This is the big OS, BGX 2.2ci glow thumper. When horizontal or vertical mounted, it normally primes with a good choke 3 to 5 turns, and then starts easy with a single backflip.

Yes, I can get my thumb over the carb to choke, but because it's inverted, when I remove my thumb, the primed fuel runs right down and out of the carb. The fuel is not being drawn up and into the crankcase and cylinder.

Any good ideas on how to get the prime to get sucked up and stay in the cylinder ?

... zak

More fuel than you think makes it into the crankcase

You could either start the engine with the plane inverted on a stand, or use a heavy duty electric starter, which will draw the intake charge better/faster.

fit a nipple to the back plate, and inject 1cc of fuel with a syringe (on ST2300), plug the line, and flip. That worked very well for me and made starting ultrareliable. With carb choking, it was always uncertain how much fuel made the trip up through the carb.

" With carb choking, it was always uncertain how much fuel made the trip up through the carb. "


This seems to be the problem.............. The fuel is making it to the carb, but not through the carb. There has got to be a better way then drilling the backplate. []

... zak

Tell me if you find it. The method is used by Aerobatic pilots, who need to start their engines when they want it to.

Get a helper to hold the plane on a wingtip on the ground so that the engine is pointing 9 or 3 o`clock, then start it up. Or one of the afore mentioned methods

I liked the syringe prime method very much. It never left me in doubt about the amount of fuel primed into the engine, end the plane would start while sitting on the wheels [8D]
Standing a delicate lightweight plane on a wingtip whilst flipping or turning the prop (of a 26cc engine with excellent compression) is not for the faint of heart, and is prone to harm the precious plane.

Starting glow plug engines in the inverted position has always been a problem. That is why I replaced my OSMAX BGX with a Brison 2.4. They are pretty close to a direct replacement although some modifications were necessary. The engine starts in the inverted position with no problem at all. As I remember, the BGX was really a guzzler and I paid for the Brison in less than a year with the savings in fuel costs. Bite the bullet and make the switch. Once you do, you'll regret that you didn't do it sooner. Dan.

" Standing a delicate lightweight plane on a wingtip whilst flipping or turning the prop is not for the faint of heart, and is prone to harm the precious plane. "

That's exactly the case Pe !

It is a big airplane, and difficult to handle with the wing on.

Suppose I was to prime it before assembly, wing off, and just the fuselage inverted, putting the engine upright. Now the engine is choked, and the fuel goes down the carb........................... But now I need to complete assembly, and wheel it out to the flight line, how long will that upright prime last ? 10, 20, 30 minutes ? ? ? Will it still be effective 30 minutes later ?

Once the engine gets wet initially, it seems to be good the rest of the day. Go figure ?

... zak

Like I said, all it takes is a muffler pressure nipple, a drill and a suitable tap (or some JB-weld) to add a prime line to the crank case. Not too hard for a modeller I think.

Hi Zack,

You might try holding your finger over the exhaust outlet on the muffler whilst spiinning the engine with a starter - no glow driver, throttle open - that'll get the fuel in the CC. I've used this method for inverted, cowled engines with good success. Just need to make sure the glow plug isn't wetted too much.

CR

With a tightly, and fully cowled engine, adding an additional prime line would be a very difficult option for me to install at this time. It sounds like a very good idea, but I'd like to find a good alternative solution. Thanks.

... zak

Problem Solved ! The solution was to simply choke the engine before the aircraft was completely assembled. This permitted me to invert the fuselage without the big wing attached, and choke the engine upright. This insured that the fuel went down the carb, and not out. I then completed assembly, and then left the plane sit for one hour, to simulate waiting for the start of an event. After one hour, as soon as I grabbed the prop, and felt fuel in the cylinder ( a mild hydra-lock, ) I knew that I was going to be alright. The big engine started by hand easily. I then shut it down, and waited for another hour, just to see if it would start again after being wet. Well it started on the first back flip ! Yipeeeee, I nailed it ! Problem solved !

Perhaps someone can explain this, but while waiting between flights, I move the prop by hand until I can feel the piston at TDC. I get the feeling that this locks some fuel in the upper cylinder, and prevents things from drying out. Maybe Pe can comment on this ? I don't know where I got in the habit of doing this, maybe someone suggested it to me at one time, but it seems to work. Have y'all ever herd of such nonsense ?

Thanks for all of your help.

... zak

Please report back after a day at the field. I too had some things licked at home, but they just would not work out that way when a crowd gathered to check out my ways and see how I was doing. Most of the time the joke was on them. You live and learn.

You can choke it my plugging the muffler with you fingers. Just go full throttle and flip it. It will draw in plenty of fuel.

David

Thanks for all of your inputs ......................... The problem has been solved !

... zak