Hi,

I have a 1999 AC 300 4x4, has always been a great machine. I have been having a problem with a high speed cut-out. After about 3/4 throttle it starts cutting out/bogging bad. Up to 3/4 throttle runs super. What I have checked thus far:

- New plug (always easy :-)
- Set valves (needed it anyway)
- Checked compression (looks good around 150)
- Squirted some carb cleaner in the carb
- Hooked up in-line spark tester, spark seems to stay even when cutting out, that is I don't see a loss of spark.

I kept thinking it was fuel, but the new plug really made a difference (I know still could be fuel). One thing it has always backfired when going down a hill, so I always thought it was a running a bit rich. Plug always looks like it is running a little rich.

Any ideas?

I am thinking I should get a carb re-build kit to re-build the carb, any ideas where I could get this?

Anyone know how to unhook the rev limiter? I wanted to check to make sure that wasn't causing the problem (although spark seems to stay) just want to try that before messing with the carb.

Thanks for any help :-)

BTW this atv pulled out a 450 pound bear this year, about 200 yards uphill, then a mile down hill....these things my be small but they are beasts LOL.

 

I have same problem with my Artic cat 500. Dont know what to do. Checked carb,checked valves,got spark,got fuel. let me know if you fix yours.

 

Check for an air leak around your intake. Spray some wd-40 around the outside of the carb on the air cleaner side and the engine side while revving the engine a little. If you notice any change in the way it runs then you have a little air leak there.

If you do not find anything there I would take the carb off and clean it reall good checking the highspeed jet for partial obstructions and clean the air filter if you haven't done so already.

SJ

 

That was what somebody else said. The rubber between carb and intake worries me. I tighten the clams down good when its cold and its tight,but as motor warms up,rubber gets softer. When motor is hot you can wiggle carb and it seems loose on intake when its hot. Idle fluckuates also when u move carb. I checked rubber for cracks seemed ok,and clamps are ok.

 

It might wiggle a little as the rubber boot flexes but it should not twist at all. AIr getting around it will cause an erratic idle and high speed cut out and backfiring. try the wd-40 trick.

 

Pretty sure mine is carb related. I really need to pull the carb apart and clean it. Just haven't got to it. I ran some seafoam through mine and it really helped, which leads me to believe the carb needs cleaned. I put the seafoam in and we went on a long ride one day this fall, by the end of the ride it was running pretty good. I noticed when I was plowing the other day it was acting up again. I should have just keep mixing in the Seafoam for a while but ran out.

I think the suggestion about cleaning the carb is a good place to start. I am going to check the boot on mine also when I get a chance, that sounds like a good suggestion also....

 

i think the parts were 20 bucks for mine.. rebuild the carb, not much to it, and easy to get out

 

I have the same machine, similar problem, However when my mechanic buddy went through the carb he neglected to note the settings on the idel jet(s) or what ever you call them.. Can you take note of what yours are at? How many turns out? Or does someone know what they should be set at? Or where I can find that info out at?
Thanks

 

For a Keihin carb the fuel screw setting is 2 1/4 turns out for the 300.

If it is a Mikuni Carb I believe it is 2 1/8 for the 300.