filling up the airbox/cylinder with fuel when it's not even running.

[ThrottleJunky]

I just updated my sig. Let's try it out.

[natemoen]

I am going to get some inline fuel filters as the tank, though I washed the entire thing out, may have some debris in it. Should I add them right past the petcock? There are some very tiny dots of rust in the tank. I plan on doing the electrolysis treatment when I can get to it. The float needles all seemed to perform fine when I had the carb apart. It's quite disconcerting to find that they are leaking so badly into the airbox. I am wondering if my fresh oil is compromised. I really hate carburetors, and it's quite fitting that's where my main problems would lie. I'd rather disassemble an engine than deal with these godforsaken things. One last thing- why on earth would the petcocks not have a fricking "OFF" position? That is just stupid. Sure, they're supposed to be off when the bike is not running, but in the case of my left one, it's not working properly, and if a needle is stuck open, then I'm just filling up the airbox/cylinder with fuel when it's not even running.

Put the fuel filters somewhere (wherever they fit for you) between the petcocks and the carbs

You van create an off position by removing the Chrome faceplate and grinding off the little stop knob on the top side. Then when the handle is pointing up it is off. You may have to file a rush it off the selector handle but may not just so you don't hit the tank.

[tinman905]

I just updated my sig. Let's try it out.

That's good but you missed the model etc. G , SG,