Just throwing this out there, Any chance this is a sinking float issue??? Seams to come on after climbing&descending or general maneuvering.
This engine intermittent cutting out feels like a very quick “bump’’.
It happened twice during the prebuyer acceptance flight at level flightOr possibly in a 30 degree banking turn.
However it didn’t repeat during any other phase of flight.
The next time was two flights later in cruise, possibly two to 6 very quick intermittent and random cutouts, which feels like a bump and can be felt through the floor, airframe.
After refueling it occurred on takeoff and height cht, approximately 415.
The next leg was oat 101, 1200’ asl, held 30 minutes from takeoff and 429 cht and several bumps, possibly 5.
The next two legs were cooler OAT and the a/c performance was smooth.
9:00 am take off, about 89 degrees OAT, asphalt runway, full power climbing at 105 mph at 500’ high cht 422, two people, max t/o wt., and thru 700’ it followed with 6 bumps in about 10 seconds, which was followed by reducing mp, and stay in the pattern and landing.
Mag check followed. Light speed plasma 3 (left), slick (on right).
Repeat takeoff with a reduction of mp, and climb at higher a/s 140, and felt several bumps but seemed not as bad.
Again stay in pattern, return to land.
Call an A&P, he suggests removing the front metal obstructing the fins in the inlet (c/w), replace spark plug (c/w on slick), Klaus from light speed asked how the left mag sounded, it sounds great, suggested don’t remove plugs (Dinso).
Mechanic suggested providing blast tube for slick mag, (c/w), also pull carb hose off and check the filter screen (c/w no sediment or rubber particles).
I re-routed the inlet cowling baffle rubber and speed tapped the open areas.
Take off single pilot, reduced power climb, circle over field, take-off on different tank.
Some bumps felt but mostly smooth to proceed to altitude, mag check at altitude, all good and smooth, short flight to hangar where maintenance would proceed and is continuing.
So far the forum responses have been very interesting.
Of course the high CHT’s are a main focus.
One said stuck exhaust valve, which I find quite interesting.
However this engine is the best sounding and easiest engine to start even in heat soaked conditions.
I’ve never witnessed an easier starting engine.
Question? Is that because of the light speed?
So from what I have heard about on stuck exhaust valve’s it is a morning sickness common occurrence.
Also we checked all egt’s, CHT’s and they are consistent.
Another said check for cylinder wall coatings deterioration. There is a mirror like finish on mine and still the RMS cross hatching. No defects noted.
I used an inexpensive endescope, I -lan on using a bore scope soon to check condition of exhaust valve stem.
It appears the fuel line from the flow meter to carburetor appears the black adel clamps got hot.
Yes there is a heat sink on the exhaust below it.
I was able to re-route the line away by 1& 1/2 inches, so I’m hopeful this will help.
Question I have: can these bumps be from fuel boiling in the fuel line?
Another fact to consider.
In flight if I pull the throttle back in the descending phase of flight, and the engine back fires.
Question: is this a result of a difference of the two mags.
I have checked the timing of the slick, it is 25 BTDC.
Could the light speed be the culprit?
Or the lightspeed’s pressure sensor?
An advanced timing, sensor fail, causes higher CHT’s, possible causing backfire? ( fails in the full advanced position ).
I have not checked the timing of the light speed yet.
What magneto combination is best suited for these a/c?
I’m trying to maneuver through this troubleshooting phase with my mechanical sense, with the help of A&P mechanic’s, IA’s, factory reps, and VAN’s experienced operators (pilots, mechanics, engineers).
Hopefully I can resolve this shortly, however challenging at present.
Thank you for your responses.