Yamaha XS 650H Special II Exhaust Problems?

gggGary said:
It sounds like you have extreme flooding of the LH cylinder, do not keep running the engine like that, washdown loss of lube on that piston, thinned crankcase oil etc. IMHO those carbs need to come off again. I'd be willing to bet on a bad o-ring, let us know what you find. A "will fit" oring can usually be found at the local auto parts store.
Click to expand...
It very well could be, because, when we pulled the motorcycle from the barn, I remember we got it started, and gas was leaking all over the place. (Along with all the gummage in the carbs) So it must be that, I'll go ahead and pull them back off, and get some o-rings.

Though I don't know what you mean by washing down loss of lube on the piston.
 
IamTheMarcus said:
Though I don't know what you mean by washing down loss of lube on the piston.
Click to expand...

What he's talking about is if raw gas runs out of the carb into the cylinder it can wash the oil film off the cylinder walls, at which point the cylinder walls and rings wear really fast. It would have to be running a good while to cause any measurable problem though. Besides, on my own '81 the time or two I had a similar problem the gas ran into the air cleaner, not the other direction and into the cylinder. Maybe it runs the other way only with the earlier carbs.
 
Your pistons and cylinders operate with a thin coating of oil on them to protect them against excessive and rapid wear. If you have a carb flooding out, that can dump raw fuel into the cylinder and wash that protective oil coating away. Rapid wear of that cylinder can then occur.
 
I might of ran into another problem; When I disconnected the fuel tank from the motorcycle, as soon as I popped the fuel hose off, tons of gas flowed out of the petcock, and wouldn't stop, I tried playing with the lever, switching it to RES, ON, and even PRIME, but it still leaked out most of my gas, (I put it over a gas can and is dripping out as we speak...

The Petcock was rebuilt with new o-rings, etc etc.
 
If your petcock is working right, the fuel flow will stop if you put it in the ON or RES position and flow in the PRI position.
In the ON or RES position, fuel only flows if engine vacuum is applied to the back side of the petcock.
It sounds like yours isn't working right. If you tried a rebuild I might suggest replacing it with a non vacuum petcock. Mike's sells one. item #20-0019 $46.
Leo
 
IamTheMarcus said:
The Petcock was rebuilt with new o-rings, etc etc.
Click to expand...

Rebuilding the vacuum petcock is a bit complicated, if it was actually done. The o-ring on the pintle, lets call it, doesn't seal the gas unless things are just right. I think the kits have the pintle a hair too short maybe.

You can rebuild it again (a good how-to is on this site). Or you can replace it with the vacuum petcock manual replacement that Mike's sells, or you can put a $5 lawn mower valve from an auto parts store in the line between the petcock and the carbs and use that for a cutoff. What I did eventually was take the guts out of the vacuum petcock and put the two halves back together with a gasket, and plug the vacuum hole, and use a lawn mower valve. Not the safest thing maybe. It needs one of those things first thing though. Cheapest thing for the time being would be to just stick the lawn mower valve between the petcock as it stands and the carbs.
 
I've never really dealt with carbs before, (besides cleaning) and I'm a bit unsure where the O-Ring that could be no good is. Can I get a picture on where it could be? :p
 
Last edited:
IamTheMarcus said:
how do I work the pins out that the floats are on?
Click to expand...

Here is the way that is least likely to break the posts the pin goes through. Take a small diagonal cutters and work it under the head of the pin. Easiest if the cutters are sharp and thin. Then rock the cutters back to get the pin started out. Once it's out 1/8" you can just use your fingers. It doesn't have to go back in quite so hard; you can leave a little gap there.

The one I have is a lot like this one. I think I've seen them at Radio Shack. Electronic repair parts stores and the like.

Note how the handles are on the table but the blades are angled up off the table.

toolboxcutter_LRG.jpg
 
As long as the posts, that hold the pin, are braced then it is easier to get it out.

Here is a link to a very good write up, (Pictorial), on repairing and refurbishing the Yamaha petcocks, Vacuum and non vacuum. some will say the vacuum petcocks are no good and others like them. personally i like them because they are a use and forget item.

I think a lot of problems with them, is 90% of these bikes have been sitting for so long the o rings dry out and then when they are used again problems occur down the track.
 
The whole top end of the motor needs to come off. For that to happen, the motor needs to be removed from the frame.
 
Slow down. ...........Don't get ahead of yourself..........Have you done the compression test yet?

Just because there may have been some excess fuel does not mean there has been any damage to the cylinders yet. Running with an excess fuel problem will cause damage in time.

Clean the carbs rebuild the petcocks, once you have those 2 things working properly then get the engine running. Do the compression test on a warm engine .

May be no problems, but the test will help with a diagnostic and if there is some smoke then you can think about where to go from there.
 
Once I get the carbs rebuilt and cleaned properly (Same with the petcock, though probably buying a non-vacuum one), I will indeed check the compression. I'm not going to take the top end off at this point in time. :p
 
Well since the winter really stopped me from doing any real work on it, when I took the gas tank off the bike, gas was continually flowing out of the petcock (When it shouldn't be). So I am assuming the left cylinder was getting flooded. There was a little washer that I must of misplaced putting the petcock together, which went inbetween the lever and the metal plate that says "ON" "RES" "PRI" and I had it under that. (If that makes any sense whatsoever, since it's hard to explain.) I drained the oil, which was gas/oil since the gas must of leaked down into the crankcase, waiting to buy a new filter and oil. But hopefully when spring rolls around I'll be able to see if she fires.

HELP: I don't seem to be able to find 20/40 oil. So which oil would be the next best/closest? Since I live in Wisconsin I will ride her when it gets cold also.

Thanks!
 
Yeah the "wave" washer that is supposed to push the selector disk against the seal, that would do it LOL.
New rubber parts in the petcock?
 

Similar threads

R
Another dead cylinder problem.
Replies
4
Views
609
jpdevol
jpdevol
P
Semi-generic carb theory question
Replies
8
Views
753
Pat D
P
willis
Exhaust squeak.
Replies
4
Views
687
willis
willis
T
First motorcycle and a cylinder not firing.
3 4 5
Replies
84
Views
6K
5twins
5twins
WV Sparky
Throttle stumble just after idle
5 6 7
Replies
124
Views
8K
WV Sparky
WV Sparky
Back
Top