Aprilia Classic 50 (2 stroke)

[Dekani]

Hey i decided to put in a new cylinder kit with pistons and all on my bike.
After installing it, i have had a hard time starting it when cold but once I get it going it's easy to start once hot.

The other problem is a big one, this bike used to be able to go like 60 mph, but now it will make a big "bump" and die once I reach 40 mph.
I can start it up right after it dies, but it just keeps dying at 40.

On the other hand it does not have a problem with high RPM at all.

I cleaned the carburator, changed the jets, fuel line and membrane, and i also rechecked the wiring just to be safe, but to no effect..

When i broke in the rings, i let it idle for 3 times 20 minutes and i drove slow for about an hour, it drove perfectly at that speed.

Hope you guys have an explanation, cuz I'm at a loss xD

 

[Chainlube]

Got a picture of your engine? What prompted you to change the cylinder?

 

[Dekani]

Bought it used, and the old top had a crack in it.
But since there is a limited supply on spare parts , i figuered id buy a complete set and switch it all out.

I usually drive cars and fix them as well, bought this one as a hobby project.. Turns out to be more tricky then I thought haha

 

[Chainlube]

Hard starting sounds like an electrical issue, have you cleaned all your grounds? I fixed a tiller, the guy said it doesn't have any spark. I pulled the coil and sanded down the contact patch and away she went.

 

[Dekani]

No i haven't cleaned, i just tightened and checked for damages, i will definitely try that.
But that doesn't account for the 40 mph limit, does it?
I compared with the old cylinder and piston, it's completely identical except the placement of gasket.

 

[Karl Snarl]

Hey i decided to put in a new cylinder kit with pistons and all on my bike.
After installing it, i have had a hard time starting it when cold but once I get it going it's easy to start once hot.

The other problem is a big one, this bike used to be able to go like 60 mph, but now it will make a big "bump" and die once I reach 40 mph.
I can start it up right after it dies, but it just keeps dying at 40.

On the other hand it does not have a problem with high RPM at all.

I cleaned the carburator, changed the jets, fuel line and membrane, and i also rechecked the wiring just to be safe, but to no effect..

When i broke in the rings, i let it idle for 3 times 20 minutes and i drove slow for about an hour, it drove perfectly at that speed.

Hope you guys have an explanation, cuz I'm at a loss xD

Why did you let it idle like that to break in rings? You may have glazed the rings and cylinder, so it wont seal right and loss of power. When doing a top end, lube during assembly, then start. Get it to idle and move decent. Go for a 10 to 20 min ride. Get it warmed up and moving. Find a nice hill. Hammer it up that hill during your 10-20 min ride. Let it coast the other side. Hammer up the hill a few times. Go home. Let it sit till hand touch cool. Check torque. Go do the hill and warm up again. Go home. Hand cool. Check torque. Go do it again. Go home, cool, check. Your now broke in. No need for babying. You're trying to seat the rings. Need some power to dig them in to the cylinder and knock down the peaks.

 

[Dekani]

Well actually didn't know how to treat the pistons after, so visited a lot of sites and they said it need to idle for some time.. But apparently not xD

 

[Karl Snarl]

Well actually didn't know how to treat the pistons after, so visited a lot of sites and they said it need to idle for some time.. But apparently not xD

Oh never idle long on a non broke in engine. Just wears it out faster and glazes the cylinder. Ive always just went with a little bit more oil and rode them how i planned on riding them. Varying throttle a bit and not keeping it at one rpm for break in. Dont even take a full take to seat thr rings. Just 3 or 4 good heat cycles and some heavy load during it. An the oil, syn or dino ( syn is dino oil, just worked a bit. Its all dino oil) doesn't make a difference. Syn is not to slick regardless of what some people say. Just use the oil you are going to use, slightly more for the first tank, to get the metal debris from break in out and to make sure the bearings are lubed good. After first tank just go to the ratio you want, and set the jetting. Breaking them in hard makes em last longer, the race guys taught me that as a child when i was in the pits grabbing the tools for em.