Well the leak down test shows everything is ok. It held 5 PSI for over 5 minutes. Didn’t drop below 5 PSI until almost 8 minutes. I know a lot of people say to pump it up to 7 PSI but I followed Dale Swegers video and he wasn’t comfortable with going up to 7 and he used 5. So that’s what I did as well.
imgur.com/a/DkMKxcv
So I guess the runaway engine was due to me shutting off the fuel and letting it run out immediately after riding it pretty hard. Lesson learned. So now I need to carry on with my efforts to get it running properly.
 

glad to hear its ok. Do you use the intake or spark plug hole as an air port?  I'm having problems setting up a good working system for myself. 
 

I used the spark plug hole for air port with piston at bottom  dead center. Made a fitting out of an old spark plug. Broke away all of the porcelain to hollow it out. Then JB welded an old pneumatic quick connect fitting into the opening in the base of the plug. I removed the crush washer and replaced it with an o-ring. You tighten it just enough to squish the o-ring.

I made a block off plate and rubber neoprene gasket for the intake. And I bought a 1-5/8” expandable rubber plug for the exhaust port. Got it at an auto parts store. It’s a freeze plug for an engine block.

I just noticed that the previous owner put a gasket between the rubberized carb joint and the reed valve assembly. The parts diagram only shows a gasket between the reed valve assembly and the cylinder. It does not show a gasket between the rubberized carb joint and the reed valve assembly. I only bought one gasket as per the parts diagram. 

So I am wondering if it’s OK to leave the additional gasket between the carb joint and the reed valve assembly. The gasket is very old and very hard, and will probably be difficult to remove without damaging the rubberized joint face. But then it might also cause an air leak. I suppose I could put it back together and give it a shot of either to see if it revs up. Hopefully that won’t trigger another runaway condition………

Looking for opinions before I put it back together.
imgur.com/a/6b4EWvT

I went ahead and left the gasket in place. I put a light film of grease on it and it passed the either puff test. 

Now I just need to figure out why it only runs good at wide open throttle…… The carb has been cleaned several times.  Making adjustments to the air mixture screw does nothing. It will only start if you hold the throttle wide open and give it a kick. I will post some videos in the next day or two and beg for help.

They engineered it well for vibration, probably vacuum and guys constantly yanking off the carbs. Seal it how you can! if it works, it works. I have used a gasket there and have one on my 360 w/yamabond. I have not had a problem w/it yet.
At least the grease will allow you to remove the gasket and possibly use it again.

I wonder if a rectangular oring would work there.

Schu, when I had an air leak mine too was between the rubberized carb joint and the reed valve assembly however mine looked like it did not need a gasket almost looked like an oring was molded in, so I made one and put it in. Now it holds good pressure.

My issue on the 175 was trying to find a plug for the exhaust port as it is not very round and I had a very very hard time getting it sealed. Could someone give up their secret for what they use to seal up the 175 exhaust port?

Dogboy, the traditional way is to make a simple plate to bolt over the port and make a rubber gasket to seal it.

That can be a challenge so another option I've used is to get a sheet of rubber gasket material (a piece cut from an old inner tube often works) to cover the exhaust port.  Put two holes in it for the bolts.  Now bolt the exhaust flange over the gasket you just made.  (Note that the port hole will be covered with the rubber).  

If you used thicker rubber, it might be fine at 5psi but what I do is stick the expandable freeze plug into the exhaust flange opening to keep the rubber gasket from ballooning out when pressure is applied.  

The method I used on my 175 exhaust port somewhat worked and probably would work good if you can find a proper semi hard rubber ball that isn’t too porous.

I used a semi hard rubber ball that came with a set of children size hockey sticks. I sliced off a portion of the ball after holding it against the exhaust outlet and eyeballing the proper amount to slice off.

Then I made a steel strap with holes drilled to match the spacing on the exhaust studs. I then held the sliced rubber ball with the sphere against the open hole and placed the strap across the flat portion where the ball was cut and let the exhaust studs protrude thru the drilled holes. I then used the exhaust nuts on the studs to tighten and squish the rubber ball into the exhaust port. 

The squished rubber ball formed itself nicely into the unique shape of the exhaust port and would have worked well if it wasn’t so porous. Air slowly leaked thru the rubber material. So I took it apart and applied a heavy layer of grease over the entire spherical side and worked it into the ball. Did this multiple times until it no longer absorbed the grease. Put it back together and was able to hold air long enough for my test purposes.

So I think the concept is good if you can find a semi hard ball that isn’t so porous. I was thinking that a good choice would be what we referred to as a Super Ball when we were kids. It’s the ball that has extreme bounce characteristics. The ball size that I used was 2-5/8” diameter. The piece you see in the photos was the leftover piece that I did not use. I can’t seem to locate the cutoff portion that I used, but you can see that it was somewhat less than half of the diameter.

imgur.com/a/4FZQbrv