Honda 70 motor modification

[atc500x]

I have many 70cc motor in stock so I have try some modification.Here is what I do...Now the motor is in a 84 z50. Crankcase and gear are from a ct70.Clutch cover and clutch system from a xl70.Cylinder is from a stock ct70.Crank shaft is from a S65.The S65 crank have a mechanical timming advance to gain RPM.Head is from the S65.The S65 and ct70 is basically the same head,but the 65 combustion chamber is smaller than the 70,but with the same valve.The intake port give a lot better flow too.The cam is from a S65,same lift but A LOT more duration.And the piston....from a cb350F 1973,same dimension,same pin size but with a HIGHER piston top.I have grind the piston to clear valve (0.030" clearance) and clear the head.The piston dome is so high that I was affraid to hit the spark plug but it's ok.The carb is from a xl70 with a custom intake manifold.
I start it yesterday....motor run very strong,I hit 12000 rpm,and 180psi of compression...(130psi stock) The Z50 is now a beast.I now plan to do the same setup on my atc70.Everything look stock because all part I use are honda....

[WIkid500]

12000 rpm for real, did you measure this with a tachometer? What did you do for ignition? Thats a mean little motor!!! Lets see some of it in action!

[atc500x]

Yes I check t with a digital tachometer.The ignition is fro the s65 with mechanical timing advance,cam and carb help a lot....

[Dirtcrasher]

Well, since you obviously seem to know what to swap:

I got a free 1970 CT70 awhile back. Is there any advantage to any of those parts on one of my ATC70 motors?? First thing I noted was the longer crank and manual clutch and kickstart but the shaft is snapped off. I would try to plug it and just use my pullstart....

Would it be possible to use that cover, some guts and gain myself a manual clutch??

If you could tell me a bit about the 1970 CT70 motor and it's usefullness, that would be GREAT!! Thanks for any help

[Daddio]

Well, since you obviously seem to know what to swap:

I got a free 1970 CT70 awhile back. Is there any advantage to any of those parts on one of my ATC70 motors?? First thing I noted was the longer crank and manual clutch and kickstart but the shaft is snapped off. I would try to plug it and just use my pullstart....

Would it be possible to use that cover, some guts and gain myself a manual clutch??

If you could tell me a bit about the 1970 CT70 motor and it's usefullness, that would be GREAT!! Thanks for any help

The biggest things performance wise on the ct would be that they have bigger valves and ports in the head, higher compression pistons, slightly larger carbs and some have manual clutch.

When I built my atc70 I used a cl70 head and piston. The cl and ct are fairly similar as far as the top-end is concerned. I ported the head and used a Web cam. The cam is almost too extreme for regular riding. It hits like a 2stroke, the power really comes on with higher rpm's. It's way better than a stock atc70 engine though.

[KASEY]

ANOTHER SECERT, use a lifan 55mm crank ,then you can run a hidden cdi unit and have a 125cc sleeper .

[Dirtcrasher]

Ugggggggh, I have so much to learn about these 70's............

I never even rode one or paid attention to there existence until about a year ago when I bought 3 with .

Now I have 3 myself and the one I dork with actually runs decent, not great but decent. I did the points and condensor as I'm unconvinced a CDI is a necessity but it still runs like dogchit even after a carb rebuild.

I'm convinced some of these carbs just cannot be brought back to life, maybe I'm wrong.....

Anyhow, I just want to strip this motor and keep whats beneficial to me. Obviously the crank is useless unfortunately because I need one to get another 70 rolling!
Appreciate the help very much guys!!

[KASEY]

man if you need any stock parts let me know,,, i have a mountian and they are cheap...

[Race Demon]

For you guys who want to hide some of your mods,check out Powroll, the parts are not cheap but you can get good HP out of a 70 motor, I used the parts years ago then switched to the [other stuff ] for more cost effective way to build my trikes