I purchased a scratch built plane that has not had a zerk fitting added to the muffler for pressurazation of the tank. What are my options for getting the engine running? Do I have to put a Zerk in the muffler for it to run? If I need to add is it easy to add. Are there self tapping fittings?

First of all, it's not a zerk fitting. It's a pressure nipple. A zerk fitting is something altogether different.

Hobby shops will carry the fitting you need. It's just a matter of drilling and tapping the muffler somewhere along the wide part.

If you're not sure of how thinck the metal is where you drilled the hole, you can always reinforce the grip with JB Weld

You can run without muffler pressure, but I for one wouldn't advise it.
Adding a pressure tap is relatively easy. You just drill a proper size hole, tap the proper threads and screw in the tap. Then you connect a piece of fuel line from the pressure tap to the vent line on the fuel tank. If there are 3 lines going into the tank, the fill line will need to be plugged. This is not a big problem you can just stick a proper size bolt in the third line.

Let me ask, does your scratchbuilt plane have a pump? If so, you don't need a pressure fitting.

Best wishes,
Dave Olson

Lippitdoo You really need to state exactly what engine make and model you have or post a picture. Otherwise we are just shooting blanks in the dark. Many modern engines will not function properly without muffler pressure or some type of pump. The fact is most modern engines have a much larger venturi that will not provide as much suction and therefore will require muffler pressure, this is to provide more power

However

Many older engines were designed to operate just fine only on venturi suction BUT they will have a much smaller venturi for any given displacement to provide sufficient suction to move the fuel.

Soooooo Whatcha got?

John

The engine is a ASP .46. It is mounted with the head to the right side of the fuse. The muffler is mounted below the engine. The largest flat part of the muffler is on the side facing the firewall. Not experience in taping a drilled hole. How do you do this.

Get the right size & thread tap for the pressure tap your going to install. Drill the hole and slowly screw in the tap a couple of turns then back it out a quarter of a turn then in again a couple turns then back it out a quarter. Repeat this until the tap is fully in to the hole. Not rocket science, pretty easy. The pressure nipple package will have the size and thread dimensions that will work. Usually but not always 6-32. The 6 is the size of the hole. the 32 is the number of threads per inch. If it is a 6-32 tap then the hole size to drill is #36.

When you are at the LHS to get the fitting, they probably will also have the tap you need, packaged with the correct sized drill.

I'm not familiar with the engine you mentioned, but another alternative is to replace the muffler with one that fits and has the pressure fitting. I have no info on what fits.

Simply take the muffler with you to the local hobby (hopefully it's local), that makes it a hole lot easier for the salesman to help, and advise you. Any questions may have will show up at that time, and he can clear them up. This is one of the benifits of having a good working relationship, with your LHS.
You will see how easy it really is once you have done it ,Have fun fly LOTS, Snuts.

I use the pressure nipple also. I have never tapped the muffler. Just chose the right size drill bit and the nipple will self thread. You don't even have to screw it all the way in because it will be extremely tight. Saves some bucks on a tapping package too.

A lot of the ones you buy are a tapered small pipe thread and self tapping, you just drill a slightly under sized hole and screw it in. A bit of JB weld is always a big help too. I have bought others that state what size tap is needed on the package.