Carb flooding and venting, Kitfox4 912 UL

[Bob]

After a 5 year rubber replacement, we started the engine to check for leaks and balance the carbs. In the course of the replacement, we had removed a fuel regulator which the previous owner had in the line to the carbs from the fuel pump. Checking with Lockwood Aviation, we had been told that was non standard and not needed to regulate fuel pressure. After starting, the engine ran well for several minutes. Then both carbs began venting and flooding. I consulted the previous owner as to why the fuel regulator was installed. His response was the the carbs had begun to vent and flood. So, he had installed the regulator to reduce the fuel pressure and stop the flooding and venting. The solution I have in mind is to replace the both carbs.

I am wondering if anyone has encountered a similar situation, or would like to comment. Thanks.
Bob

[jiott]

Before replacing the carbs, I would suggest you replace the little rubber-tipped needles AND the seats in both carbs. Very likely they are worn and don't seal well at the normal fuel pressure.

[Bob]

I bought the 5 year Hose and Rubber Component list from Lockwood Aviation which included the fuel pump, float needles, diaphragm, Carburetor Overhaul Kit, etc. I think the seat might be at fault. Lockwood thought so too, with no guarantee that they could fix it. Rather than loose more time, I'm going to bite the bullet with new carbs. Toys that don't work are kind of useless. Thanks for your comment.
Bob

[DesertFox4]

My question is why not reinstall the fuel pressure regulator as it solved this issue for the previous owner? It’s initial installation tells me the fuel pump is over pressurizing the carbs.
If your fuel pump is putting out too much pressure to the carbs, they will overboard fuel regardless of the needle color or condition or how many internal parts you changed in the rebuilds.
What’s going to really make you angry is spending a boat load of money on new carbs and solving nothing. While a pressure regulator may be non-standard on the majority of the Rotax installation, some of Rotax’ mechanical fuel pumps produce more pressure than the carbs can handle. If it ran for many trouble free hours before, it should again if you restore it to it’s previous configuration. If you still have that regulator, put it back in where it was before with the original fuel pump and give it a try. Too many changes at once and you will never know what solves the issue or worse, nothing was solved.
If that regulator bugs you being in the fuel system, try a new fuel pump first. Lots less money compared to new carbs or even used carbs that you may have to rebuild anyway. Do the simple things first. Frustration costs money and time.

[Slyfox]

I agree put the pressure reg back on. If you really want to know what's going on, check the fuel pressure before the carbs. that will tell all

[Bob]

My question is why not reinstall the fuel pressure regulator as it solved this issue for the previous owner? It’s initial installation tells me the fuel pump is over pressurizing the carbs.
If your fuel pump is putting out too much pressure to the carbs, they will overboard fuel regardless of the needle color or condition or how many internal parts you changed in the rebuilds.
What’s going to really make you angry is spending a boat load of money on new carbs and solving nothing. While a pressure regulator may be non-standard on the majority of the Rotax installation, some of Rotax’ mechanical fuel pumps produce more pressure than the carbs can handle. If it ran for many trouble free hours before, it should again if you restore it to it’s previous configuration. If you still have that regulator, put it back in where it was before with the original fuel pump and give it a try. Too many changes at once and you will never know what solves the issue or worse, nothing was solved.
If that regulator bugs you being in the fuel system, try a new fuel pump first. Lots less money compared to new carbs or even used carbs that you may have to rebuild anyway. Do the simple things first. Frustration costs money and time.

As we began the whole process of replacement, we saw the regulator and a fuel filter on the line from the pump to the carb. At that point we checked with Lockwood and asked if that was a standard setup, or necessary. According to them, it was neither. The carb was supposed to be, designed to be, happy with the pump, unfettered. When the new carbs are installed, we will have the fuel system pretty much as it came from the factory. I hope it works.

Thank you for your reply.
Bob

[Slyfox]

standard procedure for diagnosing this problem is to do a fuel pressure test anything short of that and you are throwing your money out the window. sorry I don't believe in your way of fixing something.

[Bob]

Before replacing the carbs, I would suggest you replace the little rubber-tipped needles AND the seats in both carbs. Very likely they are worn and don't seal well at the normal fuel pressure.

The rubber tipped needles were replaced. Lockwood said it might be the seats. Whether or not they could repair them, they said, was not guaranteed.

Thanks,
Bob

[avidflyer]

I've replaced the seat on a Bing type 94 carb without problems. Made a puller, ran threads into the seat/jet, and pulled old one out. Pressed new one in. I did this so I could run my Jabiru with gravity feed. JImChuk

[rv9ralph]

Did you check the floats to ensure they do not sink. Rotax-Owner.com has the Service Bulletin detailing the process.

Sinking floats will not close the needle valve that keeps the fuel bowl from overfilling and spewing fuel out the vent lines.

Ralph