Some people had experienced problems getting the OS .91SXH to run smoothley. We're not sure why some do and some don't, but if you are having problems getting yours to run smooth, this is the Fix. Both of our helis running the 91 have now been converted to this setup, and on Kurt's the pump solved a "shake" problem that had been plauging him ever since he installed the engine. Eric's Vigor didn't have any shaking problems with the OS .91 (nor two other local pilots) but the engine "seems" slightly smoother after installing the pump.

This is NOT a power enhancement. If your 91 is running smooth and happy you probably shouldn't spend the time or money to install the pump. If, on the other hand, you have a shake that is not related to a bad part or improper gearing (the 91 likes 8.1 to 8.4 just fine) then this will probably solve your problem.

	Here are the parts you need along with your regular tank and plumbing. The T-Filter for the pump AND the check valve must be ordered separately. YS or Fourmost check valves seem to be better than the blue Perry one shown, but the Perry unit is easier to get! The red pressure line and the mounting clamp come with the Perry P30 oscillating pump. For most secure mounting of the pump, scuff the plastic clamp and clean the pump with alcohol. Position as desired then mix a few drops of JB weld and spot it on the pump, then clamp it in place and let it dry.
	Step one is to remove the backplate and carefull drill the center section and tap it with a 6-32 tap for the pressure tap. DO NOT TRY to do this while the backplate is on the engine! After drilling make sure you remove ALL metal filings from the backplate.
	I used JB weld to secure the pressure tap. If you drill the hole as shown the tap will NOT stick thru the backplate. It must not protrude inside the backplate as it will interfere with the crank and/or rod.
	Use the stiff red tubing that comes with the P30 pump between the pressure tap on the backplate and the pressure inlet on the back end of the P30 pump.

Here's the entire installation. In most cases it will be easiest to use a header tank such as the DBC tank shown here - that way you don't have to install a third fuel line on your main tank. (The 2Oz Hayes tank already has a 3rd inlet, you just need to drill it through and clean out the debris and then it's ready to use. )

The top (pink) line is the pressure line from the muffler to the tank vent, just like always.

The bottom fuel line goes from the clunk line outlet of the tank, thru the T'd fueling filter, then into the P30 pump inlet. Note the bottom of the pump has arrows that mark the travel direction of the fuel. Another chunk of line goes from the outlet of the pump through another T-Fitting (in this case another T-Filter) and on to the carburetor. The third line from the T-Fitting goes back to the fuel tank to return any excess fuel into the tank via that third inlet. NOTE that this line has a check valve in it - this check valve is oriented so that the fuel can go from the "T" to the tank, and not the other way.

When fueling, the shut-off clamp keeps fuel from going thru the pump (which you are not supposed to pump fuel through) and of course keeps the engine from flooding while you fuel. The check valve keeps the fuel from flooding the engine from the 3rd line while you are fueling.

Pretty simple really. We have been doing as Curtis Youngblood suggests and remove the internal spring (under the hex head grub screw that you adjust pressure with) and stretch it to about twice its original length then re-install it.

Our results have been about the same - minor adjustments of the high speed needle valve get everything running smooth. It appears - based on the fact that the installation really does improve the smoothness - that the 91 may have a slight leaning tendancy in the mid range, or maybe just marginal fuel draw in the upper ranges - we're not positive WHY this setup works, just that it does.

Below is the completed installation on Eric's Vigor CS. Adds a little clutter but not too bad.