Write-up: Carburetor screw adjustment guides
 

Another mod to my new-to-me 50cc SBach 342. I wanted to have access to the carburetor adjustment screws without removing the cowl. I'd heard of running guides from the screws to the cowl so I thought I'd give it a try.

First, I found some tubing that would work. In my case, the guide sleeve from some 2-56 Sullivan Gold'n'Rod did the trick. Note that this tubing is not intended to rotate the screw, but to guide the screwdriver.

http://farm9.staticflickr.com/8097/8...22f5b41f_z.jpg

Next step was to make some exit holes in the cowl. There was one there already when I bought the plane so it was a simple matter to make a second.

http://farm9.staticflickr.com/8368/8...4521d99b_z.jpg

The grommets that fit the guide tubes had a 19/64" panel mount diameter, so I enlarged both holes to fit.

http://farm9.staticflickr.com/8234/8...af6bb746_z.jpg

Grommets in for a test fit.

http://farm9.staticflickr.com/8044/8...28199b62_z.jpg

RE: Write-up: Carburetor screw adjustment guides
 

Next, I wanted to see where the tubes come to rest on the cowl when it's put on. In this case, just above the access holes.

http://farm9.staticflickr.com/8498/8...94faf129_z.jpg

I cut the tops off the backs of the grommets and epoxied them in place. And yes, it is a little too much epoxy - thanks for noticing!

http://farm9.staticflickr.com/8467/8...10eabb19_z.jpg

Now when the cowl is put on I just need a hook to pop the tubes into the grommets.

http://farm9.staticflickr.com/8467/8...28934919_z.jpg

There they go!

http://farm9.staticflickr.com/8094/8...78348bb1_z.jpg

RE: Write-up: Carburetor screw adjustment guides
 

Now it's just a matter of finding a long enough screwdriver.

http://farm9.staticflickr.com/8238/8...63ffbc8c_z.jpg

I didn't want the tubes to vibrate off of the screws, so I added some heat shrink near the tips - first on each tube to ensure the proper gap between them was maintained, then on both to prevent them from sliding out of the cowl.

http://farm9.staticflickr.com/8521/8...3db8c15b_z.jpg

I did the same thing at the back...

http://farm9.staticflickr.com/8111/8...8b8cab66_z.jpg

Then added another layer for a better hold.

http://farm9.staticflickr.com/8505/8...5ca9c909_z.jpg

RE: Write-up: Carburetor screw adjustment guides
 

Through the inside again.

http://farm9.staticflickr.com/8094/8...7261972c_z.jpg

And once again in the grommets, now black to blend in better.

http://farm9.staticflickr.com/8386/8...35ff564b_z.jpg

RE: Write-up: Carburetor screw adjustment guides
 

Very nice work, I just madea little hatch in the cowl of my P-40 to do the same thing. Thanks for all the detailed pics.

RE: Write-up: Carburetor screw adjustment guides
 

Excellent idea !!!

Thanks for sharing it.

RE: Write-up: Carburetor screw adjustment guides
 

Brilliant! ;)

RE: Write-up: Carburetor screw adjustment guides
 

I really hope I don't come off as Mr. Poo Poo here but...........I would be very surprised if the tubes do not pull out of the cowl from engine vibration. I also hope your intention is not to make adjustments with the engine running.

RE: Write-up: Carburetor screw adjustment guides
 

Running???? The only way to adjust a engine if you want it right!

RE: Write-up: Carburetor screw adjustment guides
 

You do good work! I do mine only slightly different. I use a straw from soda drink and make a small mount for it at both ends. On the cowl I mount a fuel dot just above where the straws ends. On the carb end I leave the straws about 1/4" short so it does not actually touch the engine. My thinking was If I had to pull it all back apart the straws would still be in place. If someone uses the fuel dot like me. Be sure and tie some string to it and mount the other end of the sting to the female part of the dot inside the cowl. Without a line on it the dot could be lost in the air.

David

RE: Write-up: Carburetor screw adjustment guides
 

Hi!
Agree!
All adjustment should be made as the engine is running, in a safe way ofcourse, but with the carb at the rear there is no way you can get your fingers in the prop. It's another matter with the carb up front!

RE: Write-up: Carburetor screw adjustment guides
 

I wondered about that very thing, so I went back into the shop.

First, I joined the tubes and secured them to the needle screws with some heat shrink.

http://farm9.staticflickr.com/8505/8...5ca9c909_z.jpg

Then I bound the tubes together near the tips:

http://farm9.staticflickr.com/8521/8...3db8c15b_z.jpg

That should hold them.

As a matter of fact, that is my intention. Carefully.

RE: Write-up: Carburetor screw adjustment guides
 

Nice work and thanks
for posting.

RE: Write-up: Carburetor screw adjustment guides
 

Sorry guys but I will have to dis agree here. Here isn't much room between the spinning prop and wing on a 50cc airplane and that is where you would have to be. The second aspect is that the flight conditions are very different from static. The cowl could have a positive pressure ( or even negative although not as likely ) running temps will be different between flight and static as well as load. The best thing to do is set it up reliably on the ground and then adjust to what you hear during flight. It takes a bit longer but the results are better.
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