Write-up: Carburetor screw adjustment guides - RC Groups
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Mar 07, 2013, 11:35 AM
Illegitimi non carborundum
grosbeak's Avatar

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.

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.

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

Grommets in for a test fit.

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Mar 07, 2013, 11:41 AM
Registered User
tailskid2's Avatar
Cool idea! Thanks for sharing.
Mar 07, 2013, 11:41 AM
Illegitimi non carborundum
grosbeak's Avatar
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.

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!

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

There they go!

Mar 07, 2013, 11:46 AM
Illegitimi non carborundum
grosbeak's Avatar
Now it's just a matter of finding a long enough screwdriver.

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.

I did the same thing at the back...

Then added another layer for a better hold.

Mar 07, 2013, 11:48 AM
Illegitimi non carborundum
grosbeak's Avatar
Through the inside again.

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

Mar 08, 2013, 02:43 PM
Registered User
earlwb's Avatar
That is nicely done, very sanitary and clean looking too.
You did a bang up nice job on that.

I usually just went cheap and used a large size soda drink straw from our local convenience stores. I would cut the straw down to size as needed and insert it into a hole to the needle valve to serve as a guide. The screw driver had a small length of brass or aluminum tubing epoxied on the tip to serve as a guide for the needle valve too.

Of course, usually once you had the engine adjusted pretty good, you seldom needed to mess with the needles again. So one could remove the cowl once in a while to tweak things if needed like when there is a major seasonal weather change, etc. Then put it back on.
Mar 09, 2013, 09:16 PM
Illegitimi non carborundum
grosbeak's Avatar
Thanks Earl!

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