I have a 46cc poulan convert. At full throttle it interferes with my radio. Would a throttle servo mounted in the front, 6" behind motor just inside the fire wall cause this? The receiver is new and it is FM. I do have a PCM to try in its place. I hate to mask the problem with PCM rather than find the problem and fix it. The engine does have a resister plug and standard ignition. Any thoughts or opinions?

Thanks
Shan

Have you tried using a resistor spark plug? That should be the first place to look. Second is the shielding on the plug wire. Loose or dirty connectors on the battery, switch, or servo could be another possibility. I often locate my throttle servo within an inch or two of the engine, and just a couple more from the igniton without any problems. But I'm always certain tht my componenets are in excellent shape when I do so.

Don't use the PCM Rx until you locate and resolve the cause of the problem.

You are better off knowing about the problem, and fixing it right now, rather then masking, and ignoring it.
Yes, that servo only 6" away could be the problem, especially if connected to the throttle by a metal push-rod. Is it ? Regardless, back that servo up to 12".

> Jim

Hi,

Radio interference at full throttle sounds like a vibration induced electronic failure. If so, you should check your mounting, padding etc. of all of the components.

Elson

I, like Silversurfer, have been mounting throttle and choke servos as close as one inch to the ignition box, battery, and engine for quite a while. I don't know when or where the 12" rule came into play but I and many others can prove wrong.
99% of RF is caused by a bad plug connection, bad plug wire, or using the wrong plug. Then there is metal to metal harmonics. I even had a plane that had a metal hub on a metal axle on the tail and at certain speeds would cause RF. Then there is the hard to track down bad servo extension wire or connection.
What I am saying is don't blame the location of the servo, look elsewhere, If it is only happening at full speed, I would be looking at metal to metal connections, wire connectors, Look at your control rods and clevises, are they metal ?

Gary Allison at Brison And Bill Carpenter at C&H both told me to keep 12 inches between my motor/ignition and any radio gear. I have done that in my last 4 or 5 models and have None/Zilch radio problems. Use A non metal control rod from the servo to the motor as suggested above. This may not cure your problems, but it sure did mine. Brian Smith

As stated, I can show you eight, (8) 33% and larger planes all with throttle and choke servos, ignition boxes and batteries mounted on or in the engine box. All within a 6" area. No problems.
As a matter of fact if you fly giant ARF's many show the throttle servo mounted on the engine box in there assembly manuals. Some even come with the servo mount already cut out in the engine box cover.
Hope you find your problem shann.

HWS. I think your missing the point. Your running ignition motors with shielded plug wires. Shann's post says he has a restistor plug and "STANDARD" ignition. Which means to me he is running a stock mag and "NO" shielded plug wire. Hence I think a 12 inch seperation will cure his problem as it did mine. Hope that is helpful and not offensive. Brian Smith

Thanks to all for the responses. The engine mount is directly mounted to the fire wall. I think I will try softening the mount some how. Possibly some rubber bushings. I am using a metal push rod for the throttle but I do have a plastic clevis on it. I think I will also move the servo back. There is a spot for it already built into the plane so it would be an easy move. I will try it this weekend and see what happens.

Shan

No offense taken Brian.

If possible, When you move the servo back, install a plastic push rod up to the motor. One of my ships was glitching with a metal push rod and a plastic clevice. . Bill Carpenter told me "sometimes" the interference is carried through the metal push rod. It would be a cheap fix "if" it cures your problem. The best to you with this problem.
Thanks H. Wayne.....Brian

I tend to agree with bugman that you probably have a vibration problem which occurs at that particular RPM. I also agree that using a non metalic push rod on the throttle is good insurance. I often violate the 12 inch rule and have never had a problem with my battery and electonics much closer to the engine compartment as close as 5 or 6 inches. I'm running mostly Quadras with magnetoes and no shielded plug wire but do use resistor plugs and am very careful to never have any loose metal to metal fittings anywhere on the plane.

I moved the servo back. Replaced the metal rod with plastic. Placed rubber gromets between motor mount and fire wall. Rapped the receiver in more foam. The problem got about 75% better but still there. So I replaced the receiver with a PCM receiver and the problem completly disappered. I flew the plane with no noted problems what so ever. It flew and ran perfect. Enough power to hang on the prop at 75% throttle. The PCM may have covered the problem up but it flew perfect. So if that is the case then oh-well. I have tryed everything else with the exception of changing the ignition and that would defeat the purpose of placing a converted chain saw engine in it(cheaper).

Thanks to all for your help
Shan

Add a shielded Bosch cap and you should be able to run PPM no problem. Most of the RFI noise comes from the spark plug and shielding will go a long way preventing RFI. EVEN on A MAGNETO

I went the same route for a while, eliminating this and that and the inteference would get better but not completely gone. I, like you, finally bought a PCM receiver and never had another problem. I don't even own anymore FM receivers except for electrics. People can say, "well you are just covering it up", and they might be correct but I don't have any interference!!!
Blue Skies,
Jim