ORIGINAL: pe reivers
This type of carb with the straight groove still has a rich midrange, though not as rich as to make the engine die. Lots of nitro in the fuel will blanket the design flaw.
Idle adjustments are critical. 1/16th of a turn is sometimes too much, and it is easy to overshoot best settings. Use the throttle acceptance method. When satisfied, use the fuel line pinch method to check rpm rise before the engine dies. If there is no rpm rise, you are heading for deadstick landings.
The almond eye in the spray bar should have nice pointed ends for easy idle tuning. If the end has a small radius, it indicates a dull tool in the milling operation, and idle setting ease suffers big time if you ever can get it right.
Once you know how not to overshoot correct settings, a carb can be tuned well in about 5 minutes time. Once set, you'll never have to touch that idle needle again.
My SuperTiger S90K I've found to not tolerate any nitro. It wont run for very long using even 5% nitro. Not worried about this. I know when using the fuel line pinch method you want a slight rise in RPM without killing the engine. If it dies very quickly pinching the line its too lean, I know.. been through that. I like going off using a tach to set the high end, but I'll revert back to the pinch method for a time or two and see how it fares. Obviously there are flaws in the design. I do think the knurling of the needle detents to be rather coarse, perhaps a problem with some ST carbs where the optimum setting could very well be between clicks. My retention clips hold the needle pretty securely but it will not hold it between "clicks".. any suggestion to this?
The spraybar orifice has nice sharp corners and is diamond shaped. It does have the older flat machined spraybar which did have a very minute amount of swarf on the edge of the spraybar orifice. I gently smoothed those off with an Xacto knife so the edges are smooth and clean.
Should I be concerned with the size of the hole through the spraybar and fuel nipple despite the carb barrel being of the "corrected" or "more-corrected" variety? My fuel inlet nipple measures 1.68mm I.D, but I didnt pull the spraybar out to measure yet. I'll have to do more experimenting when my wife isnt home. I was driving her nuts yesterday running my ST...