Bad miss on mag check then smooths out.

Just a thought. Maybe a plug starting to foul and clears itself.

Murray Parr wrote:

Just a thought. Maybe a plug starting to foul and clears itself.

That sounds reasonable. Is there a way to tell other than replace all the plugs? 

How big an rpm drop? Plugs are usually bad or good and not intermittent. If it's a bad or severe miss it isn't a single bad  plug. Usually a bad plug, plug cap or wire is around 300 ish rpm drop

Hi Walt

There is another thing to consider.  If it is auto fuel, hot, then you may be running lean.  The hot fuel may not be stable and you are getting some vapor.  4000 is the leanest in the carb running range.  The factory default is for position 3 on the needle clip positon for each carb on the 100 hp carb settings.  Once the engine runs for a bit the fuel flow, recirculation from the return line, will clear the hot fuel and as you note it runs normal after that.  Perhaps just something to look at.  

If you suspect this perhaps try adding some Avgas, it will have a higher RVP and should clear that up.  You can mix it no problem, I would put 50/50 in to try it.

Cheers

Rotax Wizard wrote:

Hi Walt

There is another thing to consider.  If it is auto fuel, hot, then you may be running lean.  The hot fuel may not be stable and you are getting some vapor.  4000 is the leanest in the carb running range.  The factory default is for position 3 on the needle clip positon for each carb on the 100 hp carb settings.  Once the engine runs for a bit the fuel flow, recirculation from the return line, will clear the hot fuel and as you note it runs normal after that.  Perhaps just something to look at.  

If you suspect this perhaps try adding some Avgas, it will have a higher RVP and should clear that up.  You can mix it no problem, I would put 50/50 in to try it.

Cheers

Absolutely sure it is not a fuel issue of the type you describe. The same fuel is in the tank that was in it yesterday when I pulled out at 105f and flew to 10,000 ft with no issue. This miss problem was this morning with ambient of 75f.