T-ster

I have an older 3W 100 in a 33% Edge. I built the plane around 7 years ago and had 40 or so flights on it and the engine, then other hobbies came and went and it sat in the house for 5 years. I used to run it on AvGas 100LL (due to the lack of smell), but when 9/11 came it became more difficult to buy AvGas so I ran it for the first time in 6 years on 93 octane. It ran fairly well, but had some coughs and burbles at times during the flight. I cut the 2 flights short because I didn't want to practice deadsticks.

Last night I started to adjust the carb to get this puppy running correctly. I went back to factory settings (1-1/2 L, 1 H; w/ a Tillotson carb). It ran ok, but the idle was somewhat rough, but the high end was strong. I first started to lean the low end down to 1-1/4 , but didn't seem to help the idle, so I started to richen the low end (screw it out) and the idle sped up and it smoothed out (ended up back at 1-1/2 turns open). However, now running it up to full throttle it would run fine until 3/4 throttle then would slow down and sometimes die. I then started to richen the high end, but all of a sudden couldn't get the engine to start. If I would choke the engine it would start and die (just like it should), then turn the choke off and couple of flips and it would run for a few seconds and die. (It appeared the fuel would run back into the tank from the carb, after choking.) I let it sit for 15 minutes, then it started ok. I richened the high speed to 1-1/2 and it seemed to run much better throughout the range, but coming down to idle it seems to almost die at first, then speeds up slightly (which it has been doing most of the time), then stabilizes the rpm and seem to run ok.

I'm confused that richening the low end seemed to lean the high end. Doesn't make sense to me. Or, is it possible with the engine running in the plane on the ground it started to overheat and cause the hard starting and changing mixture settings (I didn't run it for more than 5 minutes total, I would guess.) I'm using fresh fuel, by the way.

It is running decently, but not real confident in the engine after these runs as the setting seem to somewhat change. Do I need to put in a carb kit or maybe just fly it and see if some running cleans out the cobwebs?

rc bugman

My Feedback: (30)

Hi,

If it has been sitting for 5 years and it is running eratic, I would think that a carb kit would be in order. The pump diaphram may be hard and the carb may have a bit of varnish in it from the long sitting.

Elson

altavillan

My Feedback: (1)

Yes you need a carb kit. For temporary running try removing the carbs gaskets/diaphrams and gently rub some raw synthetic oil into them to loosen them up. Check the filter screen for debri. Most likely the fuel pump diaphram is not pumping at a concistent rate causing the needle fluctuations.

DMcQuinn

My Feedback: (13)

I agree - carburetion issues - likely can be fixed by disassembling the carb, cleaning it out, lubricating the two diaphragms (as mentioned by previous poster), and reassembling. Note that on any gasser I have ever run, the factory settings are usually a little rich (I'm in St. louis - 600 feet). So expect to lean both needles from that point. My experience on the low speed side is that the factory always say to go 1.5 or 1.75 turns open, etc. but I often end up at one turn open or even a little less. I think the factory guys want to make sure the engine starts - so the owner does not get a bad first impression. Too rich on the low side and the engine will still start. But too lean and it will never start.

T-ster

I purchased a carb kit, however after talking with Bobby at Cactus Aviation I believe the problem is the phenolic block. If it warps is can allow an air leak.

Anyway, last night I sanded the phenolic block with 600 wet/dry sandpaper on a piece of glass as well as replaced the innards with the carb kit. Bottom line, it runs excellent once again. whew. My guess is the phenolic block was warped as all the gaskets and diaphragm looked fine.

Thanks for the advice. I'm back flying again!