dmajchrzak

My Feedback: (17)

I've got a Tigershark 90AR that I've tuned the high end for a moderately rich run with some smoke and oil out the exhaust. I've leaned the low end so the idle is nice and transition is pretty good. All of this is done with the plane level. Engine is 90 deg. mounted. S&W 15% nitro.

But....
1 - point the nose up and she dies a quick death. I'd think fuel pressure problem but at full throttle and level attitude it's pretty rich. I richen it further to help nose up, but that ruins my performance at level.

2- I've also noticed an RPM slow down when removing the glow starter. I'm running an OS #8 plug.

What am I missing?

cmassa

How long are your fuel lines? Lines that are too long can cause fuel draw problems. Also make sure the clunk is not against the back of the tank when the plane is vertical. Check for kinks and holes in the tubing. All of these things could cause problems with the nose up.

Just a few thoughts.

Chris

big max 1935

My Feedback: (9)

Try a idle bar glow plug & maybe one step up in nitro if it slows down when you remove glow heater, maybe fresh fuel would help. MAX H.

NM2K

My Feedback: (14)

If your fuel tank is reasonably close to the engine, the fuel lines are in perfect working order and not too long, along with a properly sealed engine backplate and carb that is properly seated in the crankcase, then it may be fairly safe to say that your engine has fallen victim to the horsepower race. This is what compels engine manufacturers to include oversized carbs with their engines.

I've never owned a Tiger Shark engine, so I do not know what their practices are, but I would not be surprised if this is the reason your engine is having a problem with fuel draw. And that is what it is, after all.

An easy remedy would be to replace the carb with an appropriately sized Perry/Varsane/Conley carb. Another solution is to use a Perry VP-30 fuel pump or a Cline Associates fuel pressure regulator. The latter two devices will require that you drill and tap a hole in the engine's backplate and then install a pressure fitting. Not difficult to do, but a bit of work.

Is it worth the money and effort? Only you know the answer to that question.

bruceisla

My Feedback: (1)

I noticed you mentioned 90 degree mounting .... I'm assuming you are using a Pitts style muffler. Could be insufficient fuel tank pressure caused by low exhaust backpressure. If it's a two outlet exhaust you could try closing one pipe (even temporarily) to see if there is an improvement.

downunder-RCU

I have to agree with Artisan on the too big carb, it's far too common lately and made even worse if you use a low restriction muffler. However there's one thing you can try before going to the expense of a better (smaller) carb. If you've got a good ear for revs or a tacho then open the throttle slowly until further movement gives no rise in revs. Note how far it's open and set this point to be full throttle on the stick. What you now have effectively is a smaller bore carb that gives better fuel draw.