Fuel vapor "Spraying" from carb

[motoman]

Oh oh, and press in float seat, vs. threaded on the early models.

I've had them both open a few times.

Don't know if it's been asked but check your voltages at the red input coil wire plug in with key on.........if below 11.5V you've got primary voltage issues, bad connections etc. Idealy should be 12V there, but will run fine a tad lower. I've found that 10.5V or lower at those primary connections will give the bike running fits as soon as more fuel/throttle are added....JAT.

[conquest87tsi]

Will check that out tonight Motoman. What is the cause if it is below the voltage cut off? That wouldn't be a coil issue would it? That should be the power to the coil correct? Would that mean not enough battery voltage? Bad connection/ground?

[conquest87tsi]

Bad TCI maybe?

[TopCatGr58]

Okay, let's remember that you have a 79 machine, and so it has the 1.5 ohm coils, the 1.5 ohm ballast resistor, and so once the bike is running the voltage on the red/white wire at the coil will be ~9 volts due to running thru the ballast resistor. When you just have the key on, the TCI bypasses the resistor to provide stronger starting spark, so it sends a full 12 volts to the coils for starting.

We haven't discussed the PILOT JETS! Are the true Mikuni brand, or aftermarket like MikesXS? There are 2 styles of pilot jets, and if the wrong style=VM series, they will run poorly at idle and low rpm, usually rich fouling the plugs.

Also there are a few bastardized 80's transition carb sets that Yamaha put on before they ran out of the early model parts/bodies, and so IF there is a fuel sharing tunnel between the pilot jet tower and the main jet tower, then they are the odd ones that use the rubber pilot jet tower plugs because the pilot jet is being fed thru the mainjet and sharing tunnel. IF they do NOT have the sharing tunnel, then NO pilot jet tower caps are required, they will feed directly from the fuel bowl.

Also, a better bench synch technique is to use the 3 small holes at the TOP of the engine side of the carb throat, the butterfly should just partially obstruct/block the hole closest to the position of the butterfly completely closing. This is actually a bit more precise than the breadstick tie method.

T.C.

[conquest87tsi]

I sycc'd and attempted to adjust the idle mixture last night. Got 2.5 carbs adjusted and my bike didn't want to keep running. Battery was close to stone dead. Didn't have enough amperage to keep it running. Once I had it sync'd the vapor spray disapeared. However now I am getting a fair amount of smoke from 3 or 4 (right pipe).

I know I will have to investigate further, but before I replaced the jets(with mikuni 120's) and set all float heights to 23mm both had the same amount of unburned fuel(smoke). Very little. Now it is just the right pipe. I will see what happens after I get the idle 100% tonight.

I did also notice that there is A LOT of vapor coming out of the crank case breather. I mean A LOT. Is this normal? My little filter is very oily and you can see the crank case gases coming out when running. Could both of these things be a symptom of bad rings in cylinders 3 or 4? A bad oil ring could explain the smoke on that side, and a bad compression ring could explain the excess crank case vapor. If it is excessive.

Sorry for the book, but I havent had the uneven exhaust like this before. Either one of the right cylinders is rich, or i have some bad rings. Just don't want to pull the carbs again.

[natemoen]

Ignore the smoke for now it you get more miles on it. it could just be crap in the exhaust.

[motoman]

Will check that out tonight Motoman. What is the cause if it is below the voltage cut off? That wouldn't be a coil issue would it? That should be the power to the coil correct? Would that mean not enough battery voltage? Bad connection/ground?

Can be sure your battery issue isn't helping matters. Fully charged, still should be the same volts at the primary coil wires(red/whitetracer) when key is on, not started or running. If not, highly likely ign. switch wires plug-in or switch contacts have bad connection. Other than that, +1 on TC's input.

[CaptonZap]

A quick check with a compression gauge will tell you a lot about the health, or lack there of, of your cylinders.
I think O'Reillys, Checker, et al, may rent them, and it is a lot easier than pulling the carbs. CZ

[conquest87tsi]

I actually do have a compression gauge. I will add checking the compression to the list.

Tonight I'll be setting the idle mixture and finishing the xs750 final drive install. If getting the idle mixture squared away doesn't fix the smoking I will check the compression.

Anyone know where to find the 3mm spring and ball bearings for the choke rod? I got a carb body that doesnt have them. Kind of a specialty item I'm finding. This is for my extra set of carbs by the way.

[natemoen]

PM crazysteve, he sells replacements for the spring an ball in the choke rod.

[crazy steve]

...Anyone know where to find the 3mm spring and ball bearings for the choke rod? I got a carb body that doesnt have them. Kind of a specialty item I'm finding. This is for my extra set of carbs by the way.

You can actually still get these from Yamaha (they will be a special-order item) but at $9 each for the springs and .80 each for the balls, a bit spendy. I have replacements sets for $5 (three each, one for dropsies..) with a SASE. PM me if interested...

[conquest87tsi]

Dang it. I should have checked the thread before I ordered. I just ordered 6 3mm balls from an airsoft supply store. Not sure what they use them for. Paid a little too much, but whatever. I still have the spring i guess.

Where this all started was that I had to replace my #3 carb body. I bought one from a XS11 member who believed a #1 carb would work. Well I was ignorant and believed him. A #1 does work, however, it does not have a threaded hole for the idle adjusted.

So I drilled out the casting, bought a 5mm x .5 tap, waited a day for the mail, tapped it. Then was reassempling and realized two things.

1. The original #3 carb did not have a hole for previously mentioned spring and ball, becuase it is not supposed to.
2. The replacement #1 carb does have the hole for the spring and ball.

There will not be a problem with using the #1 carb on cylinder #3 without the spring and ball will there? The hole doesn't lead to and internal passage way does it?

The reason I need the ball is because I lost the one from the #4 carb during dissasembly. Well, I didn't lose it during dissasembly. I lost it because I have never had the carbs seperated before, and for the life of me couldn't figure out why I had a bb on my bench. In the course of finding out what the "bb" was it evaporated.

[crazy steve]

...There will not be a problem with using the #1 carb on cylinder #3 without the spring and ball will there? The hole doesn't lead to and internal passage way does it?

Nope, ignore the hole. The spring/ball at the number 4 carb is mostly just to take 'slop' out of the choke shaft as there's no detents on the shaft at that end. It does help add a bit of additional friction to help keep the choke 'on' but that's it. There are detents in the shaft at the lever end, that ball/spring does the majority of the work. That one does have to be in place or you'll have to manually hold the choke on.

The balls are easy to find, any 1/8" diameter ball will work. The springs are the problem; they need to be pretty stiff to function. It took me several tries before I found some bulk coil spring that had a high enough spring rate to duplicate the OEM part (a bit of a PITA, as I have to hand-cut each one to length with a small cut-off wheel). Too light, and the enrichener plunger springs will pull the choke closed.

The ability of those springs to disappear is amazing....

[conquest87tsi]

The ability of the ball to disapear is amazing as well. We'll see if the spring is where i left it when i get home.

[CaptonZap]

I know you want to ride it, but it doesn't take that long to check the compression, and if something IS wrong, it might keep you from making anything worse by riding it in that condition. CZ