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Old 03-09-2020, 01:42 PM   #28 (permalink)
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Join Date: Jan 2010

I finished my conversion, but have not flown it yet. I can update on that part later.
I started this with the idea that I could revert to the stock configuration if this didn't work out. I wanted to avoid any machining of the crankcase or head that would prevent that. The only machining that was really needed was to cut one cooling fin on the head to clear the OS carb's inlet.
I would say this worked out pretty well.

There are 3 minor issues that showed up during the conversion:
- The adapter plate for the carb needs a little work to get it to fit perfectly on the crankcase's carb mounting boss. This may vary from crankcase to crankcase. But, it was a problem on my crank
- The head needs some modifications for the one of the cooling fins to clear the ventury of the OS 61G carb. This is not a problem and should not affect cooling. The mill work does not prevent going back to the stock YS carb.

- The carb's fuel nipple obstructs the mounting screw on the left front of the engine (see pics). I am mounting this in my Goblin 700BN, and I cannot use the SAB supplied 4 x .7 cap-head screw in that spot. I can get a shorter screw to fit, but I cannot get my hex-driver to engage the screw's head to torque it down. The worst case is that I will have to remove the head, remove the carb, torque down that screw and then reassemble the carb & head.

The pics are included.

Also, keep in mind that the 4 screws that hold the YS regulator are 2.5mm diameter - not 2.0. This is important because typical 2.0 screw will thread into the crankcase, but you cannot torque them down.
If you do decide to cut the YS regulator screws to hold the new cover plate, you cannot go back to the stock configuration without buying new screws. Besides, the YS screws are flathead - they will not seat properly on the new plate without you adding a counter-sink to the plate.
Side Note: The supplied plate to block the YS regulator mount seems to have 4 holes drilled for 2mm screws. To get the 2.5mm screws through the holes on the plate, I had to chase them with a #39 bit.

I added the OS velocity stack - because it looks cool. I don't think its needed for performance. But... it does look cool.

In general, the cost of the adapter plates is less than I would expect for the quality of the parts (Thank you Mr. azfishguy76 !!)
If there wasn't a need to machine the fins, this conversion is almost "bolt-on" ready and shouldn't take more than an hour or so.
If you are careful removing the YS carb and regulator, you can reuse the gaskets. I bought a new regulator gasket and made a new gasket for the carb adapter plate.

The donor crankcase came as a "short block" with no carb - so that was a huge benefit. It needed a new rear bearing and the glowplug hole was cross threaded, but those were easy to fix.
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"Those who can make you believe absurdities can make you commit atrocities." (Voltaire)
Watch out: There are a lot of absurdities being thrown around lately.
+ > RIP: John Lewis

Last edited by ticedoff8; 03-10-2020 at 02:16 PM..
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