Topper cylinder

[250_Sprint]

As was mentioned, end result is too much charge due to oversized port and duration to cover the port.
Basically, not enough restriction.
We are always looking for ways to get these machine to inhale and exhale more, in your case, you want to restrict.
Playing with smaller jets and restricting incoming air may be a complicated rabbits hole but one you might dive into until a suitable cylinder solution is found.

I know, it’s backwards and your results WILL vary.

[FL54]

Thanks Sprint. I’m waiting to hear back from Jim’s Forever on a replacement cylinder. If they don’t have one, I’ll go ahead and reassemble and cross my fingers.

[pumpguy]

Did some checking and the source I found confirmed the Topper is a reed valve engine. The comments I made earlier about inlet port duration would only apply to a piston controlled inlet port type engine and wouldn't apply to a reed valve engine.

From the looks of the Topper engine, I expect this is a case reed type engine. If true, the condition of the cylinder's ports shouldn't have any bearing on the inlet gas flow.

On the other hand, the condition of the reeds and the reed seating surface are really quite important. I would suggest you inspect the reeds and seats to be sure they hold gas against the pressurized crank case.

Might also be a good idea to look into pressure testing 2 stroke engines. There's quite a bit of information on this to be found online. Setting up the hardware to do this test isn't all that difficult; just some hardware store items, a low pressure pressure gauge, and a squeeze bulb from a blood pressure cuff should fill the bill.

[Mutt]

Only the 62 - 66 Topper motors are reed valve engines. The first 2 years are piston port motors. pressure testing your motor can be a true headache. I had a motor that had good shafts and new seals. No matter what was done, there was always some bubbling at the seals at 6 psi. Cranked the motor up and it ran fine.

[250_Sprint]

I would think the reeds would remain open as long as the engine was taking in a charge, then close.
I am new to reeds with this MB5 I am resurrecting from sleeping 35 years. I shown a flashlight on the backside of the reeds while in a dark room to see how well they seat. You might do the same.
A leak down test may shed light on leaks but getting your over-the-counter tool not to leak might prove difficult to seal. Mine was.
Read up on the role reeds play in the 2-stroke just for some basics.
Don’t lose hope.
Remember to have fun.

Think of the looks you will get when your friends see you roll up on the Harley-Davidson Scooter!

I used to stop traffic with my 1966 Harley-Davidson 250 Sprint-H.
Let’s keep them alive and educate the public on what used to be on every road.

[FL54]

Thanks Pumpguy, Mutt and 250 Sprint. I’ve checked the reed valve on several occasions and it is in good condition. I found that it’s easier to remove the carburetor attached to the manifold than to remove the carburetor from the manifold. This exposes the reed valve. I also replaced the crankcase seals and manifold and carburetor gaskets. Still waiting to hear about
a replacement cylinder but from the comments it seems like I should go ahead and reassemble and hope for the best. I would like to get to ride this bike before the snow flies and it’s been tying up my lift for too long.
Thanks again,

[panhead_kicker]

Another Topper owner chiming in…
What do any of you guys think about using paint as the head gasket for the Topper. This was always the factory method; they never used an actual gasket here. HD high heat silver was the sealant. I’ve used this on both my Toppers with no issues. (Flat mating surfaces).

[FL54]

Well, I reassembled the cylinder and head and had marginal improvement. I now have just over 50 lbs compression if I can trust my Chiwanese compression tester. End result is that there is no improvement on the road. Bike still labors to reach 30 mph. Still waiting on Jim’s to find a replacement cylinder. Apparently, there are Topper parts strewn amongst 4 buildings and they haven’t yet had the time to do a thorough search for a good replacement. Only benefit is I’m getting pretty good at taking this thing apart.

[Mutt]

do yo have the early or late model head?

[FL54]

It’s a ‘63 so I assume it’s a late model.