I have a 98 AC 300 and it starts very hard in cold weather. It was fine all summer but since the weather has turned cold it starts very hard. When I first try to start it, I'll choke it and it will start but as soon as I give it any thottle,it stalls and won't start back up. Anybody have any ideas??

 

My 250 (same motor except the jug, piston and crank) is cold blooded also. You just can't use the throttle in the cold until the engine warms up. Set the choke full on, crank and let it start and run (do not touch the throttle thru any of this), slowing backing the choke off over several minutes. If a restart is necessary, full choke and no throttle for the restart. The reason for no throttle is there is no choke butter fly valve (they create extra vacuum thru the whole carb to pull fuel into the motor), but a fuel valve that opens. If you open the throttle there is no vacuum to "pull" the fuel into the motor. I have also found a that when it does get cold an trouble light with an incandecent 100 watt bulb placed face up under the front of the motor will help a lot. We usually are not in a hurry so the slow warm up method works fine for us.

 

Laker,

Check your valve clearance too. If your valves are out of adjustment it can make it hard to start.

SJ

 

Thanks for the advice guys. I'll give it a try.

 

bear is right, i had to do the same thing with my kingquad 300!

 

Hi guys, I have a 2001 400cc 4x4 manual. It sleeps outside since I don't have a garage or shed! Since the winter arrive, it has never start again... During all summer and fall, it was fine, but now, it rrrrrrrrrrrrrrr but nothing has happen, I charge the batterie and also use and external power source, still nothing. Is there a different adjustment for the carburator for summer and winter? I leave in east Canada, and already it is in the 20s and 10s during the night. Any suggestion? I don't want to spend a fortune on this "old engine"

 

Starting proceedure become even more important in cold weather. You should use the same proceedure that was given for laker's 300. Another thing to try is a 100 watt trouble light under the front of the motor or a heater blowing on the engine for a couple of hours or better yet, over night. How old is the gas? Anything over a month or two in your temps is suspect unless you used fuel stablizer. It's best to drain the tank and carb (it has a drain screw on it the will drain both, but is slow) and start with fresh gas.

 

What about carb adjustment with the screw?
Anything to do with it?
Also, it seem's to me that the choke cable
may be jam, it does not go from one end to the other.
For gas, it's not too old and I have put some gas line anti-freeze
into the tank to prevent humidity in the gas tank.
I really think it has to do something with the carb, but I do not
know anything mikuni carb...
Any advise?
Thank's buddy!

 

Some guys are always talking about rejetting for the winter and they lean it out, which makes no sense. I don't touch my mixture screws, summer or winter and have no problems. I don't even adjust my mixture screws when I go from my base altitude of sea level to as high as 7,000 feet. Yes, it runs a little rich at idle but they all start and run.

I will bet that that gas anti-freeze contained ethonal or methonal alcohol, which are contributing to you problems. Use isopropyl alcohol only, never the other two, they cause fuel seperation and are very corrosive. There is the possibility you are feeding your engine straight water. You need to drain the carb into a glass jar and see if there is water in the gas or even any gas there at all. Then drain a sample from the tank into a jar and check it also.

After the carb is drained, you might try pulling the spark plug and squirting a little gas into the cylinder, reinstall the plug and see if it fires. If it does, you have a fuel problem. Oh yeah, a new spark plug is cheap insurance, I replace mine every spring.

 

One other little trick that you could try for the 300. I use a heat gun and blow directly into the air intake just before start up and through the engine warm up. The warm, dry air getting into the carb when the engine is cold really makes it easier to keep the motor running until it is warmed up. Otherwise I have to restart a number of times or stand there with my hand on the throttle when the choke is backed off.
On a different note, I've always wondered what was the advantage of this enrichening system of choke vs the butterfly valve. The reason that I ask is that on the system that we have, it's extremely difficult to find a position of the choke that will keep the engine running once full choke has to be backed off. I initially thought something was wrong with my 300 (my 1st atv), and I brought it back so they could "fix" the choke, but they told me that it was working properly. And then when I got my 650, the choke acted exactly the same way. It's possible, but very difficult, to find a middle ground with this system. The choke seems to act like it's completely on, or completely off, which obviously makes it tougher to keep idling throughout the warm up. And I don't think that it's just me, because I have read other people's complaints about this also.
Any thoughts on why this would be, and has anyone else here noticed the same thing? Just curious.