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xl125 slipper pistons?

By turboguzzi,
in Vintage Dirt Bikes

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Swiss

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There was no rev limiter in 1975 except available power vs. load! HA!HA!

With your long hour races and the idea that you feel you can run a full long season without a rebuild, I would stick with a 10k or 10.5k redline, and only over-rev when necessary like when you have a little bit too long straight and don't want to lose time upshifting just to have to downshift a millisecond later for the next corner. The engines will run reliably to 12k with a stock stroke, but they will also require more care and better rebuilds (more often) when running at the higher redlines. I would tune to a peak power at about 10k, since you will be running at least that high. You will need to shorten the exhaust primary pipe and your meg is probably longer than it needs to be to match up with a shorter primary.

I wasn't talking about a dual pipe engine, but about a double wall pipe inside the headpipe. Honda did it sometimes to help protect the chrome plating on the pipe from discoloring, and it reduced the inside diameter and doubled the pipe weight.

You do NEED a diet on the bike. Start by removing the unused garbage like the headlight and the light mount brackets and lighting switches and wiring. Rewire down to minimum specs and I would convert to a '76 XL magneto ignition to run with out the battery. Yes, weight DOES matter (why I got the nickname Swiss for swisscheese!). 6.5-7lbs equals 1hp in a bike and you are going to struggle to find hp in the engine. Remember that my dirtbike weighed about 175lbs and your "racer" streetbike weighs close to 220lbs? So that is 45 lbs or about a 6.5-7hp "loss" of acceleration that you are willing to accept? YOUR body weight might not be flexible enough to come down to 175, but your bike can come down below 200lbs and it WILL help you coming out of the corners and accelerating down the straights. Consider taking about a pound off of the outside edge of the crank flywheels. This will help acceleration a LOT! Just a little machining required. Look at a replacement plastic tank that might pull a couple of lbs off the top of the bike weight. Rebuild the seat and get rid of the HEAVY Honda seat padding replace with a RR style fiberglass seat base or even a newer tail piece. Why do you still have the speedo and cable on the bike? Again dead weight, run with the tach, you don't need 2 speed indicators on a race bike. If you feel you need to know how much speed you are capable of, get one of the inexpensive bicycle speedos and hook it up. They only weigh a couple of ounces for the whole thing. Think about pulling the wheel bearings and machining some aluminum replacements for the bearing spacers, and then the steel wheel spacers that the axles go through for both the front and rear wheels.

On some of the dirt bikes they used steel supports underneath the rear fender. Remove it if you have one. Leave the front fender brace as it helps as a small fork brace. Find some real rear shocks, the stock Honda shocks are next to useless. Measure the length and think about lengthening the rear shocks by about 1/2 to 1" or drop the forks a similar amount until you find the limit to stability. The steeper front end will help with tighter cornering.

Swiss

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ohiomotoxer

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When I worked at Wiseco I remember someone calling about a piston for the SL125. IF I remember correct a fzr600 piston was used or was matched up to this persons specs for what they were doing (AHRMA vint mx) but I think he was way out of the rule book limit for AHRMA.

Give Wiseco a call and ask for Adam talk to him see if he remembers or have him move you over to Jeff, tell em Z sent ya.

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Swiss

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Aaron,

I looked back at your pictures and noticed that you didn't have a rear fender on the bike, so you don't need to worry about removing it. However, since you don't want to build up a new frame how about changing the one you are racing or maybe one of the ones with higher mileage. Cut off the rear frame extensions, where ever you have some flat sections of the frame, drill some holes from 1/8" up to 1/2". When I built my 125 I bought some lengths of Chrome-moly tubing and machined it to the axle diameters and then threaded the ends for lightweight hollow axles. Same for the swing arm pivot bolt. A fiberglass seat assembly should be fairly easy to find on EBay for a few dollars. You will need a small one off of a racing 2stroke or maybe even one of the little fiberglass pieces from one of those cheap $200 50cc Pocketbikes that are sold all over the country for kids. Might even be able to use the fiberglass tank off of one of them. They aren't much smaller than your 125 is. I noticed that you even had the horn on in some of the pics?

Swiss

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adowdell

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yeah, still had the horn, I only had the bike for a couple weeks prior... I think the cb will get a diet during winter break, next week is dead week, and then finals shortly there after so all my major design projects and stuff are coming to head this next week, and I have drill this weekend...

I've got a xr200 carb coming, i've got to find time to tear down that stuck motor before I can send the cam in.

I've also given one of my tanks to a friend to paint over christmas break, he has done some pretty impressive stuff with an 05 R1 that he unsalvaged... doesn't help it go fast, but...

I've been thinking about the seat and what should be done with that... Might just toss the seat, and do a little fiber glassing myself... Always wanted to do some of that as well, but if I can get something like that off of ebay for pretty cheap, might be easier... I know that I can get some "padding" locally, that will wear pretty good, if I can uild a descent base to stick it to.

I'm thinking that I'm definitely going to have to get a welder, If for no other reason to get rid of the solid mount pegs, those things are dangerous. It'll pick the tire off the ground if the peg hit solid enough...

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adowdell

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I went with the XR200 carb... You can't beat $60 SHIPPED.... It's over $500 for a carb for my drz that's worth while...

It'll be a couple days before I start looking really hard core at cams... Probably just have mine reground, unless a new one is cheaper... I've got several maj. projects due here in the next couple days, and I have to focus on this stuff...

Oh, and the tank is back.... Wow is all I have to say, gold flake flames, under and brandy wine red, with some other ghost black/and dark blue flames... I haven't got chance to see it in the daylight, but I bet it really shows it's colors. I'll post pics of it also when i get a chance... I'm going to have to scrub the dust off of the frame now...

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adowdell

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That seat is sweet! I think something like that would be perfect, i've done some repair fiberglassing, Surely it wouldn't be that hard to build somethinglike that my self. Lot's of sanding and what ever... I may start reading up on fiber glass stuff.

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