MOPED ARMY

If that is not a Perfect answer to a Specific Question...there is none to be found...WOW! Well done,Sir. Now we need Vespa Guru's....Impressive. Peace!,B.

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Thanks, yea I'll do that, I need to talk to them about the dellorto intake anyway

So you think it's shorter at the crown end? I was interpreting that as it was shorter at the skirt end, which might like... increase the intake port duration? (I totally just made that up.)

And yeah, talk to Ike. He's awesome, he'll hook you up.

would this be a good replacement?

http://cgi.ebay.com/ebaymotors/Tomos-Golden-Bullet-A3-Standard-Engine-Piston-Kit-NEW_W0QQitemZ220397905552QQcmdZViewItemQQptZOther_Vehicle_Parts?hash=item3350bd2690&_trksid=p4506.m20.l1116#ht_500wt_1756

So couldn't you just trim your piston skirt on the intake side a little?

You could probably look to see how much the skirt obstructs the intake port and trim it. That said not everyone wants to dig into a running engine and start grinding things.

Some people swear that you can get the Dellorto off if you unbolt it at the intake/cylinder joint (rather than at the intake/carb joint) and mess with it. I think if you do that and completely remove the idle screw, it might be possible, but it's still more of a PITA than just dropping the engine in the first place. Although ... you don't have to completely drop your engine. If you remove the front two mounting bolts and leave the bottom/third one, it should pivot down and give you access to the carb. You still have to mess with the chain and exhaust before doing that, though (bleck), and if you let if pivot too far, you could potentially hurt some of the wires from putting too much stress on them.

I don't know about anyone else's engine, but it's damn near impossible to get a good look down that intake and see what the piston is or isn't doing. Not only is it right under the frame, the intake port also offset on the outside. I guess I could drop the engine, but... uggg.... I'm kind of wondering if you would get better flow if you smoothed out/opened up the intake port (so the offset isn't quite as strong). I guess your intake is still only 12mm though, no matter what you do to the intake.

If it were me, I'd take off the head and cylinder, then take the piston off. Then away from where everything else is sitting, I'd probably dremel it down, and then finish up with sandpaper to make sure everything was reasonably smooth. I'm no expert though, so if that's the wrong way to go about it, I hope someone will enlighten us. I'm also not sure whether you'd just trim the portion of the piston that covers the intake port, or whether you'd just trip the whole top side of the skirt.

I can't be sure but one might take a peek into the intake and make sure the piston skirt isn't obstructing the intake port at top dead center. I tried this with a spare cylinder but I only have a 50mm piston.

so any news???

I mean, I have no idea how I'd go about trimming a skirt, I think shit would get fucked up.

If I just replace the 52mm piston with a 50mm piston would that work? Wouldn't that fuck up bore and stroke specifications?

I'd like to know how much of an impact this piston ordeal has on my power. If I get a different pipe, sprocket, and open the airbox, would that be enough compensation to get my GM riding like an SP?

Just trying to figured out how much of the weigh of my problem has to do with the piston. Anyone have any experience with this???? I'm sure someone has done it.

Gotta be people out there with A3GM motors.

Ok, yea i wish... I found out that theres an A3 SL that only has a top speed of 20mph! it has a 55 mm piston. Glad I don't have that! lol.

So I should try go for replacing it instead of "trimming the skirt"?

I might just get the tomos dealer to do the labor so i don't fuck it up. I wonder how long of a job it would be. My uncle thinks changing the piston size fucks the bore and stroke up and that I'd have to get a different cylinder and other shit too. He said, "With an engine, 2mm is the difference between it working and not working."

*Again, if anyone has done this, please, feel free to share your experience.

Oops, sorry, I forgot to look. I'm nowhere near my Tomos right now, but I swear, I'll check the gearing on it as soon as I can. I bet that you could change out the piston by yourself and save a bunch of money on shop charges. Just take off the head and cylinder, then remove the circlips, push the wrist pin out, take the old piston off, put the new one one, and reassemble the same way you took it apart.

Oh, and on the piston sizes, here's my not-drawn-to-scale diagram:

Nope, mine's an SP. I'm still working off the theory that shortening the piston skirt length increases intake duration, which means that the fuel has longer to enter the engine, which means that you should get more fuel into the engine to combust. I'm far far far far from an expert on how two stroke engines work, though, so maybe I'm off on that assumption. Also, there are going to be tradeoffs for anything you do, and I don't think it's a good idea to mess with something if you don't know what the tradeoff will be.

There are formulas you can work though (I think) that will probably tell you how much of a difference that intake duration makes, but (a) all that stuff is over my head, (b) I don't have a tool that I think could accurately measure the things that need to be measured, and (c) even if you did do all the math, you're still dealing with an itsy bitsy intake port and an intake manifold that's only 10 or 12mm or something.

I might be down for the "hack on our piston skirts" plan, but I'd need to look at it more closely before I started doing that. I also have it in about a million pieces right now, and I'm supposed to loan it out to a friend sometime sooner rather than later, so I'm in a bit of a time crunch to get it back working (faster or not) again.

The whole point of this is to make it go a little faster, right? I guess I'm too lazy to read back through all of this, so I'll just ask: what all have you already done to it, and how well did all that work? There are a lot of things that are easier and safer to change besides the length of the piston skirt.