I would not change the way you have your ignition set up. 4.8 volts up to 6 volts (do not use a 6 volt battery on ignition when fully charged it will go above 6 volts and can damage the ignition module)is fine, the way you have been doing it. Although it may be ignition related, I would check a couple of things first. You say that when you pulled the throttle back the engine smoothed out. Correct? If so I would check some simple things first. Here is a list I think might be of some help and also a question or 2 thrown in.
1. How old is your fuel tubing?
2. Do you use an inline filter?
3. I suspect that you might have possibly picked up some debris in the carb or the engine went lean due to temps. (I lean more toward the debris as you ran some flights before).
4. Is your clunk connected?
5. Remove the carb from the bottom of the engine and disassemble until you can see the screens. Take a magnifying glass and look at the screens. If you see a white powdery residue, the carb is dirty and needs a good cleaning. You can go to your chain saw or lawn mower shop and buy an overhaul kit for all Walboro carbs for about 7 to 15 dollars.
6. Now is a good time to replace all your fuel tubing and ensure there are no leaks between the carb and the carb block.
7. Since it is cold you might want to richen up the needles a tad. If the engine went lean and the cylinder head got too warm it will stumble.
I do not want to start a debate on oil but I have to ask what mix you are running. Notice I said mix not brand. I know a ton of guys who run 100:1 however I do not recommend it. If your comfortable with that ratio, more power to you. However if you are not flying for competition I would run 32:1 at all times.
Hope this helps. If you need more assistance let me know. I can be reached on my personal e-mail at
[email protected]
Regards
Glenn Williams