What is this carb screw for?

[Yamaha Tri-Moto]

ATC 350X



What is the screw circled in red for?

Whats a good starting point for turns for the idle screw in blue?

The manual says 1 3/4 turns for the fuel screw on the bottom.

Will the stock carb and jetting work well with a supertrap exhaust or do I need to rejet it?

Thanks

[x-rider]

The screw in red is to drain gas out of the carb bowl. Hard to tell from the picture, but the blue one looks like a remote air mixture screw on a bracket? The screw is on the bottom of the carb pointing down.

[El Camexican]

The red one is a drain plug for your float bowl. You can also use it to connect a clear hose and check you float height.

[Yamaha Tri-Moto]

Ok I'm happy to hear that it is just a drain screw.

The main problem I am having is it strarts right up easy in 1 or 2 kicks when cold, but after it runs for a few minutes its almost impossible to get started again unless you let it sit for an hour or so. When it's warm it also has a ton more compression, I'm a 200 pound guy and am pretty good with kick starting but this trike is killing my foot. The previous owner said he had the decompression thing fixed but i'm not so sure.

[BOB MARLIN]

If the decomp wasn't working I doubt you would know it, unless it has a high comp piston. There is a definite starting sequence you have to follow or the 350x can be a pain to start.
Slowly move the kick starter untill you feel it come up on the compression stroke. Then as you feel it go just past top dead center let the kicker lever return to the top and give it a good kick.

I weigh the same as you and I can't really tell the difference between the x's I have that have a functioning decomp and the one that doesn't. The only time I've needed it to work is when I put A Goki on one.
You can watch the decomp levers move if you slowly actuate the kicker. The lever on top of the case will move, pulling the cable that is connected to the lever on top the head, and they don't move much. Most of the decomps break when someone isn't careful when reinstalling the clutch side cover. The little arm inside has to be in the right location or it snaps off the mount when you tighten the bolts.

[El Camexican]

Starting off with I don’t know anything about the 350 X, it seems odd to me that you say it has more compression when it’s warm. That almost sounds like the ignition timing is too far advanced.That’s something that would typically cause harder starting as well.

Again, I don’t know anything about that engine, I don’t even know if the timing is adjustable. Hopefully someone else will pipe in here.

[Yamaha Tri-Moto]

Thanks for the tips

Turns out my decompression cable snapped after I got it. Is it common for these cables to snap or did I do something wrong while kicking it over?

I also removed the gas tank and discovered someone had cut a huge hole in the intake boot, so I taped that up. Hopefully that solves some issues.

I see a lot of posts on here about trouble getting the 350X started, looks like I just need to figure out the process. Fun bike though.

[350for350]

Mine didn't come with a decomp cable and I don't plan to put one on it. Mine seems to like just a touch of throttle when it's warm. I have to touch the throttle when the kicker's about half way down or it will kick back. I also never ride it without wearing MX boots.

[wonderboy]

The screw that you circled blue in your picture is your idle adjustment (throttle stop) screw. It is the one that adjusts how far the throttle slide and butterfly close when you let off the throttle. The fuel screw (pilot screw) is a small screw that goes vertically into the bottom of the carb (circled in red below). This is the one that is initially adjusted to 1-3/4 turns out to start.

[Yamaha Tri-Moto]

The screw that you circled blue in your picture is your idle adjustment (throttle stop) screw. It is the one that adjusts how far the throttle slide and butterfly close when you let off the throttle. The fuel screw (pilot screw) is a small screw that goes vertically into the bottom of the carb (circled in red below). This is the one that is initially adjusted to 1-3/4 turns out to start.

May be a dumb question but since I have a super trap exhaust on it would I have to turn that screw out more or in more typically? It's currently at 1 3/4 When I adjust that screw now i don't notice much difference in the way the engine idles. Do I need to ride it to notice the difference between adjustments?

[350for350]

You may not have to adjust it at all. You'll probably need to change out the main jet for a bigger one. You also may have to adjust the needle as well.

[wonderboy]

I'm definitely not a carb tuning expert, but from what I know, the pilot screw is the main contributor to the mixture while at idle, or more correctly with the throttle closed (engine can be coming down from a high rev with the throttle closed and this is what is governing the mixture). As you open the throttle, the main and other jets begin to have more of an effect on overall mixture. My thought is that exhaust systems typically are to help with breathing as you open the machine up (higher revs) so I'm guessing that you won't need to adjust the pilot if the only difference is the exhaust (assuming it was correctly set before the exhaust). For what it's worth, if you want to adjust it, the accepted convention is that since the screw is on the cylinder side of the carb (as opposed to the air intake side of the carb) it is metering fuel, so screw it in to reduce fuel (lean it) and unscrew it to increase fuel (richen). Again, this is primarily for throttle closed mixture adjustment.