Experimenting with the GT15HZ600

[brw0513]

Originally Posted by Doug Darby

Personally I have never tried the plug chop mainly because this video and process was designed for 4 stroke car engines.
.
.
I just think the oil in our fuel will give a totally different read. But maybe I'm off base here. Just my $0.02 worth.

I'm not convinced yet that this particular process would suit anything other than a 4 stroke engine either. But when I went to see Mick Doohan and Kevin Schwantz fang around Eastern Creek Raceway on their 500GP bikes in Sydney in the early 1990s I recall seeing all the 125GP pilots doing plug chops on the main straight.

Originally Posted by Doug Darby

Are you running the HZ carb too?

I've just put the 90 size crank with the UNF 5/16-24 thread into the 600 engine so still using the OS Part #28181020 61HA carby.

[banshee rider]

Originally Posted by brw0513

I'm not convinced yet that this particular process would suit anything other than a 4 stroke engine either. But when I went to see Mick Doohan and Kevin Schwantz fang around Eastern Creek Raceway on their 500GP bikes in Sydney in the early 1990s I recall seeing all the 125GP pilots doing plug chops on the main straight.



I've just put the 90 size crank with the UNF 5/16-24 thread into the 600 engine so still using the OS Part #28181020 61HA carby.

Wow that's a name I haven't heard in a while
Checkers or Wrecker- Do or Die AKA Kevin Schwantz

[brw0513]

I've been doing more testing with the GT15HZ600.

I could never understand why the engine wouldn't reach peak revs at WOT. But I may have found the answer.

It seems the factory setting for the mixture control valve was out by half a turn i.e. needed to be screwed in another 1/2 turn. The factory position meant that at WOT, the very end of the tapered needle within the carburettor rotor was essentially fully withdrawn from the control valve. There was no metering of fuel at WOT so the engine was over the top rich. The photo below shows what I found.

One thing that is a bit of a worry is that the rotor needle looks a little worn and now it will be riding on a different spot in the mixture control valve. More testing soon to confirm findings.

I've also tried a few other things:

1. I replaced the GT15HZ600 head with a GGT15 head and G5 glow plug. The engine ran so well I couldn't tell the difference. Unfortunately I forgot to fully tighten the plug and it backed out. Perhaps this burnt the element so it's no worky now.

2. With a brand new NGK CM6 plug I did a plug chop, not from WOT, but from the point of maximum revs. The eyebrows in the picture are where I accidently touched the porcelain with the hacksaw blade. After this I chucked it up in a lathe and turned the threaded portion of the body off. The dark brown ring is probably burnt oil. There is a lighter coloured incomplete ring just above (maybe not complete because it was shadowed by the earth strap?). To me the appearance looks a little lean. This suggests to me that a plug chop is a valid technique to determine fuel mix with this engine.

[Doug Darby]

If you close the rotary barrel of the carb. And then screw the mixture control needle all the way closed, how many turns do you get?
In 65 deg ambient my engine seems to work fine at 1-1/4 to 1-1/8 turns open from closed. How does that compare to the setting you believe is best?
As for the needle being outside of the barrel and providing no metering of fuel, I always assumed that at WOT the high speed circuit was controlling all the fuel flow so the needle should be withdrawn? Again my engine is working well at 2-3/8 to 2-5/8 turns open on the HS or main mixture knob.
Anxious to hear what settings you are using.

[brw0513]

Hi Doug.

I think we might have a difference in terminology (carb exploded view attached for ease of reference).

I'll have to do some more testing to confirm my idea.

When you say:

"If you close the rotary barrel of the carb. And then screw the mixture control needle all the way closed, how many turns do you get? Do you mean:

"Close the Carburettor Rotor fully, then wind in the Mixture Control Valve Assembly"? If so, then I've not got that information yet.

My HS needle position to give max speed with the 12x6 prop (14,050rpm) was 2 1/2 out from bottom + 1 click leaner. What I need to prove by testing is how this 14,050rpm top speed will move versus Carb Barrel opening for a different position of the Mixture Control Valve Assembly. If my theory is correct, the max RPM i.e. power will be the same, but I should be able to achieve it at WOT. If not then the engine will bog if ever throttle curves or governor action tries to drive the throttle barrel past my current barrel opening that results in the 14,050rpm speed.

I might have misunderstood your description, but I can't see how the metering needle i.e. the tapered needle (which has a "very slight working taper" and "much more abrupt "finishing point") fitted inside the Carburettor Rotor would be intended to become completely withdrawn from the bore of the Mixture Control Valve Assembly. That final "finishing point" taper is just too severe for the small quantity of fuel this engine sips.

The GT15 plank engine manual is starting to make sense to me now - as is the GT15HZ600 itself. That GT15 manual talks about run-in while rich without touching the Mixture Control Valve Assembly, then go back to the Mixture Control Valve Assembly, then go back to the HS needle in an iterative manner. It also says the HS position needs to be established from the lean side, as opposed to the rich side for nitro engines. I've seen how the HS needle position could be different, admittedly only by a flew clicks, by approaching max rpm from the lean vs the rich side.

In saying the above, I've just fitted a 12x4 prop in an attempt to get a WOT speed of around 15,000rpm. My plan is to run the engine in a heli frame at 14,500rpm.

It sure would be something to spend some time in the OS testing department.

[rbort]

The idle mixture screw is just for idle mixture and transition to part throttle. Once you get past 1/2 throttle and traverse towards WOT, the high needle is metering all the fuel and its not unusual for the idle needle to come out of the barrel. This is usually SOP in alot of the nitro motor carbs.

You need to adjust the low needle so that the engine will idle reliably forever not just for a few seconds after closing the throttle, and after waiting at least 30 seconds up to a minute, advancing the throttle gives as positive as an advance without hickup. When you close the throttle suddenly, it should slightly race for a few seconds, and then slow down to a stable idle meaning it richened up. Then you're about right on this needle.

You adjust the high needle for max rpms at WOT. You keep closing it until the engine reaches peak. Closing it more nothing happens and closing it more the engine will sag. Then you open it back up to as far open as possible with the peak rpms, in other words you're closing it so the engine "just" breaks into peak rpms.

Hope that helps.

-=>Raja.

[Sowa]

Raja and Doug are correct here the LSN or mixture control needle primarily has effect to about 50% throttle. Basically everything from idle to a hover is covered by the LSN.

You should be resetting the LSN (finding zero) with the throttle fully closed. You can damage the carb by doing otherwise.

Originally Posted by rbort

When you close the throttle suddenly, it should slightly race for a few seconds, and then slow down to a stable idle meaning it richened up. Then you're about right on this needle.

That sounds like a motor that's hanging on the pipe?

[rbort]

Otherwise the low needle will be too rich and the engine will eventually slow down too much and quit at idle. I'm talking airplane with a propeller here, which is what he's talking about, putting a 12x4 prop on it and running it to set the needles.

When the throttle is chopped to idle, if it stays fast then its too lean, if you accelerate it will just gasp and die. If it goes to idle right away and slows further as time goes by, then its too rich. If its too rich, it will stumble when you accelerate or won't idle too long and eventually quit if you let it be. If you find yourself having to throttle back up and down because its going to quit, then you're too rich. You want it to stay faster idle for a few seconds (within 5) and get into a solid slow idle that lasts forever, in other words even 2 minutes+ later (or the whole tank) its still running the same and not threatening to quit or quit already.

Ok, I'm getting out to the field now, forum break time!

-=>Raja.

[Doug Darby]

brw0513...
You have translated my poor description into Australian very well. That seems to be exactly what I was asking.

If you don't lightly close the the rotary barrel when you screw the needle in, there is a chance it will slowly open the barrel and the next thing you know, the screw goes all the way in and falls into the carb. Ask me How I know!!!! lol

Raja are you running the OS in an airplane??

[carey shurley]

Its almost ready!

[brw0513]

I was hoping to have done some more testing by this stage, but got some unexpected health news recently.

So I've had time to think about this subject and the feedback offered here. But no time to tinker. Anyway, I might have also made a friend at OS in Japan over this particular topic. No feedback yet, but I might get a meaningful reply when my contact comes back from leave. Here's hoping anyway.

I'm thinking now that, during flight, the needle within the carb rotor is not meant to come so far out of the mixture control valve that it exposes that extreme taper at the end. Said another way, I think it is possible that the intended engine speed, and hence rotor speed, should be reached before WOT.

I'd be very interested to know from those who are using this engine successfully, if their "used portion" of throttle curves or governor intervention ever drives the carb to WOT during actual flight. I'm thinking your rotor never quite reaches WOT in an application where the engine is working well for you.

Pure speculation here, but I think the 61HA carb fitted to GT15HZ600 is designed by OS to deliberately go very rich at WOT and give the engine the chance to bog without risk of damage.

Originally Posted by Doug Darby

If you close the rotary barrel of the carb. And then screw the mixture control needle all the way closed, how many turns do you get?
In 65 deg ambient my engine seems to work fine at 1-1/4 to 1-1/8 turns open from closed. How does that compare to the setting you believe is best?
.
.
.

I've now done a few experiments with the carb under a magnifying glass to try to answer this question.

The GT15 (very similar carb to the GT15HZ600) manual Page 2 Section 3 includes a procedure to check the mixture control valve manual position. Using that procedure it seems 1-1/4 turns in from full out is close. The manual hints the mixture control valve should not need to be moved more than 1/4 turn from this position.

The procedure in the GT15 manual requires a certain feel to identify when the rotor needle "grabs" the mixture valve. I found there to be an easy way to get close to the point of this "grab" feeling. This idea may have been described by someone else here on HF. With the carb rotor at WOT, gently wind in the mixture valve and carefully watch the rotor for the first hint of movement. By the time the rotor moves, the rotor needle is already within the mixture valve - i.e. too far in by around 1/8 turn. This gives a good starting point to wind the mixture valve out to find when that "grab" feeling disappears. Backing out another 1/4 turn per the manual and the mixture valve ended up just over 1 turn in from all the way out.

[Doug Darby]

I'm curious how do you determine, decide, or measure "all the way out" ?
Aka when the needle completely unscrews from the carb boss? Like the needle falls out in your hand?

[brw0513]

Originally Posted by Doug Darby

I'm curious how do you determine, decide, or measure "all the way out" ?
Aka when the needle completely unscrews from the carb boss? Like the needle falls out in your hand?

By "all the way out" I meant turning the mixture control valve slotted screw head anti-clockwise until it binds in the aluminium casting. In hindsight a dumb description given that the valve would fall out if it was screwed clockwise far enough with the carb rotor removed.

I've been doing some more bench running but haven't really learned anything worth sharing for now.

I thought I had nipped the engine up after running at 15,1000rpm WOT for around 3 mins (to do a plug chop). It slowed then wouldn't rev, but would idle nicely, after letting it cool down for 10 mins. But taking the head and muffler off revealed no damage The CDI unit was next on the culprit list, but alas it was working fine a day later. The CDI battery was recharged and the spark was replaced. Maybe the battery just got too flat - 2 cell LiFe???

Can anyone provide a recommendation for a governor for the GT15HZ600?

[Doug Darby]

I simply run the nitro governor in the NEO it works well. I don't see why any gov that works with any gas engine won't do nicely. Personally I am not a fan of stand alone governors. I like the simplicity of the FBL with gov unit.

[brw0513]

I've done some further testing over the last week or so and have the GT15HZ600 running sweetly now. I just need a 570G kit to put it in

In summary:

* The engine is a GT15HZ600 fitted with a GT15HZ crank.

* Hatori 3D pipe.

* Coleman fuel at 25:1 with Deluxe Materials Power Model 2T-S oil. Around 7 litres of fuel consumed to date.

* Running on a test bench with a 12x4 prop at 15,300rpm WOT. Max stable temp seems to be around 135 deg C measured by TTO spark plug temperature sensor (with the benefit of the 12x4 prop for cooling duties). It did get hotter at leaner settings during experimentation.

* Will idle well in the 3200 - 3500rpm range (10 min periods tested) when warmed up. Idle temp is 68 deg C.

* Transitions well from idle to WOT.

* Final Mixture Valve setting is 90 deg leaner than the factory set position (more discussion below).

* Final Needle Valve position is 2.5 turns out from closed then 2 clicks leaner.

From the beginning my target was get to the engine running very well on a test stand with a prop that would let the engine rev to around 15,500rpm. The intention is the use this engine in an airframe at 14,5000rpm governed.

Lessons learned (for my engine, based on my test results) :

1. My carb setting (combination of Mixture Valve and Needle Valve) was very rich from the factory at WOT. Perhaps OS do this deliberately.

2. The running in and carby setting instruction provided in the GT15 manual is very good and was very helpful. It suggests running in, in a rich state (3 to 3.5 turns out on the Needle Valve was good), then explore the Mixture Valve setting at idle, then go back the Needle Valve position. This is an iterative process and probably common knowledge to many. But not to me, at least initially.

3. The Rotor Needle includes a very steep taper on its tip. One of the photos bellow shows the relative position of this Rotor Needle tip at WOT almost entirely out of the bore of the Mixture Control Valve. This photo is only included for reference - I doubt the engine would run at WOT with this relative relationship. There is another photo below that shows how my carby was delivered with the engine BNIB. The steep taper on the Rotor Needle is reasonably well exposed. In this position, the engine only ran at around 4,800rpm at WOT (with the Mixture Valve also at its factory position) and was slobberingly rich. I'm convinced now that this steep taper is not meant to be exposed outside of the Mixture Valve if you intend to use your engine at up to WOT. The engine WILL run, and possibly very well, with a "removed" Rotor Needle relative position but not beyond a rotor/mix valve position that starts to expose the steep taper. I actually think the only purpose of the end steep taper is to ensure alignment of the Rotor Needle with the bore of the Mixture Valve.

Based on learnings and the GT15HZ manual, my future GT15HZ600 run-in process would be:

A. From BNIB, take the carby off. Have a look under a good magnifying glass to verify, at WOT, that the Rotor Needle is ¼ exposed from the bore of the Mixture Valve. This will ensure rich running at WOT.

B. Fit a 12x6 prop using an adaptor if required. This will help keep the revs down for the moment.

C. Burn around 2 litres of fuel at WOT.

D. Per one of the photos below, use a brass rod filed to a flat head so the Mixture Valve can be turned while the engine is running and warmed up to at least 70 deg C. Note the guide used to help position the brass rod! This is not in accordance with the GT15 manual, but I presume OS makes a different call so dumbos don’t lose a finger.

E. Turn the Mixture Valve open by 60 degress to ensure it's on the rich side. If the engine quits, then 60 degrees is obviously too much so try a smaller value in 15 degree steps. Set the idle speed, via servo position to get an idle around 3,500rpm.

F. Turn the Mixture Valve in slowly to see the revs rise, then fall. Wind out again and repeat 6 times. Identify the point where the revs are at their peak. This is not the best position for the Mixture Valve - it will be too lean here. The Mixture Valve optimum position is richer than this by up to 90 degrees but don't move it yet.

G. At WOT, the engine will still be rich. Go to WOT and wind in the Needle Valve slowly but continuously. Use a bent piece of wire fitted to the end of the Needle Valve to help with this process. The revs will rise very sharply at a certain point. Continue to lean the Needle Valve and the revs will slowly tail off. Once you are sure the revs are dropping off (may be up to ¾ turn past the point where the revs leapt high) then start to richen the Needle Valve very slowly but continuously. The revs will start to rise. 90 degrees richer from the point of maximum revs is about the optimum place for the HS needle. You are aiming for good sharp running at the richest position possible. Do this process a few times to make sure you understand the engine's behaviour.

H. Measure head temperatures while doing the Needle Valve adjustments. Don't let the engine get hotter than around 145 deg C. If it appears it's going to exceed this then let it idle for a few minutes before shutting down. Wait until you can touch the head before starting again.

I. Let the engine warm up then go back to idle. The Mixture Valve is still a bit lean at this point so richen it up by 1/4 turn. Try to set the idle to 3,500 rpm. If it won't idle there then it is probably slightly too rich now - if so make a small leaning adjustment. With the engine reliably idling at 3,500rpm (readjust servo position to achieve this), snap open the Rotor and listen for the response. The engine should sound a bit doughy because it should be rich on the bottom end at this point. Lean the Mixture Valve by 1/16 turn then snap the throttle open again. It will start to respond better and better and start to sound strong and more willing to rev. You are aiming for a good snappy transition at the richest Mixture Valve position possible.

J. Once the engine has become snappy (don't go leaner past the point in Step F above), then re-adjust the idle speed to 3,500rpm. Repeat Step I above.

K. Now go back to WOT and repeat Step G.

L. Go back and repeat Step I.

M. The engine should stably idle for 10mins, settle at a head temp around 69 deg C.
If the WOT engine speed is not around 750rpm or so above your intended operating speed in the heli, then fit a smaller prop and repeat from Step D above.

The above might sound complicated but it’s not really.

I am now confident my GT15HZ600 is ready to fit into a donor airframe. For me and my ability, I think the test stand and prop running-in method is the only way to go.