Hey guys...I need some expert advice here. I picked up a used plane/motor deal and the motor is giving me fits. Unfortunately, like with most deals, I have no actual history on the motor. It is a nearly new Zenoah G-26, ..maybe just a couple of gallons of fuel through it... the piston appears shiny and clean, like new,...standard Zen' stock muffler, 40:1 fresh Amsoil oil/fuel mix, APC 16-8 prop. Here are the symptoms of my problem. It is very difficult to achieve a good prime for starting. I must use an electric starter and I must spin the motor...fully choked and wide open throttle, for perhaps a full minute before fuel is up and she is ready to fire. That's quite unlike any Zenoah I have ever run. The fuel plumbing is Tygon, with no air leaks, and the tank is on line with the carb, and positioned just about 5 inches in back of it. Once running, the motor seems to be OK...on the ground! Idle is around 2200, full throttle is 8600RPM, transition is great too, however, I am unable to shut it down with the throttle alone. I must use the ignition kill switch, and I have (2),...a manual switch on the fuse, and another on a servo operated remotely from the Tx. ...a very handy item to have!!!
After take off, things seem to change. The top high end is OK...I cant tell much difference there, but as soon as I begin to reduce throttle, the motor RPM drops dramatically....much more than what would be anticipated by the minimal throttle stick movement. Mid range, if you can call it that, sounds like it may be much too rich, but it is so weak and unreliable, I have not flown much at that throttle setting. Idle in the air is non-existant....it will immediately go dead if the stick is brought back to the idle position. Challenging, but not much fun.
The carb shows some signs of having been worked on...at least the original stock throttle lever and spring were removed...I guess to accomodate a different (nose-wheel steering arm) type of throttle connection. I added a black plastic velocity stack on it, (the kind you see on the Walbro Go-Ped carbs) which does prevent fuel mixture from spilling out and messing up the side of the fuse. This fuel "saving" did make it run somewhat richer, but a 1/4 turn on the low needle seemed to totally correct that issue. Other than that, the stack doesn't seem to make any noticeable difference to the running of the motor. So....do I have a defective carb or what? Thanks very much for your comments.
Jim

I think you named the problem, "The carb shows some signs of being worked on." If the previous owner took the butterfly out, I'm betting he didn't put it back in the right way. There are tiny air bleed holes in the carb throat that the butterfly MUST be in the correct relation to, or the engine will do just what you describe. I'm not sure of the proper orientation, but someone in RCU will know, or you might find a good closeup pic of the carb throat on the web. If that's not the problem, buy a rebuild kit (they're not expensive) and CAREFULLY rebuild the carb. There are tiny filter screens inside that can be easily clogged by dirty fuel.

On my G-23, the idle needle spring wasn't strong enough to hold the needle still in the air. A quick visit to a local lawnmover repair shop got that fixed.

You might want to lean out that oil mix, too. Amsoil is an EXCELLENT synthetic oil that runs cleanly and lubes very well at 100:1. Try it at 75:1 instead of 40:1.

Also, NO discoloration at all on the piston tells me it may not be completely broken in yet.

Good luck with it and keep us posted!

Dr.1

I have never had the problem, but I understand that carb butterfly can be installed backwards and cause a headache.. Look in the carb throat and you should "not" see the head of the screw that holds it in place when closed. But see the bottom threads of that screw instead.
That is the way mine are and both run really good. I'm sure Ralph or DP will show and give you some "good" advise. Brian

Thanks Brian...I'll go check that right now...but I think there may be more than one problem here. That may fix shutting the motor down with the throttle, but the inability to suck gas in the beginning will probably be another little ordeal. I'll let you know.
Jim

The block under the carb is sometime not made right..Lay the carb gasket on the block and check to see that the pulse passage is milled far enough around to let the pulse go through the gasket..I had one here last week that was about 1/16 short and the pulse would not reach the matching hole in the carb..
The carb needles are usually about 1 1/3 to 1 1/2 open on both when set right...
The carb disc is machined with a bevel on the edge to completely close..If it's wrong it might not close off all the way...[8D]
Check the lever that lifts the inlet needle, it should be flush with the casting..A straightedge across the casting next to it should just barely touch the end of the lever...
Check the gaskets on the carb...The diaphragm with the metal center goes on TOP of the gasket on that side, the diaphragm on the other side goes UNDER the gasket...

Hey Guys...we are making progress now. Brian...you were right...the throttle plate was installed backwards. I have reversed it.
Ralph...following some of your other tips, I blew into the fuel inlet and the needle held tight...no leak.
Next...should there be a gasket both on the carb/block interface...and on the block/motor interface...? or just one...wich one?
I'll go check to see if the pulse hole and gasket are lined up....there is an arc in the block for the pulse to travel...I'll have to try and see if it leads to the proper hole in the carb. I think now my only problem will be getting it to suck gas from the tank...without spinning it for a minute with an electric starter.
Thanks for the tips...more to follow soon.
Jim

On my 2nd new G26 the spacer block was upside down and the pulse hole was covered. I could get it started with an electric starter. but it would shut down past 3/4 throttle. Would not idle.
Yes there should be a gasket between the carb and spacer and between the spacer and the motor block.
It is a great motor and you'll be pleased with it when it is running right. Brian

The supplied gasket(s), if installed between the carb and the spacer block will allow a huge air leak between the pulse channel in the spacer block and the carb bore...and they are symetrical, so turning and/or reversing them does not improve the situation. Between the spacer block and the motor, the same gasket appears to fit well. It had only one gasket on it when I took it off...but I forgot which side of the spacer block it was on.
The motor did run after accomplishing the initial prime, so if I am thinking correctly about this...the pulse only keeps fuel in the chamber for running, but does not accomplish the initial prime...right??? So, what do I look for to get the thing to prime itself?
Still working away at this little beast.
As for Zenoahs in general...I have a G-45 and a G-62, and they are both extremely reliable. This new little G-26 is just being a difficult learning experience for me, and I really need to get it all sorted out this weekend so I can fly in a local Big Bird event next weekend.
Oh well...it's all good fun.
thanks for all the help guys.
PS. It sure would be nice to have an exploded view on this to show where everything is supposed to go.
Jim

The gasket between the carb and block is different, and the pulse channel in some of the blocks doesn't go far enough and is too close to the hole for the carb, so if the gasket is missing or not exactly in place the pulse will leak...Horizon needs to look closer at the blocks they supply t
They have the right idea, the execution leaves something to be desired..
The carb would fill with fuel when choked if there were no pulse channel at all, and sometimes will barely run with the pulse channel completely closed...did it yesterday, forgot to put the pulse channel in a carb block I made for a conversion...

Brian...you were right...the throttle plate was installed backwards.

I said it first...

Dr.1

Well it looks like I am missing the correct gasket for between the carb and spacer block. I will have to try to get one quickly...would that be an item a small engine (lawn mower & weed whacker repair shop) may have? If I can't get it locally...a mail order may arrive too late for the next weekend fly-in. I suppose I could try to cut one....I'm not looking forward to that little detail. I wonder if a silicone hi-temp gasket goop, carefully applied, would do the trick?
so this fun goes on...and on...and on!
jim

Dr1...sorry...you did say it first...I'm a little forgetfull sometimes.
Thanx to everyone for all this good info.
jim

Get a piece of gasket material from your local lawnmower shop and cut a new one. Take your time, it's not that hard. Use a SHARP #11 blade and a piece of glass to cut it on. I wouldn't use goop, it's too easy for it to clog the breather holes.

Dr.1

Not a problem, Jim. I'm glad you got the problem figured out. The orientation of the butterfly is one of the easiest ways to mess up a Walbro-type carb. If you ever take yours apart, make sketches first.

Dr.1

Sketches...gee..I need digtal photos of this mess!!!
thanx again
jim

Some semantics...There is a difference between INSTALLED backwards and ROTATING backwards..The plate is beveled..If it's installed backwards it won't completely seal off the carb to shut the engine off, even if the rotation is correct...

What Ralph said, plus it ain't round.

I was wondering what those depressions were for on the throttle plate. I find that they provide an alignment onto the throttle shaft...pretty clever, eh?
I think i've got it right now.....however...when I tried to run it earlier, it would run out the prime and then quit. I guess I've lost the pulse. I'll have to pull it off and give it another good look in the morning. Anyway...it's too dark to play anymore.
Nice thing about living here in S. Florida....I can play with these toys every day of the year, just about....and being retired, I can fly on the weekdays with the rest of the over the hill gang....no more crowded weekend flying.
Ahhhh, another day in paradise.
Thanks for all the help guys.
Jim

Capt Jim,

Screw you! In Minnesota we are suppose to get rain and snow tomorrow and Tuesday. I can't wait to get out of here. We have a house rented starting Jan 7 for six weeks in Spring Hill which is north of Tampa. This year I'm going to have a plane with me. Last year we spent four weeks in New Port Richie, obviously we enjoyed it since we're coming back for a longer time. Yes, we are snowbirds. When people ask me how retirement is I tell them, "It's not what it is cracked up to be............it's better!"

Good luck with the carb, you getting some good advice. My G26 runs like a champ, although the carb is quite touchy.

Chuck

"Nice thing about living here in S. Florida....I can play with these toys every day of the year, just about....and being retired, I can fly on the weekdays with the rest of the over the hill gang....no more crowded weekend flying.
Ahhhh, another day in paradise. "

Hi Chuck....Welcome back to Florida. The state is very long, from top to bottom, and the terrain, trees, and weather are markedly different as you travel south. You may want to look into visiting much further south....the weather is quite a bit nicer down here....warmer!!! Cold fronts in the winter typically do not get further south than Floridas big lake..."Okeechobee", so although you will find the Tampa area weather much more to your liking than the frozen north of Minnesota, you will still be wearing a sweater or light jacket in the mornings, and evenings, and you'll probably want to turn on the heat at night. Down here, it's pretty much shorts and tee shirts all year round. This time of year, the air conditioner is turned off, the house is opened up, and we sleep with the windows open and a nice breeze drifting through. I complain terribly about the miserable winter cold whenever it gets below 60 degrees...down here....you'll not hear much complaining from me.
heh heh...come on down!!!
Jim
PS Although retired, I'm still an active Realtor...just in case you decide to stay!

An exploded view of your Walbro carb can be found here:
http://wem.walbro.com/walbro/group2.asp?FamilyName=WT

and one of your engine can be found here:
http://www.zenoah.net/products/hobby...60G231_408.pdf

Hi Ryan...thanks so very much for that great information.
Now I have something to really look at!!!
Jim

OK guys...this just keeps on becoming more and more weird. Along with the other corrections i have done with this carb, I soldered on a small brass tube to the diaphragm cover plate vent hole, so that I can lead the vent inside the fuse to calm air. Now that i've reassembled everything and started up the motor, it primes much quicker now, and starts right up....however...it runs out the prime and quits. If I start it and go immediately to full throttle it will continue to run, but any attempt to lower the RPMs will incur some surging, and if the RPMs get anywhere near 3/4 or 1/2 throttle, it will quit just as quickly as if the ignition were switched off.....which of course is not happening. Now what do I look for now???
Jim

Still sounds like the disc is opening the wrong way...It should open toward the 3 small holes in the venturi..
I just ran 2 conversions this afternoon..If the needles are open too far the engine will cut off just like you describe...Most G26s run with the needles open at 1 1/2 or less...The carb is so big it's touchy...I always start at 2 turns and set the high first...Then set the idle speed for about 2000 rpm...slowly close the low needle, the engine will speed up...Re set the speed to 2000 and lean the low needle some more..Do this until it no longer picks up speed and the idle is 1800-2000..Now when you open the throttle it will die..Open the low needle a little at a time until you can get a good transition, then re set the high..It should be good to go...The low needle needs to be a little rich for good transition, so the idle speed will be controlled by the low needle as well as the speed needle..Hard to put down in writing, it's something you have to mess with to get it right...

I got both the needles on my G-23 set at 3/4 open. Runs great.

Dr.1