G-23 running a 16x6 prop sags and stops. A year ago when preparing a G-23 for a plane, on the test stand the high end mixture would not lean out even when closed fully. A carb kit was installed and the only pump in the kit that fit was the one that looks like acetate. The new atmospheric diaphragm evidently solved the too rich problem and the motor seemed to dial in and was adjusted for 8100, two hundred below max of 8300. The engine seemed to respond well to the carb rebuild and after a short bit of bench running was installed in the plane and flown but quit about five minutes into the flight and the dead stick was not pretty and resulted in the second crash of the Taylorcraft. Now rebuilt the second time the engine was tested and displays a problem.

It started easily as usual and ran up to the same 8100 rpm (no carb adjustments since the dead stick). After about a similar time frame as what happened with the dead stick, the motor sagged a few hundred rpms and died a bit hot. After allowing to cool down, it was richened to drop the rpms to 7900 and that was as low as the top end would go with the needle out so far it was loose. Over heating at 7900 is less but still evident, again this is on a test stand with no cowl. Fuel is 40:1 Penzoil. The engine has a pitts exhaust. The test today did explain why the dead stick happened.

The most the rpms can be dropped by the high speed needle is 400 rpm with the needle loose and about to fall out, from a high of 8300. The test stand fuel tank is breathing ok so its not a vacum in the tank issue. Are the acetate pumps ok? Should I go to 32:1 or a different oil for this engine? Is 16x6 over propped? Does the pitts muffler have too high of back pressure? Why is it heating up when richened 400 rpm? The motor hands over smooth albeit with lots of compression and does require putting 24V to the starter. It idles fine and transition is fine until after about five minutes of run time when it starts getting warm and sagging and then transition has some hesitation indicating perhaps the low is a bit lean. I only had a short window this afternoon and didn't richen the low end from where it was set previously.

Any ideas where to look first?

Acetate diaphragms do not pump as well as the black ones but you may have another problem also?

I had a similar problem not too long ago with my EI G23 spinning a Xoar 16x8 and running on 90 octane with Red Line mixed at 40:1, where it would start normally and run without a hitch until it got all warmed to a max of 8,300 rpm and then it would start to sag as if lean on the low needle and only by very very slowly increasing the throttle from idle to high would the engine not die, but was also very hesitant to go to full rpm. My attempts at richening the low end made no difference and then Ralph suggested I replace the metering pump diaphram which I did with one of the rubberized units which solved the problem. HTH.

Karol

Thanks guys... I'll start with another carb rebuild with a rubber pump.

The tan Teflon pump diaphram is reported to pump the best. What carb are you using? Is this magneto or electronic CDI? Have you checked the timing? Have you tried a smaller prop? Are you adjusting ther carb needles only after the engine is fully warmed up? Are you using a heat insulator between the engine and carb?

I get 9300 with a a MAS 15x8 on electronic CDI using Coleman fuel and Pennzoil Outdoor 2 stroke oil at 32:1, through a Walbro 167 carb. The Coleman fuel is reported by some to run hotter than gasoline, but I have not had any sagging problems with the engine fitted to a 1/4 scale Sig J3 Cub. Just my experience. Good luck.

The numbers on the carb are 197A and then there is a 204. There is a rotation hub of insulated material between the carb and engine. Prop used yesterday was a Zinger 16x6 and when the TCraft went dead stick it was an APC 16x6. From my experience a 16x6 is generally about equivalent to a 15x8 and it simply depends on the general speed of the plane which is chosen with a faster plane enjoying the 15x8 and a slower like the TCraft a 16x6.

The engine is magneto and I think the timing therefore fixed.

The motor was plenty warm when trying to adjust the high speed but it would not adjust rich enough to stay cool. As outlined, the high speed adjustment just didn't do a lot in the way of richening the mixture.

I picked up a carb kit and will report the results.

You got me thinking however, and I think I mis spoke about the rpms after the rebuild. That was many months ago and my memory isn't what it used to be. Looking at my notes, I ran it on the bench after rebuilding the carb and it ran 8650 on an APC 16x8. After installing in the TCraft I went with an APC 16x6 and touched up the high end with cowl on and got 9300 and backed off to 9100 thinking the G-23 only very slightly stronger than a G-20 that runs 8900 consistently with an APC 16x6. I quoted in my post 1,000 less than was the results after the rebuild evidently because that is what I was reading with yesterdays test.

That might explain yesterday's heating issue, as there may never have been adequate fuel to develop full rpms though it could be other issues like a slightly bent crank or what not.

Last, an inspection of the acetate pump shows that the pump diaphragm area is significantly distorted (bubbled) in the direction of the outside plate. I don't know what that means. It might be that negative crank pressure is greater than positive or that when hot the diaphragm decided to swell and just happened to go that way... who knows? I can hold it in my hand and using thumb to depress the bubble actually hear the acetate pop across much the way one played with a childhood clicker toy. I wonder if positive crank pressure was enough to punch the bubble across in order to pump effectively... I've some doubts.... again, we will see what takes place after rebuilding using rubber.

The pump had no more than twenty five minutes of run time.

Re the possibility of a bent crank. the G23 uses a double threaded rod that screws into the crankshaft as the prop shaft. It's relatively small diameter lends itself to being easilly knocked out of true. This prop shaft is easily and inexpensively (circa $8.00) replaced.

Re the acetate diaphram. It will not hold up to heat as well as the Teflon. The rubberized diaphram does not hold up to the 10 percent ethanol laced gasoline we have for pump gas here. Some fliers using gasoline get non-ethanol adulterated gasoline at a local marina, but not all marinas have this.

Spaceworm... back at you again. I just opened the rebuild kit and might be seeing the tan teflon pump you mentioned. It looks as if there is a choice of three pumps in the kit. The traditional black rubber looking with combination of check valves and pump on same membrane, the acetate (which I know I'm not going to use) and the one I've never seen before is the tan fabric weave looking but it is a diaphragm only having no check valves but there is a black check valve membrane having no diaphragm.

Do I want to go with them in combination or the traditional black?

Well... there was no choice in going with the traditional black as the flapper valves on it did not align with both ports so the teflon was used. And... that jogged my brain why the acetate membrane was used on the previous rebuild... because the black one in the rebuild kit didn't fit.

At any rate... problem is solved... motor runs great with no overheating. Can put hand on crankcase directly after stopping motor after ten minute run and it's not too hot to hang onto... sure couldn't do that yesterday.

The other interesting thing is that rpms are slightly less than was available yesterday where I could squeeze 8300 out of it but had dialed it back to 8100 and then on to 7900 where it still sagged and quit. Today it would reach only 8200 but it was happy running there and showed no sign of heating or sagging. Humidity today after rains is thirty points higher and temps are eighteen points cooler so that could be reason for 100 rpm difference. Evidently the Zinger 16x6 loads a little heavier than does an APC 16x6. I didn't have an APC off of a plane so didn't try one.

So, Karol... your advice to get shuck of the acetate membrane pump was good advice... thanks.