Cafe Racer Forum banner

1970 CL100 Cafe Project - Bore Information?

10462 Views 31 Replies 10 Participants Last post by  monkey
Yo! Sorry if this is a subject that's been covered already. I'm new to the forum and couldn't seem to find anything. So! I bought a 1970 CL100 back in July from the second owner, who bought it back in 1973. He used it sparingly, but maintained it well until about five years ago,. It has sat since then. I stripped the bike to a motor and a frame, and all seems straight forward thus far except for the motor. Given the scooter-esque displacement, I'd like to add a little more get up and go, while simultaneously getting rid of any compression problems that may or may not be present. So, hey! Let's just bore it, right? BUT... I have no idea what the best compromise between sustained reliability and performance may be... I've heard of people boring the cylinder to fit a 750 sleeve and piston, and that it's extremely reliable, the only difference being that the 750 piston requires a 15mm wrist pin rather than the 14mm in the 100. That can be reamed, correct?

But is that even the best option? What would be the displacement, horsepower, and performance gains on this? Would anyone happen to have firsthand experience with doing such a modification on this bike? Any and all performance/reliability tips would also be greatly appreciated.
Land vehicle Vehicle Motor vehicle Motorcycle Automotive tire
See less See more
1 - 5 of 32 Posts
It doesn't matter.
The OP already took it apart.
  • Like
Reactions: 1
Ive been down the rabbit hole of making a Honda single faster.
On paper it can be done.
And if racing another stock bike it will be faster.

But other then that there is zero point. has some old articles about hopping these things up.

I agree that doing a big bore isn't the worst idea.
But the OP needs to understand what he is getting into, and be realistic about the outcome.
There is no cafe racer style.
you are talking about choppers.
I own, and have owned a few of these Honda singles.
Been down the "make it less slow" and all that before. Personally I now just prefer them stock. I view them as best in this role.
BUT completely understand the desire to learn and just generally make something out of random parts. In that respect these bikes are great for that.
They are small, parts are easy to get and cheap. Honda made millions of these things. I would rather see someone learn to mix and match junk on one of these then blow apart a 4 cylinder and drown.
The idea should always be fun.

But dont brush off what people are saying by using the cop out " ill learn it myself". If that was the case then you would not be on the internet seeking out help, you would be in the garage doing something. So take some advice and you will have a leg up.

That motor that kerosene was talking about might be something fun for you to build.
What I would do is service the shit out of the bike you have and ride the wheels off it. While doing that find a spare motor and build it up.
You will then be wrenching on a fun project AND riding the bike. Then one weekend swap the motors. Another thing you gain with this is a good baseline.
the 18hp of the new motor will still feel slow, unless you have been riding around for a while with 11hp.....

And we do still need to talk about how bad these bikes are at "cafe racer" builds.
The motors HATE to run with short pipes or pods. Rearsets are hard to mount. ect ect
Play to a bikes strengths. "racing" aint it.

Here is mine

Bought it with 1100 miles from the original owner's family. I use it to run out for beer (that rack is epic), pick up parts and just general running around.
It is a blast. Have run it out on the beach, and taken it though the woods. Just a nice bike to have around.
See less See more
  • Like
Reactions: 1
1 - 5 of 32 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.