Spree cutting out at top speed or under load

[pitscooter]

I have been having a problem with my 1987 Spree cutting out whenever I am going faster or under a load going up a hill (max gas usage) it will start cutting out. If I back off the throttle and coast for a bit, it works fine until I go faster (25 mph) or under a load going up a hill. If I buzz around 15-20 mph, no problems. It seems like a fuel shortage because when I back off the throttle and coast, the apply the throttle it works fine. Here are the things I have done:
1. Thoroughly cleaned carb. I have 2 other Sprees and can do this pretty well.
2. Installed a new factory petcock.

Here are my guesses but wanted some other insights as it could be ignition related when it gets warm (doesn't make sense if no problems at 15-20 mph though). Even when I push it and surges to the point it shuts off, I can restart it immediately just fine.

1. The rubber intake connector to the airbox is leaking at carb. It currently does not have a factory clamp, but I could just use a tie wrap.
2. Vacuum or fuel lines going to the petcock are bad. Either sucking air or getting clogged on fuel.
3. Something is still wrong with the carb. Swap with one of my working scooters and check.
4. Could be junk in the bottom of the fuel tank which I can't see. Fuel tank is like new and I've mostly drained it, but who knows what someone may have dumped in before I bought it. Put an inline filter between petcock and carb.
5. There is a factory inline fuse up by the battery. The connection seemed to be spotty but I think that fuse is just for the starter system and not the ignition system.
6. There is some kind of ignition short when it gets warm. It could be the alternator or generator?
7. Bad spark plug or connection with plug. Do these us the threaded connection at the top of the plug wire connection or just standard as they come out of the box. I removed the aluminum cap and just kept the threaded portion exposed for the plug wire.

Again, the scooter starts perfectly, idles fine, runs at lower speeds perfectly. When it surges and even shuts off at high speed or under a load, it starts up immediately and works fine.

[pitscooter]

I thought I would follow up with an update so others can learn. The scooter runs great now. I replaced the vacuum and fuel lines, then zipped tied and taped the air intake at the carb to eliminate air leaks. The latter is what I'm guessing was the issue.

If you decide to replace your jug and piston from those available aftermarket online be sure to take the time to use a port grinder or dremel to ease the edge of all the ports. They are razor sharp and will likely snag a ring. Mine did and broke the ring. I had to replace it again after only about 10 miles.

Also, using premix (rich is ok) along with the oil pump during break in is a good idea. I ran a couple tanks and took it easy for about the first 30 miles and that helps break it in well. Finally, the proper way to set a piston and rings is initially through heat cycles. This is pretty easily done on a new rebuild by starting the motor and idle for about 5 minutes max to warm up, then shut it off and allow it to completely cool down. Do this 3-5 times to set the piston and rings. Then follow through putting on some miles with the premix getting it broken in.

[eclark5483]

They say heat cycling is the way to go, but that's not an exact science. On both of mine, I rode them at around 40mph+ all the way home from the shop at around 8,000rpm with brand new pistons. Didn't wanna take it to 11,000rpm until break in was done. That was about a 3 mile trip, then a couple more miles to my home through traffic. Still rocking it solid after over 4 years. We ride them almost every weekend if the weather is nice. A s for premix in the tank with the pump, this is fine for break in and recommended. I typically tell people to run 80:1 in the tank in addition to the pump for a couple tanks then switch to regular fuel.