[SSTAT]

Its not a murder mystery. I have A 2002 400EX with a full HMF exhaust, K&N and stock lid. Ran perfect for the three years I had it, rarely had to choke it in cool weather. Finally it died suddenly, it had the original carb and I tore the accelerator pump rebuilding it so it was cheaper just to buy new. I found out when I took it apart the prev owner never jetted it like he said he did. Anyway new carbs come with the pilot screw sealed with a plug. So I pulled it out, had a dealer use the special tool to remove the new "D" topped pilot screw and I replaced it with the one in the HMF kit (42) at the same adjustment as the old carb along with the 160 main. Thing is it felt loose, like no resistance at all when adjusting the pilot so I was afraid it would come loose out of adjustment so I put a dollop of silicone over the top of the screw just to keep it steady. I rode it last fall and it ran fine but felt just a little more sluggish than before. Now this spring it will only start with full choke, after 30 sec at half choke it pops and sputters with any throttle input, then it starts to die but runs better back on full choke, then sputters with any throttle input, then just dies. After a couple of minutes it starts right up and does the same thing. Any attempt to turn the choke off completely kills it. Im wondering if the new design pilot screw is a larger diameter than the old one, or maybe a new design altogether, maybe I should just slot the "D" topped screw that came with the new carb and use it instead? What did I do wrong? Thanks -

 

[mrbb]

have to ask, is the NEW carb a OEM carb, or a china knocks off?
if NOT oem, well?? most aftermarket carbs are many times JUNK, hit or miss on quality IMO!
if you have old carb, and its original, maybe buy a rebuild kit for it! and try that one again!

next will be, sounds like this NEW carb needs a carb cleaning, carbs are not really clean and forget about them a YR is a long time fort things to go wrong from a small particle to get into a carb, or more likely this crappy ethanol fuel, causing issue's with just IT causing carb parts to get coated with gunk/varnish like film and throw off settings and how it flows fuel and air for you!

 

[joeyou]

It sounds like like fuel starvation. Are you sure you're getting gas from the tank to the carburetor? When you're having the issue (when it dies) immediately loosen the carb drain screw and see if you have a steady flow of gas coming out of the carb. If it's getting gas, have you checked to air leaks between the carb and the head?

 

[SlammedRanger]

There is no way a oem 400ex carb (250.00) is cheaper then fixing the accelerator pump diaphram. (15.00) so my bet is its a china carb. Which is best used to hold down papers on a desk. If somehow you found a oem 400ex carb new for under 20.00 dollars i need to buy every single one they have so i can make some serious money selling them for 200 dollars. My .02

 

[SSTAT]

Its an OEM carb from a honda dealer. I literally installed it, rode it around the yard for 5 min and parked it. Man, slammedranger I looked everywhere for just that diaphragm on the internet and I couldnt find one anywhere, this was last fall. The thing was running so perfect I really wanted to reuse the carb, I did rebuild it but when I put it back together I pinched the diaphragm and split it, ate the cost of the rebuild kit. Oh well. When its cold it idles and revs just fine, this makes me think its an idle problem ie. the pilot screw, you guys dont seem to think so. I appreciate the feedback, I'll check those things mentioned.

 

[SlammedRanger]

When you put the mixture screw from the hmf kit in the carb did you put the o-ring washer and spring on its pointed end and the other o-ring on the other end in the groove near the flat tip side?

Btw. Rockymountainatv will have the diaphragm. And any place that sells oem parts will aswell.

 

[SSTAT]

I tried! I put in the oring down toward the pointed end and that was fine but the one at the top would get shredded as I screwed it in, it was too tight, then I tried the old one and it got shredded too. But the one that came out of the brand new carb didnt have an o-ring on it nor a groove for one. I figured this was why it seemed so loose, but the top oring on the old style pilot screw wont fit down in the hole. I even looked through my oring kit to find one that would fit but no go.

By the way, I went back out tonight and the damn think fired right up and ran great. Maybe just some dirt in it. Thanks for all your advice. And if anyone knows of a solution to the above issue let me know.

 

[SlammedRanger]

I had to put a dab of grease on the o-ring on my brandnew oem carb i had on my quad. I put the mixture screw out of a moose brand rebuild kit in it. Tossed the D screw in the trash lol