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Rebuilding one of our carbs is cheap and easy but can yield great results for the effort!
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Rebuilding a Gasser Carb

Making my favorite engine my favorite again

Text, photos and video by Tom Hintz

Posted – 9-15-2015

My DLE40 Twin has been my favorite gasser engine for a couple years because it starts and runs well all of the time. Until recently that is. Recently it began running rich, then lean and then got to where it just didn’t want to run at all. I am reasonably sure that a gas engine can’t get depressed or suicidal so I opted for a mechanical cause for the problem. After investigating everything else I settled on rebuilding the carb as making the most sense.

I got a carb kit for about $10-$12 and the process – which includes shooting the video – took about half an hour. (Use the search box on this page to find a carb kit for your engine) This was my first gas airplane carb rebuild but I have rebuilt just about every other kind of carburetor in existence so I was confident I could muddle through. Just to be safe I kept my IPhone at hand to take pictures that I could refer to if I got lost or simply forgot where something went.

Something I did not show in the video was “hosing” the carb down with aerosol carb cleaner. It really didn’t need it but I did it anyway. I also blew the cleaner through the passages, again just to be sure. I always hold a clean white paper towel on the other side of the carb when shooting out the passages so I can see if something came out. Other than carb cleaner nothing was noted coming from this carb.

Pump Side First

Using our fancy modern phones to take pictures (left) can save the day when you forget where something went! The rebuild kits come with all of the parts and we should replace all of them. (right) Not every bad part looks bad to the untrained eye.
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I chose the pump side of the carb as a starting point for no good reason other than it was facing up when I started. There is a hole in this cover that some think has to be aimed in a specific direction (relative to the carb….if you are thinking something like North or East go wait in the bus) others are sure it doesn’t matter. While I am more on the “doesn’t matter” side I took a picture so I could put it back where it was.

The pump diaphragm did not have any obvious tears or other malfunctions but this is a key piece that comes in the car kit so it gets replaced, along with the gasket that seals everything. Beneath the diaphragm is the needle valve and this also gets replaced any time you rebuild the carb.

There is a top and bottom to the pumping diaphragm so I took a photo once the cover was removed to show me that the small nub at the center of the diaphragm was facing up before I took it out.

I looked at the rubber tip on the needle valve with a magnifying glass and could see a ring worn into it by the seat. I could see no damage to the seat in the carb so replacing this needle valve along with its holder, pivot shaft, spring and screw will fix this wear issue.

Installing the needle valve assembly is a little tricky only because these are tiny parts and there is a spring under them that wants to shoot everything back out until the retaining screw is inserted. I placed the spring in its pocket and then used a small needle nose pliers to set the rest of the needle valve assembly in place so I could hold it down with a finger and put the retaining screw in. Sounds easy, took three tries but the whole process took like 5 minutes.

Checking my photos I installed the new diaphragm and gasket before installing the cover with the hole where it was from the factory. This motor ran great for hundreds of flights so I am not messing with what the DLE factory had done.

A small needle nose pliers (left) made handling the small pieces easier for me. There is lots of chatter on the forums about this reed block being bad but I could not find anything wrong with mine (right) and the engine runs like new without "fixing" it.
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Doing the other side of the carb was easier yet. One screw holds the cover on and there is a gasket and a thin sheet with two flap valves in it. One of these flaps looked bent out of position when I opened it up so that wasn’t helping the performance of the motor. This piece is included in the kit and is always replaced during a rebuild.
The fuel inlet screen is also located on this side of the carb and a replacement screen is included in the kit. However, my screen looked perfect, even under the magnifying glass so I left it alone. Getting the new piece of screen pushed down into the well isn’t the toughest job but I decided to leave well enough alone. I use filters on my fuel can as the gas is pumped out and in line as the fuel gets to the carb. Not finding anything in the carbs filter screen was not surprising.

Before reinstalling the carb I looked over the reed valve body. There is lots of chatter on the forums about this block needing to be sanded to get it perfectly smooth. Some are seeing variations that prevent one or more of the reed valves from sealing properly. I looked carefully at all edges of all four reeds and can’t find anything that remotely looks like a leak. Here again I decided to leave well enough alone. Any time you try to fix a supposedly perfectly flat surface by hand I think you are increasing the chances of sanding in a bigger error. It’s your carb, you do what you want.

I put fresh gaskets on both sides of the reed block (also serves as a thermal break between the carb and engine case) and carefully ran the mounting bolts down. I always tighten bolts like this in small increments going back and forth between the two so I don’t distort the relatively soft reed block material.

At the field once I got fuel to the carb the DLE40 Twin fired right up. I did have to lean it out quite a bit demonstrating that I had probably been compensating for wearing components within the carb for a long time. After tweaking the adjustments the DLE40 Twin ran great. I am making final tweaks to get it perfect but it is starting and running reliably, something it refused to do before the carb rebuild.

This is a cheap, simple bit of maintenance that can make your flying days way more enjoyable. Using your cell phone to document how things were as the carb comes apart will make it easy to get this right even if it is your first time.

Video Tutor

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