This is a Hp .61 I recently acquired. It's a pre-'72 with the 4-bolt head. I asked in a previous post about the hole drilled in the exhaust flange. It seems to have been added by a previous owner. The real question I have is the backplate. Every photograph of HP 4-bolts show the standard 4-bolt backplate we're normally accustomed to. Whats up with this one? The engine appears to have been test run, at most, and if it helps, is an early production run, with a serial number in the 50's. I was going to use this on a Phoenix I I'm currently scratch-building after I acquire the original clip-on muffler. Any info would be appreciated....Mark

That's not the kind of carb I'm used to seeing on them either? Looks like a ASP?

Here's a picture of the carb.

KaosDriver, it looks like the backplate is threaded in. If you had a length of flat bar that was a snug fit in the notches, I bet it would screw out.

Well its not exactly alike but close to the two different eras of ASP carbs I have.

I was thinking the HP carb had square sides to it?

I better keep quite. I've only seen other's HP engines. And not that many of even them. I don't own one.

Yea Tim, I believe it is threaded, I'm just curious as to why it's different from other HP 4-bolts I've seen. Thanks, Mark

Looks like my four bolt. I don't have the original carb, but the carb looks like a larger version of my HP .40. I don't recall any four bolt HP's with anything other than the screw on back plate.

Thanks SP, I'm wondering if HP had aomething like a Custom Shop? I hope someone knows.....Mark

I Google Imaged this HP .61f of 1969:
http://www.btinternet.com/~wemxt03/start/engines/HP.htm
1969
HP entered the mainstream model engine market, they did so with a revolutionary new Schnuerle ported rear bell valve 10cc engine designed by Austrian Paul Bugl, the engine was of course the HP61. This innovative rear induction power-house was shortly followed by a front induction version, the HP 61F.
In order to facilitate the rapid introduction of a front induction version of the HP61, a new crankshaft and front housing was bolted on to the rear of the existing crankcase where the rear bell valve had been. The part of the main casting where the crankshaft had been was removed. Lacking lugs to bolt a back-plate to, a thread was cut internally and a large plug type back-plate, as found on many small diesel engines, was screwed in. The only disadvantage was that the exhaust stub was now on the right side of the engine, it was on the left side on the rear induction version.

Thanks Tim, I believe that pre-'72 units had the screw-in backplate, post '72's the 4-bolt backplate. Thanks to everyone who's replied....Mark

It also seems to have pure Schneurle porting, i.e. two angled ports on either side of the exhaust port, without the customary boost port, unless, that is, it is machined, or cast internally.
Most current engines (not the OS.40LA) labeled as Schneurle do have this extra port, but it was not a part of Mr. Schneurle's original design, back then.


Mark,


Looking in through the exhaust port, is there a boost induction port on the other side of the cylinder?

Dar: Looking through the exhaust flange, there is a small rectangular port on the opposite side of the cylinder.....Mark

KaosDriver is right. It has a very small boost port, it is ground in the casing directly under the oval HP 61 label.