First bike, mod guidance

Robert Macleod /

Hey all,

I have had a Puch Magnum Mk2 lying around with a pretty cool story behind it. It was my grandad's, and he let me take it to rebuild and use about six years ago. Needless to say, I just got it running now. It was ridden by Robin Williams around the island where he filmed "World According to Garp", and parked at my family's house where the filming was done after the filming ended. It is pretty beat up cosmetically, but I just want to be able to ride it again. Being young and speed-hungry, I would love to get a little more out of it while keeping the original look to a degree, so aftermarket pipes, for instance, are out of the question. I have been looking around the forums but am a little overwhelmed at the options. The bike as it sits is all stock, 12mm carb, stock exhaust, and intake. Right now it hits about 25-30 full bore. Any routes I can take to get just a bit more? Rejet, modify the exhaust a bit, and new intake are what I am thinking but want to hear what options are out there while keeping the stock cylinder and exhaust. Any help is huge

IMG_2096.jpg

Re: First bike, mod guidance

Luke Stroehlein /

Hey, what a cool story and a pretty bike. Not trying to be a downer and others may disagree but 25 to 30 stock is pretty damn good. Without at least a bigger carb and a pipe you'll essentially be wasting money on things like intake or jets. The stock engine was engineered to run with that jet, up jetting on a bone stock setup will throw off the afr and probably cause you to four stroke. Either keep that bike how it is and enjoy it for the nostalgia and the story, or visibly modify it and enjoy increased performance. The potential and availability of aftermarket parts for these bikes is endless.

Re: First bike, mod guidance

Robert Macleod /

So far I have stripped the entire bike to the frame for a clean and because why not, I was bored and stuck at home. Rebuilt the carb with new internals, new cables all around, new shift pucks, tires and tubes, fuel line with filter, tuned said carb as best I could, rebuilt cylinder with new gaskets and piston rings, brake pads, and a bunch of cleaning. Planning on buttoning it all up tomorrow just to ride, for now, pics to come. Unfortunate that I can't get it registered in MA right now with everything going on :(

Re: First bike, mod guidance

That was a good movie. Cool story.

Re: First bike, mod guidance

Luke Stroehlein /

Sounds like you're doing all the right things to make it a good reliable cruiser. Just leave it stock.

Re: First bike, mod guidance

Yup, clean and inspect points, cam, and follower, clean and re-grease steering head and wheel bearings, get some new tires tubes and chains, and you should be all set.

For just a little extra oomf while keeping the stock spirit you could swap to a 14 or 15mm Bing and intake and get the larger header pipe from Treats (sold out at the moment tho) https://www.treatland.tv/puch-stock-pipe-angled-p/puch-stock-pipe-angled.htm

Re: First bike, mod guidance

Rob,

Awesome bike and history

I used to have a maxi and my intentions with it were to learn about 2-stroke tuning by making the most mods I could to stock parts.

I like where you are going with this project.

I did put a techno boss pipe on my maxi because it looked very close to stock and was essential to squeezing more speed out of a moped.

Besides that, I bored out the stock carb to about 15mm. I cut away some of the piston skirt on the intake side. That advances the intake timing and increases duration. I drilled boost port holes in the piston above the wrist pin and Ground out matching boost channels in the cylinder which where a little advanced of the transfer ports. I think I read about that forcing a little cool mix through the piston which is good for temps and lube. They were small - maybe 1/4”, not very deep, and just off to the sides of the intake port. I think I also made an aluminum shim (about 1mm) to put under the cylinder and the sanded off a matching 1mm from the head. Maybe even polished those surfaces and ran without a head gasket.

Most of that can be done incrementally. Start small. With a lot of tear down and rebuild. Get good at cutting gaskets and make new ones each time.

When it was done, it would pull my 200 lbs ass up to 36 mph on flat ground and could rev high enough to reach 48 bombing down a hill. I rode WOT everywhere for up to an hour at a time. If I rolled down a hill and not back up another, it would maintain ~40mph on flats. Until the next incline or headwind stole some RPMs.

I don’t have pics anymore of those mods, unless they’re in old threads here on MA. All the info is somewhere in the vaults of this forum. Thanks to corona, I also have lots of free time. Feel free to ask me anything if that ^ crap sounds good to you.

Re: First bike, mod guidance

I have a 15 mm bing $50 shipped. (edited)

Re: First bike, mod guidance

Incelforlifebaby!hotandhorny69 646260 /

That bike is sweet! I wouldn’t touch much, and story is a story, do you have photos with the guy sitting on it?

Yes definitely keep us stock, if you want a bike to cut up call me and I’ll give you a maxi for next to free

Re: First bike, mod guidance

Robert Macleod /

Thanks all for your help! Put everything back together today so it's basically the way it was factory. Going to focus on getting it registered and actually ridden on the road instead of bombing up and down the long driveway for a change, and really get a feel for how it rides. Did get some good pictures of the finished product, so I figure I'll share those. Behind the bike is an '81 Toyota FJ60 if any of you were wondering, nice to finally have some good weather to get out and drive it.

IMG_2099.JPG
IMG_2100.JPG
IMG_2101.JPG

Re: First bike, mod guidance

> Robert Macleod Wrote:

> -------------------------------------------------------

> nice to finally have some good weather to get out and drive it.

You must be talking about the the Toyota as that is driven and the Puch is ridden .

Both are in very nice condition . ;)

Re: First bike, mod guidance

Do you have any documentation about the robin Williams story on the bike? May make the bike more valuable in the future? Robin Williams was a great american actor and that movie is now a classic. May look into the docs and just keep the bike as is and hold on to it. Never heard of a moped story like this. This could be the most valuable magnum in history if you can get pics and shit with him. Very cool. (edited)

Re: First bike, mod guidance

doesn't look too beat to me. you've done everything right so far and 25-30 completely stock is exactly what it's supposed to do. Fresh tires properly inflated, a clean regreased wheel bearings, and a new properly lubricated chain might net you another 1-2 mph. you could also check for and clean any carbon build up in the exhaust port and header and of course you could gear up a tooth in the front.

being that it's a za50, you'll want to replace the shift pucks as well and change the trans fluid as preventative maintenance step.

Re: First bike, mod guidance

Robert Macleod /

> Dave & Bummerzz Wrote:

> -------------------------------------------------------

> being that it's a za50, you'll want to replace the shift pucks as well

> and change the trans fluid as a preventative maintenance step.

Shift pucks got swapped out for atomics when I went through the trans, and with that put in some fresh oil. The only real modification I have done was to add an oil pump delete kit from treats. I still have it on hand should I choose to use it, but I figured it would simplify everything a little more, and having total control of fuel: oil mixture was appealing.

ZA-50 shifts smoothly right at about 15mph on flat ground. Really likes to settle in at about 20-25mph with everything all said and done. Really hoping I can find a picture in the old scrapbooks somewhere of Williams on the bike, right now it's all just the story I have heard from my grandfather who gave me the bike.

Re: First bike, mod guidance

Robert Macleod /

Hey all,

Been a while, but I wanted to ask about the gains I can expect to see from dropping a gear tooth on the front sprocket? I currently have an 18T front and 40T rear giving me a .450 ratio. I want to drop down to a 17T front sprocket, or up to a 42T rear. Curious about the top end MPH gains I could see. Thanks

Re: First bike, mod guidance

> Robert Macleod Wrote:

> -------------------------------------------------------

> Hey all,

>

> Been a while, but I wanted to ask about the gains I can expect to see

> from dropping a gear tooth on the front sprocket? I currently have an

> 18T front and 40T rear giving me a .450 ratio. I want to drop down to a

> 17T front sprocket, or up to a 42T rear. Curious about the top end MPH

> gains I could see. Thanks

Dropping the front or raising the rear will get you more low end performance .

What you gain on the low end gets taken away from the top end .

Re: First bike, mod guidance

Robert Macleod /

> P D Wrote:

> Dropping the front or raising the rear will get you more low end

> performance .

>

> What you gain on the low end gets taken away from the top end .

Shoot, I misspoke there, was in a rush. I meant adding a tooth in the front to a 19T or dropping the rear to a 37T. Looking for more top-end speed, while not utterly destroying the low end. Not looking to win any drag races, but at least being able to sort of keep up with traffic would be nice.

Re: First bike, mod guidance

> P D Wrote:

> -------------------------------------------------------

> What you gain on the low end gets taken away from the top end .

Just remember that the opposite of that^ is also true .

Re: First bike, mod guidance

Tou can upgrade the carb to a 15bing. And grab one of these pipes

https://www.treatland.tv/puch-maxi-chrome-stock-pipe-tecno-p/puch-maxi-stock-pipe-28mm.htm

Which may boost ya up a little. You could take off the cylinder and open up the intake and exhaust ports a bit. Get it jetted and tuned and you should be mid 30's easy especially with the re-gearing as mentioned. Or just keep that guy minty and find another sweet bike to mod up for fast fun. Super cool story. I love Robin William's. Would be cool if someone came across Hot Rod's red tomos...

Re: First bike, mod guidance

Go to a 37t in the rear. ZAs have good torque and can pull it. Also, you can reuse your chain (may have to shorten it).

If you go to a 19 in the front you may have to grind your engine case a little and you may need a longer chain.

Re: First bike, mod guidance

Robert Macleod /

> Jay Rivett Wrote:

> -------------------------------------------------------

> Would be cool if someone came across Hot Rod's red tomos...

That gives me the idea to soup one up so maybe he could have made that jump (given a properly reinforced takeoff ramp)... HAHA. It would be cool to build one to look like the movie but turn it into something that would send Rod into low earth orbit.

Re: First bike, mod guidance

I'd love to see a video of Robin Williams on the bike, having issues, and then screaming, "Shazbott" at it.

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account