I am at wit's end here.
I have an 2000 300 4x4 that stalls frequently. Doing it since it was new. It runs fine as long as your on the throttle, climbs well and for the most part, runs great. It stalls easily when you come to a stop or slow almost to a stop to down shift before climbing a steep grade. Sometimes it will idle just fine for several minutes in neutral or it may stall as soon as you stop (in gear usualy).
The spark plug is always coated with fluffy black carbon, a sign I thought of running rich. I replaced the plug (gapped at .65mm) and reset the fuel pilot screw back to the factory 2.75 turns out. No change. I lowered the float arm level in the bowl (factory spec was .5 inch height with carb inverted, I went to about .55 to .6). Still stalled and plug still fouled black. I set the jet needle e-clip onto the second notch (one toward Lean from the factory third notch). Still no difference. Checked vent hoses, cleaned all the ports, checked needle valve.
From what I read in the forums, this has been a common post but nobody had the diffinitive fix if there is one. My dealership changed hands and the techs there are new to AC, don't know the product well,I don't trust them. Any input would be a great help. Thanks.

90 QuadRunner LT4WD
90 Mojave 250
00 AC 300 4x4
03 Zuki LT-Z400
83 Yamaha Venture Royal
78 Honda CB550/4

 

Try adjusting your valves. Our 250 did the same thing and stopped after a valve adjustment. When it starts doing it again I adjust them and it runs fine. The 250 and 300 are real tempermental as far as valve clearance goes. If this doesn't work try removing the screen between the filter and carb in the air box. This will give better throttle response but you may or may not have to rejet, I didn't. You may also try cleaning the deposits out of your muffler, this can choke it down too. Good luck and let us know how it goes.

 

Dtssr, you have a similar problem that I had. It took me lots of trips to 3 different dealers to solve it. Arctic Cat has never fully addressed this problem with the 300. I almost gave up and sold the bike. You have to upjet to a bigger main jet, probably 135 or 137.5. Setting the e-clip lower will help, I use the 4th position. The pilot jet is a 45 I think. I use a lot more fuel because the bike is running richer, but the backfiring has all but been eliminated. If I find the slip with my settings I will reply to the forum. You can solve this problem, but it takes lots of experimenting.

 

I was thinking of a Jet kit, but was not convinced that the $70 cost would result in a fix. So you moved the e-clip to the fourth notch, one toward richer than factory setting? I thought with the black sparkplug the bike was running too rich. The 90' Quadrunner is always black too, and that machine has always run great. Yes, post what ever jet settings you have.
Also, since it's primaraly stalling at idle or low end, does anyone have thoughts on re-setting the fuel pilot screw on the bottom of the carb? How do you get at it while the carb is mounted? Seems like you can't adjust it while motor is running, you can't get into the space!

 

I have an AC 300, 1998, I have the same problem but only in very cold weather. I did nothing to it but after it warmed up it ran fine. A valve adjustment may be in order.My 300 was very fussy when I first got it but after break-in it's been running good since!

 

Dtssr; I found my carb settings.

Pilot Jet 45
Main Jet 135
E-Clip Fourth position

The main idea is to run slightly rich. This will help eliminate the backfiring on steep decents or abrupt stops at speed. I am not confident in playing with the carb other than adjusting the e-clip. Sounds like you don't mind taking the carb apart. My bike backfired so much that the baffles in the muffler blew out. It was also stalling and fouling the plug. Now I have reduced the backfiring by 90%, bike idles good and no plug fouling. I burn more fuel now, but the tank is large enough for almost any ride, and is bigger than any other manufacturer. But as I said before, I had to visit 3 dealers and lots of experimenting to fix this problem. Apparently most of the 98-00 300's have problems with stalling and backfiring. Many magazine articles/reviews have mentioned this is common to AC, but unheard of with the Suzuki 300. It seems like a lot of the AC dealers are not well trained on the bikes, I finally found a great mechanic at the third dealership that took a personal interest in solving the problem.

Good luck with your bike, keep us posted!

 

Dtssr; I found my carb settings.

Pilot Jet 45
Main Jet 135
E-Clip Fourth position

The main idea is to run slightly rich. This will help eliminate the backfiring on steep decents or abrupt stops at speed. I am not confident in playing with the carb other than adjusting the e-clip. Sounds like you don't mind taking the carb apart. My bike backfired so much that the baffles in the muffler blew out. It was also stalling and fouling the plug. Now I have reduced the backfiring by 90%, bike idles good and no plug fouling. I burn more fuel now, but the tank is large enough for almost any ride, and is bigger than any other manufacturer. But as I said before, I had to visit 3 dealers and lots of experimenting to fix this problem. Apparently most of the 98-00 300's have problems with stalling and backfiring. Many magazine articles/reviews have mentioned this is common to AC, but unheard of with the Suzuki 300. It seems like a lot of the AC dealers are not well trained on the bikes, I finally found a great mechanic at the third dealership that took a personal interest in solving the problem.

Good luck with your bike, keep us posted!

 

Thanks! I'll move the clip to the forth notch and try that for a couple days. If it helps, I'll leave well enough alone. If not, I'll get the jets to replace the stock ones.
I'll let you know.

 

Well, may be some success at last.
Today I set everything back to factory settings and then did the valve adjustments. The exhaust side seemed to be out if anything. Set both sides to factory spec.
It seemed to run a little better, no stalling when riding around the yard. Then after a few minutes of level riding, I went up a small incline and she sputtered and stalled out. Since it was hard to restart, (no gas)I thought of adjusting the float again. I raised the float level back to where I had it, about .6 inches instead of the factory .5 inch.
The cat purred.
My son and I then headed out for a 12 mile round trip over mixed trails. (He on the 90' QuadRunner for the last time, being sold this
weekeend. :-( )
Abosolutly no stalls for the first time since I can remember. May be to early to tell for sure, but valves and float adjust may have done it.
Thanks to all who posted and I'll let you know after Sunday's ride.
DTSSR
90 QuadRunner LT4WD (Going :-( )
90 Mojave 250 (Sold!)
00 AC 300 4x4
03 Zuki LT-Z400 (The Rocket!)
83 Yamaha Venture Royal
78 Honda CB550/4 (Sold!)

 

You really have to keep the valves adjusted on the 250 and 300 Cats. I adjust ours about every 75 hours or so. As long as they are adjusted it purrs like a kitten. I am having a little problem with the main jet it will bog at full throttle. I figure this a rich condition. Any input? It runs fine every where else in the powerband.