Does any one know what the compression should check at on a 2002 model? Still cant get my sons to run. How do you know when its time for a new piston or rings?

 

I have the service manual at home. I'll check and try to post back here.

General rule of thumb on 2 strokes is that you need at least 100 PSI for proper operation. If you're already reading lower than that, I'd say something needs to be done.

 

I had checked the compression before doing some work to it about 2 months ago and it was 120. I never checked it after doing the work. I decided to check it now that it wont crank and it is only 100. Part of the work I did was shaving the head. So shouldnt the compression have gone up and not down?

 

I checked the manual tonight. Amazingly, there is no spec for compression. I read all the way through the specs and the engine teardown/rebuild sections - nothing. The only thing I found was the compression ratio, which is 5.6:1. If we presume normal ATM of 14.7, then theoretically the max pressure would be (5.6 * 14.7 =) 82.37 PSI, which sounds awfully low.

More important is the fact that you've now reported - that compression went DOWN after you shaved the head. That suggests you have a torn gasket, bad or badly seated rings, didn't torque the head bolts in proper sequence, etc. Given this new info I suspect you reassembled something improperly. Did you use all new gaskets? Did you use anerobic gasket compound with them too?

 

I reassembled per the shop book (which as you said does not give the compression specs) with all new gaskets. I did not use any kind of compound. I ran this quad, with no problems, after doing the mods. for around a month. Did not have any problems with it until I washed it after my son had gotten it very muddy. It cranked with one pull before and after washing it. But after letting it sit to dry it would no longer crank. I have checked and rechecked everything one should, if they thought water was the problem. Since doing the mods the atv ran much better and would rev like never before (sounded like a pi$$ed off weed eater). It was rode hard all day long the day my son got it muddy. It makes me think something internal engine wise is wrong and just happened to show up after being washed and drying off. The atv has never been rebuilt and has a lot of hours on it to be a 50.

 

OK, now that we have more data....

You added water and it stopped running properly. What else do you know? Do you have spark? Have you tried fresh fuel? Have you put a bit of fuel into the spark plug hole to see if that will run it momentarily?

 

I do have spark, but when I first ohmed the coil I got a bad reading. Turned out I had to replace the spark plug cap. Drained and flushed fuel and oil. If I unbolt the muffler and use a spray bottle to spray gas into the carb. opening, and leave the choke on, it will crank and run for several minutes. But dies if I attempt to change anything. The muffler has the spark arrestor removed and I have looked inside the muffler and it is clean. This is why I checked the compression, and found that it was lower than it was a month or so ago before I did the mods.

 

If the engine has fuel, air, and spark it will fire. It's missing one of those. Since it will run when you manually provide fuel, it seems pretty clear it's a fuel problem. I'd clean the carb and check all its circuits, plus confirm that fuel flows freely out of the check valve (remove the hose from the carb temporarily).

Report back!

 

Have had the carb off about 3 different times now. It was completely broke down (all jets removed etc.). If it was a carb issue then why would it cut off when I rebolt the muffler? (just asking) Also I do have a good stream of free flowing fuel from the valve. I am thinking about pulling the jug off and checking it and the piston. What are your thoughts on doing this? Also does this thing have a reed valve of some sort? I dont remember seeing anything about one in the manual, but then again I did not look hard. I am thinking there should be some sort of device between the carb and jug. Thanks for your help, I really need some!

 

I've rebuilt that carb a couple of times. They're not complicated, but the one tricky thing I found was the float. The manual's instructions and photo for setting the float height were useless. I had to fiddle with it a while to get it right.

If the float is wrong you may not have any fuel in the bowl. When you have everything buttoned up, and try to start it, do you get fuel on the spark plug? In other words, do you KNOW that fuel is making it through the carb and into the cylinder?

I'm still deeply suspicious of the fact that you can manually put fuel through the carb and get the engine to run. Lots of things have to be working correctly for that to happen, and it points very strongly at a fuel delivery problem. The float could explain that, or a stuck needle+seat.

Please report on the condition of the plug tip after drying it off completely, reinstalling, and pulling the cord a bunch of times.