magnum stuff

So hopefully you say gabe’s awesome polini guide, and I thought I’d show you mine. I’ll be honest, the quality of my work is subpar. The exhaust port is nice, but the intake embarassing. Regardless, it runs really well, and its done stupid speeds, and It’s going to only get dumber.

In the cylinder (exhaust raised a lot, widened a lot, intake opened completely) The little scuffs, one at the rear of the port and the other 2 in front were me not good at using a dremmel.

The intake, again opened up all the way, and I filled it a bit with JB because the malossi 4-petal has a lot of wasted space in there

Transfers opened up just a bit. The most important part is opening up the upper transfers. Plenty of meat on the cylinder, so its un-tapped potential. Also, remember you MUST open up the outer portion of the exhaust port to to actually match the flange of your exhaust. Polini’s are tiny, just a bit bigger than stock, but much smaller than 99% of expansion pipes (except proma circuit, they are a perfect match).

Paz originally built my ZA for some other fella in SF. He didn’t go super deep with the upper transfers, but everything is nicely done. A roller rod was pressed in at the same time. The crank has 2k+ miles on it, so super solid!

Thats my ugly polini. I’d like to get another one in the near future as I worry this one may be slowly heading out. It was seized before I bought it, and there is now a fair amount of discoloration on the nicasil around the exhust port. All the cross-hatching is gone. Compression is OK, but not as good as it could be. That, plus I’d like to re-port another with a lot more care.

So in semi-related news, I’m going to make this thing rip harder than it ever has. Either selettra or HPI ignition (selettra is a few OZs lighter, but I think HPI has a little better curve), and my flatslide mikuni.

I want to race something come april, and even though this probably won’t be competitive, with the right gearing (N8P forever!) it should have really good pull. I don’t want to scrape up my LTD seat or tank, so I’m going to be using a freespirit pan and my spare C5 tank. That plus my disk brake EBRs. My goal is to have it running and semi-tuned by tomorrow. I’ll keep posting. Whistler from the 20th to 27th!


derbi, attempt 4
August 20, 2009, 2:56 am
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racer renditions:
1-gila, 24 oko, metra bendy pipe. Seized in the canyon in LA, got it running, matt raced it, seized it again.
2-gila, 24 mikuni, metra bendy. seized by matt again.
3-gila, 24 oko, puch cdi, zen. seized racing
4-current build.

so the previous builds all had their own issues. I thought number three was solid, and it ran well, but super noob jetting made me seize it. So yea, now its being done better, maybe not perfect, but better no less.

I wanted to run a metra 80, but those pistons are not available, so I’m going to run my polini instead. New intake, ported the exhaust and transfers a bit more, cleaned up the case matching, milled stock head ghetto polished, and its going to run a 24 mikuni. I got the selettra cdi just cause, so we’ll see what that does. The zen has been re-angled too many times, and it needs to be done once more. Hopefully everything together will equal a sweet blaster. I need to get a piston tomorrow, fix the pipe, and it should basically be good to go after double checking the timing. I don’t know if it will be crazy fast, I doubt it, but it should run well. I just want a shit ton of midrange like tom’s bike so its quick through the turns. I’d like to change clutch springs too, but we’ll see about that later. Paired with amazing brakes, I should be able to get some decent lap times.

check out these sweet bikes:

Kind-of Limited
March 22, 2009, 5:41 pm
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So I threw my limited tank on thinking it was clean, but its not. Shit clogged my carb really bad and I don’t have the time before LA to properly clean and coat the tank, so it will be a one of a kind-of limited. It running really well, my same polini setup on a za50. 20t front sprocket coming soon for crazy speeds. Maybe you will be passed by this ugly thing at LA. When you see the brightest headlight ever, its this bike. I’m pretty excited cause all my mopeds are running well, and I’m done for rally action so I can just study for finals this week. You are probably jealous.

December 11, 2008, 2:39 am
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So today was mostly uneventful, I simply got derbi all torn down for powder and paint. Everything came apart really easy which was nice, and the whole frame wasn’t super grimy like most 30+ year old mopeds. The forks were a little gross, but thats how it goes. So everything is apart and awesome. I’m going to get the frame, swingarm, fork tubes, fork ears, handlebars, and 1 or 2 other things powdercoated while the wheels and a few other bits will just be spray painted to save a little cash. I was really surprised by the weight (or lack there of) of the frame. Its probably half the weight of a maxi frame, yet when riding they feel so solid. I guess thats just quality spanish engineering.

I also redid the gaskets on my magnum today, so for the first time (ever?) I’ve got no leaks! Its running super strong with the proma circuit, maybe does 50 with 14×36 gearing, but it gets there in a hurry. Really fun for around town.

Here is whats coming next.