99 yz400 carb issues

I am working on my friends 400, trying to fix the popping on decell...(a lean condition) so I pulled the carb off, inspected and cleaned everything. I found that it had a 170 main jet so I installed a 175 (per yamaha manual) and lowered the needle clip one position and installed a Zip-Ty fuel adjusting screw 1-1/2 turns out. It has a White Brothers E-series muffler 12 disc's also. I put it all together and tried to start it and fuel was coming out the overflow tube, I figured the float was stuck so I pulled it all apart and checked it out, didn't seem to be sticking but anyway I messed with the float level for a while and it was still pouring gas out! I then readjusted it to the stock level (9mm) and put it together and it stopped pouring gas out! :) So I then tried to start it...I did get it to start but I can not seem to get the idle set? It will start and seems to run fine with the choke pulled but as soon as I push the choke in it dies, every time. How can I get the fuel screw adjusted properly if it won't idle without the choke pulled? If I bump up the idle it doesn't help, it then won't start unless I turn the idle down again. Does the throttle cables have a lot to do with this problem? I adjusted them also and it didn't seem to help either!? I am pretty sure the slide was installed correctly (I was watching that carefully) Any suggestions????????????????? :)

Make sure the hot start button is nut pulled out or stuck. Same thing was happening to me last weekend after making adjustments to the carb, the hot start was out was the only problem (thanks to my buddy, I never use the HS).

I've got a 50 pilot, 150 main and JD red at 3rd clip with a Power Now on my 99 YZ400F for humid summer riding at around 1000-2000'. Stock setting for the fuel screw is 1 3/8 turns out I think. Also check the AP. When you take the bowl off, the AP piston linkage will come out of the lever causing a lean condition.

Lukejt

Thanks Lukejt,

Well the bike seems to rev up ok with the choke out so I would think that the AP is working correctly?

What do you think about the throttle cables? If I have to move the idle up so much, maybe the position of the throttle cable is not correct?

I do not use the hot start either but I was also playing around with that, it did not seem to be stuck, sometimes I would pull it after it was running and it would kill it.

What if I do have the slide upside down, would it run with the choke on?

Thanks Lukejt,

Well the bike seems to rev up ok with the choke out so I would think that the AP is working correctly?

What do you think about the throttle cables? If I have to move the idle up so much, maybe the position of the throttle cable is not correct?

I do not use the hot start either but I was also playing around with that, it did not seem to be stuck, sometimes I would pull it after it was running and it would kill it.

What if I do have the slide upside down, would it run with the choke on?

I'm fairly certain the idle speed control acts on the slide pulley, so it operates more or less independently of the throttle cables.

Sounds like your hot start works okay....

Also sounds like it is either a clogged pilot jet, maybe clogged pilot AIR jet (behind carb bell there are two air jets), or the slide is in upside down...

...if so the cutaway, well, there is no longer a cutaway, so you have no room for air/fuel at idle. The choke circuit contains air and fuel mixed so, yeah, it seems like the bike would idle on the choke alone if the slide plate was in upside down.

Hope this helps, good luck.

thanks Hick:

I am going to pull it apart again and check the pilot system and the slide. I hope this is it! :)

After you check what Hick said, you are going to have to experiment with different jets and needles etc. Just make one adjustment at a time and take a test ride. You will get a feel for whats needed and if your adjustment made an improvement or not. I'm pretty sure if the bike runs better with the choke on you need a richer pilot jet.

Last weekend, I was able to play with the carb for a few days and take back to back test rides. I ended up making the pilot richer, from 48-50 and making the main and needle leaner. Don't know why, but this is how the bike ran the best. I can wack the throttle open as fast as possible and the bike just rips. I think there is a bit of popping on decel, I've got a 155 main on order.

I've also got a White Brothers E series with 12 disc's. I used to have a DSP full TI system with a big megaphone pipe. The DSP system wanted a richer main, and had a different (more) power band for sure (I smashed the header). I don't race, and I like that the WB is much more quiet than the DSP.

Good luck!

Lukejt

Thanks Lukejt,

I all ready went thru the carb again, didn't find anything I could see. The slide is in correct and I took a piece of a nylon bristle and went thru the jets and I think that the pilot jet had some crap in it, but it was not a lot?! If I still have the same problem I will be getting some larger main jets to try.

I appreciate everyone's input on this and trying to help me out! :)

Well I bought a 48 and 50 pilot jet, installed the 50 and the bike seems to start and run great now! I'm going to take it out this weekend for a full try out!

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