-StephenSampson-

Lately I have been having some issues with my OS55AX.... The motor runs beautifully once it is started but it gets hydro locked usually 2-3 times before starting it. And it's not just the first flight of the day but every consecutive flight.

The motor is mounted inverted on a 40-sized Sukhoi SU-26 3D and I have a pitts muffler installed however it is not an inverted pitts because the LHS was out of stock at the time I purchased it (not sure if that matters or not)... I am not sure if the fact that the motor is mounted inverted is causing the issue or if it is perhaps the combination of it being mounted inverted with a standard pitts muffler but it is annoying regardless as it keeps ripping the spinners off of the plane...

Any input would be appreciated.

playntraffic

Are you pulling the fuel line off the exhaust when you refuel?

Are you using a three line tank system?

Where is the tank supply line in relation to the carburator?

ameyam

I dont think this has got antyhing to do with the muffler. This problem is common to inverted 2 strokes. What happens with an inverted engine is, when standing idle, any fuel that is in the carb flows into the cylinder. Then when you try to turn the engine over, this fuel creates a lock. Couple of ways you can avoid this:

First, check that tank centreline is in line with centireline of carb. It is not critical and some people never had problems even if it was not in line. But, we have the bad luck so check and lower if required.

a) Having an inverted engine means you must be having a cowl. Cut the tubing between the tank and the carb and extend both out through a small hole in the carb. Connect them externally with a small brass tubing. When you fuel, disconnect at this point and fuel up till tank is full, then close the line coming from the tank with a fuel dot or even a small screw that prevents fuel leaking away. Just before you fly, take out the dot / screw and connect the two tubings. This solution will essentially prevent fuel from flooding the carb before you want to.

b) Alternatively, raise the fuel line within the cowl to just above tank level and then lower it again and connect to carb. Tie the raised end in place suitably. This solution will create a siphon that will prevent fuel un-necessarily from coming into carb when standing idle as the tubing passed over the top of the tank. Once the engine is running, it will draw the fuel by pressure automatically. Problem with this is that while fuelling, you could accidently flood the carb

Others please correct me if my solution(s) is wrong

Ameya

vertical grimmace

My Feedback: (1)

Start the engine with the plane inverted.

airraptor

My Feedback: (66)

The muffler could have a problem for sure. specially if the vent line is hooked to it. if the muffler has a ny left over fuel it can run back into the cylinder once its turned over.

leave the line to the carb one piece. you want it as short as you can get it.
Use a three line tank set up.
for the muffler presure tap/tank vent line is best to disconnect instead of the carb line during refueling.
use the 3rd line to fill the tank.

If you cant get to the mufler pressure line then use a dubro tank filler. hook it up like you would to a carb but instead on your muffler pressure tap. now when filling the tank put your overflow line in the filler and if have long enough fuel tubing run it back to you fuel jug.

now use another filler or a fuel dot and fill the tank. this way the cowl is clean and once set up very easy to refuel with out worrying about flooding the engine.

ameyam

You are right airraptor, that is one way too. But once you reconnect the line, fuel will run into the carb again simply due to the head of fluid in the tank above the carb.

I replied from my experience with the same problem. A siphon setup helped a lot, especially since my tank was much above the carb. Finally, however, I lowered the tank and the problem reduced. I expect it to improve further due to the upright carb on my FS-91. The engine still backfires though and I have to use the chicken stick or electric starter to save my fingers

Ameyam

airraptor

My Feedback: (66)

Amayem..
he has a two stroke engine the 55AX. with the engine inverted no way can the fuel run in the engine and hydro lock it just sitting there. the fuel might drip out of the carb though. if his engine was up right past 90 from inverted the fuel could run into carb and fill the crank which in turn would fill the crankcase. his hydro locking is coming from the muffler.

If engine mounted inverted is a four stroke then the carb could fill up from fuel and hydro lock.

-StephenSampson-

Actually there is no cowl on the plane because (as stupid as this sounds) the cowl that came with the plane is about an inch or so to small in circumference to match up with the fuselage (no it is not deformed it is just simply too small) and I have not bothered to get another one... however I want to leave the engine inverted in case I get a proper cowl in the future. Plus I don't want to deal with the hassle to be completely honest it's just a small plane.

What I've done is cut the line going to the muffler and added a t-fitting in there. I took a piece of fuel line and just let it hang down. Normally when fueling I would simply take the line from the tank off of the muffler fitting but the way it all mounts it is too hard to get at the muffler fitting since the firewall is very close to the fitting. I am hoping that by unplugging this line off of the t-fitting when fueling any fuel above the vent line in the tank will run out of this line rather than through the muffler into the cylinder head...

I work a lot so I may not have a chance to try this for a week or so but do you guys think this is an adequate solution?


PS: It is not flooding through the carburetor because when filling the tank with fuel I take the line directly off of the carburetor.

Uncas

My Feedback: (1)

Could you post a picture. I am trying to imagine your setup - an inverted engine with a non-inverted (sidemounted?) Pitts muffler. Does the low point of the muffler drain into your engine exhaust? If you used an inverted Pitts the muffler exhaust would point down and drain fuel away from the engine.
Also do you pull the line off the muffler when you fill? (previous question) Do you wait until fuel is dripping out the muffler to tell you the tank is full? I always pull that line off and watch for fuel to come out to verify the tank is full.

-StephenSampson-

So there are two pictures... Previously when fueling I did not remove the line to the muffler because as you can see it is too tight to get it on and off easily. I would simply pump slowly when I knew the tank was almost full and wait until I saw a little bit of fuel trickle down the line. The purpose of adding the t-fitting was in the hope that fuel would come out of that little piece of tubing rather than into the muffler... Then I would plug that piece of tubing

playntraffic

If you are not running a cowl then reinstall the motor mount and turn that engine sideways.

I know that some of my engines sputter a little fuel, espically at startup. With the muffler mounted that way it looks like it could easily pool up in the muffler and flow back into the head.

albsurfer

I agree with playntraffic. I own this engine, and fly it inverted all the time. I have had problems, too. If I reduce the heighth of the fuel tank above the carb, it starts easier. As soon as you reconnect your fuel line to the carb, it siphons fuel into the carb, and four of us verified on two different planes (one not mine) that fuel was getting into the engine as soon as we turned the crank over, thus flowing into the head in larger amounts and flooding the engine. Besides lowering the tank, I use an A3 plug if the tank is still above the carb. One thing someone posted in a forum was to run your line to the carb higher than that tank outlet, then down to the carb line. It helps on two of my planes to prevent flooding. The other option is to start it inverted on a stand, then flip it over. Close the carb all the way after a flight to help prevent siphoning. If it is locking up too much, REMOVE THE GLOWPLUG and let the fuel drain out, then reinstall it so you don't damage the engine.