Tinkering with a SV 17cc RC gas engine
Today I got to test run my poor SV 17cc engine which has some problems. One problem was it ran way too rich and the needle valves were essentially useless at dialing it in. But when I examined it more closely I found that it had a Walbro WT694 carburetor on it, which has a 12.7mm venturi in it. So I don't know if someone had swapped out the carb earlier or that was the carb that came with it. But in anycase I think the intake bore of 12.7mm is way too large for a 17cc engine. I think that a carb with a 9mm bore would be better for the engine.
So I rummaged around in my parts boxes and found a Walbro WT520 carb, which has a 9.53mm venturi bore in it. But when I tried the carb on the engine, it would barely pump any fuel at all. So when I checked it has a stupid blue plastic pump diaphragm on it. So I visited out local small engine repair shop and bought a rebuild kit and put in a black rubber pump diaphragm instead. Now when I test ran the engine the carb started working like it should work. Now the engine had a more linear throttle response and the high speed needle would actually adjust the mixture too. The previous big bore carb was at full throttle way before the carb throttle was at full open. But now with the smaller bore carb the engine was at full throttle when the throttle plate was fully open.
So now the performance was a lot better as I got almost s 1,000 RPM improvement over what it was doing slobbering rich with the oversize carb on it.
With a 13x6 Master Airscrew propeller I tached it at about 9,800 RPMs full throttle. With a 14x6 Master Airscrew prop I tached it at a little over 8900 RPMs. Now granted using my Model engine power calculator spreadsheet is only showing the engine developing a little over 1 hp means it is not going to be a powerhouse of a engine. But it is useable for certain planes or applications. The engine develops power about the same as the old baffled piston .60 engines we used to use, such as the Veco .61, K&B .61, Fox Eagle I, Fox Blue Head .60, HB .61 and so on. So choosing a airplane from that era that these .60 engines came from would have the size about right then. Of course maybe some of the more modern .50 size plane we have today might work OK too.
The engine isn't a powerhouse as it uses the classic piston port induction, no reed valves. It uses the piston skirt to control the intake port into the crankcase. The port timing is also mild. One could reverse the ignition timing and have the engine run in reverse equally as well as it does forward. But that capability also causes it to lose power though.
The Walbro WT520 carb may not be the best carb to use. But it did have what I thought was the more proper inside bore size for the intake venturi being it is a 9.53mm sized venturi. But there are many carbs with intake venturis around that same size too. One of the other carbs may be a better choice too. The carb does not have a choke on it, but it does use a remote primer bulb though. Except you need to use a third fuel line into the fuel tank as the overflow will travel through the remote primer bulb too. So you don't want to dribble fuel on the plane as the engine is running. Also without a choke you could have problems on cooler days getting it to start, warm up and run, before you can go full throttle and fly it. With a large prop, using a "smart thumb" might be dangerous to your fingers. But I am thinking about bolting on a slide choke setup I took off another trimmer engine a while back. This is a simple sheet metal affair that lets you slide a piece of metal across the intake to serve as a choke. Also I needed to drill and tap a hole in the pump cover as the engine uses a external crankcase pressure line to furnish the pulses for the pulse pump in the carb. Note that I also put on a machined metal throttle arm onto the carb too. This needed me to cut off part of the idle speed adjustment bracket, which isn't a big deal if you use the throttle trim or end point adjustments for idle speed.
So anyway, now I am motivated to make a exhaust tip baffle to insert into that huge gaping exhaust outlet on the muffler. The engine is just too loud like that with it open. Then I'll have to decide on a plane to mount it on too. So it might be a while before I use the engine on something.
SV 17cc engine test run
SV 17cc engine with 13x6 Master Airscrew Propeller on it.
SV 17cc engine with 14x6 Master Airscrew Propeller on it:
Here is a video clip of me trying out the throttle on the WT520 carb used on the engine.
I didn't get to fly today, as I had to do chores around the home. But I managed to get a little time to fabricate a quickie muffler baffle insert for the SV 17cc engine. As you can see from the other pics, they made a nice stainless steel muffler, but it does little to nothing to quiet the engine down any. So I made a simple baffle insert to stick into the exhaust outlet to help quiet the engine more. I'll find out how well it works when i test run the engine again using it.
I still have room to drill out the holes more if needed should the insert wind up being too restrictive and reducing the power too much. I can also chop a little off the bottom if needed too.
I did a test run today with the engine using the muffler baffle insert and it definitely lowered the noise level quite a lot. I was surprised it worked that well too. It also only caused the engine to lose about 200 RPMs off the top end with a 13x6 prop. Plus the idle speed and idle performance improved a lot too. I could idle the engine lower than before. So much so that the engine starts to develop a slow surge with it changing idle speeds going slower and faster and slower again. So it turned out to be a pretty good success story for the engine.
Here is the engine going wide open and it didn't lose a lot of power with the baffle insert.
Showing the slow surge or idle oscillation it was doing. It was slow enough to take pics of it.
Here is a short video clip of me running the engine with the baffle inserted into the muffler. Also at the engine of the clip I alternate with the baffle out, then in, then out and back in again too. It does make a big difference in noise levels having the baffle inserted in the muffler.
I accidentally ran across a engine review about the RCS SV-17cc engine in RCM Magazine in their January 2010 issue. This is a issue where Dave Gierke does a large article about glow fuel and oil also. But the SV engine review is on page 58.
My performance numbers are about the same although I was running a higher oil percentage in the fuel they they did for the engine review article. But the calculated horsepower figures are really close to being the same too.
The engine performance figures with different propellers detailed are (using a 32:1 fuel to oil mix):
Wildcat Smart wood 14x6 8,400
Evolution composite 14x6 8,300
APC composite 14x8 8,200
Moki composite 15x6 7,900
Zinger wood 15x8 7,600
Master Aircrew composite 14x8 7,300
I mounted the SV-17cc engine in a Great Planes Escapade .60 RC model airplane.
The engine performed really well. The plane is a little underpowered with the engine, but not by much though, only if you are someone wanting unlimited vertical performance. It flies well in the air and ran really good. No problems at all. I used regular pump gasoline and Amsoil 2 stroke oil for fuel. The propeller is a Master Airscrew 13x8.
Here is a video I made running the engine and flying the Escapade plane too.
Here DB Noise level of my SV-17cc engine while standing on top of the plane with the meter about 5 feet away from the engine. This is with my homemade baffle insert installed in the muffler. Now normally they measure the DB noise level while standing at about ten feet from the muffler side of the engine, while the engine is at WOT. Also you have the plane on a table test stand about 30 inches above the ground level too.
Without the insert the DB noise level is about 100db or a touch more.
If I held the DB meter at about 3 feet above the engine, the DB noise level goes up a little more. But it is still within the 95db max club rules at our flying field.
Someone had asked about how much the Escapade 60 weighs with the SV 17cc engine on it. It took me a while, but I found my weighing scale and weighed it. I found that the plane weighs in at 9 pounds 4 ounces with the fuel tank empty. I am also running separate battery packs for the radio and electronic ignition in the plane.
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