83 ATC 110 spits and sputters

[kbags948]

Hey fellas,
,
I recently rebuilt my 83 ATC 110. Top end and new intake and exhaust valves. Cleaned and rebuilt the carb with all the stock settings and a fresh plug. I was pumped to hear it fire up after only a couple of pulls. Once I got it warm I set the idle and began to put around on it. After going through the break in procedure (a few days of light riding with gradual increase in speeds) I noticed that the engine would fall on it's face when wide open. I assumed it would be a jetting issue, but after speaking to several friends, whom all have 110's, they recommended that I check my base timing. We checked it and all seems in order. Still have the same issue. Anyone have an idea of what might be causing this? It starts like a champ and idles and shifts nicely, but won't get up and go.

Thanks!

[hokeplaya05]

mine is doing the same thing....when i get a chance i am going to dial in the air/fuel mixture screw on the carb, i believe that may be the problem. could be worth a try

[kbags948]

Hey thanks for the response! I've done some tweaking on the carb as well, but so far it hasn't done the trick. Let me know how yours goes.

[barnett468]

Hello kbags948;


OK, if it was PROPERLY jetted before AND all you did was bore it out or increase compression by installing new rings then you might need a slightly larger main jet. if you installed a larger cam or replaced a heavily worn one with the same profile new one you might need a slightly larger main jet. If you installed a less restrictive exhaust system, you might need a slightly larger main jet.

Since you touched the carb AND installed a new needle and possibly needle seat, I would check the actual gas level first by doing the following:

1. get a small 10” long piece of clear plastic tube.
2. connect it to the float bowl drain fitting.
3. hold it close to the carb with the open end even with the top of the carb.
4. open the gas valve on the tank and drain screw on the carb bowl.
5. the gas in the tube should be from even with the bottom of the main carb body to 3/16” below it. If it is outside this range, I would correct it.


since it starts and idles well, your pilot jet is extremely close to being the correct size imo, providing the idle mix screw is around 3/4 to 1 3/4 turns out.

without more info, i would also try moving the needle all the way up, then all the way down to see if you notice ant changes. if it runs better up your main jet is likely too small. if it runs better down, your main jet may be too big..

if you change the main, i suggest changing it by 2 sizes, 1 is not much.


I would also recheck the valve clearance in case it changed.

[kbags948]

Hi barnett468,

Thanks for the comments and pointers.

My first inkling was to play around with the jetting, but I had some friends telling me to check the timing and valves that I assumed they had to be right. I've had many 2-strokes apart in my life, but the 4-banger is a little new to me. Actually all I did was replaced the cylinder with a better (used) one with a stock bore and gave it a fresh hone. I installed a new piston and rings and lapped in new valves. There is a noticeable increase in compression from before, for the old cylinder was pretty clapped out and measured approx. 52.52mm on a mic. and had quite a bit of taper top to bottom.

I should have some time later this week to try the procedures you've listed above. I'll respond to this thread as to how or what I found out.

Thanks again!

[barnett468]

You're welcome, no prob, just hope one of them helps.

you have already done the hardest thing to do on a 4 stroke which is change the top end, so there is not a lot more to know on a stocker. you pretty much use the same technique to jet both a 2 and 4 stroke.

yes rechecking the timing and valves was a good suggestion by your friends. if you have points, i use a continuity tester to set them. they should break continuity when the F mark on the flywheel is lined up.

we'll look forward to your next post proclaiming success, lol.

[effort=results]

Is this a points motor or cdi. Also have u readjusted your valves after break in.

[kbags948]

Hi efforts=results,

It's a CDI engine. The last I checked them was mid-way through the break-in. I rode it for a while last weekend, so I should probably get it warm and check again. Thanks for pointing that out. Side note: How extensive of a break in process should there be? Any suggestions? I know you're really just trying to get the rings hot so they seat properly. I rode it 5 times or so at various speeds letting it fully cool between sessions. Is that sufficient? I also changed the oil after break in.

Thanks you guys!

[kbags948]

Hello kbags948;


OK, if it was PROPERLY jetted before AND all you did was bore it out or increase compression by installing new rings then you might need a slightly larger main jet. if you installed a larger cam or replaced a heavily worn one with the same profile new one you might need a slightly larger main jet. If you installed a less restrictive exhaust system, you might need a slightly larger main jet.

Since you touched the carb AND installed a new needle and possibly needle seat, I would check the actual gas level first by doing the following:

1. get a small 10” long piece of clear plastic tube.
2. connect it to the float bowl drain fitting.
3. hold it close to the carb with the open end even with the top of the carb.
4. open the gas valve on the tank and drain screw on the carb bowl.
5. the gas in the tube should be from even with the bottom of the main carb body to 3/16” below it. If it is outside this range, I would correct it.


since it starts and idles well, your pilot jet is extremely close to being the correct size imo, providing the idle mix screw is around 3/4 to 1 3/4 turns out.

without more info, i would also try moving the needle all the way up, then all the way down to see if you notice ant changes. if it runs better up your main jet is likely too small. if it runs better down, your main jet may be too big..

if you change the main, i suggest changing it by 2 sizes, 1 is not much.


I would also recheck the valve clearance in case it changed.

I ended up playing around with the needle height this past weekend. It seems to clean out pretty good on top with the clip in the lowest position (rich), which means my main jet is too small, correct? There is an 85 (stock I believe) in it now. One of my buddies has a 90 that I was going to throw in it. Will that be enough you think? I'll want to move the clip back to the middle position following I presume. I haven't tried the plastic tube test yet. What do the results of such a test indicate if I may inquire?

[YTZ drew]

The plastic tube trick is an easy, accurate way of checking float level, which is an important adjustment that affects the operation of every other circuit in the carb. On a lot of these carbs the float is not adjustable, so if the fuel level isnt pretty close to what it should be as described by barnett, it probably means you need a new needle or a float.

As far as the 90 main jet goes, try it and see how it responds. I think that a 90 is only 2 sizes bigger than an 85, and one jet size doesn't change much. I usually jump 2 at a time to help me figure out what the motor wants, then try an in-between size to fine tune if I need to.

[Sddoublee]

My 2 cents is to check valve clearance if you haven't already. Also make sure the small jet in the carb is clear. I fish a copper strand of wire from a typical stranded 14awg automotive wire through the jet and spin it. That's a good way to see daylight at the end of the jet especially if your eyes are getting old like mine. Then blow it out with compressed air. My experience with Hondas is it's normally not an electrical problem and it's one of those doh Homer Simpson moments. Also, intake o-ring if it ain't right it won't run right. Tight and sealed is important. Check the basics first. Good luck. Also make sure your timing gear isn't off a tooth. It's not hard to mess that up. Cheers!

[kbags948]

Thanks for the post. I actually just disassembled the engine back down to the cylinder. I have the head on the bench to check the valves. I removed the intake first, for that was the bad valve when I first tore it down. I recently installed new intake and exhaust valves/springs/O-rings. Everything looked ok, so all I did was lap them in. Well at first glance the other day (once I got the head off) I could see oil had leaked down past the intake valve, evidently it's not seating tightly. Should I just lap it in some more, or do I have a seat issue? If this valve hasn't been seating well this entire time I might be looking at the real cause of the sputter wouldn't you say?

Side note: The carb has a full rebuild in it as of late including the float needle. The kit didn't come with a seat. I'll perform this check once it's all back together next time.

Thanks for all the help everyone!!

My 2 cents is to check valve clearance if you haven't already. Also make sure the small jet in the carb is clear. I fish a copper strand of wire from a typical stranded 14awg automotive wire through the jet and spin it. That's a good way to see daylight at the end of the jet especially if your eyes are getting old like mine. Then blow it out with compressed air. My experience with Hondas is it's normally not an electrical problem and it's one of those doh Homer Simpson moments. Also, intake o-ring if it ain't right it won't run right. Tight and sealed is important. Check the basics first. Good luck. Also make sure your timing gear isn't off a tooth. It's not hard to mess that up. Cheers!