ORIGINAL: kochj
If that is a new motor, perhaps you should try the non-synthetic oils first for mabay a couple of gallons and then go to the synthetics. This will seat the rings quicker and give you more power and more consistent running engine. If you try adjusting the fuel rich and lean both ways and it still hesitates on take off, make sure all of your seals around your carb is good and nothing has loosened up. If not the case, check the inlet nipples that attach to the fuel lines to make sure they havent lossened up as well. If you do all that and it still is hesitating on throttling up, call BME and tell them you may need to send the engine in to them! BETTER SAFE THAN SORRY...... I am not sure were else to take it,,,, I have spent over 10hours straight trying to get an engine to run right and then I found it had a faulty ignition when I sent it in for warranty..... Oh, one other thing ... Try changing the spark plug for new one and then see if it still stumbles.....
Hope I have helped.
I can try one gallon on non-synthetic oil as well. I ran the engine on ashles oil, however on a test stand, reach and at only mid throttle for only short periods of time each. I consumed 2-3 gallons in this process. However the engine never has been ran in the air on non-shynthetic oil so far I switched to synthetic oil for the maiden flights.
When I started troubleshooting the engine "stumble at take off" couple of weeks ago, right after the very 1st maiden flight, I opened the carburetor, found a small piece of transparent plastic flake in the diaphragm(?). The screen was found clean. Replaced the fuel filter for a larger diameter (Sullivan). Solder a brass nipple on on the diaphragm and connected a tube to the inside of the fuselage. Inspected the clunk which by the way was too close to the rearmost wall of the fuel tank, this actually prevented the clunk from freely moving inside the tank! Lucky me I did not have a dead stick during the very 1st maiden flight !
RTK
As mentioned earlier make sure the engine is warmed up, especially before changing any needle settings.
Does it ever hesitate/stumble in flight when you go from an extended low throttle setting to high throttle setting?
All those actions did not make any differnce as far as the "stumble at take off" goes, however the engine was running definitely on the reach end by then, that might account for some weird inflight transitions that I observed during the 1st maiden flight .
Now couple of weeks later, after leaning the needles, the engine runs better in the air. I did my 1st torque rollings and seems transition pretty good in the air.
I have not running the engine in the air for a long periods of time yet to see if that stmble is reporduced.
If I can fix the LG, I would try something this comming weekend, otherwise I will wait for the Graph Tech LG substitute to arrive, perhaps more than one week from now.