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Perry VP-30 pump

There are two basic versions of the Perry pump, the VP-20 “Shaker” pump operated by engine vibration and the VP-30 which uses pressure pulses from the crank case to operate. Usually, the VP-20 is used with a four stroke engine and the VP-30 with a two stroke. Sometimes, for whatever reason, people want to use the VP-30 pump with a four stroke engine.

Since most four stroke engines require a vent to the atmosphere, some alteration of the standard pump installation has to be made, and the adjustment of the pump is slightly different from the instructions included with the pump.

First, as the instructions state, mount the pump as close to the engine as practical, and use the supplied hose to connect the pump to the crank case vent nipple. Only one caveat here, if the pump is mounted behind and in line with the crank case use at least a one inch spacing between the engine and the pump.

Now with the pump positioned cut the red hose and insert a tee, use the largest bore tee you can get to go in the red hose. Warming the red hose will help, put the straight legs in the red hose, the case vent hose will go on the tail. The vent can be regular silicone fuel hose, but keep the stiff red between the engine and the pump if possible – the pump will work much better.

Red hose? It is a very stiff hose that does not tend to balloon with the pressure. Normal silicone will absorb some of the peak pressure pulses, use silicone hose as a last resort.

Now we get to the fun part. Adjusting the pump.

Strong advice – have your engine fully broken in, and the needles set for a normal tank with muffler pressure. The first time you set up one of these pumps you don’t need to be worrying about the engine as well.

Remember please, to plug the muffler pressure port and use only an atmospheric vent into the fuel tank, adding muffler pressure is another complication you don’t need.

Now with a length of silicone hose (try six inches to start) on the tee for the case vent, start the engine. Let it warm up, then go to full throttle. Ideally it will take about twice as many clicks to reach peak as it did with muffler pressure. If it takes more than a full turn to reach peak cut an inch off the vent hose. Huh? Right. The restriction in the vent hose is controlling the pressure pulses into the pump, and therefore how strongly the pump is working.

If you find the mixture too lean on first running you have two options. Try doubling the length of the vent hose, or put a restrictor in the vent hose. An ordinary remote needle valve can be used, if one is handy. An alternate is a short length of brass or aluminum tubing, pinch it a little at a time to increase the restriction. The needle has the advantage of being adjustable for both more and less restriction. In other words mistakes can be corrected more easily.

Once you have the high speed set as we want, adjust the low speed in the normal manner, checking both for good idle and good transition. If all is well, you have finished.

Now you may wonder about the pressure regulating screw in the pump. So far we’ve not touched it. We will use it for fine tuning only if needed.

After the low and high speeds are running nicely check the mid range. The pump pressure regulator will have the greatest effect from mid to ¾ throttle on the Saito two needle carb, if too low the engine will tend to stumble a bit going from mid to full, too high the response will be slow. And it’s really hard sometimes to tell the difference. Pinch test time. With the engine running a little over ½ throttle pinch the hose between the pump and the carb. We want the rpm to rise just a little, 50-100 rpm, before it falls off. If it rises too much turn the pump regulator screw out about ¼ turn and try it again. If it falls immediately turn the regulator screw in about the same amount and recheck. Please note also, this will affect both the low and high needles, you’ll have to check them with every change of pump pressure. And this is where many people decide it’s “Good enough.” It can be a bear.

There are many advantages to using the pump, including being able to put the tank anywhere it’s convenient and not worrying about fuel feed, the engine can be run closer to peak mixture since you don’t have to worry about going lean with a low fuel level or a nose up attitude, and so forth.

It can take a while to get everything right, but when it’s done I think you will be well satisfied.