CT-90 conversion to CT-140! yx140 engine swap.
So here’s my 1970 Honda CT-90 (90cc) right around the first day I got it. Pretty nice bike eh? only 1000 original miles! OK, fair enough fair enough, but how fast does it go? Engine screaming like a deep water oil drill, she goes 45mph on a flat surface – drill baby, drill! Plenty of speed for the forest trails ’round these parts, but for the street?, that just didn’t satisfy me. I need MORE.
OH NOES!!! I GOT A FLAT TIRE! Well that’s just perfect. While I’m changing out the tire I might as well replace EVERYTHING else on the bike, eh?! eh!!?? any objections!?!?!?
So back to what I was saying before the unfortunate tire accident – MORE. How much more? hmmm does 50 more cubic centimeters of metal muscle sound good? yes, ok, now we’re off to a good start.
Nude CT-90. Ok, we’re gonna move along and give her some time to get decent.
*cue engine entrance* Meet my new friend! a YX-140 engine from… *shhhh*china*shhh*
Ya know what else? That red color doesn’t really suit me… and there are some rust spots here and there… ooo! ooo! sandpaper party! everyone get your particulate masks on!
Completely n00d and all sanded down by yours truely. Now she’s ready to party, I have a feeling she’s not going to remember this come morning.
Aweeee snap. Rustoleum flat black – the blacker the berry, the sweeter the motorcycle. Motorcycle juice, mmm. (And a glass of Belgian Wit – loosens me up so I can chit chat with the paint canisters.)
Above: The crank case vent was hitting the frame… can’t have that. So i pulled it out, and redrilled the hole at an angle (pretty roughly I must admit.) It wasn’t a perfect hole, or a very good seal, it was just plain shoddy workmanship… That’s where JB-WELD comes in. Turn that mechanical frown upside down, top dead center. I tried to have the engine tipped over on it’s side through this so that metal shaving and JB weld droppings didn’t find their way into my brand new engine… I think it was 95% successful, the other 5% is vitamins and minerals.
Above: Now we just need to add some blinkers (in 1970 motorcycles didn’t need blinkers I guess?) So I bought a cheapie $30ish kit. Just need to drill a couple holes… and…
Now we’re in business! That’s the money shot!
I’m still just breaking her in, so no top speed runs yet.
So here’s the run down:
New engine should get 100mpg. Hopefully I can cruise at 55mph in traffic (I will probably need to adjust the gearing.)
New engine kit cost : $300ish
Blinker kit: $30ish
ehh I don’t feel like doing a final cost run down, but it was worth it dammit! There are only about 20 parts on this entire motorcycle, and the tires are cheaper than tires for my bicycle (WTF?)
I got a lot of my parts from “DR ATV” and I got my yx-140 engine kit from T-Bolt USA which is the best deal I could find that included the carb, CDI, etc. I had good experiences ordering from both places.
Other than the engine vent needing to be moved, this engine fit PERFECTLY. The intake manifold and carb also fit PERFECTLY… well, when fully torqued the carb is just barely resting against the frame, so I may use a drill and slot the holes on the intake manifold where the manifold meets the engine. That should allow me to rotate the carb away from the frame about 1/2 a centimeter or whatever i need.
This is totally my little dream machine now. It sounds really small, and it is, but it hauls ass, and is just as capable off-road as it is on the road. Insurance is DIRT cheap and I can ride 250 miles on the 2.5 gallon tank (for $7 dollars?)