Flying Horse 66cc build (2024)

Hi I'm new to the hobby and living in Austin TX. I recently got a 1963 JC Higgins bike and am installing a new Flying Horse 66 from Bikeberry. Being new to this and not knowing any better I also got the CNS carb. Bikeberry left the NT carb in the box, but I haven't tried it yet.

The rear sprocket center hole was much too small for the coaster brake. I milled the hole larger to fit.

I took off the head and found grit in the cylinder, perhaps metal filingsFlying Horse 66cc build (1). The rings were rough cast - they would gouge the walls instantly. I sanded the outer edges of the rings smooth with 800 grit sandpaper, being careful to keep the edges sharp and not rounded over.

I lubed and assembled (noting that the ring gaps must be centered around little alignment pins within the grooves).

I found that I needed the chain tensioner. I reluctantly drilled a small hole through the tensioner bracket and lower frame rail and bolted the bracket on there securely so it wouldn't get pulled into the spokes. This bike has really hard American steel and the bolt fit very snugly so, considering the force vectors, it should be fine.

The clutch cable was way too long. I pulled off the end cap and shortened it with a dremel, then put the cap back. There was no ferrule to secure it. I found one that was a little large and put some solder on the end to make sure it stays in place. The solder also keeps the cable from fraying.

It ran, but it vibrated like a mother.

I found that the wiring instructions were totally wrong. It should be like this:
blue from engine goes to blue from CDI (ignition)
black from engine goes to black from CDI
green from kill switch also joins to blue
other kill switch wire goes to bike frame
white wire is not used - that is a 6v supply and should just be clipped.

The carburetor seal is the black grommet all the way up in the housing and must mate securely to the intake tube. Just shoving the carb onto the intake tube results in an air leak unless you really make sure the black grommet in the back seals it. I used a little silicon gasket goo to help keep it secure and got it good and snug prior to putting the whole assembly on the engine.

Still way too much vibration and the crank case is leaking premix oil because it was not properly sealed from the factory. I suspected that the crank was way out of balance. So then I ordered a sprocket puller tool and some extra gaskets and watched the YouTube videos of a slightly drunk Canadian kid "rebuilding" an engine and beating it all to ****. That was actually quite useful.

The disassembly went ok, but it was impossible to thread the puller tool onto the clutch. The threads had been damaged too badly by the assembly monkeys. From the video, however, I knew I could just leave the clutch on there and drive the shaft out from the other side. I kept the parts organized on a table. I would put groups of screws together, tape them to the table with masking tape and then write on the tape what they were. I used a big red sharpie to mark the side facing me on things like the magneto, lock washers etc. so there would be no confusion when it went back together. I did not beat on the motor or use pry bars like the Canadian kid. I grabbed the magneto magnet with channel lock pliers and wiggled it free. That took a little effort, but eventually it all came apart nicely.

The main bearings were gritty and crappy, hardly the vaunted Japanese bearings I expected. I replaced them with SKF-brand 6202 unsealed bearings with C3 clearance, suitable for high heat environments. The clutch drive bearings seemed OK.

This motor has bolt-on weights on the crankshaft. The 2 halves of the crankshaft are pressed together around the piston rod. So that means I couldn't get the rod out to weigh it properly. I think the crank should balance using the full reciprocating weight (piston, clips, small end of rod and bearings), plus 50 to 57% of the weight of the rotational mass (large end of piston rod and bearing). Well, I couldn't weigh it so who knows. I drilled a 3/8" hole into each of the bolt-on weights, in the center of the grooved cutouts where they would be on the side where the piston connects.

I also trimmed the piston skirt on the intake side, just a little bit so it would fully clear the intake hole.

I cleaned the clutch with brake cleaner spray and then lubed the clutch and drive gear teeth using Honda Moly 60 gear paste. It is 60% moly and available at the Honda dealer for around $15, tax included. I used a pipe cleaner to put a little on each tooth. This stuff will stay put and not foul the clutch. To reduce noise, the clutch cover got a few coats on the inside of disc brake quiet spray, which leaves a thick plastic coating. I also used 2 clutch cover gaskets when reassembling.

For re-assembly, I used engine assembly lube, lubed the bearings, and then sealed the crankcase well with blue silicon RTV gasket maker. I used red high-heat RTV on the intake and exhaust gaskets. I also used a wee bit on the head gasket, although that may not be such a great idea. I did not use the bottom cylinder gasket, just a little more blue RTV. I figured that would raise the compression slightly.

I wanted to replace hardware, but metric 6-1.0 studs were not locally available. The local bolt shop did have 100mm bolts so I cut the heads off with the dremel and used those. I replaced most of the nuts, too, but did not replace the main cylinder studs or bolts holding the crankcase together.

To make a new intake gasket I pulled out the studs, then used the red Sharpie to ink up the port then pressed the gasket material against it so that the port shape was printed on the gasket material. I cut it out with small scissors so it made a perfect gasket.

I adjusted the float on the CNS so it would shut off fuel a little sooner and I moved the needle clip to the second to lowest notch. The first test ride was hopeful. It pulls up the mild hill near my house and it is running better.

It still vibrates too much, but not as much as it did. I think the balance is better, but still not quite right so I may pull it apart again soon. First I am going to try stiffer motor mounts. I used rubber padding and just read that stiffer material vibrates less.

Yes, I could just get a decent Morini motor, and probably will for the next build, but I enjoy tinkering. I think that's half the fun. If anyone has tips on getting this 66cc Flying Horse properly balanced I'd love to hear it.

Flying Horse 66cc build (2024)
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