Hi All,

I have a Hangar-9 P51 Miss America Mustang with a Thunder Tiger .65 mounted inverted. I broke in the Thunder Tiger engine a couple of weeks ago and went to fly it today. It starts up easier with the plane inverted and idles and transitions great. It had been running fine when putting the plane upright during break in and now it runs for about 20 seconds and stops quickly after turning it upright. There are no bubbles in the fuel line and it will start upright once it has been run and is warm. However, it will not stay running upright. I have the fuel tank as far forward as possible and can not lower the tank any further in the fuse. Any thoughts or suggestions would be welcome. The centerline of the tank is close to the level of the spray bar on the carb, but still no luck.


Thank you for your help,

Tom

I guess the fuel tank is too high from the carbulator, though you say
you can not lower it.
There are engines that are not sensitive to the fuel level and that
are very sensitive to the position of the fuel tank, vary according
to carbulator and engine designs.
I think most 2 stroke engines and some 4 strokes belong to latter.
Lowering the fuel tank or using a fuel pump may solve the problem.
2 stroke engines have disadvantage in inverted running compared
to 4 stroke because of their lower combustion temperature.
That's my guess.

Tsutomu Mabuchi

I would think that since you cannot lower the tank, you probably need to invest in a, "Cline" fuel regulator. Your situation is similar to running with an, "Over primed" engine. In other words, the engine is, "Drowning" in fuel constantly due to the siphon effect. The fuel regulator will alleviate this problem. It also occurs with 4 stroke engines as well. I had to use an on-board glow system on my H-9 P-47 for the same reasons. I am running an OS 91 Surpass II and at anything less that 25% throttle, mine started to smother out. With my 4 stroke, the on-board glow system has pretty much cured the problem. I am looking at either making or buying a tank that will fit into the front bay of the fuselage and have the tank centerline at the same height as the carb. This should enable me to not run the on-board glow.

Thank you for your responses. I may try a smaller tank which would let me put it all of the way in and down into the front bay. Also looking into the cline regulator.

Thanks again for all replies.

Tom

Anytime Tom. I think that the regulator will solve your problems (with the engine flooding problem anyway)

This may sound stupid, but do you have the fuel line and the pressure lines mixed up? Check that first. If the lines are flopped it would run fine upside down and would die once the plane was flipped over and the pressure brass tube sucked air.

1) Isn't Thunder Tiger 65 an airbleed carb? Most engines nowadays have no problem mounted inverted, except for airbleed 2-stroke. There is no low speed fuel limiter valve; rather, low speed adjustment is done via controlling the air inlet (airbleed) hole size to mix with fixed amount of fuel intake @ idle. If fuel tank is higher than carb inlet nipple, gravity will draw the fuel down, which is more fuel than the some airbleed can mix.

2) I am not sure about Cline regulator, but I know for sure Perry pump will not work, as you will just flood the carb at idle, again, for the same reason caused by air bleed carb.

3) To adjust, open the airbleed adjustment as large as you can, and see if it will stay idle. If not, try lowering the tank so it is completely below the carb. Try this low profile tank:

http://www2.towerhobbies.com/cgi-bin...?&I=LXK835&P=0

The Cline regulator is not a pump, it is a demand regulator. My H-9 P-47 will (with the feed line disconnected from the engine) empty the tank due to siphon efect. Try this: disconnect the feed line (the one that goes to the carb) and put the end into a container that will catch the fuel.(try to keep the end of the line at about the same level as the carb is) Attach your fill from your field pump to the fill line, and begin to fill the tank. when the tank is full there will be some fuel come out of the feed line. See if the tank empties. If it does, you will need some type of regulator (not a Perry pump) If the tank does not siphon itself empty, then you either have a mix up on the plumbing, or a bad glow plug, or mechanical mis adjustment of the carb.

What plug are you using?

If your Thunder Tiger .65 does have a low speed needle valve I'd try leaning that out a little before I try anything else. Most of the time when you envert a 2 stroke engine you have to lean out the low end. Just an idea.

Don't buy things you don't need. You can lower that tank by cutting into that bulkhead. Most of my fleet is inverted and a couple P-51's also. Just be creative and rebuild that bulkead area. Its not that big a deal. I have done this and my inverted engines run just fine with no Cline

Just need to watch out how low you go or you won't be able to get the wing in. Clines are great. I have them but you don't need it and it is just one more problem when it comes time to look for problems

CH, I got a question. I have the H-9 P-47 (60) and I have my tank as low as possible without making a cutout in the wing. Does anyone make a tank that will mount between the firewall and the first bulkhead (chin mounted) that might work in the '47? If I had a tank that I could mount in the chin, It would resolve not only mine needing a regulator, but might very well eliminate the need for an on board glow driver as well. Little help here please. My tank C/L is 3/4" higher than the carb on the OS .91 4 stroke.

Bill

My reference to the wing I guess comes from using oversize tanks. I don't like to run out of fuel. Graupner makes square tanks. Little more pricey than the Sullivans/Dubros but may help. I have had no structure problems at all. Just need to be a bit creative. Need to watch how low you go or you may take out the slot for the front of the wing to go into.

But this is just what I do and it seems to work. Engines all start up and run just fine.

CH, You ain't listning. I need a tank that will fit between the firewall and the first former in the H-9 P-47 (.60 size) otherwise, I am going to have to cut a tunnel in the top of the wing at the center in order to get my tank C/L closer to the carb height. I can do this without comprimising the wing mount, but I druther not. Surely someone has a tank that is shorter (front to back) and wider that will fit in the needed space. My carb is 3/4" lower than the tank centerline, and the fuel siphons out when the engine is shut down.

Bill