How to set your pilot screw adjustment.

[stvemerz]

I will keep on doing what i've got going...just surprised that even light tan...it does not backfire...Right now I'm at like 2 3/4 turns out...and upon heavy throttle...I get a puff/fume out the exhaust..maybe back it in 1/4 turn....I'm starting to wonder...is the 152 main..to small....is there a 154....I have a 42 pilot...so I know thats good..and 3 down on clip....Not so sure....at least the main is easy to change....Any ideas..still looking for the paper brwon bag color...Will post again when I work on it...

[AbnMP13]

I'm not sure on how many sizes there are but I do know they are cheap.

[TRAV05]

newbie question where is the fuel screw on the 400exs or is it also called the pilot screw i just need to turn my idle up
thanks

[hornetgod13]

The pilot and "fuel" screw are the same thing.
If you need to adjust your idle than there is a different screw for that. The idle adjustment screw on a 400EX is on the left side if the carb. It's in the front side and it's a large straight slot screw. If you turn it clockwise it will increase the idle. Counterclockwise lowers the idle.

[MtnEX]

OK, I'm really frustrated and desparate, so I'm going to add a question to this how-to thread... because I'm not getting anywhere anywhere else.

I'm like the other guy... I had a black plug on all circuits it seemed on my 400EX... Full Yoshi Exhaust... K&N in stock box w/lid... 1200 ft.

I pulled the airbox lid and that was not enough to lean it out, so I went into the carb. 155 main, needle clip in the 3rd, 38 pilot.

I found the pilot screw to be several turns out... and the needle holder/needle jet not turned in fully, just partially and the locknut set. I also am not sure I was getting in the main due to adjustment.

I set the pilot screw at 2.5 turns out, screwed the needle jet/holder all the way in til it stopped, set the locknut, put the 155 main back and raised the needle clip to the second slot down..... after cleaning everything of course.

Now I seem to have a very light tan plug on all circuits, no popping or anything. I think with proper gas (shortage) and a regular NGK plug I might be more brown (we'll see).

What's driving me nuts is the poor starting. That first start of the day is a pain. It starts, then dies repeatedly. Then once it does run and get hot, the idle RPM increases a lot.

So I know I'm off. The trouble is I do not have the luxury of a cool tool to use to 'hot-tune' the pilot screw and idle screw together. So I have been using one adjustment a day on the pilot screw.

So far I think I have been from 2.5 out to 3.5... no change really other than I could tell the exhaust was rich... then all the way back to 1.5 turns out. I think I've been everywhere between 1.3 and 3.5 except 1.75 and 2.25.

I'm lost.... do these things have to be RICH on the pilot to start well?

[Ian400ex]

Originally posted by AbnMP13
How in the world do I loosen the screw on the 400ex, it's shaped like the letter "D"?

Haha, my thoughts exactly when I was jetting, I heard you can use a .22 shell but tbh I'm just getting one from dynojet like Ray said.

[Ian400ex]

Originally posted by MtnEX
What's driving me nuts is the poor starting. That first start of the day is a pain. It starts, then dies repeatedly. Then once it does run and get hot, the idle RPM increases a lot.

My starting use to be perfect and now it's as you described, weird, seasons mess with it any?

[MtnEX]

Yeah, season changes will mess with it and so will your filter.


Another thing it can be in compression... although nobody wants to hear that...

I know this now because a guy brought his here for me to work on because after his last ride it would not start for the next.

I went all through it and found a little, but not what I expected to find as far as a clogged pilot or whatever.

Then it would hit, but was way worse than mine. I mean we are talking almost killing a battery on a hot day to finally get it going. Once hot it didn't start back great but was nothing bad like before.

So I sat down and thought about everything. Then I pulled the tank and checked compression. I think the best reading I got on it was 90 PSI cold?

He didn't want to hear me telling him it was compression.... that I should be checking it hot and so forth... so I had to post a thread on here to show him...

I've seen this a few times so far. In this case it was the air filter passing dust and crap. Another was a fresh rebuild that ate the rings in short order. And another was just a guy servicing his bike... and I believe what happened is he changed his plug and stuff laying around it fell in the hole and eat it up.

[07RedRider400]

soon im going to have to adjust my idle speed because im going to be putting in a timing advance key which ive been told raises the idle speed.
however a couple years ago when my bike was stock (ive had the carb jetted by someone who knows what they are doing because of exhaust and intake mods) I tried changing the idle speed by twisting the throttle stop screw (silver one on left side with flat slot) and it just twisted back to where it was before.
i dont remember if the quad was running or not when i did this
but would it being off have caused this? if not how can i get the throttle stop screw to actually work and stay where i want it to?

[yelian103]

I've looked everywhere for this but can't find it. Do you happen to know the part# and the site that sells them? As you know there's no way of getting back there when the engine is up to temp unless you have the tool for it so I just set mine @ 2 turns the last time I pulled the carb to clean it. It's got a bit of a hiccup on idle which I'm sure it's due to the need of fine tuning. BTW, great info on jetting. Thank you.