Let's see if we can get a SVS article together. Post what you know about SVS.

http://www.liquidcooledairpower.com/lc-topendheat.shtml scroll down to sticky exhaust valves.

Musky, I know you already have access to Yamaha's technical bulletin related to this subject, but thought I'd help out by dropping it over here to help where I can to consolidate the available information.

http://weislake.com/sig/mucker/2-16-07.pdf

Thanks!

Symptoms may include :
1.Carbon build up on the plugs and in the pipes (almost always on the rear jug)
2.Starts up fine and runs poorly after running and the valves start to stick.
3.Puts on one hell of a light show at night while backfiring (can be like riding a bucking bull.
4. Compression tests give different results after each test.
5. Hold a dollar bill to the suspected pipe and it will suck it in and blow it right back out.


.....just to get you started....Coug and please dont tell me you read the same thing somewhere else ....

OK. Typed this out quick to get things started. I'm sure I forgot things or said something wrong. Hop in and fix it, add to it, subtract from it.......

SVS = Sticky Valve Syndrome
It is when the exhaust valve in the rear (usually) cylinder gets fouled and doesn't close all the way or stops moving all together.
Some symptoms:
The bike will start fine but within a short distance it will lose power, run rough, backfire, there may be flames shooting out of the rear cylinder pipe, If you hold a piece of paper over the rear cylinder pipe it will suck in, blow out, suck in, etc, there will be a very different sound to the exhaust note between the front and rear pipes. Compression will be low on the rear cylinder when checked. In many cases after the motor is warmed up well it will run fine.

Cause(s):
Carbon build up from being jetted too rich, unburned or partially burned fuel or poor combustion . If the bike is jetted too rich it will result in an excessive build up of carbon on the exhaust valve stem and or seat. This can also be caused by lugging the motor or burning premium gas. Also by using too much choke or leaving the choke on too long. And coking. This is when the oil lubricating the valve stem burns off leaving behind deposits.


Too much oil:
If the oil level is too high it will overflow into the crankcase vent hose, run down into the airbox, and get sucked into the carb and burned. Causing a build up on the Valves.

Too tight of tolerances:
The clearance between the valve stem and guides may be too tight. Causing the valve to stick with minimal build up.

Possible fixes:
Temporary:
Run Seafoam, Ringfree, or MMO in the gas or spray directly into the carb throat to clean things up . An oil change may be needed depending on the method used. (See note 1)

Preventative - Easy and first:
Jet leaner.
Keep the RPMs up on the motor while riding.
Don't use the choke anymore than necessary. (See note 2)
Run only regular gas.
Lower the oil level. Run 4 qts max.
Use oil with low ash and high flash point.

Mechanical fix - If nothing else works:
Pull the heads and ream out the valve guides. Also install stronger springs. After reassembly follow the other fixes stated above to prevent a re occurrence.

Things to read:
Heat

Tech bulletin

Note 1. You can do a "Shock treatment" which is pouring the entire can of Seafoam, Ringfree, or MMO in a full tank of gas and running the bike hard until the tank is empty. This method requires that you change the oil immediately after the tank is empty. You can add 3 or 4 ounces of your cleaner per tank for as many tanks as needed. This does not require an oil change. You can also spray the cleaner directly into the carb. this does not require an oil change either.

Note 2. The "choke" on the Roadie is actually an enricher. It doesn't shut down air flow. It gives the carb more gas.

Blip

Musky


A possible cause is coking which mentioned in the first article when the oil lubricating the valve stem burns off leaving behind deposits....

Use oil with low ash and high flashpoint....

Under causes ....carbon build up by unburned or partialy burned fuel or poor combustion ..also mention changing the oil after a shock treatment of cleaner..and as Doc would say it is an enricher not a choke since it changes gas flow not air intake and I hope I am not getting getting picky here as it is good to see someone putting this some where to be viewed ....... Coug

Thanks Pop

Typing faster than my brain works. And I'm a slow typer.

We'll get back to the cooked oil on the other thread

Musky

It is COKING oil

Coke is the solid residue remaining when oils undergo severe oxidative and thermal breakdown

Cheap oils will undergo breakdown sooner and faster....especially dino oils..dont be surprised if yammi suggests use of their fully synthetic oil as a possible preventitive measure..now that they have one

Yamalube Full Synthetic Oil

and could possibly be the prime cause of SVS we have been looking for