Any 3W 170 owners around?

[Joe Hunt]

I'd like to know what carb and what carb gaskets you are running?

[Joe Hunt]

Okay, I figured it out... and basically it was not worth the time to figure out. :/

So my carb has been leaking at the gaskets to the spacer (the spacer between the carb and the reed block) since I first started it up. I've put 10 flights up (trying some field fixes along the way) anyway, because I wanted to fly the plane and I was keeping the engine running with my thumb (reminded me of the BME 115 days)... just leaking all over and making about 1/2 power.

Well, this weekend I decided it was time to figure out what was going on. First thing to do was obviously to pull the carb. When I did I could see that the gaskets had been leaking on one side, the side with two slotted holes in the gasket.

I could see that there wasn't a need for two slotted holes, just one round hole. Or so I thought, but I was slow on the uptake:

I got sidetracked with the casting on the carb:

So, I got a sheet of glass and some sandpaper and sanded it flat:

I was looking everything over, including this gasket, but the problem still wasn't clicking in:

Even though it was right there in front of my face:

I gave up the fight Saturday night after running the motor with the sanded carb and still having it leak like a fountain. I decided to put RTV on it instead of gaskets and let it dry overnight and see what that did. Sunday afternoon I started the engine and the leak was gone, bone dry on the outside of the carb now. Although it wouldn't run above idle even though I had been careful not to get RTV around the impulse holes. I'm ready to punt this motor into the dumpster. haha But, I start boxing it up to send to Gerhard to let him deal with it. Then I decided I hadn't done my due diligence until I make some gaskets that fit better than those double slotted ones. So, I run to the auto parts store and get me some gasket material:

I cut a gasket to fit on the carb correctly:

I put it over the spacer (the one between the reed block and the carb) and I finally realize what is going on! I'm pretty slow sometimes. haha The impulse hole on the spacer does not line up with the impulse hole on the carb. The spacer was not made for this carb! There was/is a teflon piece between the spacer and the carb that might have originally been put there as a heat insulator... but now I realize it is doubling as an adapter! Nothing wrong with an adapter, mind you... that is, if it is designed to... um... not leak. So, now I cut a different custom gasket for the spacer... two ideal gaskets made. Great, you say, but what good are perfect gaskets with a flawed adapter?

The adapter does not mate with the carb perimeter (the hole drilled in the teflon to adapt the two offset impulse holes was drilled so big that it is outside the carb body, that was unnecessary, half of that hole doesn't need to be there, but even drilled perfect it would only leave 1/16" of mating area, but that is better than a hole, for sure). And, with the gaskets that the carb came installed with (because they were slotted) there was an open gap to the outside world. That's how it was delivered to me, with a nice open air gap between the carb and the reed block spacer. Now, my gaskets cover that gap, but the carb housing still isn't wide enough to push the new gaskets onto the teflon adapter. Now, if whoever drilled out the holes in the teflon adapter had done so absolutely perfectly then you might have 1/16" of mated surface area there. What does that tell you?

Let me put it in simple terms. haha

This:

Doesn't work with this:

Any questions? haha

[Joe Hunt]

Okay, called Gerhard, he's sending me out a Tilitson, which I think is the carb this reed spacer block was made for. He says lots of people are running the Walbro WGA9 the way mine was sent to me. That maybe it usually has the tiniest micron of mating area, but that with tolerances mine has a 1/32" gap to the outside (that hole/gap was in the teflon adapter =and= the gasket -- refer to the pics above). That I'm the first person that has had a leak there. I'm just lucky, I guess. haha Anyway, I grow weary of working on this carb gasket adapter leak...

[Joe Hunt]

Okay, the aluminum spacer between the reed block and the carb was designed and machined for the Tilitson. The impulse hole in the carb lines up with the impulse hole in the aluminum spacer. There is plenty of mating between the aluminum spacer and the carb even with the large holes drilled in the universal teflon insulator and the slotted holes in the universal stock gaskets (I call them universal because they are not cut and drilled for this one single application). However...

However... I was able to run the walbro without leaks. I had to cut my own gaskets. Although it is possible to get a teflon spacer that has not been ground out too much, use the stock universal slotted gaskets, and just barely get it to work. So, if you receive a Walbro or want a Walbro you can get it to run without leaking from the impulse hole.

Having said all that, I'm stoked to have a Tilitson on this 3W-170CS. One if doesn't leak at the impulse hole. haha And, two it's all I ever ran on my 3Ws and I'm used to them. The idle is better now, the high end is better, and the mid range is better.

[Joe Hunt]

So, yeah, I swapped the walbro for a tilitson on the engine today. I had to solder on another included 3W throttle arm. As always I set it up for linear travel so I did not solder it inline with the manufacturer's throttle arm.

[Joe Hunt]

Here's a shot of my custom gaskets, dry after a few flights on the walbro carb:

This shows how a universal slotted gasket with the ground out universal teflon insulator/adapter (insulator/adapter when it is used with the Walbro, insulator only when it is used with the Tilitson) will leave a gap to the outside world unless you get some that just manage to close the gap but have no real mating area.

[Joe Hunt]

I wondered why the universal teflon insulator/adapters (adapters for the offset impulse holes on the Walbro carbs) had grinds to their big old holes (making them nearly impossible to have any mating area from carb to teflon). Once I had a Tilitson in my hand I finally had all the pieces of the puzzle. The big old hole in the universal teflon insulator covers up part of Tilitson impulse hole. So, they grind them a little... which makes the situation with the Walbro carb even worse. They grind both big holes in the universal insulator, so even if you flip it over the problem is the same.

[Joe Hunt]

Bottom line... the engine is made for the Tilitson. It can work with stock universal parts with the Walbro if you're lucky but it does not follow "best practices" to be sure. If I was to run a Walbro I'd do custom gaskets (I did) and make a custom teflon insulator/adapter (I bought the material and was going to make one, but now I'm stoked running the Tilitson).

[Joe Hunt]

Gerhard's service and support (at http://www.aircraftinternational.com) continues to be absolutely top notch. In this picture you can see I have black exhaust all over my muffler. The muffler is cracked across the weld. I sent Gerhard a picture and he sent out a new muffler the same day. He's answered all my emails and phone calls promptly and he's very knowledgeable. He also said he wants to show this gasket situation to 3W Germany. So, anyway, yeah, Gerhard has been great. And, I do love the motor. But, I'd also love to have all my time back.

[dunny]

What are your expectations for the Tilitson carb Joe- are we looking at better mid range and transition compared to the Walbro?