LGM Graphix

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Hi guys. I just picked up a ziroli dauntless with a new GT80.
On Saturday I got it started but it would not get better than 4400rpm. This was with a 20x10 solo three bladed prop which I know is a bit to small. Even adjusting the high speed needle wouldn't give me better than 4450. I had oil coming out of the right cylinder exhaust but not the left.
I have checked the plug gaps. Checked that there is spark, checked the gap of the magneto and flywheel, ensured that the carb is opening fully, took out a filter that was to small, tried it again today and now it won't even start.
I'm at a loss. Gas engines are new to me but internal combustion engines are not.
Anything else somewhat obvious that i am missing that anyone can think of?
Thanks in advance.
Jeremy

Lifer

My Feedback: (1)

What does the owners manual suggest for props?

wildbills21

Rebuild and clean the carb, there is a screen in the carb that gets plugged, check the black pulse tube from the case to the carb. low speed needle 1 1/8 to 1 1/4 high speed needle 1 1/2 to 1 5/8. This is a baseline start, every motor is a little different depending on prop. If it has spark it sounds like a fuel problem.
wild bill

av8tor1977

My Feedback: (6)

New spark plugs? Also try swapping the spark plug leads from side to side and see if the dead cylinder also swaps sides....
AV8TOR

LGM Graphix

My Feedback: (22)

The manual suggests a 24x10 or 22x12. I have one coming that should be here today or tomorrow. All I had was the solo prop which is a little to small for the engine, a 22x10 3 blade is what I've read on RCU is the right size for a 3 blade.

Wild Bill, the carb is the next step although on a new engine I would hope that wouldn't be the issue. I started with the needles set where you suggested but it wouldn't even start until I was 3 turns out on the high speed. I guess that would likely indicate a fuel flow issue in the carb although the cylinders and plugs were wet when I pulled the plugs to check them.

What do you suggest gapping the plugs to? The manual says nothing about plug gap, I found online anywhere from .024" to .038". When it did run they were at .024" and after not being able to get past 4400 rpm I regapped to .031". I put them back to .024" after not being able to get it to start at all, but it still won't. Guess I need to find a carb rebuild kit. Having no gas engine knowledge, do I need to get a kit from zenoah or are they available at a small engine shop? In other words, are they an industry standard carb that is just being used on an RC airplane engine?

Thanks guys.

Truckracer

My Feedback: (19)

While it could be a carb problem, don't rule out a cylinder problem. Are both cylinders firing? Without knowing any history for the engine, I'd do all the basic checks to make sure the engine is in good health and here, in no particular order are a few things you can easily check. Is the compression similar between cylinders? Check that by removing one plug at a time and while rotating the engine through compression, do they feel relatively the same? Has the engine ever been overheated which wouldn't be uncommon in a scale plane where users do their best to use as small of air inlets / exits as possible? Perhaps a stuck ring if that is the case. You might want to remove the mufflers and inspect the piston / rings. Zenoah rings seal quite well so if there is excessive staining on the piston skirts below the rings, suspect stuck rings .... and especially if one piston looks different than the other. From there, confirm that both cylinders have good spark and that they are indeed both firing. You can confirm this by simply touching the cylinders / mufflers after a short run. They should be of fairly equal temperature. Check all bolts for being tight, etc. Has the engine ever been damaged by a ground strike? Again, if you remove the mufflers, turn the crank just until the pistons start their upward movement. Are both pistons in the same position on both cylinders? If not, the crank may have slipped on one or more crankpins and need repair or replacement.

Again, just performing a basic engine inspection while confirming that all systems are OK should reveal the problem. I'm not familiar with the prop you are using so it might just be way more load than you think it is and there may not be any engine problem at all. These engines like to turn up and will pretty much fall on their faces performance wise if overpropped. A typical 24-10 you suggested will probably turn around 6800 though the engine will perform its best if propped for 7000 or more. You just have to find the best compromise prop that will pull your airplane the way you want it to perform while keeping that Zenoah happy. A 24-10 usually falls in that compromise range.

Regarding carb kits, the GT-80 uses a Walbro WJ-64 carb and the rebuild kit is a K10-WJ available from any small engine shop or a multitude of Ebay or other online sources.

Plug gap isn't critical and you should be fine where you are at .024" or so.

LGM Graphix

My Feedback: (22)

Hi truck racer, as I mentioned, the engine is new. It was run briefly by the fellow I bought it from but never at full power. I ran it once. The compression is good in both cylinders and both plugs have spark. No chance that it has ever had a prop strike. I'm going to pull the engine off the airplane so I can remove the carb and clean it next. Hopefully it's just something gummed up in there.

LGM Graphix

My Feedback: (22)

Everything I've read in the warbird forum says the mejzlik 24x10 is the best prop for this engine so that is what I have got now. The solo prop in a 20x10 like I ran it is to small, everything else I've read says in a three blade prop it should be a 22x10. As I say, I'll clean the carb first and see what happens.

Truckracer

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What kind of mufflers are being used on the engine?

LGM Graphix

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They are the stock mufflers but they have copper extensions to exit in a scale location. I expect a little extra back pressure may lower top performance but I would not expect them to drop it by 2800 rpm.

Truckracer

My Feedback: (19)

Bingo! My bet is that exhaust is a major problem there. If yours is the older GT-80 with the stock steel mufflers, it would probably only turn a 24-10 in the 6200 - 6400 range at best and then adding those extensions will further restrict its performance. You might want to do a test run with the mufflers removed just to get a baseline RPM reading then go from there. You need to prove to yourself the engine is good even if it is new. At minimum, try a test run with those extensions removed. You'll be surprised. That engine does not like exhaust restriction.

The older stock mufflers are horribly restrictive themselves!

[email protected]

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just send it in for reapirs better then messing with it

LGM Graphix

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It's a new engine but off warranty. I want to exhaust all options before sending it in. Shipping round trip will cost me $100 alone.

Truckracer

My Feedback: (19)

Zenoah engines are very reliable and little goes wrong with them if treated well. I believe the OP should be able to resolve his issues w/o sending the engine in.

LGM Graphix

My Feedback: (22)

I will try opening up the exhaust but first I need to clean the carb and try to get it running period.

Truckracer

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Sounds like a reasonable approach.

LGM Graphix

My Feedback: (22)

I learned a long time ago, change one thing at a time. Otherwise if you change to much you'll never know what fixed the problem. What mufflers do you recommend however over the stock that are less restrictive but don't take up anymore space? Can you open up the stock mufflers to make them less restrictive?

Truckracer

My Feedback: (19)

I don't have any personal experience modifying the stock mufflers but know it was common practice for some people and they had good results. They were still quite heavy though which is probably not a problem on your warbird. You might be able to find some old threads that describe the modifications. Regarding aftermarket mufflers, I have flown with B&B, Slimline and Bisson mufflers on the Zenoah twin and all have worked well. The B&B is not much more than an exhaust diverter though and is quite loud but they are reasonably priced. Today, I'd look at the Bisson or Jtec mufflers as both are of good quality. I think you'll find most of the aftermarket mufflers are much more compact than the stock ones. Both of these companies custom build mufflers so maybe you could get something with an exhaust location more suited to your airplane.

FireBee

My Feedback: (34)

My Buddy has one: my notes from him are: xoar 24x10. 6800/7200 top end. NGK BPMR7A plugs with Slimline Smoke mufflers.

go to post 3 and clean that little screen. I have had new engines with lint or something blocking that screen. Also need large fuel lines if I recall for Gt-80 (vice 3 turns out on the needle) and I use the felt pickup fuel clunks too.

Also check the carb stand off block. Make sure no cracks are in that block as people will crank down on the screws too tight and crack it; cause air leaks between carb and engine.

PLANE JIM

My Feedback: (109)

I was having a similar problem with a G62-actually had a dirt dobber build a nest in one exhaust tube of a pitts style muffler-dropped rpm way down until I clean the nest out

rt3232

My Feedback: (6)

To the OP

Had a similar experience with a G-62 some years back, So while you have the carb off and before you open it up, take a single wire out of a wire brush ben a short 90, one end and check the needle bleed holes, (long story, but I found what appeared to be a half circle sliver) the wire would not go in the hi speed hole. and after pulling the aluminum plug and removing the piece and re assembling the engine has run great ever sense.

Got the idea from a small engine shop and they told me it was not an uncommon thing

Cheers Bob T
AMA13377

LGM Graphix

My Feedback: (22)

Well I frustratingly and disappointingly give up. Engine is going to go back to horizon. It went from running poorly, to not starting to now not even getting a spark. If this was a used engine I'd chalk it up to something screwed up by the previous owner but while I am the second owner it is a new engine.
I cleaned the carb, plug gaps are right, air gap is right, tried bypassing the kill switch, new gas, everything set as per suggestions and manual and it's gone from poor run to weak spark and won't start to no spark at all. Everyone tells me how great these engines are and how reliable but so far I'm pretty let down. When it's new I don't expect to have to spend extra money on it but it's warranty is up based on time already. The fellow I bought it from has offered to split the repair cost with me which I appreciate. Hope the turn around will be quick on it.

Lifer

My Feedback: (1)

Sending it in isn't giving up. I gave upon an engine once...I threw it in a lake.