jalvarez1245

Hello all, this is my first post on this forum and my first GP airplane. I just finished putting together a Phoenix model p-51 with a OS 55 ax engine that is mounted inverted. The engine runs great and it has lots of power but when i bring the throttle to idle it “floods” out, it idles for five seconds and then quits. I should mention that due to the fuel tanks location it inherently sits above the carb. There is realistically no way of dropping the tank.

I was reading a few other threads about this and was interested in getting either a cline or iron bay regulator but it seems like you can’t find either these days.

thanks for the help!!

mgnostic

Is the engine fully broken in? I ask this because a new engine will be more sensitive in this regard. You may need to lean out the low speed needle just a little bit. The engine ought to be able to idle and accelerate without loading up. It may also be helpful to go to the next step hotter glowplug. You might also try a fresher batch of fuel or some fuel with with the next step higher nitro content. If you are running 5% nitro try going to 10%. This will have diminishing returns past 15% nitro but it may help. Just throwing out some things that have helped me in the past.

R8893

My Feedback: (20)

I started using a new OS 55AX this year and had to lean the carb low end almost 3/4 turn from the factory setting. Also a student came to the field last week with a new 45AX and we had to lean the low end of that too--about 1/2 turn at least.
Chuck

speedracerntrixie

My Feedback: (29)

You're on the right track wanting to add a regulator. The issue is with the tank being too high, no amount of needle settings is going to fix the issue. Options are to lower the tank, mount the engine on it's side or upright or add the regulator.

Truckracer

My Feedback: (19)

I agree that to completely eliminate the issue you will have to do what speedracer suggested. But I have had acceptable results even with tanks too high. You will have to be careful of the tank wanting to siphon out the carb when the plane is sitting at rest and of course the low speed needle will be adjusted leaner than normal. Not ideal but workable. One of my favorite small planes still has this setup and it works well in the air and I don't baby it. With that said though, lowering the tank as suggested is a better idea and usually achievable with a bit of work. I'm not fond of regulators as they have a learning curve and I wouldn't suggest a person with minimal experience try one. They are also rather hard to come by these days.

jalvarez1245

Thanks for the quick replies! The problem with adjusting the way the engine is mounted is that the plane is cowled.

I’ll look further into relocating the fuel tank and leaning out the low needle.

Thanks again

mgnostic

It is a bit of a pain but I think it will be well worth the effort to take the cowl off of the airplane and put it on the test stand for a tuning session. Even if the cowl does change the tune of the engine you will be a lot closer than you are now. Relocating the tank to a lower position would probably help but it doesn't look like you have a lot of room to do that. If you have a lot of foam cushion under the tank you might move it all to the top of the tank to get it located slightly lower in the fuselage. One way to test the fuel tank issue is to fill the tank only 1/3 to 1/4 full. If the problem goes away than yeah, you have too much head pressure (fuel too high above the carb). The idea is to get fuel level below the spraybar of the carb. If the problem persists then you have some other tuning issue. Ig it does turn out to be a fuel tank issue one way to lower the center line of the tank is to go a a smaller tank. Yes, it will cut into flight duration but it will have the effect of lowering the centerline of the tank. Just tossing out some ideas that will hopefully help avoid carving around on the nose of your airplane. Take the time to try all of the reversible stuff first.

daveopam

My Feedback: (9)

I wonder if a remote needle from OS would help with fuel tank position? The tank will also work on it's side or inverted as long as the vent line is positioned right.

david

jaka54

Hi!
There is only one solution and that is ...lowering the tank so it sits with the center level with the carb as the plane sits horizontal.
Modifications doing this can nearly always be done Do not be afraid cutting away formers in fuselage to obtain this.