Afternoon folks, was hoping for some direction to a newbie ATV rider/repairer. The ATV has started to stall while driving, it feels like you took your thumb of the acceleration but you didn't, you can give it some more gas but it stalls out. The first two times, I waited 5 minutes or so and it restarted and stalled after 1.5 miles or so. In case its important, we got this ATV from the wife's father in January, he would start it with half choke and "goose it" with a little gas until warmed up and you could turn off choke, it also smoked a decent amount, its a 2 stroke and I didn't think too much of it. It has stalled between 1 - 2 miles of riding, going strong and poof. After the first time, and at home after cool down, I poked around and found the two gas lines from the tank were splitting and one started to leak after I reached in to feel it. So fast forward a few weeks and yesterday I replaced all three fuel lines, fuel filter, spark plug(old was greyish). The air filter box has a neck on it that plugs into a rubber boot that also plugs on the carb, that neck was completely broken off, I glued that back in place and used some tape to seal up any gaps for a temporary fix. It took some cranks to get gas going again and it stalled but was hoping that was due to no gas in it for a few weeks. I can start it now without the choke and it doesn't put off much smoke so I know I solved a few issues but I cruised down to the mailbox (1/2 mile or so) and it stalled. This time it wouldn't start with the 5 minute wait and would only start and stay on with full choke, I drove it with full choke past two houses and then took choke off and let it stall and pushed it the rest of the way home. Sorry for the long one but was trying to give some before and after info. Any help would be appreciated, I'm learning as I go and am somewhat mechanically inclined, I would rather fix it and experience and learn that take it to someone and only hear why. I was thinking carb but not sure if throttle cable or emergency shutoff or.... thanks folks.

 

Check compression before you go any further.

 

Yikes... will do that and report back what I find, thank you.

 

Dry compression was 95 PSI, manual I have says it should be 115. Also the new spark plug I put in, the ground electrode is gray, the center electrode is black and there is a little black residue on the rim. I only ran the spark plug in it during start up and idle for a little bit and the 1/2 mile or so test run. Quite a few start up tries and running at full throttle, didn't think the plug would look like the old one so fast.

 

That was why I said to check compression. 95 psi is too low. May crank and run awhile until the engine gets warm, then the piston rings loose sealing against the cylinder walls and dies. Time for a new top end at least before major damage happens.Plugs won't last long and foul out when engines are like this. It needs to be torn down and have the cylinder measured for the next over size piston and rings.

 

Welp, looks like my Father in Law unloaded this on us just in time
Ok OPT, there are a number of places to order parts or piston kits, not sure if this type of job is best left to a professional and requires a number of specialized tools or if an average joe with some time and patience can pull this type of thing off? Is there a place you recommend for parts and by torn down are we talking completely opening up all the engine for a look see or getting a piston kit and going from them? Or... do I just send it to you..... kidding of course. Appreciate you guidance sir.

 

You can use a manual if you wish,but it's a simple removal of the exhaust and carb,remove the head nuts and head then remove the cylinder. You can take the cylinder to any good machine shop or dealer for measurement for an over size piston needed. Wiseco is the best piston out there instead the cheaper cast pistons that are on ebay.Product Search Engine For All Products - Wiseco Piston Inc.

 

Thank you for the info OPT, after I get back from a Texas trip, I will see about getting started on this, hopefully there won't be anything else found once the head and cylinder are off.

 

OPT - I was thinking this may have been caused by the broken air filter box and I live on a dirt road with dirt trails around, this quad until January hadn't seen that environment. If thats the case, do I need to clean out the carb and maybe the engine itself? I know it has an oil reservoir that injects into the carb but not sure if there is a oil area for the engine that needs to be drained. I'd hate to put in a new piston and rings and discover I should have done something else, appreciate it.

 

These old style air boxes were bad about the neck cracking at the bottom and if it was operated for very long, that in itself could be the reason for the low compression.Just sucks in raw unfiltered air straight into the cylinder. You can epoxy the box neck like many have done or replace it,but sounds like the damage is already done.Oil pumps were practically bullet proof on the old 250 and 300s. You don't have to change the oil in the tank,just add to it.The drain at the bottom of the engine is in case the the engine was flooded with gas. Again at 95 psi I'd pull the top end before a piston skirt breaks leading to more costs.Plus always check for ANY up and down play on the rod itself after you remove the cylinder. If there is any play(side to side play is ok) the lower end will have to be split,new rod kit,crank bearings and seals also. Premix first tank of fuel on a new top end or complete rebuild at 50:1 ratio to assist the oil pump in brake in.