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Tips for Carb adjustment top80


matt_k
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After a recent flight of around 2 hours i checked the plug on my top80 and it looked a little black.

My Pap manual says default setting 1.5 turns from closed and adjust accordingly till Cafe au lait.

Whats the best time of running to test right adjustment and at what revs?

Any tips?

(walbro carb)

Bit windy to fly eh!

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Black & oily or black & sooty ? Ideally you should be checking the colour of the porcelain about 1/4" from the base, not the tip.

Low speed screw is best adjusted at idle with a rev counter. Make a note of current screw positions first so you have a 'fail safe' to go back to. Turn it in or out in tiny increments and note the rpm until it drops off again. The highest rpm with smoothest idle is your best setting, but I usually open the screw slightly to make it a tiny bit richer for safety. Check there is no hesitation when you open the throttle quickly.

Max rpm can be checked or adjusted in a similar way, observing safety precautions of course, with the motor either on your back or strapped securely to a solid object with no dirt, debris or loose objects nearby.

Final checks are done in flight, after either a good 5 minutes level flight or 2 minute full power climb, kill the engine without letting it idle (even a few seconds idling can ruin the plug colour) then glide down and check plug colour. If cinnamon brown you are all good.

An overly rich engine tends to idle jerky and sound 'chirpy' (if it has a rubber drive belt) with visible exhaust smoke and a tendency to 'four-cycle' during acceleration phase. Too lean and it will also idle erratically and either hesitate or die completely if you open the throttle quickly.

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Rumour has it that Diego has run a Top80 at full throttle for 24 hours continuously on a fuel/oil ratio of 100:1 with no problem.

I have always used 65:1 in my Top80 as Miniplane recommends and never had a problem. PAP suggest 50:1 in the Top80's they sell but that is when people start getting coking problems.

I also know someone who has been running FB simoninis at 60:1 for years with no issues despite FB suggesting 50:1.

In my experience too much oil causes problems BUT running leaner oil mixes requires disciplined mixing.

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