1972 sl70 pit bike

new here butnot new to old hondas , this is my 3rd vintage honda ( had a 74 z50 ( later put a yamah dt80 motor in that, to fast , wrecked it and sold it ) and a 75 xr75 before this ) also rebuilt the engine twice on a friends ct70 and fixed up a 1971 sl70 for another friend of mine. but heres mine when i first got it together


a pic of the z50 with dt80 motor while i was finnishing it up before it was wrecked and sold ( note to anyone else , 2stroke 6 speed 80 motor is a bad idea in a stock heavy z50 , they dont like to stop :smirk: )


,anyways i got this sl70 around 3 years ago in a box for free , it was missing the seat,carb,rear wheel,side engine cover, the engine needed a rebuild and the tank was incredibly rusty . i put it mostly together with a z50 engine and an xr80 back wheel just to take it for a test ride, it sucked so i took it apart and have been modifying it ever since. didnt take any pictures of what i initially did to it and how it evolved but heres a list of what it currently has

- 1972 sl70 frame/ rebuilt 4speed motor

- 1993 xr80 tripple clamps/front forks ( direct bolt on mod i hoghly recomend)

- 1975 xr75 tank ( needed to clear xr80 forks since they turn tighter lock to lock )

-1973 xr100 rear shocks to level it with front forks and support me better

-1993 xr80 front/rear wheels

- 1975 xr75 carb

- xr100 throttle cable

- xr80 throttle tube/assembly & xr80 levers

- intake flipped upside down ( ill explain why if your interested in knowing )

- handmade exhaust with procircuit 2stroke muffler ( getting replaced soon )

- uni air filter

- z50 output sprocket , i think its a 9 tooth? i dont remember exactly i just know its 3 or or 4 teeth smaller than the stock sl70 output gear

had it like this for awhile and it was pretty quick and could hold its own against a friends 1984 xr80 when we'd pitbike race on tight tracks , but i wanted more on the top end to keep up with him and bigger bikes on straights so i re jetted it and ran it on alcohol , to fast and i thought i was going to blow it up so now im going back to gas but with more intake mods.

as of tonight ive hogged out the intake manifold inlet to be the same I.D. as the xr75 carb , polished the intake manifold inside and flipped it back right side up , polished the carb venturi also aswell as the main jet holder and the pilot jet , gave the side exit holes on the pilot jet and main jet holder a slight taper , went up to a 125 main jet from a 1986 xr250 carb which is about 3 times longer than the stock 70 carb jet which im thinking will give i more on top sort of how a carb spacer works? , tappered the end of the main jet to a point ( got a reason for this but its alot to explain ) , also jb weld coated the float to make it more boyant, the 125 long jet may be to much so i bought 4 stock size 100 main jets and want to have 3 of them turned up slightly probably to 105 , 110 and 115 . also will be shortening the exhaust and playing with different mufflers to gain some more grunt out of it as well as venting the top valve adjustment cap . as you can probably tell i like screwing with stuff and experimenting to find what works and what doesnt :smirk:

heres some pics of it and the carb/intake mods




the usual suspects when my xr650L and my buddys big bikes get boring


let me hear what you all out there think and any input/ideas on any garage mods any of you have done on these horizantal honda motors also

nice bikes man! that z50 dt80 is sweet! hope you didn't hurt yourself to bad lol you got any experience working on honda Xl's?

lol didnt get hurt to bad, the bike and i went through a neighbors bushes, i got knocked off and the bike went through their fence.

i havnt had an XL yet but i do like them since they are really similiar to the sl's, id eventually like to have a full collection of each model of sl from the sl70 all the way up to the sl350

just got the carb buttoned up and test rode it, what a difference, the mods to the carb and intake really woke it up! much quicker rev's with no backfire or sputter any more. im really surprised the longer 125 main jet out of the xr250 carb isnt to much for it but it seems to like it alot! im only 2 1/2 turns out on the mixtre screw now where as before with the short 100 main jet i was at 5 turns out and had slight sputter when keeping it held at steady throttle. i feel that the larger jet and porting the intake manifold to match the carb is what smoothed it out and that porting the intake manifold to match the carb and polishing the carb and intake as well as the jets gave it the slighter faster rev's :smirk:

That's awesome man. I love it when a plan comes together and just works! Good feeling.

but the reason I asked about the xl is be cause I have one that needs some help and im not really a Honda guy. I have had yamahas and suzukis my hole life.


If you would mind looking at this and telling me some in site you might have I would really appreciate it

Cool project. Love those old Hondas. I remember back in the 70's racers were stuffing all kinds of engines in mini bikes. I think it was Jim Pollaroy (sic) that stuffed a 250 Bultaco Pursang motor in one.:smirk:

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