I've decided that I'm not good at two things. Talking my way out of tickets, and taking up close in focus well lit photographs. So, I have a few things I've done recently. My magnum has been running at about 32mph, and the bing was starting to leak when the fuel was left on, so I decided to jump up in carb size like I've wanted. I took the cylinder off and opened up the intake from 15mm to 19mm to match the intake I got from Brian. I have not widened the port on the inside just yet, I want to see what I can get without porting before I jump into that. So with that matched, I reassembled it and my 19mm race carb clears the head just perfectly so that I can still change jets without messing with its location. That's a nice thing compared to my Maxi where jet changes are a big production. With the 19mm carb, I noticed a much better throttle response and power at all RPMs. It also starts nicely now, on the first kick. It probably went about 34mph after the carb upgrade, but I feel a little lean, as the top 1/4 of the throttle just seems to make the bike louder, not any faster. I've got a 93 main, my next smallest is a 105, but I might try to find some middle ground with jets on Tuesday when the shop is open. So I had a better running bike, but I'm still lacking power. Today, I took an extra magnum sized cylinder head I had and tried my hand at "milling" which could be more accurately described as "eyeballing it". I could turn it down by hand, but that takes a long time, and I've got two spares, so I might try the quick and dirty method, Bandit style. I took a thick piece of glass as my flat surface (which happened to be the end table in the apartment). Then I encouraged my wife to leave and go work out, since I doubt she would think kindly of me possibly destroying her end table. Once she was out of the house, I busted out the tools, taped some 80 grit to the glass, chucked a spark plug in my drill and began to spin that big old head.
It looked really funny, and took a lot of skill to try and keep the drill steady. It turns out spark plug holes aren't exactly centered, they seem to wobble a little. I turned it down from nearly .9 inches to about .25. I didn't want to take it all the way to the fins just yet, I wanted to keep a little bit of squish band. I proceeded to tape some 150, 200 and then 600 grit sand paper down and ran it for a few minutes on each, ending up with a nice shine. You can see the finished product it in the background of this picture. The out of focus part is a stock head, and you can see the feeler gauge showing the difference between the stock head and what I've turned mine down to.
I put it on the magnum and noticed no air leaks so far, as well as a huge increase in torque throughout the power band. I can actually accelerate up hills once I hit second gear which is a new feeling for this bike. I left my compression tester in Nebraska, so I have no way to get a reading, but I can feel it, and that's good enough. I also bought some spark plug wire and a boot, and made a new plug wire for this bike, since the old metal cap was starting to fail on me, working its way off and what not. The spark seems super perfect with the new wire and boot.
I would like to take one of my other magnum heads to someone with a lathe and actually turn it down "the real way" so I'll see what I can work out, but I feel good about my method since it worked well, and I didn't break the end table.
The last few months I've been trying to understand why someone would buy one 16" white wall tire from the moped shop, and leave the other sitting on the rack, taunting me every time I walked in. I finally found a place that had them in stock, and made a purchase. The showed up today and since my wife was at work, up the elevator comes the bike! Changing the front took 15 minutes, including polishing the rim up with steel wool. I also discovered how to remove the speedometer cable, by twisting the actual housing of the cable, which was a new-to-me trick. The rear tire took much longer. Something to the tune of an hour and a half. Side covers off, engine mount bolts loose, push wheel back, deflate tire, remove belt, hold the moped in one hand up in the air while pulling back and down the deflated tire so there is enough room for it to drop from the subframe. It took about 20 minutes to clean the wheel up, and I got to mess around with that transmission in a rear wheel for the first time, what a novel idea! To put the wheel back on, I had all kinds of trouble, and I also forgot it needed to be flat to get in there, so I had to let all the air out, and then once again hold the bike with one hand up 2 feet in the air while bringing the wheel into the right position lining the variator up into its bracket. The next 45 minutes was spent trying to stretch the belt back over the variator, which was no good. So then I disassembled the variator so I could just put the belt on without stretching it and cheat. Unfortunately, I have no piston stop, and I couldn't find my usual rope, so I had to wad up some cloth to feed into the cylinder, and it did not work as well as rope. Maybe I should get a piston stop as a gift to myself for Christmas. After assembling the variator, then realizing I didn't have the inner cheek properly aligned, I had to remove the whole shebang again, including the "piston stop rags" which took a while to get properly inserted into the cylinder. So finally it came all back together, and here is the finished product.
I think I need to up jet just a smidge more, I'm in the mid 60's with a stock cylinder, 13:13 high flow filter and the Sito exhaust. In case I didn't write about the Sito, I like it, it clears my pedals, kick stand, looks stock, sounds quiet, costs $50, bolted right up and gave me a 3mph top end boost and some low end grunt.
