Hi all, happy new year. Posted here before about my sons pride and joy tat had a no charge issue that was solved with help from here. Hes been riding it and loving since last early last year. Last winter we did a full rebuild of motor,top end and bottom end and was running great for a while, a month or two then it stopped running and he was frustrated on left it. This is where the dad in me steps in and wants to fix it for him.Spark seemed erratic so a new coil was installed and it barley started but did. Convinced it was carb a cheap amazon was bought and crudely installed,it ran,kind of. He purchased some mikuni carb body's from e bay and have tried 3 different carbs all cleaned in ultrasonic and blown out. Case as been pressure tested with only a very very small leak on head gasket. Timing has been confirmed twice, 3mm BTDC, 
So today here's where were at, starts up cold first/second kick then sounds like it runs out of fuel and dies.Pull plug, wet, has spark, clean it and heat it, reinstall, fires up and sounds like it runs out of fuel. Do that procedure again and kick it forever and no fire BUT pops through the exhaust once and a while, hence why timing was confirmed again today. Im very suspect of the ngk br8s plug, even though its what the manual says to run, I feel plugs today are garbage.
Both him and I would love this sorted, he's at the point of paying big $ to have a shop look at it, I'd rather him save his money saying we can sort it but man is it frustrating.

 

First thing to do is to make sure that the pilot jet is a) not blocked and b) the correct size.

I would run it with a standard B8ES plug, not the one with R (for resistor) in it.

In addition to what Al mentioned, I would like to add a few other things to consider:

* verify fuel valve is clean. Just open the valve and let it flow in to a container.
* verify VENT on cap is VENTING. There is a small vent hole setup.
* set timing to 1.8mm, with yoke open. I believe 3mm is wrong. I have the A model. I thought they were the same bikes.
* verify floats set
* verify fuel valve clean/functional
* pull reed valves for inspection while carb off
* condenser check for 0.22uF
* compression. tighten head gasket

What Uncle Al and Paul said but add this on too.
Take an air hose to the vent tube on the gas cap. (we had a spider crawl into the vent hose and blocked it up proper causing it to run crummy with hard starts.)
Also, could be time to clean out the exhaust for better performance and easier starting.

Pull the flywheel & check the key. If broken then do it up extra tight next time.

My mistake, it is a b8es plug, no r.
Have verified the fuel flow but interesting suggestion on the vent hole, will check tomorrow.
Pulled exhaust, free flowing.
Reeds seem ok, 1 "pedal'? has some gap but very minimal, .005 maybe.question about reeds, i'm use to 4 strokes, if I put reed block to my mouth and suck in forcing pedals to close, I still get what I would say is leakage meaning its fairly easy to draw air through reeds, normal?
Float is set at 21mm
Interesting about the timing, the manual says 3mm, your suggesting 1.8mm?
Will check condensor tomorrow as well.
Has others had luck with warming up copper head gasket and reusing?
I would assume pilot jet is correct size as all 3 carbs are stock size for this bike.
Thanks very much for the suggestions and will report back.
 

Timing is 1.8mm or 72 thou--ingrained in my memory as worked there then--Yamy shop.
So i'll say again--Flywheel crank key gone west.
Unless i'm late to the party & it's been checked. Good luck.
Ps, if you've been setting the timing at 3mm then in theory the gap must be very wide.
Probably still shutting but there'd be a limit where they don't shut if the adjustment has that much movement.

Timing is definitely 1.8mm BTDC with advance blocked open.  Not sure where the 3mm spec came from or how you're measuring piston position.  Plug gap needs to be 0.020" to 0.024" which is often overlooked as new plugs tend to come pre-gapped at around 0.032"

Comment I have is that it could be as simple as being flooded and/or needing a new spark plug.   

When I was a kid, I left the petcock on countless times overnight which flooded the engine.  If it wasn't flooded too bad, it acted exactly as you're describing, start and die.  But it obviously wasn't out of fuel because the plug is WET!

The whole "clean and heat the plug" was something I did a lot of.  But that trick didn't always work.  Oh sure, it would start briefly again but the cleaned plug would short out right away.  I would use either the gas stove (if mom wasn't home!) or a propane torch to heat the tip dry.  Only fix was to replace the plug.  

Beware that there are a lot of counterfeit NGK spark plugs out there.  I prefer Autolite 4054 instead of the NGK B8ES and they are readily available at most automotive parts stores in the USA.  

One more thing is that US model had electric start with a generator.  Critical to connect a voltmeter to the battery and see what the voltage is while you're trying to start it.  I've seen that model have enough power in the battery after sitting to kick start and run a few seconds but then voltage drops like a rock and no more spark.  

It is a e start model, my son did say voltage was critical so I will check even though it has a brand new agm type battery.
The 3mm comes from the yamaha manual we are referencing, but I will change the timing. Its has been 3mm ever since the day we first set the timing, so years.
I will see if autolite 4054 is available in Canada,interesting about the ngk being counterfit. I remember trouble shooting a problem in a bmw mini and 3 out of the 4 plugs where not firing. Plug these days aren't what they use to be.
Looks like I have some things to do in the shop today,Thanks!!

I'm guessing a bit that if it's an electric start model and if the timing was set at 1.8 with advancer closed--then when started it'd probably go to about 3mm.
But that's not right as should be 1.8 when advanced & close to tdc when retarded.