[NSRCA-discussion] Fuel Regulation in 2C Engines

[jeffghughes at comcast.net]

While you may be able to improve the throttle-down in a two stroke, I doubt if you will be able to match that of a 4 stroke. Two strokes generally run lower compression ratios and pack the case with fuel. Both make it tough to throttle down quickly. It's real noticeable in bigger engines like motorcycles.  I used to have a big Kawasaki 750 triple that had almost no off-throttle braking. Nearly killed myself the first time I drove a honda 750. Backing off the throttle of a high compression 4 stroke is almost like applying the brakes. 

-------------- Original message -------------- 
From: vicenterc at comcast.net 

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 press! 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 will 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
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