Piston on my secondary carb doesn't open even on full throttle. We figured this out by using mirror and looking at it through air intake.

It is not stuck. It goes very easy.

From where it gets vacuum?

Does air vent hose needs to let air both ways? Or only one way? What is the function of plastic (barrel like) element on it?

Any help would be appreciated. My friends are leaving for a trip on Friday and I would really like to join.

Velja

Membrane does not have holes on it.

From where it gets vacuum?

What makes you think the slide is not opening??


Air flow through a venturi creates the low pressure to raise the slide.
It is explained in the Yamaha manual.

Note.....you can't check the opening of the second slide without proper LOADING.
You would have to rev the engine to 8000rpm for some while and risk a catastrophic event!!

Engine must be connected to a dyno to check or the carbs removed and fitted to a flow bench.

As I said. We open airbox. Placed mirror against air intake and light into it. I open throttle to the end and piston doesn't move at all. But I think you have the point. Thanks for that.

I believe this one is is turning wheels. I can hear them.

http://www.youtube.com/watch?v=gtSam0RgPl4

So in new light let me restate my problem :|

I have big chocking in mid range. I did put open exhaust. Spark plug is almost ideal little lighter then it was.

Motorcycle is unusable.

The rubber hose with the plastic barrel is a breather pipe, it should flow both ways, the plastic barrel is just a filter.

If the slider moves easily, there are no holes in your diaphram (membrane) & you can blow both ways through the breather pipe there is nothing wrong with the carb. As Actionman said, you need to load the engine or it will just breath through the left hand carb body.
You could start your engine, partially cover the left carb & blip the throttle. this might cause enough air to flow through the right hand carb to lift the slider.

As you have fitted an open pipe Velja, I suspect the chocking in mid range is a fuel/jetting problem.
You say the spark plug is lighter than it was, try lifting the needle in your right carb 1 notch (move the clip down) & see what happens.

Jetting can be a pain & take a while, can you refit your old exhaust?

Keep us informed, I'll check this forum a few times tomorrow to see how you are getting on

Rick

I just got motorcycle from Yamaha authorized workshop from carburetor repair. They failed. They say everything is in order but it doesn't work . I think they expected to clean it and send it back to me. I paid them some money for effort.

If not same it is worse now.

Choking is worse. It starts earlier. I mean on less rpm then earlier.

Now it fires with bigger noise when i release throttle -> through exhaust.

On idle it has some strange tjuf, tjuf noise in carburetor area.

One interesting thing. I thought (been advised from few people) that this is a lean mixture problem. But on my way home, during the ride, when it started working bad I gave it a little choke and it only worsen the situation to the point of shutting down.

I did a lot of reading last few days and at least I know how everything works now.

I am angry and ready to take it off an on 10000xTimes but I will make it work.

As before if anyone has any advice based on above i would appreciate it.

i am thinking about ordering few jets, and I thought about ordering ones with larger number, but after today ride home when I gave it little choke and it only worsen the situation I am not so sure.

I think that first thing what I am going to do is give it a ride and inspect spark plug again.

Just to be one with open mind. Do I maybe have electricity problem. Am I overseeing something all the time. Spark plug when I removed it last time wasn't bad at all.

Forgot to tell that I cant bring old exhaust back. I cut off part that goes on pipe to fit new one :|.

All this brings me to my first inspection of things when I bought motorcycle. Then I found copper wire in main jet.

Spark plug:

*3rd picture although worst is most representative in colors i.e. it is closest to what I see with eyes.

Check that the pilot jet is not blocked.It is down inside the hole in front of the main jet, a small flat blade screw driver is needed. Pull it out and make sure it is clean, it has small holes in it. My bike was popping bad on deceleration and chuffed and sneezed through the carbs ie lean. Found that the pilot jet was blocked.
Regards Eric

The tjuf sound could be an air leak, possibly the rubber mounts.

The problem with pulling the choke open is it lets a lot of fuel in, I've tried it myself when I thought I needed more fuel & had the same results as you, then I've either fitted a bigger jet or lifted the needle & got better carburation.
In theory opening the choke should have proved the engine needed more fuel, in practice it just confused me more.

And the problem with looking at spark plug colour is it only shows how the engine was running when it was turned off. If you rode the bike below the hole in your power & it runs smoothly, the plug will show a smooth running engine.

You can check for air leaks by either making sure the carb mounts are dry, then sprinkle flour or talcum powder (the stuff you put in babies nappies ) over the rubber mounts, start your engine, if the powder gets wet, that's where the leak is.
Or start the engine & spray a fine petrol mist or "easy start" over the rubber mounts, if the revs go up, you have a leak. Just be f*ckin careful & have a fire extinquisher ready

The easiest way to check carburation is to put your bike on a dyno with a gas analiser.

I would check for leaks then lift the needle 1 notch & see what difference it makes.

Rick

Thank you Rick. I don't know if I mentioned before. I got brand new rubbers from ebay. I checked them with starter spray after mount.

I also did close air inlet and after new rubbers engine shuts down within 10 secs with air intake closed. With old rubbers it was increasing RPM.

New rubbers only improved staring of engine. It doesn't need choke to start when its warm like before. And when you start it with choke it doesn't go to 4k rpms like before.

I am not sure that there is Dyno anywhere near.