I have to revive this thread for a little more help. I have installed this engine on my airboat inverted as I intended. The first time I tried running the boat, The engine seemed to run fine. The boat just wouldn't plane out using any of the props I had. The engine started cold fine - Set the fuel mixture on the high side to 3 clicks rich of peak. I didnt have the tach handy so I do not know off hand what RPM it was running at. I set the idle mixture as close to dead-on as I could - the transition was flawless. The boat just wouldn't plane out. Later in the run, I was seeing air bubbles in the fuel line. Very small. I added a little more insulation to the fuel tanks compartment to better isolate the tank. I installed new fuel lines from clunk to the carburetor, including some fuel line clamps to ensure a positive seal on the fuel fittings.

Fast forward to today. I re-worked the engine mount moving the engine further back - 2" to be exact. Same fuel system, fuel, glow plug, and radio settings as first attempt. Engine started cold fine as usual, set the mixture in the same fashion as before. Tried planing the boat several times, all the while the engine ran just fine. Once it got down to about 1/4 tank, it started quitting. I refilled the fuel tank, restarted and same thing - engine kept just up and quitting. At first I had seen a few tiny air bubbles only at random so I moved the fuel line going to the carb away from the engine more and I didnt see any more bubbles. I ran almost 1/2 quart of fuel without seeing any bubbles. SO... with glow left on, it would stay running longer and better enough to try running the boat in the water more. Not much quitting with the glow left on. If I pulled the glow off, it would quit within 5 seconds of pulling the glow, no matter the RPM. I adjusted the idle mixture richer and dropped the idle rpm some to see if it just wasnt drawing well enough. No dice. It got to the point where even leaving the glow on just having it sit on shore while throttling the engine some it would still quit. No air bubbles seen in the fuel line any time it quit. SO the $1,000,000 question is this: If the fuel is fresh (5% nitro/20% castor), the glow plug (MC59) is fresh, The fuel mixture was set 3 clicks rich of peak/idle mixture set for flawless transition, and the fuel tank and lines was isolated from the hull as much as can be done, Is the quitting simply a matter of a lack of fuel draw, or is the fuel putting the element out? It seemed that it was flooding out in the low to part throttle settings, so I set the idle mixture as lean as I could maintaining that perfect transition. At the end of the run, It was not staying running with the glow left on - after running on high throttle trim for 3-6 seconds, it sounded as if it was loading up and shortly after would quit. I am just gonna go on a limb and guess fuel draw as the culprit. The engine is currently 1-1.5" further away from the tank than it was on the test stand where I had it running perfectly. The fuel tank is 3" back from the carb(front of tank to center of carb), and 6.5" below it. (center of carb to center of tank) This is story overload, sorry. I didnt have a camera set up to take a video so I had to explain it. What am I doing wrong? It worked fine on the stand, but not in the boat.....

The engine-related variables:
Main prop used is APC 9x7, also tried APC 10x5 and 10x6
Fuel is home-made 5% nitro / 20% castor / 75% methanol. Nothing else added.
Brand new McCoy MC59 glow plug, Brand new FOX Idle bar plug, and a K&B plug (unsure of heat range - it came out of my early '90's K&B Sportster drone engine) the MC59 proved to be the best plug of the plugs I tried.
All new Dubro medium fuel tubing with clamps
6oz Hayes fuel tank
Jettstream muffler