We have mostly quads, but this is actually a 2004 125 TTR Yamaha dirtbike. I ASSUME it's probably the same engine as a Breeze or Mini-Grizz. This carb question should be pretty generic tho.

I have adjusted the valves, and they're perfect. When I choke the carb for a cold start, it takes 3-4 kicks to get the first start. I notice gas comes out the overflow on the carb too. It quickly stalls, then about 3 more start/stalls, it will finally idle high with choke on. It's a little rough/finicky, and wants to stall. You have to be very careful with throttle, or it will stall.

Once it's warm, it runs like a dream. Should I take carb apart? It runs and idles perfect once it's warm, so I can't see jets being an issue. But what's with the gas overflow and hard cold start???

Air filter is clean (this was causing poor cold start before). Spark plug is pretty new (only a couple of hours on it).

 

Those carbs have some extremely small pilot jets, and its posible this one is closing up. How many turns out is the mixture screw?
If you do remove the pilot jet, just replace it with the next size bigger.
The reason it overflows, is the needle and seat are probably a bit crusty, so clean them good when you replace the jet.

 

I've never checked the mixture screw, nor have I had this carb apart. It sounds like it wouldn't hurt to get in there and have a look. The gas only overflows on cold start, choke.

I thought pilot jet was just for idling?

 

Pilot jet is for closed throttle operation...choke on or off. Sounds from your discription that it is lean (runs better hot, dies when cold). Make sure the mixture screw is at least 2 turns out, and you could probably go to 3 to 3.5 turns out. See if that helps. But the best fix is a larger pilot jet. I think the stock is 12.5, which is the smallest made. A move to #15 would make a huge difference in cold starting.
Its possible that the enrichener is leaking, and thats causing the overflow when the choke is on. Once the motor is warm...if you pull on the choke...does it overflow then?

 

Do yourself a favor and shim the needle with a small washer. It made a HUGE difference when starting in the cold and took out the flat spot in mid-range.

 

i had the same problem with mine. try turning the gas off. that sometimes will hellp because when you don't turn it off, all the gas in there will just be sitting in there but if you turn it off then it keeps the gas up in the actual gas tank. i also got my valves adjusted on mine which helped a little bit.

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2007 yamaha wolverine 450 SE
2004 yamaha blaster
2005 yamaha 125

 

thanks very much guys. I went to yammy today and mentioned both suggestions. HB, yammy parts guys agreed the ttr 125 has had issues with cold start. they told me to go to 20 pilot jet, and play with the mixture screw a bit ( a little further out). DT, they said shimming the needle might also help. I'll try both.

 

The bigger pilot like HB said will really help you out. My daughters had a flat spot right off of idle so the shim REALLY helped that deal out. One of these two or both should really get your quad in shape starting wise.
Let us know how things work out for you.

 

hey DT, why didn't you lower the clip on the needle (to raise the needle), instead of a washer/shim? I asked the Yamaha guy about what you suggested and he said there should be a circlip on the needle to make this adjustment.

 

There is no multi groove clip on my needle. I think it is a 99 or 2000 Breeze. I wish it did have one but it was no biggie. Mine had a flat spot off of idle and that fixed that problem right up.