LTZ400 breaking up

[Stunmai]

So I bought an '04 400 actually a DVX, all stock except for a slipon. Seemed like it was running out of fuel after about 30 sec of wide open throttle, it would die. Would restart after sitting a minute.  Disassembled and cleaned the carb, fuel screw was plugged and at 1 1/2, I set it at 2 1/4. Cleaned tank, replaced petcock and fuel line.

Now, it idles and pulls hard in midrange, but pops and breaks up attempting WOT. While sitting in neutral it starts popping and breaking up at about half throttle, while riding it seems to start when throttle is held open.

Removed the air filter lid, and while in neutral the popping/breaking up starts a little earlier, at about 1/3 throttle.

Is this a lean condition? Stock 130 main jet. Would the simple addition of a slipon and staying with the 130 main cause the popping and breaking up?

Any ideas? Thanks in advance!

[Stunmai]

Wow this board is almost dead, too bad...

Have taken this carb apart now 3 times to verify cleanliness, and its spotless. Engine still starts popping and breaking up as before, at 1/2 throttle in neutral and at full throttle while riding.

Pulled the fuel screw out to 3 3 1/2 turns for kicks and just made meaner popping and backfiring.

Anyone?

[hatchdemon89]

valves might need to be re-adjusted

[Dirty Foot Adventures]

I would call Rick @ RTR Performance Engines....he will get you straight for sure

[mrbones]

What color is the spark plug? A white like colored plug would indicate a lean condition. That is the most likely scenario considered the exhaust modification.

[yfz122]

Yes you are running lean. And possibly need to adjust your float. Your quad came out of the factory tuned a little lean. So any exhaust or fuel/air flow change will effect how it runs.

[Stunmai]

Update- I had Rick look at it last weekend, and he assured me that it was running just fine! The upper end breakup was it hitting the rev limiter. Now I have a suspicion after doing some research, that maybe the reverse limiter was kicking in (while in forward gears) once in awhile, maybe due to it sitting before I bought it. But now it certainly is running nice. Rick was friendly and helpful and I would most certainly see him in the future and recommend him for troubleshooting or performance mods.