My son's LT80 has a top end sputter that I just cannot seem to get rid of. It is a little bit hit and miss, but mostly hit. I am running std Jack Moore motor and clutch mods and a stock carb and exhaust. It runs strong, just missing a little at the top. It is driving me crazy. I am looking for any input as to what might be going on. I believe it to be somehow related to an electrical issue. Just am not sure where to begin to remedy the problem. I did pull the flywheel and clean. This seemed to help a little, but did not FIX the problem. While running at the race on Sunday, the track owner even mentioned to me that it seemed "a little FAT"…..So it is noticeable. I just don't think that it is fuel related. I think I am running a 82 main jet? Thanks in advance for any help!

 

Last time we took our Pred-90 out (doing donuts on the ice), its engine "sputtered" at its top end as well. Checked the plug and it was loaded with carbon. Signs of too much oil in my premix. I also installed a hotter plug as well. Raptorlegs pointed out that I was running too much oil in my gas. I'm thinking the 10 degrees below freezing and lack of cold weather jetting had something to do with it as well. LOL!!!

How's your plug look? It should be beer bottle brown. Is your temperature dramatically different this time of year as well? Where you last raced, was its altitude dramatically different as well? Each of these things have an influence on "dies at top end".

To read your plug, surf:
http://www.exriders.com/techarticles/sparkcolors.html
http://www.motocross.com/motoprof/mo...lug2/plug2.htm

On an E-Ton brand, I also once read about their Spark Arrestor / Muffler being full of carbon. You may want to check that "carbon & crud" container on your unit as well.

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If its electrical, you could idle its engine and bring your it to a low warm state. Then, take a garden hose and spray all it wiring. Start from the bottom of the unit and slowly work your way up. If its engine starts to sputter, you found where an electrical fault "could be". This garden hose with spray sometimes finds electrical problems.

If that can't find it with external water, then its probably an internal problem. Change the plug, and swap out the coil with another LT80 coil. In the my old days, I had a set of plugs where one of them randomly stopped working at its top end. Took me over 3 weeks to find that problem. Hopefully, you've tried another plug and plug cap. And, hopefully you have another LT80 around that you can start swapping parts with. Those intermitting problems are always the hardest to find.


Hope these ideas help as well....

.

 

If electrical Spike's right, the plug is the best place to start.

If you determine it to be jetting. Here are some simple tests to help you determine if your main jet is lean or rich:

If you suspect a lean condition (not enough fuel):
Partially block your air filter/intake. Does performance improve? Yes, then jet up. No, then you're not lean.

If you suspect a rich condition (too much fuel):
Get on an open stretch where you can run it at full throttle. Turn the gas off. Does it run better as the carb runs out of fuel? Yes, then jet down. No, then you're not rich.


Works for me. If you try 2 main jets and you can't tell the difference, always go with the larger. Better to be a little rich then and little lean. Keep in mind you need to test the main jet at full throttle.

 

82 would be fat as it was sent to you with a 77.5 main. I don't understand how fat would make a top end miss tho. Usually lean gives a top end miss.
Maybe adjust the timing a lil each way and see if it helps.
I like spikes idea of swapping out electric components if possible.

 

Thanks all for the input.......

So, I will replace the plug and cap and coil.......

I did try advancing the timing ever so slightly when I had the flywheel off and cleaned all that up.

I have actually had this problem since Sept or so....So the temp does not seem to affect it.

I was trying the 82 to see if I could get it to quit sputtering.....Does not seem too fat to me!!!

Can I use a coil from any year? This LT is an 87.....I think there was some sort of change somewhere along the way in the coil?

Will keep you posted.

Thanks,
Todd George
Minnesota

 

Mine falls on it's face, lean or rich. A hair rich, it'll stutter intermittently. Got some juice out the tail pipe when it was rich, too.



(lol! I can't say that without laughing! [img]i/expressions/face-icon-small-blush.gif[/img] [img]i/expressions/face-icon-small-happy.gif[/img])