Just shimed the needle's on my buddy's brute force, and it was running very good, excellent throttle response, but it still coughed and weezed at idle, so I started fiddling with the rear pilot screw, bad idea. Now it has no power, and won't get over 25mph. I cranked it all the way back down, and set it to 3 turns out, but it is still running just as poorly. When I look at the plug, it is black and these plugs are brand new. Spark is good. I hope somebody has some thoughts on this before my buddy starts asking if I'm done with his 4 wheeler. By the way, what are the factory settings on those pilots, I may try putting them back to stock. The bike idles fine, by hits the wall quickly when you give it gas. Please Help.

 

Is your idle RPM set at the correct spec? This problem usually happens when the idle speed is set too slow. 2 1/2 turns out with the screws is the stock setting.

 

Idle is good, pilots are back to stock, and still running terrible. Could something else have gone wrong? I am out of ideas, but I need to get this thing running pretty soon. Could a coil have crapped out, and still give off spark? It did get pretty wet between adjustments, but that was yesterday, and everything looks very dry now. Only the back cylinder is running poorly, is that unusual? Any help is appreciated. Thanks in advance.

 

It sounds like it is running on one cylinder. Check your connections again.

 

first place I'd check would be the rear plug, make shure the porceline isnt cracked. 2nd I'd pulle the filter cage and screen off and start it , see if its overfilling the rear carb with fuel, if so you may have stuck the float a little or may have some dirt in the float needle seat. 3 check the pilot jet and make shure its not clogged. if it were me I'd put my money on the float needle and seat. or a sticking float. also check the choke move it back and forth and make shure its not sticking. /Brute manual at bottom of page

 

Alright,
I have found the problem, but how can it be fixed. The rear carb is not getting any air to it. The part that the needle slides through is not opening. The front one flutters open as you increase throttle. Sorry, I can think of the name right now, but it is the large cylinder with wings on it above the butterfly.

 

You need to adjust the rubber diaphragm. It is not seated properly most likely.
A way to check; there should be slight resistance on the slid when you push on it.
Another way is start up the machine and give it throttle and watch it. Make sure it moves slightly.

 

did you by any chance kink the vent line ? no air the diaphram wont work.

 

If it is the diaphragm misaligned, take the 4 screws out make sure the tit is aligned. Push in hard on cover and move slide. There should be resistance, if not slightly rotate cover over diaphragm until slide works properly. Then once you find the sweet spot put screws back in and tighten while holding lid on firmly. If you can't find the sweet spot inspect the diaphragm for a tear and/or kink in vent line like bruteforcebob said. Most likely though it is just repositioning of lid on diaphragm.

 

It was the rubber diaphram. It must have shifted when i pulled the needle. Everything is running great now. Thanks you guys for all the help.