Question for the spark flyers out there

[Andrew Borgogna]

I have a Forster .35 on my Lil Zilch and it starts and run well on spark, but not as well as it does on glow.  On glow the engine runs very smooth, but on spark there is a miss every few seconds.  I don't know if this is just normal or if there is an adjustment I need to make.  In particular the gap on the spark plug and/or the dwell on the points.  The plug is gaped where the maker (Kavan) set it. The dwell is a guess on my part, I put an ohm meter across the points and rock the prop back and forth and adjust until I get a reliable swing on the meter.  I probably should set the points with a feeler gauge but I don't have anything small enough to fit in the points housing. 

The engine runs well on spark its just the occasional miss that bugs me.  Also, the engine starts easily by hand on glow, but I don't even get a pop on spark.  Yet just bump the spinner with my starter and the engine springs to life.  This may be due to the fact I use a transistor ignition module.  My big Zenoa is the same way, can't hand start but starts easily with an electric starter.  I was told it had to do with the very narrow spark duration from the electronic spark module on the Zenoa.  Anyway any comments will be greatly appreciated, if the weather holds up my VSC ignition Zilch should make its first flight this weekend.
Andy

[Jim Kraft]

Andrew; The Forster timer is a little funky to my liking, but they do seem to work OK. I generally cut a piece of a playing card about 3/16" wide, and use that to set the points, which is about .008". The plug should also be set at about .010". I would check the points when closed with an ohm meter, if you have one, and it should be 0 ohms or maybe 1 or 2 ohms. If the engine has some time on it you can raise the timer as far as it will go, after starting and the engine should be happy on a 10-6 prop. If every thing is right it should start easily with a transistor and hand starting. If you are getting more than about 5 ohms across the points you should clean them. Sometimes they get oxidized and need to be filed or cleaned with some 600 grit wet or dry paper dry. The plug gap on the Forsters seems pretty critical, and I would make sure it is not over .010". I do not have a 35, but I have one of the old 29 rear valve motors, and it runs very well with no miss on a transistor with either glow fuel, or gas oil mix. Hope this helps, and maybe some others will chime in here.

[Joe Gilbert]

Andrew You have one of the best right there with you in Jim Kraft. I think that vibration can and does bad things to your points. If you have not already,  put a ground wire from point mechanism to the engine so that even if every thing viberates there will be a good ground between them.

[Andrew Borgogna]

Thanks to all for you replies, the miss could be any of your suggestions and I will give each a close look.  I am including some pictures of the plane and engine, just because everybody likes pictures.  One last thing you will notice a nylon tie rap on the advance lever.  When running the lever backs itself to the full retard position.  Since I use a starter and not my fingers, starting in the full advance is not a problem.  Hope you enjoy the pictures.  The Ringmaster is my other VSC-20 plane I intend to fly both at the next VSC. 
Andy

[Jim Kraft]

Andrew; Really nice looking planes. After reading your last post I thought of something else. You said that your timer would move to the retarded position after starting. This is a problem with a lot of old sparkers, and I have used various devices to remedy this, such as using a slice of bicycle inner tube to use as a band to hold the timer advanced, but still be able to retard the timer for starting. Having said that, there is a screw in the lower part of the timer, with a short spring, that goes through the back of the timer in a slot. That screw can be tightened to where you can not move the timer at all, and you could do this instead of the tie wrap. Or you might try just tightening the screw enough to hold it where ever you put it. This could also be your miss problem as the timer may not be making good contact with the engine case, causing high resistance in the ground side. As Joe Gilbert pointed out, (no pun intended), you need a good ground path back to the engine case, but with an enclosed timer, there is no way to put a ground wire on the movable point its self. But you do need  a good path from the timer to the engine case. Just something else to check.

[Andrew Borgogna]

Thanks Jim I will check the screw and tighen if needed.
Andy

[De Hill]

How big are the wheels on your Zilch? At Tucson, on the grass, you will need at least 2" or maybe 2 1/2" wheels.

[Andrew Borgogna]

De
They are clearly not that big, I guess I didn't give that much thought.  I will be sure to get a set of larger wheels before VSC.  I flew it yesterday and of course ran into problems with the spark hardware.  I got a couple of flights in on spark and several more in on glow.  Today I will trouble shoot the spark equipment for the problem, I have a spare electronic module if that turns out to be the problem.  Nobody ever said flying with spark would be easy, the good news is the plane flys quite well.  I am still breaking in the motor and with each flight the engine runs got better and better.  I was able to do most of the old time pattern as I gained more confidence in the plane, but all in all I am quite pleased with the handleing of the Lil' Zilch.  I will keep those interested updated with the progress of the project.  One good thing I have a good technical backround in electronics so I don't think there is anything in the spark area I can't resolve.  In the mean time I can continue practice and triming with glow as necessary.
Andy

[Larry Renger]

I was out with Andy yesterday for the first flights.  I am really pleasantly surprised at the performance of this model.  It is about 2/3 the area of a Ringmaster and weighs more, we think, but it maneuvers very nicely.  My guess is that the high aspect ratio wing and relatively long tail moment give it an edge over what it would do in a more conventional layout.  It also has a very respectable airfoil with a nice, round leading edge.

Anyone know the original design date for this model?  Andy's was built from a replica kit.  We guess that with better wood selection, several ounces could be trimmed from this design.

See y'all at VSC!