Hi guys, I've got my DT175 running and it goes pretty well, but I'm still chasing carb issues and I have come across something which may be causing me some issues. My chassis code is 3U5050619, which seems correct, my cylinder has the code 2A7 00 on it, which also seems correct. But my carb has the numbers 3U5 00 on the side of it, with jets, needles etc which seem to match what a 3U5 carb should have (160MJ, 20 pilot), but the info I have says it should have a carb with numbers 3J1 with a smaller main jet (150), and different pilot and needles.

Could this be causing my issues? there seems to be variation between information in manuals/online as to which MJ and pilot sizes I should have. Can anyone shed any light on this?

Another issue I have is that the bowl keeps leaking out the overflow which may mean the float needle needs replacing, but I need to know which part to buy

Thanks

First thing I'd do is fix the carb from overflowing, that may fix whatever issue you are having. Then go from there...

ok can anyone point me towards a 3U5 float needle? I cant find a patr number

A 3U5 model was for the Oceania market....  3J1 was for the US market.   Most info on the Internet is for US models.

I'm certain with a 3U5 VIN, the 3U5 spec carb is correct.

I would install a larger pilot jet from my experience... at least a 22.5 or 25.  (I use a 25 in mine)

Without seeing the carb, one can only assume it would be the same basic type as the 3J1 with different calibration?  (Unfortunately picture hosting here is not working at the moment...  you have to use a third party host like imgur)

Any good Mikuni distributor should have the parts you need.  The needle and seat will be a certain type...  and within that type there is a size that should be stamped on the jet... likely a 2.5 or 3.0...  you may have to remove the jet to see the stamping.

Easiest thing to do might be to simply contact a Yamaha dealer in your country and see if they have and/or order the needle and seat?  Yamaha is a great and often overlooked resource for parts.

Or try the readily available from Yamaha USA 3J1 part 1V0-14190-25-00

Here are a couple of links to Mikuni dealer Niche Cycle...  they often show pictures with dimensions... 

www.nichecycle.com/ncs/categories/carbur...g/needle-valves.html

www.nichecycle.com/ncs/categories/carbur...-seat-by-mikuni.html



 

Thanks for that, do you know how to remove the (I think) emulsion jet? That the needle valve sits in? I have removed the main jet and o-ring, but cant seem to get the brass fitting above it removed

I think that it is a push fit, so tap it gently.

I had to tap mine out for the DT400 , it was stuck fairly tight.

Do you tap it out from the top?

I don't remember but if you look down the tube you'll see where it has a grove in it that corresponds to a little nipple inside where the tube fits into the carb then it will become obvious which way it comes out.

No Mikuni I've ever seen has the needle jet (emulsion tube) tapped out from the top.

Main jet (or jet setter on earlier flange models) with thick washer holds the emulsion tube in place. Remove the main jet and washer and tap it out from bottom out the top of carb.

The only emulsion tubes that come out the bottom are the ones that thread in from the bottom... they just unscrew.