The other day I was puttering down the road on my 1999 Scrambler 400. All of a sudden it cut out a couple times and then stalled. I can't get it to start now, in fact it doesn't sound like it even comes close to firing up. I just put in a new spark plug, and it has plenty of gas in the tank. I'm very frustrated and am open to any suggestions.

Thanks,

Colin

 

Check your compression first and make sure you haven't lost a piston. Look at the old plug and see if you see any small pieces of metal on it.

 

Colin - Three things are required for any internal combustion engine to run: compression (a sufficient amount), fuel / air mixture, and spark (at the right time) ... sounds pretty basic but you can trace almost every engine problem back to one of the three. The first thing I would check is the spark; pull the plug, stick it back into the plug lead, hold it against the cylinder head (hold the lead - don't touch the plug) and hit the starter to see if there is a spark. Its best to do this in a low-light situation so you can see the spark - oh, and make sure you don't have any gas fumes collecting on the floor around you (the flash is pretty but the smell is nasty). If you have spark and it happens at what you think is the right (or close to the right time) check compression - did you hole the piston? Did the machine smoke more than normal just prior? If so, the oil metering shaft could be stuck in the WFO position and its oiling too much (not very likely, but possible).

 

I just checked the spark and it is sparking good when I put the plug against the cylinder and turn it over. I don't have anything to check compression, but I pulled it a few times and it feels like it has good compression that way.
As far as feul, I checked the flow going into the carb from the gas tank and it was flowing fine. When I would tip the carb feul would flow out of it, so it seems like it's getting feul, but when I took the plug out it was dry. That was the new plug after turning it over a bit.
When I try starting it with the choke on, it will backfire and still not even come close to starting.
I hope some of this makes sense to you.

Thanks,
Colin

 

Kinda wondering if you've sheared the crankshaft to flywheel key. Where are you located....maybe someone from here is near you.

 

I'm in northeastern West Virginia.

Colin

 

Have you tried pouring a little premix gas in the spark plug hole or spraying some starting fluid in through the intake? This will help you determine if you are getting gas or not.

Waylan

 

Waylan,
No I haven't, but that's a great idea. I'm deffinately open to suggestions.
Ken,
If it was the flywheel key that was sheared, what could cause this and what are the symptoms? Is the flywheel easy to get to?

Thanks,
Colin

 

If I were you I'd accurately check the compression before spending much more time messing with it. Just using your finger over the spark plug hole isn't really telling you alot. You can still feel compression sometimes even when your piston is damaged past the point of being able to start.
If your compression is good then I'd look elsewhere but if that's the problem then you're wasting your time looking at other things.
Those stock pistons seem prone to failure and if you haven't replaced it yet you need to make sure that's not the problem. If the compression isn't over 100 then it's rebuild time.
Good luck with it.

 

One simple way of checking for low compression on a 2-cycle is to pour a capful or 2 of motor oil down the plug hole then try to start it. It will boost compression for a few pulls and if that's it the motor should at least try to hit or maybe start. My guys do that all the time with the weedeaters, chainsaws,etc that come in and wont start. The other thing you can do is pull the pipe off the cylinder and just look at the piston. The exhaust side will almost always show scoring because of loss of compression You can see about 50% of the rest of the cylinder as well. Bubba