My XT tops out at about 72 mph GPS on a flat level road with no discernable wind. But I weigh 240, and carry about 20 pounds of stuff with me, and have at least another 30 pounds of accessories on the bike (luggage rack, metal basket, kickstarter, centerstand, and an aftermarket tank that holds 4 gallons) But I don't think weight makes much of a difference when it comes to top speed on a level road with no headwind, though it may take longer to reach that speed. But the sputtering is not normal. I have ridden mine from below 1000 feet to around 12,000 feet, and while it does run a little rich and loses a little performance at high altitude, it's still perfectly ridable, and doesn't sputter. In my experience, sputtering is usually caused by fuel starvation, though there are other things, such as an ignition problem that can cause it. Just a bad spark plug can cause incomplete combustion at high rpm.

...


What Front/Rear Sprockets are you running?


I dropped one(1) tooth on the front sprocket.
That was all I changed.

I carry around 240lbs.

First gear is real low.
I can now take off from a flat hard surface at an
intersection, in 2nd Gear.

In the dirt, it is perfect for me. I love 1st gear.

On the top side :

If I go through the gears on the highway
and hit a rise or slow down a bit, in High Gear,
It begins to bog and says, "Downshift" !!!


youngfred

I'm fairly sure the problem you're having is due to a seized caliper piston. More likely caused by corrosion in the groove forcing the seal tight onto the piston. The only cure is to strip, clean out the groove, and fit new seals & a new piston if it is in any way marked. Do it before it has you off.

I followed all the above here and cleaned the carb and found it surprisingly clean. The clip was floating around loose on the fuel pin and there are a couple of missing o rings. Put it back together right and revved it up and then took off up my steep driveway and it sputtered in 1st with about 1/2-2/3 throttle and then died dumping the bike on me on the hill. I've ordered a new carb and waiting for it to arrive.

In the meantime, took all your advice and took apart the caliper. The brake fluid still didn't drain properly from the line and the fluid in the piston was so bad even after flushing the line that I decided to break down and clean the master cylinder too. Wow. Just wow. So much junk in the brake system. I can't believe it. There's this gummed up stuff stuck to the inside of the cylinder and bore and on the piston. It won't come off with cleaner or even with scrubbing using a toothbrush. What could this be? Do I need to just give up and order replacement cylinder and caliper sets or is there something else that could clean this up? I've never seen this before. It's almost like a rubber like sealant got spread all over.

Looks nasty! I'd try CRC Brakleen or Berryman B12 carb cleaner. It's just a matter of finding the right solvent. Make sure to replace all the rubber parts with new ones. It's hard to guess what caused this. For obvious reasons, you'll want brakes to be working perfectly. Good luck.

Welp. The whole brake system is toast. I was able to get the "gum/glue" off the caliper, piston, master cylinder but everything is pitted. It turned to a white powder on the master cylinder but I don't think I should even save that.

Here's what I tried: brake cleaner, then simple green and tooth brush, then simple green and a soak in almost boiling water and a toothbrush is what finally did it. Was going to try the suggested cleaners next but discovered the pitting. I really hate that I'm going to spend the money on a full brake system still not knowing why the bike sputters with a lot of throttle.

Thanks for the suggestions everyone! I'm slowly working through them.

[img]https://imgur.com/a/DrlPBnU[/img]

You need to take this one problem at a time. As I understand DOT3 brake fluid, it does attract moisture from the atmosphere which would explain O2 induced corrosion (pitting). If the machined surfaces are pitted throw those parts in the garbage, replace with new parts and move to the next problem.

You should check compression, valve clearance and plug. You're looking for ~145 PSI as I recall. That's what our bikes measured at 15k miles of hard riding. Someone with a service manual hopefully will jump in on the compression reading. I'm going from memory. Good compression means generally a healthy combustion chamber, valves and rings. Good luck.

That stinks that the brakes are corroded. Perhaps this is an opportunity to upgrade the marginal stock system.

As for the carb, did you warm the bike up? These bikes are notoriously cold natured. If I started mine and immediately tried to climb a hill, it would fall flat on its face too