350x dies out at half throttle

[rugbyflanker]

Rebuilt the top end of my 350x. Got it all back together and now it totally looses power in the middle of the throttle. Ran better with a smaller main jet and no air box lid. I have now adjusted down to a 132 main and plug is still black.
I have cleaned and went through the carb 3 times and checked the timing marks on the cam gear to make sure it wasn't a timing thing. Any help or ideas?

Sent from my SM-G920V using Tapatalk

[big specht]

Do you have any spare coils to try ? I went thru a issue like that on a R and it end up being a secondary coil that was causing the power loss

[rugbyflanker]

I have tried a different coil and CDI box off a running machine with the same results.

Sent from my SM-G920V using Tapatalk

[BOB MARLIN]

Timing ?. Does it pick back up after half throttle ?.

[rugbyflanker]

Yes it does pick back up closer to wide open throttle. I did have the valve cover off to confirm the timing marks on the cam gear were parallel to the head at TDC. Is there a pick up thats adjustable on the flywheel? I haven't had the bottom end covers opened up on one in a while.

Sent from my SM-G920V using Tapatalk

[ps2fixer]

Black spark plug normally indicates too rich. At floored (after engine is warm) does it run fine, or just better than mid? Mid is kind of a tricky area since the pilot or the main jet can effect it, I'd think the main would be the larger effect, but both needs to be right to have a well running engine.

Also to be sure, you're running the OEM CDI or something actually made for the 350x right? Not a random China CDI, or a CDI from a different machine? My money would be on carb tuning though. Also are you running OEM jets, or off brand, the off brand ones are a different numbering system which makes it a nightmare to compare the two. Also you running a stock carb, any engine/exhaust mods? Ported, big bore kit etc?

Stock main jet is 138 (142 for later production from my understanding), stock pilot is 42.

To answer the question about the pickup coil, or as honda calls it, the pulse generator, it is non adjustable and runs off the fly wheel. You might be able to bend it slightly closer to the fly wheel to have it send a bit stronger signal, but no timing adjustment unless you drill out the mounting holes.

Also wondering, before you rebuilt the top end did it run normally? What all changed besides freshening up the top end?

[Dirtcrasher]

Well, if you did the top end correctly, stop thinking the issue is there. Have you done 4 stroke top ends/valves before??

It is possible that you set your rings wrong, either oil or compression - it happens.

But compression is compression, and timing is timing. Nothing inbetween should be the issue.

I run a 175 to 182 main jet in my 39mm carb on my 350X, I run almost a 190 on my 452X with a 41mm carb.

Oil fouling isn't going to make the engine cut out, it would run horrible within the entire throttle range.

If it ran well before, and you didn't TOUCH the carb before these symptoms, you can rule out the carb. If you did touch the carb, is it possible you made a mistake in there? Or need to change some jetting??

It's easy to go up or down a few sizes, see what that does.

If the carb overall could possibly be a variable, why not buy yourself a 400EX carb for under 75$, toss it on and see what it does. At the very least, you will have upgraded your carb and if you have an AM exhaust and some holes or no air box lid, you will want that carb anyhow.

I'm not here as much anymore, but I'm glad to try and help...