I have meant to make a post about this bike since we finished it last summer, but haven't had the complete photo shoot we did of it. Now that I have some time on my hands, I thought I'd just go ahead and post it, and perhaps update it later with some of the more detailed shots.

Made specially for a Chicago customer, this Magnum incorporates some of the must comprehensive customizations MLM has ever done. The main thing the customer wanted was a powerful and flashy Magnum that would stand out from all the rest. We went a little overboard.

Starting with the frame, we cut off everything that it didn't need. As we hard wired everything, we didn't need most of the wiring brackets, harness, lights etc.; besides we ran it all through the frame. Long-time Motion Lefter Eric Vandiepenbos notched the frame and then using mysterious and time consuming methods, put a little folded slot in where the cables (brakes, clutch, throttle and wiring) would come out above the engine (pictures later). He also helped us fabricate and weld in the gusset and the rear of the frame loop. Then we brazed in all the unnecessary holes, rough factory welds, and imperfections, even adding a specially made arbour-presses semisphere where the tube frame terminates under the seat (pictures later, but you can glimpse it in the above picture).

Devon's initial idea for the bike was the Negrini tank, originally to be left polished and powder coated (my Puchavus tank was sort of a test run). While this does look great, it takes a many hours of work, and any imperfections which might occur during the time it sits at the powder coater's shop (even an hour) can ruin the finish, and by this point we were already overdue for delivery. Besides, it just isn't polished aluminum alloy... So we ended up powder coating it to match the fenders. The fenders come off a '78 Motobecane Traveler, obviously bobbed to withing an inch of their lives. The front fender goes for a standard cafe look, but the rear fender we decided to have have spring with the swing arm with a notch for the chain; more sport bike, then cafe. We left the swing arm stock, rather then adding a robot-arm to retain the vintage look. Spokes, nipples, hubs, brake drums and rims were polished by yours truly. 

The engine we knew right away was going to have be a single speed large port Metra 80 with a 24mm Mikuni. We found a clean set of cases, had them bored out to fit the massive cylinder skirt of the Metra, then ended up spending way too much time trying to get enough aluminum added to provide a sufficient base gasket sealing surface around the massive transfer ports. I think I went through the cases at least twice port-matching those things... Next we fabricated one of our notorious intakes, which, though without proof, Devin is convinced add to the intake acoustics. The Mikuni, through experiments with Devin's Pinto (in which the carb would run dry at high rpm's), required larger hosing and even petcock. The float bowl dumps we ran, neatly coiled, into the engine mount with rubber grommets. Terminated with a glorious chrome Simonini expansion chamber, accompanied by the necessary left-side pedal extension, the engine set-up was peppy and had an even, wide power band. 

We chose a dark, almost black high-gloss blue for the frame, forks and swing arm and silver for the tank and fenders. The wheels, hubs and headlight rim, neon green, with matching vinyl on the tank and fenders. M-bars, IRC 2.5" tires and a completely custom "bumstop" seat, along leather tank belt, and a water-jet cut MLM logo in stainless steel under the tank completed the bike.

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With 18:45 gearing, and a stable frame, the bike accelerates quite fast . The ride is firm and stable and is gives one far more confidence at speed (easily 60 when properly tuned over time as the cylinder breaks in) than the usual moped, cough-Puchavus-cough...
 
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The bike runs great. Unfortunately, the customer had a get off (sort of) and didn't realize the expertise necessary with such a modified engine, especially if its a two stroke, so there have been a lot of preventable problems... but then that's the name of the moped game...
  
Well, a moped is sort of an unpreventable problem, but c'est la vie.

MLM Custom Magnum

Posted on

Saturday, September 26, 2009

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