cutting shoestring cowl
 

Anyone have any ideas as what the best method is for cutting the glass cowl on my shoestring? I am fitting a 91 fs and am not quite sure how to run the exaust without butchering my cowl. The motor is mounted on its side. Any advice comments or pictures of 4 strokers mounted in shoestrings would be great
thanks
vansrv-8er :confused:

cutting shoestring cowl
 

I use a Dremel with the little sander bit on it. Start with a small hole and just make it bigger to the shape I want. I am about to do that with my own Shoestring next week with a G90 sideways.

You have to install and remove the cowl several times but looks good at the end.

cutting shoestring cowl
 

You need the bisson or slimline pitts muffler stated in the manual. Mine is a beautiful installation where only the pipes come out at the rear of the cowl. I also have an on board glow driver so no glow-plug hole, only needle valve and pipe holes. Use a dremel tool and paper templates taped to the fuse to find hole locations.

Yak

Opps, I just reread that you have a 4-stroke...no way around bigger holes...sorry.

Mount it Inverted
 

If you haven't started cutting yet, you should really consider mounting the engine inverted to preserve the cowl's nice lines (see attached pic). I used a saito 91 on mine, but I figure the set-up of an OS 91 would be about the same.

FYI, the bolt spacing on the engine mount is perfectly square, so you can simply rotate it 90 degrees and the holes will still line up.

cutting shoestring cowl
 

thanks for the comments and pics boys! I like the inverted look nice and clean! Probably helps cooling as well. How does a 4 stroker run inverted? I experimented with a hot knife and it cuts like butter but watch out for the fumes by the smell I think they are caustic. :D

cutting shoestring cowl
 

I had an OS .91 4 stroke in my first one. With the engine mounted horizontally, it fit completely within the cowl. I made a 2 inch hole in the bottom of the cowl for an exhaust exit. I suggest you get a flex tube and 90 degree adapter, and use that instead of a muffler.

cutting shoestring cowl
 

I've run several 4-strokers inverted w/out any problems. The experts say thats because the plug is offset in the head - not right at the "bottom" like most 2-stroke engines, the plug is less likely to fowl due to fuel/oil accumulating there.

Just test flew my Bucker Jungmann last weekend w/ an inverted Saito 150 and it ran/idled just fine.

cutting shoestring cowl
 

Picture of the .91 4stroke

cutting shoestring cowl
 

Another pic

cutting shoestring cowl
 

I have another question. I have never had a 4 stroker before and picked one up brand new for 170 bucks from a guy who has transitoned to gliders. It is a 91 fs about 1994 vintage. My question is what does the nipple on the bottom of the crank do?
The instructions dont say a word about it. I have noticed that when I crank the engine there is a slight puff that comes out. Is it for pressurizing the tank?
Thanks
vansrv-8er

xx
 

That is for drainage of left over oils, just add a piece of fuel tubing and run it out of cowling.

cutting shoestring cowl
 

Forget what I said. I missed the Fourstroke. if that is what you have, go inverted.

cutting shoestring cowl
 

Inverted it is! I turned the engine mount and it fit perfect just like you said. I used the hot knife method for the cowl and it is working pretty good. You have to go over it with sandpaper afterwards. All I have to do now is redo the throttle pushrod for when I went inverted it moved the throttle body a little. Anyone have any pics of thier muffler setup on an inverted 4 stroker?
Thanks for all of your responses!

keep it just under the vne 225 kts
vansrv-8er