Timmay4 wrote:
So I hooked that tube up- turns out it goes to the air filter housing- just a breather tube. No vacuum involved- It didn't change how it ran. The bike starts and rides fine with the TPS disconnected and everything else hooked up. Its only issue is from an idle when I crack the throttle , if I do it too fast/too much it backfires out the carb, and wants to stall out- if I roll on the throttle its fine.... does that sound like TPS? Or should I be looking for further issues still? I'm thinking I may have to take the carburetor back off and go thru it again- I know its not an electronic issue unless its timing related- your thoughts? TPS is still 10 days away- will go thru the carb again- is there a specific jet you suggest I replace that may cause this issue?

We *Really* need to know what your carb's current jetting is in order to help sort it out, Timmay. You've gotta delve into the Scary interior of your carb and see what jets are in it.
First, get a small mirror and look at the under side of it. See if you see two brass plugs under there or just one.
Let's start with that and we'll go forward depending on what you find.

tore down the carb on the weekend again. My carb is a Mikuni BSR40. Jet sizes for main is 170 (comes up thru the top of carb,pilot 35 (unthreads from bottom) from what I could make out of the numbers. I cleaned everything again and took for another ride. Almost flawless except again at idle once in a while would fart and cough. I rode for about an hour. When I got home I tried going from closed to WOT and it would stutter then grab and rev out. On slight throttle it would starve for fuel. I just got my new TPS in the mail today. I bench tested it immediately- very concerning. from the positive on yellow, and negative on black, I got a variable voltage depending where I moved the TPS - which I expected- I can adjust this to range once installed. I tested the positive to blue and negative to black as per manual and I got infinite. I tried testing over and over to ensure I wasn't getting a misreading etc. Unfortunately I either got a faulty part (which this is a genuine Yamaha part) or the manual is wrong, or I am doing something wrong..... I'm going to disassemble carb again tomorrow. I'm going to pull out the pilot screw and adjust to two and half turns out and see if that helps. The bike idles great, runs WOT great- I don't think this is electrical. Also when I pull out the choke part way the problem seems to disappear for the most part- I will update once done tomorrow- any further tips or advise? What about the coasting enrichener diaphragm? My other thought is go buy an after market carb and get rid of all this crap (I also left the fuel heater and sensor unplugged on the last ride- infinite resistance means it won't heat fuel- don't need them).
Thanks

pic

Throw the #35 pilot in the trash and install a 37.5 pilot. The 170 is correct. The clip on the needle should be in the 4th groove down from the flat end. PMS at 2 1/2 turns out. Is the studder when you go to WOT just you hitting the rev limiter @ 4250 rpm? It hits pretty quick in the lower gears.

The blue and black should measure 4 - 6 KOhms or thereabouts depending on the temperature. Obviously the resistor is connected at the black wire or you wouldn't get a reading with the yellow wire. Try checking the resistance between the blue and yellow wire. This will tell you if the blue is disconnected at the end of the resistor. The reading isn't important just shouldn't show open. If there's no reading then the TPS is in fact bad and the dealer should be able to return it for a new one.

Since you haven't installed it Yamaha should accept it back.

Thanks- I just got another one today that tested good- unfortunately as I figured bike still has the same stumble. I've done an ohm test on my pickup and it reads within spec- and it was just replaced two years ago has less than 200 hours on it.... comes in about 280 ohms within spec.... I was told to also check the voltage of it (the pickup could be rubbing slightly on the reluctor tab and possibly causing an issue with the coils- what should that voltage be?

Following this, I'm going back and testing leads, caps, coils, wiring from CDI to coils.... I know how to do all that.

I've also traced out my wiring as per diagram. Here's my remaining questions:
-These other items are all connected to the CDI unit. Which ones could interfere with spark (not just starter)?

-engine stop switch (though you'd think it would do it all the time not just low RPM and stutter).
-Side stand switch (though doesn't seem to make a difference in neutral or in gear)
-decompression solenoid (possibly slightly sticking?)
-Speed sensor (spedo works fine)
-ignition switch(key is worn but don't see an issue with the switch itself (on or off)

If I can go thru and do a check on these all again- and understand if the above switches could have any possible effect then I can outrule ignition... then back to carberation.

Thanks
Tim