SL 100 Vintage racer project

I have a 1970 SL 100 thatI'm making a vintage MX racer out of. I raced back in the 70's, mostly on Euro stuff,CZ,Maico etc bu I had a SL100 play bike back then and raced it once in a while. Anyway I am trying to make a cheap, legal vintage MX'R out of this and have got it handling nicely.I have not spent a lot of time and effort trying to get a lot of horsepower but instead working on the weight and handling while keeping with the spirit of the vintage era. I have early forward leading axle front forks which are illegal in the classic but is ok for the sportsman class. I can quickly change the forks to run in the classic but really like the way it handles now and the lack of weight makes it competitive. I really want to get rid of the battery but have not figured it out yet. These bikes will start and run without a battery but won't run well? If anyone out there has a secret for this I would be interested. I run the small spillproof 6V computer battery which works well but I would like to get rid of it altogether and save a little more weight. I will post some pics soon, check it out. thanks , wayne huff

My other thumper is a hybrid 77 XS 650 Yamaha. It is magneto powered (modified DT 250) has good lighting, runs great, no battery. It took some engineering (rigging) to do but it works really well. Actually with a set of knobbys I could race it! It's light and 18/21" alloy wheels, but that is another story.

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I have a old SL100 stator if you want to experiment. $15 plus shipping

Go here:

http://www.oldrice.com/xl_page.htm

Tons of info, including the original article sharktaco refers to, along with half a dozen other articles from back in the day on making the early SLs into (then) competitive racers.

Good luck!

Kirk

Thanks Sharktaco, I may very well take you up on the stator soon after I get a little deeper into this.Sorry to be slow replying, being a newbie i'm learning to navigate slowly on TT. wayne

AHRMA announced that they will have a 100cc class in Vintage MX in 2008.

I heard that AHRMA will be adding the 100 class also. That will make up my mind about whether to "punch it out" or stick with my 99cc, or whatever it is stock. It runs quite well for a little four stroke and may be more competitive now not running against the really quick 125's out there. But hey, it's mostly for fun anyway.

Do a search on SL100 and Battery. Someone had a method where a large coil replaced the battery.

In order to get it run run good without the battery you need to lock the mechanical advance in the full open position. Spread the weights out and tack weld the assembly in the ful advance position. The rest of the battery elimination is pretty straight forward. Just remove the battery and rectifier and plug the harness from the stator to the ignition coil, the factory connectors even plug back together. There you go you made made the switch from a batery powered ignition to an e.t. magneto.:banghead:

Interesting.

I'm curious - why do you have to lock the weights in full advance? What does that have to do with battery elimination?

The rest of it, I sort-of follow - using the normal battery-charging circuit to just power the ignition coil. Also, why eliminate the rectifier? The ignition coil was originally intended to function with DC. The opening of the points interrupted the DC current, and the collapsing field sparked the plug. If you eliminate the rectifier, now you'll be using AC in the coil, which "collapses" every time the AC sine-wave reverses itself. Does that still work?

Just curious.

Interesting.

I'm curious - why do you have to lock the weights in full advance? What does that have to do with battery elimination?

The rest of it, I sort-of follow - using the normal battery-charging circuit to just power the ignition coil. Also, why eliminate the rectifier? The ignition coil was originally intended to function with DC. The opening of the points interrupted the DC current, and the collapsing field sparked the plug. If you eliminate the rectifier, now you'll be using AC in the coil, which "collapses" every time the AC sine-wave reverses itself. Does that still work?

Just curious.

If I am not mistaken the reason that the advance needs to locked open is because of the fact that you have a contiually collapseing field and you need to eliminate the variable timeing otherise you won't have sufficeient coil saturation time. I do know from experience that if you don't lock the advance open it will be near impossible to start and won't run well until you reach high rpm.

Thanks, that sounds simple enough but I sort of tried that already except for locking the advance. DeiselGoober's fix sounds like it may fix the problem because it seems to be a phasing problem that affects the timing. Also at the rpms the problem occurs is when the advance should already be at full.I haven't had time yet to work on it more but hope to soon.I do have another method of locking down a rotor without a woodruff key. I use valve grinding compound to mate the surface of the taper to the rotor. This works and I have never had one move, even without loctite. Thanks everyone

Thanks to all the the info I got ,I did not have to reinvent the wheel. I do have the little thumper running great with no box of lead and acid. I am not quite through but I have come up with some easy fixes to locking the timing to full advance etc. I will leave detailed instructions soon.

If anyone else but me is going to do this right away, let me know, I can save you a lot of work and worry and will explain everything.

Thanks DeiselGoober,Sharktaco, and all the rest.

Even if I don't get to race this thing I am having a blast making a real racer out of the little thumper.

We had a local young rider here in the early 70's who dominated the class on his SL 100 and was usually in the top few riders in the overall. !! His name was Steve Webster, I beat him once on a Noguchi powered Yamaha MX100 which was my wifes bike. It was extremly fast and it still was hard to beat Steve and the 4 stroke.

thanks again, I should be through with this part of the project after the holidays.

thanks again, wayne

Thanks, the old rice is fun and loaded with info when your working on a nearly 40 tr old machine. With all the help I now have an SL 100 running well without a battery. I need to test a little more and get further along after the holidays and I will document everything. If anyone besides me is wanting to do this soon I can save you a lot of time and trouble with what I have learned. Back when these things were new most people ran constant loss and I just never liked that idea. But! I have it worked out and will try to post the details soon. Hint it's not hard but needs to be precise.

wayne huff

I have a 1970 SL 100 thatI'm making a vintage MX racer out of. I raced back in the 70's, mostly on Euro stuff,CZ,Maico etc bu I had a SL100 play bike back then and raced it once in a while. Anyway I am trying to make a cheap, legal vintage MX'R out of this and have got it handling nicely.I have not spent a lot of time and effort trying to get a lot of horsepower but instead working on the weight and handling while keeping with the spirit of the vintage era. I have early forward leading axle front forks which are illegal in the classic but is ok for the sportsman class. I can quickly change the forks to run in the classic but really like the way it handles now and the lack of weight makes it competitive. I really want to get rid of the battery but have not figured it out yet. These bikes will start and run without a battery but won't run well? If anyone out there has a secret for this I would be interested. I run the small spillproof 6V computer battery which works well but I would like to get rid of it altogether and save a little more weight. I will post some pics soon, check it out. thanks , wayne huff

My other thumper is a hybrid 77 XS 650 Yamaha. It is magneto powered (modified DT 250) has good lighting, runs great, no battery. It took some engineering (rigging) to do but it works really well. Actually with a set of knobbys I could race it! It's light and 18/21" alloy wheels, but that is another story.

Wayne, Forward axle forks are legal for sportsman class racing but not for the new 100cc class. The are also illegal for Classic Class racing.

What Computer battery number are you running ? Did it work ?

Thanks,

Dwight

Hi Dwight, So my forks have to go, I need to read the AHRMA manual a little better. I want to keep the bike true to the period, thats the whole point and half the fun. I hope my alloy rims are legal. They came off a 75 MR 175 as did the forks but I think that type of rim was available then. If not they will have to go, at least for the races.

The little battery I use on all my small bikes that need one is available at the batteriy specialty places(batteries plus etc). This one is a WERKER,Bat# WKA6-5F It is a 6V 5AH AGM sealed maintenance free battery. I like them because they are small, spillproof and really seem to last longer. Even if you get lazy with the charger. They do have blade type connectors so you will need to adapt it to your harness(easy). I think it was under $10 also. I have one in my 78 CT70 that has been in there for a couple years now. My SL cranks and idles as well as it ever did, without a battery!, but I still have not had a chance to make a couple laps around my little track so I can declare it a done deal.

Thanks, wayne huff

Wayne, Forward axle forks are illegal for sportsman class racing unless the bike orginally came with them like the Maico. You can run 1974 XL125 forks but not 1975 model. The 1974 are straight leg but have about a 1/2 inch more travel than the 1973 SL125.

What Computer battery number are you running ? Did it work ?

Thanks,

Dwight

Dwight,

On the Left Coast never did see a 74 XL125 without a forward front axle ....... checked and Honda Identification manual shows it forward also.....? Was there a mid year change? The 74 MT/CR125 was forward. 74 XL100 now was straight, like the SL100/125.

Old School Al

Dwight,

On the Left Coast never did see a 74 XL125 without a forward front axle ....... checked and Honda Identification manual shows it forward also.....? Was there a mid year change? The 74 MT/CR125 was forward. 74 XL100 now was straight, like the SL100/125.

Old School Al

You are correct , Honda leading axle forks are illegal for "CLASSIC CLASS" racing but not Sportsman. I believe what I was thinking of was some were taking the dampers from the 1974 forks and putting them in the earlier forks for more travel. You can't use 1975 and later forks. You can use alloy wheels because the Honda CR125 had them. BUT, The new AHRMA 100cc class rules do not allow suspension components, or any major engine or frame parts from larger machines . So you still can't use 125cc forks on the 100. Some are upset because they were running 250cc forks on there 100 and 125 cc Hodakas and Hondas.

Now they can't.

Dwight

You are correct , Honda leading axle forks are illegal for "CLASSIC CLASS" racing but not Sportsman. I believe what I was thinking of was some were taking the dampers from the 1974 forks and putting them in the earlier forks for more travel. You can't use 1975 and later forks. You can use alloy wheels because the Honda CR125 had them. BUT, The new AHRMA 100cc class rules do not allow suspension components, or any major engine or frame parts from larger machines . So you still can't use 125cc forks on the 100. Some are upset because they were running 250cc forks on there 100 and 125 cc Hodakas and Hondas.

Now they can't.

Dwight

Dwight,

On the Honda XL125 the forks should be the same for 74 and 75, and almost the same except for small cosmetic details on some later years. If I remember correct on the CR125 74 and 75 the same forks, changing in 76 and running through 78, change again in 79. We ran the 76 CR125 forks on our (one) 74 and (two) 75 XR125 ISDT's in 1977. MR175's ran the XL/early CR forks 75-77 I think.:banghead:

Old School Al

Dwight,

On the Honda XL125 the forks should be the same for 74 and 75, and almost the same except for small cosmetic details on some later years. If I remember correct on the CR125 74 and 75 the same forks, changing in 76 and running through 78, change again in 79. We ran the 76 CR125 forks on our (one) 74 and (two) 75 XR125 ISDT's in 1977. MR175's ran the XL/early CR forks 75-77 I think.:banghead:

Old School Al

BUT you still can't use them on a 100cc class or classic 125cc Class bike. You can't run 35mm leading axle forks on a Sportsman class bike unless the bike came with them originally. Especially the Leading axle Ceriani and Mazzochi forks.

Dwight :busted:

BUT you still can't use them on a 100cc class or classic 125cc Class bike. You can't run 35mm leading axle forks on a Sportsman class bike unless the bike came with them originally. Especially the Leading axle Ceriani and Mazzochi forks.

Dwight :busted:

Yes, I'm aware of the leading axle rules.:banghead:

Old School Al

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