I have a TT. 46 and when I ran a 10x6 prop it would shut off quickly. I swapped to an 11x5 so it would come in slower on landing but now when I kill the engine it takes about 7-10 seconds before it dies. The carb is as far closed as it will go but it just doesn't want to shut down quickly. What could cause this? Unbalanced prop or air leak somewhere? Other than that the engine is flawless. Thanks.

It's definitely not the prop causing this. There's another issue somewhere. If it is running for 7-10 seconds with the carb barrel fully closed, it's sucking air from somewhere.

I had this happen with an engine.... albeit one that had crashed a couple times.....

I wrapped a bit of teflon plumbers tape around the carb and re-installed it....and it worked perfectly....

I may give that a try. My instructor was saying that sometimes the machining on the carb can be slightly off but I don't think this is the case because I don't think it had trouble shutting down last season when I was flying.

The typical places for airleaks are:

Carb - this is easily cured by removing the carb and applying some silicone to the o-ring and re-installing the carb.

Backplate - again, easily cured by removing the backplate and using some silicone.

High speed needle valve - you have a couple of ways to take care of this. Replace the o-ring, OR take a piece of LARGE fuel line and put it over the needle valve, tensionor spring an needle valve body. This is also good for repairing the needle valve when the spring tensionor breaks.

Front bearing - While this is not a common thing on TT (it is on SOME other brands that begin with a "T" ), it can happen. Your choices in this case are - send it back to the factory, replace the bearing yourself.

I would suggest trying the first 3 fixes. They are easy to do and will take care of the problem 99% of the time.

Hope this helps.

Thanks I'll give those a try. When you say silicone do you mean just silicone sealant? I'm not sure if there is any other kind but I just want to be positive I'm using the right thing.

The material is called high temperature red RTV silicone gasket material. It does work very well and is easy to use.

Thanks everyone for the help. I gave all the suggestions but the front bearing a try and still the same thing. I swapped this engine out for another so I can fly next weekend until I get this fixed. I took a pic of the carb fully closed by hand. Notice the small gap, could this be the problem?

I think you found the cause !! There should be absolutely NO gap when the carb barrel is rotated to the "Stop" position. Back off the barrel stop screw a little, to allow the barrel to close off that gap. That should do it !!

Ugo

Thanks for the help. I'm guessing the carb. is the problem as it is getting worse and is beggining to stick. I took the barrel out and cleaned it and lubed it but it is not any better. I'm suprised this would happen with less than 20 flights on the engine. I'm going to have to see if I can find a new carb.

EDIT: Looks like I may just buy a new engine since the carb. appears to be ~$50.

Disassemble the carb, clean it & look carefully at the bits. There is a bit of crap somewhere in there that is jamming the works, or has caused a scratch, or gall in the metal. Polish off any abrasions or burrs. Check the spring that stabilizes the throttle barrel -- make sure that it isn't broken or installed off-center (or backward). Check the barrel retaining screw & make sure that the end is not burred & then put it back togegher carefully so that it is not jamming the barrel (most likely scenario). A good idea is to get help from someone who knows their way around a motor -- they're pretty simple & they're easy to fix & set-up.

There is no reason to buy a new carb or motor.

Hi!
All you have to do is to back off the barrel stop screw as has been said earlier...so that the barrel can close, and if the barrel is stuck or is hard to move...just remove the carb barrel and have a look at the carb housing.
You certainly don't have to buy a new carb...????[>:]

Regards!
Jan K
Sweden

Well I looked closer and what appears to be happening is the low end idle "needle" was bottoming out. So I backed the low end screw out and it closes all the way. I backed the barrel stop screw out as much as possible, it still didn't allow it to close all the way. Hopefully I have solve it. Thanks for your help.

Yeah you sure don’t need to go out and get a new carb, there has to be a way to get that thing to close 100%

Good luck to ya

Have you checked the throttle closure with the engine out of the plane? -- it absolutely should close fully. Check your linkage adjustments to ensure that you are getting the correct throttle throw from the servo.

IT looks like the barrel is turning too far closed making the small opening on the other side. If thats the case it just needs to be backed off a bit. If it was fine before, the carb linkage supports may have come loose or maybe the servo tray??