I'd be backing off more than a couple of clicks. When I launch my West .50, it is usually struggling on and off the pipe and somewhat rich. It unloads quickly enough.

From your description, you are sneaking up on the right needle setting from the lean side.. you really want to do that? If you are using a clunk tank and running it dry, the mixture will progress from what sounds like could already be a lean setting to more lean as the fuel level gets low. Although you are making life easier in terms of hand launches, you might be allowing temptation to make you twist the needle when it perhaps shold be backed off a bit more. With a clunk tank chopping it before the tank gets really low is a smart idea, saves plugs and engines.

There is much good reading at www.jettengineeering.com, if you go to this section. It mentions a few of these issues.

Technical Reports & Instructions Engine Operating Instructions

R/C Carburator Set-Up

Bubble-Jett Fuel Tank/Tanker Instructions

Fuel Tank Installation

As to pipe setup - shorter pipe setup simply means you need to prop it to run faster. If the pipe/header setup is too short for the prop being used, however.. then yes, you'll munch plugs and have fits because you'll have a heck of a time finding a needle setting lean enough to launch without cooking the engine as soon as it unloads and wants more fuel.

This business about setting the needle rich has to do with the operation of a venturi - fuel draw increases as the square root of intake velocity, not in linear proportion to it. So a fixed needle setting only provides a controlled ratio of X:Y fuel to air at one rpm. So as the engine jumps up in rpm with the boost from the pipe, the mixture heads lean from the unboosted or partially-boosted needle setting. This is usually paraphrased as "the engine needs more fuel, obviously" - but it's not truly obvious why this is other than it's running faster, unless you understand this.

The higher the boost level, and thus the higher the ratio between unboosted and boosted rpm, the greater the allowance that has to be made. Mildly tuned systems, easy. FAI C/L speed engines - the exact opposite. Setting the needle back a couple of hunderd rpm like you would do with a muffler is not going to work. You need to back off many hundred rpm with a tach. If the needle becomes touchy, falling off into a gurgling rich setting, you are propably overpropped for the pipe setup, or too short for the prop in other words.

If I am tach-less at the field (as opposed to tactless which is a more steady condition) I needle it up onto the pipe with the nose a bit high, then I back off until it starts to waver at falling off again. Power is down at launch, but should be adequate as the only aircraft we're talking about are overpowered, right..? If the setting is off in the air, I kill it and try again.

MJD