I've got a restore just completed that idles but bogs down before the powerband (maybe 1/2 throttle) and stalls with a wet spark plug.
The slide need in the carb is Y75 (middle position). The stock needle is supposed to be 5G4. I assume the needle is wrong but I just wanted to check here for verification and I'm also wondering if anyone has one to sell. Looks like there is a rebuild kit in Germany on eBay but just checking here first. I can't imagine the person before my changing the needle but maybe they did.
The carb body is Mikuni 443 62

Thanks!

If you're read posts here on carbs, you'd have seen many warning against "carb kits"... specifically using calibrated parts other than perhaps the float needle and seat from a "kit".

Your "Y75" needle sounds like a "kit" needle. Other jets have probably been replaced with questionable parts from a "kit".

Best bet is to source and buy original Mikuni parts from Yamaha or from Mikuni. Stay away from the "kits".

if you got the wrong needle based on the Yamaha manual, then you should get the correct one for sure.  Probably need to check the "Jet, needle" that the needle slides into
Would also check the main and pilot jets too...I once took correct main for granted and melted my engine.
You should be able go onto eBay and find correct one, or Niche Cycle in FL has lots of stuff as well as Partzilla.  Do not use any jets without the two Mikuni squares because the prevailing opinion of experts is that they are not accurate.

Regarding the bogging...might want to try with air cleaner out and/or silencer off....the latter could be clogged up and impacting things, wrong needle or not.  But I would start all of this with the proper needle, needle jet, pilot, slide, etc.

good luck!

I checked all the other jets and they are stock numbers. Just the needle was different so I just thought I would check here first.

"Kit" jets often are marked with the stock numbers.  Do they have the Mikuni "Square within the corner of a square" trademark symbol?

 

They are all stamped. But I did have a carb rebuild kit from YamBits which included that other needle as well as a main jet and and idle jet. I found the original jet and put it in and still had a similar issue. Too rich.

Then I removed the air filter and it seems ok now. I think the air filter was from Yam Bits and it is oiled. It must be restricting too much. I wish you could just put all the stock parts in and it would run right. Still needs some tuning.

Thanks

Y 75 is a Keyster number . A stock Mikuni needle will likely cure your ill's .

"I wish you could just put all the stock parts in and it would run right."

They generally do.  Problem is you aren't using "stock parts". I'll repeat myself...  if you have a Keyster needle you most likely have other "counterfeit" jets even if they have the original numbers on them.  Important that they have the Mikuni symbol and they all will if original...  even the tiny pilot jet.

Some kits have original numbers stamped on parts...  does not mean they are the same part.  Many counterfeits out there.  I've never seen a "kit" that came with original Mikuni parts so important to look for the Mikuni symbol. 

On the air filter, foam could be inferior or over-oiled as you said.  Modern "sticky" air filter oils don't work well in my experience.  Twin Air filter oil is the exception...  it's a "dry oil" or something...  I've been using it since the 1970's. 

Yamaha does still sell the air filter. 

 

Thank you. Yea, I have all the old stock parts in and got it working without the filter. Will try removing the extra oil.
Dumb question... Is the choke on when it's out or in? Pushing it in covers the air hole from behind the carb to above the slide and forward so I assume it's on when out. But it just seems so counter intuitive.

Jeff

Pulling the knob out is the "cold start" position.

Knob pushed in is "normal running".