ES-SX-350X Carb rebuild Tutoral

[Flyingw]

My bad, that hole is not drilled on the 86 carb. As far as the main goes, that's all dependent on you pipe. Every motor breathes differently. Some have to rejet for the DG, some don't. What's you plug look like?

[longbedGTs]

I'll pull the plug in the morning but won't it be inaccurate since I haven't been able to run the motor with the choke off? I'm getting a better understanding of jetting(thanks to this thread and others) so I'll probably end up picking up an assortment and just experimenting until the plug shows a nice color. Thanks for the help!

[Gator72007]

Thanks for the write up! Last weekend i finally got time to mess with my 250sx's carb, its always had a dead bog if you cram the throttle so i spent a few hrs going through it and then adjusting the needle height and air screw, well it still boggs, but not near as bad as before. I got done that night and googled 250sx bog and came across this post and read all pages, in the end it looks like its inherent of the carb. If anyone finds the cure let me know

[Flyingw]

That problem has me stumped. Some carbs do, some don't but most have that problem to some degree. I have taken more than one carb with that problem and swapped every part out only to have the same problem so the problem is in the body somewhere. Most of the carbs still out there work ok if you don't stab the throttle. Once it gets past that flat spot, it works just fine.

[Gator72007]

Yea mine is fine to ride and ride aggressively, and not a real problem, but its always bothered me that i cant cram it to wot from low rpm's
I havent been on here in a good while, i read a few days ago about the 250sx/es 350cc big bore kit now available,
Thats something id like to do one day and then upgrade to a different carb

[longbedGTs]

Got it all buttoned up with a 45 slow jet and what do you know it runs with the choke off! Took it for a short ride around the house(didn't get out of 2nd gear) and it seems to run real smooth other than the slight bog that gator mentions above. I almost forgot the instant torque of the 350, it was great! Pulled the plug and it's pretty black which makes sense because I had to back the pilot out about 1 turn or so to get it to idle smoothly(had an intermittant "huff" with the pilot at 1 1/4 turns). It's probably about 2 to 2.5 turns now but idles really smoothly. I'll keep an eye on the plug color though as I don't want it to run too rich. Initially, I had the pilot jet oring in the incorrect place. Do you think that might have been partly the reason it wouldn't run with the choke off? Thanks again!

[captainweezy]

Such a great thread here Jim. Like your rear diff tutorial I have used these many times. this deserves to be a sticky.

[whiteman350x]

Ok i know this post was started forever ago but, in post #2 you said the qa04a the 85 trx250 carb will not let the es/sx run right but i never saw it explained why. I know I have an 85 trx carb in my pile and want to know why I should avoid it.

[atc007]

Nothing at all wrong with the 85, just drill for cold start if your weather gets much below 20D. Simple fix.

[Swany10]

Ok i know this post was started forever ago but, in post #2 you said the qa04a the 85 trx250 carb will not let the es/sx run right but i never saw it explained why. I know I have an 85 trx carb in my pile and want to know why I should avoid it.

I think the answer is in post #132 on page 9

QA04 or the QA09 (TRX250) don't have a primary jet

I'm looking for a replacement for my QA02 carb, ideally a QA07 or QA08. I saw an 86 TRX250 near me for sale for cheap and thought about getting it for just the carb, but I didn't know if the carb was compatible with my 86 250ES. That led me to this thread, and from what I can tell it wouldn't work for me.

While I think I found the answer, I don't really understand why it is though, the motors are the same, why don't the carbs swap?

[Flyingw]

Actually It will work. When I posted that comment, I was fighting with a couple of bad carbs. I have since rebuilt and run the TRX carbs on my test stand and they do run ok on an ES motor but the stock TRX jetting needs to be fattened up a couple of sizes on both the slow and main jets.

[Swany10]

Interesting. Does the 86 TRX carb have a screw in start up jet like an 86 ES does? I like the idea of getting my bike "back to factory" and finding a QA07 somewhere, but for practical reasons all I really need is good cold (MN cold) start performance. Would it make more sense to just drill out my QA02A?

[Flyingw]

You can drill out the 02. Yes the 86 TRX carb does come with a screw in jet. I drill all the startup jets on the carbs I rebuild for guys. All of them...

[Flyingw]

I can drill a couple of jets for you if you want to pay the postage. On the 85 carbs, get your hands on a #4 sheetmetal screw, Screw the screw in to the jet about 1 1/2 turns. I took an old flatblade screwdriver and cut a slot in to it. I put a piece of metal up against the jet tower, stick the slotted screwdriver up under the screw head and lever the jet out.

[Swany10]

You can drill out the 02. Yes the 86 TRX carb does come with a screw in jet. I drill all the startup jets on the carbs I rebuild for guys. All of them...

Well that settles it, I'll drill the one I have. If that goes badly for me somehow, I know where I can get a cheap 86 TRX carb to replace it with. Thanks for the insights.