Just a Quick question
 

I decided to pull the perry pump out of my funtana x50 as it is giving my sk90 too much trouble at idle. I would like to use just muffler pressure and am going to clog one off the exshaust outlets on the pitts to get the proper backpressure. I am curious as to what i should do with the nipple tapped into the backplate?. Should i leave, remove it?
Thanks
Cameron

RE: Just a Quick question
 

Block the hole otherwise you may have problems with tuning.

I prefer to put a very short bolt in where the nipple is (4-40 by memory but don't quote me on that). Make sure that it doesn't intrude onto the crankshaft. Otherwise a short length of pipe with a plug in it (I use the plugs from fuel dots - they are short and readily obtainable.

RE: Just a Quick question
 

IMHO you should use a short piece of fuel line and a fuel dot or plug to block the crankcase pressure line off

RE: Just a Quick question
 

G'day Mate,
I would try running it without closing off the exhaust tube, & see if it runs ok, It should not need more muffler pressure, than the muffler was designed for.
Be aware, muffler pressure & back pressure are not the same thing, muffler pressure, adds slight pressure to the fuel tank, for aerobatic maneuvers, motor should run on the ground without it, & back pressure is a function of the exhaust system to help get exhaust gasses out of the combustion chamber more efficiently.
If you look at a 4 stroke motor, they don't need back pressure, that is why you can run them with a straight through pipe, but 2 strokes need BACK pressure, that is what a tuned pipe does, & on a 2 stroke motor cycle they have expansion chambers, similar to our normal mufflers.

RE: Just a Quick question
 

Hi Cambo,why dont you try to play on low speed needle shape before removing pump?Anytime you can provide another new at low cost if fails.

RE: Just a Quick question
 

Hey guys
Pitts and pump just isn't working
I would like to go back to the stock muffler but i need at least an extra inch for the muffler to clear the underside of the fuse.
The engine runs the best on the stick muffler and only used the pitts because I didn't want to do any mods.
All Sk 90 owners, do you think this will fit.
http://www2.towerhobbies.com/cgi-bin...?&I=LXARP9&P=7

RE: Just a Quick question
 

I believe I read somewhere the SK engine is not a high rev engine, its power band is lower, like around 9,000RPM. So a Pitts muffler and pump are not really necessary or desireable. The engine will do fine under less improvements. Realizing the Pitts is there to stay, yes block up one port to improve the exhaust back pressure. Cap off the nipple on the engine plate to ensure no air leaks into the crankcase. The engine should run better but never expect it to be a screamer, it was not so designed. It will probably pull a big prop at lowe RPM with little or no objections on its part -- that's where its torque is maxed out.

See Ed Moorman's thread on the SK 90.

Good luck.

Chip

RE: Just a Quick question
 

I tried with a plugged outlet on the pitts and nothing changed. I finally tried it with the stock muffler on a test stand and WOW, the engine came to life. Top end improved by almost 200 rpms with a smoke trail coming out which means it is running rich.

Now my only options are to run the engine inverted or get some sort of muffler extension. I think mounting it inverted is the best option at the moment.

RE: Just a Quick question
 

Wow, never mind what i said before. Mounting the engine inverted is going to be a pain in the @$$. I think that muffler extension might fit. I am going to be searching through tower to find the closes fit.