350X 95% right on jetting

[350Kris]

Hello Trikesters! Been a number of years since I've been on the forum. I'm back and happy to see it alive and well. Quick question just to double check myself. My 350x is about 95% jetted right in my estimation. Here are some specs:

3,750' elevation
NOS Motor.....less than 25 hours.
07 400EX Carb
Supertrapp Exhaust, running 12 discs
K&N (no airbus mods and running WITH lid)

138 main jet
38 slow jet
Needle at stock clip (middle)
2 3/4 turns out on the fuel screw

I know those are stock jet sizes for a 350X, but note my elevation. Slight popping on deceleration. Also, a very slight flat spot on deceleration from WOT to mid. Runs very strong with good throttle response throughout entire range. Am I missing anything?

[ps2fixer]

Just taking a guess at it, but I'd guess the slow/pilot adjustment is rich enough to not be too noticeable, but I think you'd want to jump up a jet size and try around 1.5 turns out and tune from there for low end. I suspect the flat spot would be a sign the top end is too lean, use a notch to lift the needle more, or maybe jump one one size on that one too.

I haven't had a chance to rejet my 350x, but it does the same thing, runs great on acceleration, pops though exhaust on deceleration. Stock carb, airbox stock, exhaust I had to switch to a DG (OEM was welded to the last engine that was rigged up and smoking horribly). Generally my machine still starts really easy, so I think the low end isn't too far off, probably just need to adjust the pilot screw, top end for sure is too lean, it does seem to run a bit hot when I run it hard (I like my speed lol, flat lander though up here in Michigan).

I suspect there's no real need for the 400ex carb (it's a bigger size over the 350x right?). It might be slightly harder to tune because of that, like temp changes might effect the tuning more. Just thinking out loud, never ran one myself since I don't have the supporting mods to need it. I'm only around 700ft elevation and also have a K&N air filter.

[Dirtcrasher]

Lots of times merely turning your air screw out another 1/2 turn from the stock (usually 1.5 turns out) will stop the decel popping. But, that means the screws taper is good as well as the o-ring that's in there.

IMHO - 138 is too lean, I'd toss in a 142 and adjust the air screw out a bit more...

[floydechoes2000]

Good advice Dirtcrasher! ps2fixer, the 400EX carb is a pretty much bolt on upgrade for the 350X that adds an accelerator pump and slightly more modern design, never mind much better parts availability. My acceleration through the gears was very noticeably improved and my X is bone stock! Of course it's not a necessity if your machine is running well, but if you leave your float bowl in a gallon of carb cleaner a little too long and it dissolves (oops), it's a readily available option with several benefits.

[ps2fixer]

Wasn't aware newer carbs have accelerator pumps, no doubt it's an upgrade then. Might have to keep an eye out for one when funds permit lol. Machine was running great, just tuned a little lean, but it has sat long enough it needs a carb cleaning (pilot plugged). I've been running it and using the choke to tune it for testing CDI's on and rectifier/regulators lol.

[jb2wheels]

I put a 400EX carb on an 86.
Engine had 10.5:1 Wiseco piston, XR400 header with stock 350X muffler, Uni filter in stock box with lid.
It ran great and started easy with no popping near sea level and really liked a lot more jet than you have. Something like 50/152 as I recall.
I was very impressed with how well it ran compared to my stock 85.

I'd try a little more pilot - 42 or 45. You know the pilot jet is the right size if, when you turn it all the way in it kills the engine but still gets best idle with no more than about 3 turns out. My opinion.

Main jet is a little harder - more of a seat of the pants thing. My 86 with the EX carb had a terrible bog with too much main jet. I vaguely recall I stepped down 1 size from like 155 to 152 and it cleared up.

And, after all that typing, every engine and situation is different. Yours might be perfect as is where is.

[350Kris]

This is great advice all around! What about needle position? Also, where is the best place to order jets nowadays. Thanks guys. Appreciated.

[jb2wheels]

I'm lazy and it can be such a pain in the ass to change I leave them right in the middle. If the pilot and main are close enough, that seems to work.

[El Camexican]

where is the best place to order jets nowadays.

Jetsrus.com

[350Kris]

Just ordered a #42 pilot and #142 and #145 main. Thanks again for the help. Will keep you posted.

[350Kris]

Update: I threw in the 42 pilot and 142 main. I'm 4.5 turns out on the fuel screw, so I'll be putting in one size up on the pilot. I ran a 145 main also to compare and realized the 142 ran better. The 145 caused excessive popping and a small power loss. So....I think I'm good once I up size the pilot. However, here is the only concern I have.... I sometimes hit a flat spot at 1/2 to 3/4 throttle. It will cut-out sometimes other times it will just bog a little bit. It seems to be the transition from the needle to main jet. I'm running center clip on the needle.

[350Kris]

Any thoughts on my flat spot?

[Shawn Powell]

I have a similar set up on mine. I’m lower elevation but ride up to 5500 feet when I go trail riding with no issues. Full airbox lid , snorkel etc. honestly I think your still way lean. I’m running a 148 main with a 48 pilot 1 1/2 turns out. (400ex carb) I run a UNI filter , flows better believe it or not. And I think I could easily go a main jet up before I had to pull my lid or add plates to my super trap. Any kind of popping like your talking about is a lean issue. And if you have a flat spot mid throttle drop your clip one notch. But if it’s full cutting out you need a bigger main. Stock 350xs we’re running 142 ( I’m aware 138 was factory) with OEM mufflers. Good luck.


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[350Kris]

Thanks Shawn. I'll try upping the pilot and main. I'm running all disks on the SuperTrapp.