I have two 91fx and never had a problem-I have one inverted on dragonlady-the tank sits even with thrust line-never had a running or starting problem-no extra glow just stock as it is out of the box and I think I am running cheap glow plugs from tower-you know the one's eight for 10 bucks or something like that-it has been a great engine and I am running a tatone-universal muffler-the other side mounted with no problems and running stock muffler without the baffle and two foot spacer in the muffler-don't know if this helps but this what works for me =have a great day