Shorten the needles on your carburetor to solve clearance issues with some cowls...
The Walbro WT-257 carburetor is a favorite for model boat engines. It is very commonly used in the hobby by racers as well as sport boaters. Unlike the WT644 that comes with stock Zenoah engines, the 257 has longer adjustment needles which can sometimes cause clearance issues in some boats. Now we are also seeing the WT929 becoming more and more common as they are being delivered with stock RCMK engines. It too has the long adjustment needles. There are others as well.
This article is really just a short pictorial on how to shorten the high and low speed adjustment needles on such Walbro carburetors. This can come in handy in some installations where the cowl fit is very tight with the engine. In a recent build, the cowl of my boat would not sit properly because it was touching the carburetor needles. I did not want to cut a hole in the cowl so simply shortening the carburetor needles allowed me to get it to fit properly while maintaining the engine's position where I wanted/needed it to be.
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| Left to right: WT257, WT644, WT813. Notice the longer needles on the WT257. |
Needle in lathe chuck for shortening. This can also be done by hand using a small metal saw or rotary tool with a cut-off disk. | Taking away material with the lathe. |
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| Shortened to desired length. | Using a rotary tool with cutting disc to make screwdriver slot in needle. | Done. Make slot deep enough for the screwdriver to engage properly. |
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| Shortened needles installed on carburetor. *note: they could be shortened all the way down to the larger diameter area if required. |
These are the full-length needles with a CC Racing needle clamp. This setup is excellent and I use it whenever I can, but in cases where clearance is an issue, the clamp makes it even worse. | Shortened needles with pieces of silicone tubing over them. This prevents them from backing out during normal operation, yet still allows manual adjustments to be made. |
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| If you want added piece of mind, you can install a small zip tie to hold it all in place firmly. |
Happy Boating!
How about making it a philipshead instead of a single slot? Philipshead makes it easier to adjust the needles with engine is running and the carb vibrates a lot. A philipshead will hold the screwdriver easier in place.
If you use fuel/water line over the needles... just make them a little longer then the needle. That helps keep the screwdriver in the groove with the tubing holding onto it.
How about making it a philipshead instead of a single slot? Philipshead makes it easier to adjust the needles with engine is running and the carb vibrates a lot. A philipshead will hold the screwdriver easier in place.
