Thanks for the math Arlyn. Though realizing anything is possible, that will shift my focus to the fuel system for sure. Now considering swapping carbs from the second engine if necessary. Also, going back to the factory carb settings, again. I don't seem to be getting anywhere with the adjustments on my own, and no clue where I'm at compared to the factory settings. Only takes a minute to do that, and at that point, I know I'll be close. A little less potential for me being my own worst enemy at that point......

Any thought of going back to basics and replicating the old points and coil system? Pretty light and well proven.

Jim... spark advancing is likely the biggest issue. Changing it electronically to suit rpms is simpler.

Points = Yuk!!

After more flying today, carb set at factory settings (w/HS leaned to allow clean 2 stroke at WOT or when vertical), engine out problems continue when throttle pulled back to idle on back side of loop or downside of stall turn. If I pull back to half throttle, no issue. Friend Gino witnessed today, and wondered about putting a check valve in the pressure line. I realize it's going to be a pain to fill, as a second fuel dot will likely be necessary to vent the tank as it's filling.

Input?

-Al

That is not good, I was hoping you would get it licked so I could learn from your experiences. The check valve might work, I am just surprised that it needs that much pressure. I have a check valve from one of my old ys engines if your experiment works, plumbing in a vent line would not be too hard. The way our weather is going around here I will have time to wait and see what you find out. I spent an exciting Sunday cleaning and rearranging my work room. :rolleyes:

I have had the same issue with my little gasser. I found if I did not throttle back all the way it did not die as easily. I set my transmitter with a high idle switch. I also found if I throttled back to fast it would die. To fix that I set my transmitter to slow down the throttle servo. The engine will still die on occasion but it is much improved. I hope this helps. I am also waiting on the check valve idea. Good Luck

Bruce

Wish I knew something about the dynamics of the carb regulator. It may be a piece of crud not allowing the regulator to function properly. I've flown mine a lot and only had one dead stick and that was my fault. I'd tried Tygon on the muffler tap.... yep, it melted off and with no muffler pressure it went lean and died.

I've not run the other 10cc that was acquired used. It only had one flight on it and I was the pilot. The gentleman that had it was forced to give up RC because of health issues.

I have also had the same issue with the 15cc engine in my Venture 60. I just installed the new pumped carb on it and have not tried it yet, we will see. As far as the 10cc goes I still love that engine.

Bruce

I'm also interested in the check valve idea. Does anyone know if the problem is worse with a full tank of gas versus an almost empty tank?

I have not had this problem, but that may be because I'm not doing, or can't do, the exact maneuver that causes it, my engine is mounted on an Ultra Stick. My fuel line from the engine to the tank is really long since my tank is on the CG. Has anyone tried putting a one or two inch loop in the fuel line?

I did play with the full tank vs. 1/2 or lower. No difference. Wish I knew more about the regulator as well.

So far, I have never had a dead stick landing with this engine. My fuel line "head" distance, not fuel line length, is 10" and I wonder if that is providing pressure required to keep the engine from starving during a downline.

Next time I take the plane out, I'll try to duplicate the stall turn and see what happens.

It seems like if the problem is related to tank pressure, it would be possible to duplicate that on the ground.

10"? Wow, what led you to give that a try? I'm thinking glow engines with my setup. Maybe need to rethink? -Al

I do not think that a downline can consume the quantity of fuel in even a short fuel line, especially with this engine. Frankly... I'm thinking that if it is leaness causing the flame outs on downlines, it's because the regulator is over reacting to increased pressure from the weight of the fuel.

Interesting idea. If that were true, wondering if other guys, with different exhaust setups (other than Bisson Pitts), might be running into similar issues (downline, on idle = dead stick)? -Al

Most glow engines have the tank near the engine due to the problem with a venturi being able to draw fuel over a long distance. Gas engines have a pump so they are not limited to the suction from a venturi and usually have no problem pumping fuel 10 to 12 inches vertically. I have always mounted my fuel tanks on the aircraft CG, even with glow engines by using a "header" tank. I even mount my batteries on the CG, so as the electrons flow out my CG remains the same. Okay, maybe not, just wanted to see if you were paying attention.

As far as the engine going lean on a down line goes, IF it is going lean due to the reduced pressure from the exhaust because the engine is going to idle, then the pressure at the regulator would be equal to the fuel "head" pressure minus the exhaust pressure. The shorter the "head" distance (not fuel line length) the less pressure there would be at the regulator. More "head" pressure MAY make up for the reduction in exhaust pressure. The fuel "head" pressure, due to a short or long distance, would be nulled out during level flying leaving only the exhaust pressure at the regulator.

I use the terms IF and MAY above because I don't think we know what the root cause of the problem is yet. There are still a lot of variables in the equation. I'm not sure how fast the regulator can respond to pressure differences. One BIG problem on the little gas engines is that the fuel flow is so small it is difficult to regulate.

If we can get some good flying weather in between my Chemo treatments maybe I'll feel like doing some testing too.

We might get some flying in tomorrow... but it looks like the only window for about a week. I've still not bench run mine because I don't want to do it in cold weather... maybe tomorrow.


Header tanks are mostly to avoid fuel foaming. You still got to pull/push/gravity feed the fuel to the header tank.

My head hurts. This Extra is grounded while I dust off and charge the U-Can-Do. Same engine with a Mac's header, maybe a little less time on it. Will see if we can't eliminate some variables with a second plane and very similar setup going through the same maneuvers with a different exhaust. We're enjoying some pretty nice weather here this week, so I won't have to wait too long to get some answers. Should be just a day or 2.

I did go out and pulled the Extra's carb down earlier this afternoon. It was full of fuel, and not a speck of dirt or lint anywhere (of course!). Nothing that might lead me to believe there might be a problem there.

Steve, we have a gas engine here, but it's not "pumped" (not yet anyway). The 6oz tank in use here not a lot bigger than what I might have called a header tank on some of the stuff I used to fly......

Best of luck with the Chemo.

I had the same issue but was using the stock muffler at the time. I now have the engine mounted in a different airframe with the bisson muffler but have not flown it yet. With the weather we have now, and have coming, I do not know when I might have a chance to fly. My fuel line is only 6 or so inches right now, the tank is mounted about 3 or so inches behind the firewall. I have a check valve I could try, but I am going to wait until I fly it to see if I do in fact have the issue again. I will get the new airframe trimmed and sorted and then just do some stall turns with a bit of altitude and close to the runway. Preferably while nobody else is flying....

My header tank was only 1 oz. Never used it for a foaming problem, used vibration isolators on the tank and/or fuel filters to stop foaming. Used header tanks since 1948 with no issues. The old engines did not have a good fuel draw since they did not have throttles and we usually removed the venturi restrictors to get more RPMs which made the fuel draw even worse.

I'm pretty sure the carb on this engine is not drawing fuel by the venturi suction alone as used on some glow engines. I don't think my setup would work well at all, or maybe I should go buy a lottery ticket. It may just be meds making me crazy, but it looks like the carb on this engine is similar to the Walbro which uses crankcase pressure to operate a diaphragm to pump fuel, via suction, from the tank to the carb. I see a vent hole, room for a diaphragm, and a possible source for crankcase pressure to the carb; it looks like it can pump fuel to me. Will need to check with the manufacturer to be positive.

No dead sticks here either after break-in and tuning. Had several during that time but 4+ gallons later it is running fine still on the stock muffler , full tank and almost empty, conventional mounting and using a heavier sintered clunk.

We're good on the "clunk rattle test".

Too, like you guys were talking about earlier, starting with a completely normal full power climb, if I then pull the throttle and point the nose straight down, logic would say I have a full fuel line that should be able to feed the engine for quite a while on idle. That's just not happening. It quits after having dropped maybe 5 or 6 feet..... even at an idle high enough to have it scooting on a grass runway.

Let's put this on hold until I get a chance to fly the U-Can-Do.....

Took my newest 10cc to the field to fly yesterday and began with testing the engine which immediately showed a problem with the stock motor mounts being too flexible. Back home the cowl was pulled and another issue was discovered, the viton tube had split just aft of the pressure tap. I'd only run the engine perhaps a minute on the bench before deciding the mounts were a problem but noted a fair amount of oil discharge had come from the split in the tubing, which indicates to me that there is plenty of pressure at the tap.

From that clue, I'm thinking that if pressure variances between the stock muffler tap and the bison are at issue, it can't be assumed that the issue is too low of pressure of the bison.... it could be more and that might explain the reported 500 rpm gains using the bison.

I've two variants of the viton tubing here. I have what was supplied by Horizon with one of my GX seriies engines and a longer section that was bought from Horizon. The piece used on the muffler tap was slightly larger in diameter and had a course exterior texture. As noted, it didn't last a minute on the pressure tap.

IIRC, Pete had warned that some of the Viton supplied with the engines had been discovered to be inferior. I'll try the other that was purchased separately. Meanwhile, I've got to replace the engine mount and have purchased a fiberglass reinforced radial mount as they are much stiffer and have proven over the years to do well. As can be imagined, I've some work cut out for me now to position the mount to align with the cowl... much easier the other way around.

Just to register a thought I had, we were considering/thinking of the pressure created by the "column" of fuel in the fuel line on a down line. We're talking about a pretty clean airframe that's accelerating going straight down (even when the engine isn't running). Thinking maybe the weight of the fuel in that column is actually closer to zero. Consider how wannabee astronauts train for zero gravity/weightlessness.... -Al