I have had my bike for 3 years now and it has never failed me. This last month in the morning, after running with the choke on for a minute or so and slowly backing it off as RPM's pickup the RPM's start to drop and neither more or less choke keep the motor running. Giving it some throttle makes it quit firing. Just in the morning. I use my normal starting procedure. I come home for lunch and it will run as usual then, so I can ride it back to work. I tore everything off to check the plugs and run carb stuff thru the carbs and it still does the same. The plugs have a copper brown look and are in beautiful conditon. A couple of them were barely finger tight so it was a good thing I checked them. The motor acts like it does in the Spring when I first start it after it has set all winter. It doesn't like the throttle cracked any. Once again, this has only started happening this last couple weeks. The bike has been ridden maybe 400 miles this Spring and has been fine on a couple 100 mile trips. I live at 4000' and it has been out of town at around 4500' this last 3 weeks or so. It has had the usual 91 octane gas where I normally buy gas too. What is going on? Carbs need a better cleaning? When I had the tank off the vacuum line from the tank allowed me to draw gas thru the reserve gas line, I didn't switch the petcock to the main line though. That is about all the info I can give. I may take it to a local mechanic in the morning. Hope it is something simple.

I live in the northern Sierra where all the twisties are, 51, single, work on stuff when I have to or don't have the money to have someone else fix it.

 

I dropped by the only local bike shop (Sierra Yamaha, California) and a guy I know said it could be the carbs are a little cruddy. Told me to take it up a long hill and come down letting the motor pull some gas thru. Told him again that it has been on a couple trips already and I have been up to the lake a couple times already. I'm a thinkin I need to tear the carbs down regardless of how it runs the rest of the season. Andy also had a temperature sensor and put it on the exhaust header and checked the temp on each cyclinder. Number 1 and 4 were over 400 degrees after a short warmup and the two inside cyclinders were colder. He said he thought that all was not right with the carbs, the motor should run a little better.

Have a good day, off soon for a short ride.

 

Hey, So what ever happended with your F2? Did you find out what was wrong with it? I have a 94 600 f2 and mine will not start at all. I put new plugs in it and cleaned the carbs many times and still nothing. Let us know what happened with it when you get a chance.

 

Problem here is with the carbs.
Particularly the idle jet being blocked.
You need to get the carbs off (you dont need to completely remove them , just enough to turn them upside down)
Remove the idle jets (you need a small spanner or socket about 6-7 mm for these)
Soak them in boiling water (yes water!!) with a little washing up detergent and leave them to soak for a few hours.
After some time remove them from soaking and immediately blow them out with a hi pressure air line.
hold them up to light and you should be able to see through them (though it is a very small hole)
This is the most common jet to block first (as the hole is so small)
This jet controls the fuel/air mix for the lower half of the engines power & if it blocks up then the engine wont keep running (although having the choke on helps it a bit)
P.S. warm the engine up a bit if poss before removing the carbs as it makes them slip off easier.
Hope this helps ...Adrian (Scotland U.K.)

 

Thanks for the info. I'll have to do something sometime, I just hate the tight space.

Why would it even start then? I'm trying to think about this logically.

Since I work out of town and can only try this on the weekend, it may be some time. Summer stuff to do, backpacking, wood cutting etc.

 

It will start because the idle (or pilot ) Jets are not completely blocked.
Although as you stated 2 cylinders are running colder , I would look at the carbs first.(even unbalanced carbs should not be as drastic as you say)
I do all the m/cycle repairs at weekends for my friend who owns a garage & I am constantly removing and cleaning carbs (though he has an ultrasonic cleaning bath which makes it easier!)
P.S. dont forget to drain the carbs before removing them.
Good luck
Adrian

 

I have used fuel stabilizer in the winter when the bike is parked. It doesn't sound like it is helping the carbs very much. I don't like to start the bike when it is cold since it wouldn't run much and would drain the battery. I want to get a Battery Tender to keep the battery up, then I could start it up more and keep some gas running thru the carbs. My snowmobile is easier to work on, the carbs are right there. Take the air box off and the carbs are accessible. I had the pilot jets out of my dirt bike over a month ago, they sure have tiny holes. It has been sitting too. I need to go thru the carb on it I guess.

Bikeridingless in California,
Duane

 

So!! You soak carbs in boiling water?! Never would have thought that! Thanks!

 

I have never soaked the whole carb in "boiling" water , just the jets.
Although the I use an ultrasonic cleaning bath which cleans the entire bank of carbs & in warm water & detergent mix (but not boiling water)
Boiling water could warp the alloy casings!!
Mind to blow out the carbs immediately after cleaning as this is when the dirt is loose and easily blown out.

 

After coming off the hill from the lake and letting the rpm's drop with the throttle closed, my bike is starting up in the cool mornings ok. I'm assuming this drew gas thru the pilot jets or something. I also had a tank of Chevron Supreme to go thru. This morning it was in the 40's or low 50's which was cooler then it was at my moms house when I started having trouble and the bike ran without any trouble. I still am not sure I could trust it on a camping trip. The nights are cooling down nicely so I will have further testing as Fall comes on. Just have to get all my new parts on when they come in. Chain, sprockets, brake pads and soon another oil change.