[NSRCA-discussion] Fuel Regulation in 2C Engines

Sun Mar 5 16:30:33 AKST 2006

Hello Vicente and All,
When you put a Perry or OS 140 pump on a carburettor that was originally intended for suction, the metering slot may be very wrong. The likely symptom would be mid-range richness. If, and only if, the pump is capable of delivering substantially more volume than needed, at the desired pressure, then the loopback method will work, but ...

A restriction in the return line will increase the pressure, and reduce the surplus volume requirement. This has been tested! The idea of a needle valve or other restriction in the return line is a good one, and in the past, I have used a simple piece of brass tubing filled with solder and drilled out with a small drill. You could even partially crush the tube with pliers, to get an initial setting. Keep crushing until the egine runs with the needle valve only a half turn in from the setting on normal pipe pressure/suction. This still may not get you the characteristics you desire.

The general rule is that excess pump pressure means that the needle valve and idle adjustments are set lean, and the metering slot still leaves you rich in the middle. This is fixed by lessened pressure, but if a return path is used to reduce pressure, then the pump needs to be able to deliver much more volume, or the top end needle has to come out too much, and there will be sporadic leaning. It will make you crazy. Oh, I forgot: we fly toy airplanes, so the craziness is fine.

Later,
             Dean P

	-----Original Message----- 
	From: nsrca-discussion-bounces at lists.nsrca.org on behalf of vicenterc at comcast.net 
	Sent: Sun 3/5/2006 8:13 PM 
	To: NSRCA Mailing List; NSRCA Mailing List 
	Cc: 
	Subject: Re: [NSRCA-discussion] Fuel Regulation in 2C Engines

	John:

	Thanks for your advice.  I already worked the prop.  The best I found is the 3 blade re-pitched.  I just want to improve it more.  Probably very difficult task base on the feedback I am getting.

	I like your idea to tune the return line.  I have been thinking to go that route with a Perry external needle valve in the return line.  The process would be, in the OS 160, to adjust the return needle valve until the high end needle valve is about 2.5 turns open at full power.  That is the normal setting when I run the engine with no pump.  In this way,  we will be close to the original design pressure.  Normally, the OS 160 with the Perry pump sets within 1 to 1.5 turns open.  Than means that the pressure is too high. 

	Vicente

		-------------- Original message -------------- 
		From: "John Pavlick" <jpavlick at idseng.com> 

		Yeah, I tend to agree with Nat here. After some discussion about the Perry loop idea, I know someone who actually tried it. It came down to the theory vs. reality thing i.e. "only one way to find out..." It seemed like a good idea, but it didn't seem to work on our big motors. I think that in order for this to work properly, you would need a pump that is capable of way more volume AND pressure than you need. In addition to this, the regulator should be an external device, not inside the pump like the way it is with a VP-30, or the internal regualtor needs to have an eaxternal "return" line. This is how a fuel-injected automotive system works, so it is possible. The Perry loop thing works for R/C cars and smaller motors but I think the pump needs more volume to feed our big motors with that big gaping "hole" in the system (the return loop). Maybe tuning the size of the return loop wi! th a restrictor would be worth a try. Is it worth the effort? Generally a VP-30 that is properly adjusted will give reliable performance with just a vent line and no tank pressure / no return loop. Props have a big effect on what happens when you return to idle too. If you want to help downline braking, look at props before you spend a lot of time re-designing the fuel system. Also, try setting the idle a little bit richer. The slow transition to idle condition is sometimes aggravated by a lean idle mixture. Not trying to discredit anyone's theories,  just passing along some of my observations.

		John Pavlick
		http://www.idseng.com <http://www.idseng.com/> 

			-----Original Message-----
			From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of Nat Penton
			Sent: Sunday, March 05, 2006 3:48 PM
			To: NSRCA Mailing List
			Subject: Re: [NSRCA-discussion] Fuel Regulation in 2C Engines

			Diaphram operated fuel pumps made by OS ( Hanno, 140 RX, 91 SH <Perry?>) are self regulating in that output is proportional to RPM, proportional to need. These pumps can be adapted to any 90 to 160 two stroke with JB Weld and without maching skills. The tank is vented and there is no pressure in the system.

			I have had impeccable performance using these pumps on the OS91FX for the last four years. I believe the logic in the circulating systems is flawed.                    Nat

				----- Original Message ----- 
				From: vicenterc at comcast.net 
				To: NSRCA Mailing List <mailto:nsrca-discussion at lists.nsrca.org>  ; NSRCA Mailing List <mailto:nsrca-discussion at lists.nsrca.org>  
				Sent: Sunday, March 05, 2006 12:22 PM
				Subject: Re: [NSRCA-discussion] Fuel Regulation in 2C Engines

				Hi Brian,

				You got it right.  In the OS 160 we would like to set up the pressure in the header before the carb as close as possible to the original design (muffler pressure with tank close to firewall).  In this way, the carburetor metering system will work as was originally designed.  I will be doing some test and see what will work better.  

				The expert at Perry recommended to send the overflow to the tank.  However, I agree that loop around the fuel pump could work since that is one old method to control pressure in industrial pumps.  

				Vicente

					-------------- Original message -------------- 
					From: brian young <brian_w_young at yahoo.com> 

					So I guess the thinking behind doing this is that you deliver the fuel to the carb and its there for the carb to take. But the fuel at the carb nipple will only be under atmospheric pressure (since the tanks vented), anything extra is free to go back to the tank. The venturi affect of the carb will draw the fuel into the carb. I dont see why you would need to go clear back to the tank, just loop around the pump. 

					This sounds like it could take the variability of pumps out of the equation and at the same time let the pump deliver fuel to the carb, but not push fuel into the carb.

					Interesting.

					Wayne Galligan <wgalligan at texasairnet.com> wrote:

					Vincent,
					!  
					I wonder if this "T" setup would work on an OS 1.40.  I already use the check valve in the vent so a couple of "T's" and maybe I would be in business.  Would you have to change the pump pressure?

					Wayne Galligan

					----- Original Message ----- 
					From: vicenterc at comcast.net 
					To: nsrca-discussion at lists.nsrca.org 
					Sent! : Sunday, March 05, 2006 8:19 AM
					Subject: [NSRCA-discussion] Fuel Regulation in 2C Engines

					Good morning all,

					I have been using the OS 160, OS 140 RX and Mintor 140 with good results in the last 4-5 years.  We have been comparing and discussing the advantages of YS compared with 2C.  One of the main advantages of YS is that in transition when power down the engine goes instantly to 2000 RPM or less.  The 2C engines always takes too much time to get down to idle and I believe that causes us (in pattern) some problems.    

					I have been thinking that the problem is that the carburetor and or fuel system that can not regulate properly (pressure or flow).  I think in these engines, the pumps are set to deliver fuel at full flow (or pressure) without any regulation system (like the YS).  ! I had the opportunity to discuss this issue with Perry Pump and they recommended to install a by-pass line.  The idea is to send the excess fuel (pressure) back to the tank during transition.  Perry Pump recommended to install the T as close as possible to the carburetor needle valve.  Also in their web site they have an idea that he said is used for cars that is a by-pass line that loop around the pump (http://www.perrypumps.com/instructions.htm,  Click on Pump and By-Pass Systems).  I think the ideas deserve some checking since it is natural to have this type of regulation to maintain constant pre! ! ss! ure in the line before needle valve.  I tried the other day the by-pass to the carburetor but I installed the T too far from the carburetor and forgot to open the vent in the tank.  Of  course the results were bad since I was developing vacuum in the tank.  I wi! ll try these options of by-pass lines as soon as get warmer.  However, I think someone out there already tried to do this and know results so I am looking for feed back.

					Thanks in advance,

					Vicente Bortone

  _____  

					_______________________________________________
					NSRCA-discussion mailing list
					NSRCA-discussion at lists.nsrca.org
					http://lists.nsrca.org/mailman/listinfo/nsrca-discussion

					_______________________________________________
					NSRCA-discussion mailing list
					NSRCA-discussion at lists.nsrca.org
					http://lists.nsrca.org/mailman/listinfo/nsrca-discussion

  _____  

					Relax. Yahoo! Mail virus scanning <http://us.rd.yahoo.com/mail_us/taglines/virusall/*http://communications.yahoo.com/features.php?page=221>  helps detect nasty viruses! 

  _____  

				_______________________________________________
				NSRCA-discussion mailing list
				NSRCA-discussion at lists.nsrca.org
				http://lists.nsrca.org/mailman/listinfo/nsrca-discussion 

  _____  

				Internal Virus Database is out-of-date.
				Checked by AVG Free Edition.
				Version: 7.1.375 / Virus Database: 267.15.6/257 - Release Date: 2/10/2006

-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/ms-tnef
Size: 15386 bytes
Desc: not available
Url : http://lists.nsrca.org/pipermail/nsrca-discussion/attachments/20060305/2c727c1c/attachment-0001.bin 