misses on heavy acceleration

[Gotanubike]

Hey all, new to the forum. I Just picked up an 82' xs400...It is the one with the mono shock. The bike is awesome and runs good, but around 6-7k rpms or any time at wide open throttle, the engine will cut out and sputter. I checked the spark plugs and they look pretty good. Maybe the carbs? Also there is no air filter on the bike so no clogged filter. Anybody knows what cause this let me know

Heres a couple pics

 

[new kid on the brat]

the carbs are so picky on a motorcycle that if you don"t run filters you will not have enough vacuum and you will have a lean condition. try some new factory filters.

If you decide to run aftermarket pod filters you will have to change jets to compensate for the better airflow

 

[Gotanubike]

Hmmm..looks like I will have to order one? They are 30 bucks yikes.

I tried making an air filter today by cutting one out of an old fram air filter from my car(replaced it with a k&n). The resistance of air flow is noticable now with slight loss of power and still misses at wot. It also struggles off the line unless I rev it a bit and feather the clutch.

Also, I have had the bike going 160km/h when I am down in race position and doesn't seem to have any trouble then. But will top out around 115 if sitting up right.

 

[Mikail]

Hi all, new to the forum as well. Gotanu, did you get this resolved? If so, what was the issue? I purchased a '83 xs400 Maxim for the wife and it has the same symptoms as yours. It starts and runs great until you go over about a third throttle. Seems like as soon as you open the throttle any wider, the slide shuts and chokes the engine. It actually slows the bike as if closing the throttle... let back off on the throttle, and it comes back to life. I've cleaned and blown out the carbs, installed much larger mains and raised the needle one notch, but the plugs still come out white and clean. I would expect them to be at least tan if not soaked! While one of the slide diaphrams has a crack starting near the outer edge, I see no light through it. I've also tried plugging the petcock vacuum line and using the prime setting. The bike is stock except an aftermarket 2 into 2 exhaust.