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Old Aug 30, 2012, 10:28 AM
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Nav_Aids's Avatar
Canada, MB, Winnipeg
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Originally Posted by turk1 View Post
You still ignore that at WOT there is nearly no suction to make atmosphere pressure open the needle from seat to make pump to be able to feed carb.
At glow application, that no suction line fed by pressurized tank,not spray bar suction.So Gravity King s case was as expected.
At Walbro, there is venturi suction to make regulator needle open the fuel pump line to feed the engine at WOT.
turk1, I tried to explain this to you back in post Post 465. So lets try again. All engines that are not diesel injected or All engines that use a carb/throttle body Will Not Have Intake Vacuum At WOT if they do then the carb/throttle body is too small or the person is measuring in the wrong spot, eg. ported vacuum. On all throttled glow engines and all gas engines, they always have more intake vacuum at idle than at WOT. This vacuum is on the engine side of the throttle valve. The position of the throttle plate or barrel valve is has no direct effect on the amount of fuel consumed, it has only a secondary effect. The primary effect of the amount of fuel consumed is by the Amount Of Air Flowing Past The Spraybar or as in a Walbro, the fuel discharge ports, fuel pressure, atmospheric pressure, and the fuel discharge size. The throttle or barrel valve only limits the maximum amount of air going into the engine and limiting RPM, the RPM relates to the amount air going into the engine. You can have WOT and a low RPM but, the engine does not flood because, airflow is low still. Yes on some carbs and on newer barrel valve carbs they modify the size of the fuel discharge outlet. But it is still the amount of air flowing past the fuel discharge hole on a spraybar or fuel discharge outlet ports that creates a vacuum only at the fuel discharge hole on a spraybar or fuel discharge outlet ports that pulls the fuel out of the carb. Fuel pressure can make it easier or harder for the vacuum to pull fuel at the fuel discharge outlet. Since on these but, not all carbs, there is no accelerator pump we have to run the low speed needle a bit rich to make the sudden transition to higher engine speed, which results in a crappy idle. On glow engines we also have a bit of fuel pressure from the exhaust pressure to help. Did you try blowing air across the top of a straw that is in a bottle of water? or try a perfume atomizer bottle? Well this is the basic principles of simple carb operation.

As for atomshereic pessure, it is what is trying to get past the carb and into the engine and the regulator. In the regulator it is on one side of the regulator diaghragm and fuel pressure on the other side of the diaghragm. This is balanced by the metering spring, which can be changed. Walbro has a bunch of different tension springs for the metering and this also changes the pop off pressure. I'm not going to get into this because it has been gone over and over and manuals have been uploaded.

Also, barrel valve throttles have 2 openings. One above the spraybar and one below the spraybar. So when you close the throttle there is no intake vacuum pulling fuel from the spraybar. Only the air going through the barrel valve and going past the spraybar creates a vacuum on the spraybar discharge hole, pulling fuel.

On the other side of things, on my race Holley carb I can change the high and low speed air bleeds, jets, angular boosters, power valve, accelerator (pump discharge nozzles, pumps, cams, pump springs, pump diaphragms,) fuel level, and fuel pressure, so these little carbs are pretty simple.

Ray
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Old Aug 31, 2012, 11:39 AM
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Istanbul, Turkey
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Originally Posted by Nav_Aids View Post
turk1, I tried to explain this to you back in post Post 465. So lets try again. All engines that are not diesel injected or All engines that use a carb/throttle body Will Not Have Intake Vacuum At WOT if they do then the carb/throttle body is too small or the person is measuring in the wrong spot, eg. ported vacuum. On all throttled glow engines and all gas engines, they always have more intake vacuum at idle than at WOT. This vacuum is on the engine side of the throttle valve. The position of the throttle plate or barrel valve is has no direct effect on the amount of fuel consumed, it has only a secondary effect. The primary effect of the amount of fuel consumed is by the Amount Of Air Flowing Past The Spraybar or as in a Walbro, the fuel discharge ports, fuel pressure, atmospheric pressure, and the fuel discharge size. The throttle or barrel valve only limits the maximum amount of air going into the engine and limiting RPM, the RPM relates to the amount air going into the engine. You can have WOT and a low RPM but, the engine does not flood because, airflow is low still. Yes on some carbs and on newer barrel valve carbs they modify the size of the fuel discharge outlet. But it is still the amount of air flowing past the fuel discharge hole on a spraybar or fuel discharge outlet ports that creates a vacuum only at the fuel discharge hole on a spraybar or fuel discharge outlet ports that pulls the fuel out of the carb. Fuel pressure can make it easier or harder for the vacuum to pull fuel at the fuel discharge outlet. Since on these but, not all carbs, there is no accelerator pump we have to run the low speed needle a bit rich to make the sudden transition to higher engine speed, which results in a crappy idle. On glow engines we also have a bit of fuel pressure from the exhaust pressure to help. Did you try blowing air across the top of a straw that is in a bottle of water? or try a perfume atomizer bottle? Well this is the basic principles of simple carb operation.

As for atomshereic pessure, it is what is trying to get past the carb and into the engine and the regulator. In the regulator it is on one side of the regulator diaghragm and fuel pressure on the other side of the diaghragm. This is balanced by the metering spring, which can be changed. Walbro has a bunch of different tension springs for the metering and this also changes the pop off pressure. I'm not going to get into this because it has been gone over and over and manuals have been uploaded.

Also, barrel valve throttles have 2 openings. One above the spraybar and one below the spraybar. So when you close the throttle there is no intake vacuum pulling fuel from the spraybar. Only the air going through the barrel valve and going past the spraybar creates a vacuum on the spraybar discharge hole, pulling fuel.

On the other side of things, on my race Holley carb I can change the high and low speed air bleeds, jets, angular boosters, power valve, accelerator (pump discharge nozzles, pumps, cams, pump springs, pump diaphragms,) fuel level, and fuel pressure, so these little carbs are pretty simple.

Ray
Hi Ray, thanks for answering.Please mind that when I say barrel I mean glow(GT9) barrel.Also I never mention manifold vacuum but fuel discharge mouth/nozzle vacuum.
I dont agree with you as red lines saying position of barrel has secondary effect on fuel consuming.(I mean only glow).On a glow carb that low speed position of barrel is so effective that(creating a big vacuum to suck fuel from spraybar) on most Chinese glow carbs,I have to modify LSN profile because LSN cant restrict enough the spray so engine floods at idling(or low speeds) because of sucking a lot of fuel a.You would say "Oh, then close the LSN more".Cant close it after a certain position because then LSN begin to overrestrict/block the WOT fuel flow and engine stops while accelerating.
This case is greatly same on this GT9 carbs too.
The mostly closed barrel creates so big sucking (at the spray bar mouth)that regulator needle/seat opens freely to allow fuel feed and pumping by pump .Then op. tries to adjust the LSN(closing a good portion) to keep the engine run at idling without drowning.But after that adjustment when opening the barrel for WOT that suction- under barrel (spray bar mouth ) - goes down so quick that regulator needle/seat is barely stay open against spring because of the difference of suction which needs to stay open while LSN still partly restricting the spraybar mouth though WOT position.Then after such an adjustment a GT9 cant be run good at WOT.
This difference (suction) is just reversal on a Walbro.
regulator is very same as Walbro but carb works just opposite of than a Walbro needs too feed fuel.
Please dont mention of manifold vacuum to me because neither glow carb(GT9) nor Walbro carb needs it(or affects anything to work of carb).Walbro needs air flow at venturi and glow(GT9) carb needs a good profile LSN at low speeds and a good tank pressure to feed at WOT.(You may mention that a glow can be adjusted without any exh. pressure in tank but this case needs too much opening of HSN because sur)e, there is a small suction at spray bar mouth due to fast air flow at WOT).This very small suction at spraybar mouth at WOT provides running GT9 engine at WOT but incosistent because regulator needle/seat is barely keeps open against spring.My repeatedly mentioning "reversal functioning" is this.Whatever op.does to have a better work at WOT,he also must work on idling fuel feed to keep more restricted than designed system.
Another offer from me is to use a very short but heavy tapered LSN which will provide a good restriction at idling to prevent drowning and also provide a full open spray bar mouth just after mid open barrel(also will help to have better suction after midranges creating somehow a venturi effect against spraybar mouth).
On a regulatory Walbro carb ,pump almost not help fuel feed but only will provide enough fuel against fuel flow/need from engine regulating by needle/seat(but true for GT9 against LSN+HSN .)
Now I have to leave but I will continue later.
Thanks again.
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Old Aug 31, 2012, 12:27 PM
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Kingston, Canada
Joined Jun 2004
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The way we used to lean out the rich idle on the glow, barrel carbs, was to file a notch in the upper part of the barrel where it closes. This lowers the vacuum at the needle valve drawing less fuel. Don't know if it would work in this case though.

Gord.
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Old Aug 31, 2012, 03:17 PM
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Riverside Calif.
Joined Apr 2008
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Quote:
Originally Posted by turk1 View Post
On a glow carb that low speed position of barrel is so effective that(creating a big vacuum to suck fuel from spraybar) on most Chinese glow carbs,I have to modify LSN profile because LSN cant restrict enough the spray so engine floods at idling(or low speeds) because of sucking a lot of fuel a.You would say "Oh, then close the LSN more".Cant close it after a certain position because then LSN begin to overrestrict/block the WOT fuel flow and engine stops while accelerating. This case is greatly same on this GT9 carbs too.
You're right. When you adjust the LSN needle for a good idle, it does partially block the spray bar.

Quote:
Originally Posted by turk1 View Post
The mostly closed barrel creates so big sucking (at the spray bar mouth)that regulator needle/seat opens freely to allow fuel feed and pumping by pump .Then op. tries to adjust the LSN(closing a good portion) to keep the engine run at idling without drowning.But after that adjustment when opening the barrel for WOT that suction- under barrel (spray bar mouth ) - goes down so quick that regulator needle/seat is barely stay open against spring because of the difference of suction which needs to stay open while LSN still partly restricting the spraybar mouth though WOT position.Then after such an adjustment a GT9 cant be run good at WOT.

This is why a spring from a WYK carb will help.

Quote:
Originally Posted by turk1 View Post
Another offer from me is to use a very short but heavy tapered LSN which will provide a good restriction at idling to prevent drowning and also provide a full open spray bar mouth just after mid open barrel(also will help to have better suction after midranges creating somehow a venturi effect against spraybar mouth).
Or simply cut the LSN shorter, and possibly create a accelerator pump effect
when the needle exits out the nozzle at the right moment.


Bill M.
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Old Sep 01, 2012, 12:40 PM
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Turk1 I apologise, I/we did not understand what you were trying to say before but, I believe I/we understand better now. I don’t have a NGH carb to look at but, on new glow or barrel valve carbs for RC they have the LS needle or a tube move in and out of the main discharge/spraybar discharge when the throttle is turned. This provides an extra way of controlling the idle mixture and the transition from low speed to mid-range speed. After @ half throttle the LS needle or tube is clear of the main discharge and the HSN now controls the fuel flow. I prefer using a butterfly valve and port discharges for fuel control, just like most Walbro’s. Like I said before in this thread, “they do things like they do just because that’s the way we’ve always done it”. I’m beginning to think that this engine is a total dud; there are so many little things they could have done to make it right the first time; but they didn’t and it’s just because they wanted to get it out the door as fast as possible because nobody had anything marketable below 15cc’s. To copy something is one thing but, to make it work is another and NGH failed. It is definitely not a plug-n-play engine and who wants to spend $150.00 to make a $169.00 engine work, I can get a better gas engine for $229.00 or less.

I think flypaper 2, has a great idea to solve the problem you are talking about. Also I think a Webra Dyna-Mix carb would be perfect for this engine. I love my Webras.

Ray
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Old Sep 02, 2012, 01:10 AM
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Hi,Im glad I could be more clear on that subject.Flypaper, yes yours is another way to compansate the problem partly(like my offers) but not on root cause.Root cause is GT9 carb has much less suction at WOT than lower throttle ranges.Regulator simply reacts accordingly and result is obvious.
Bill,I simply cut the LSN to change the taper profile at mentioning glow carbs above but not a perfect solution.(Because low taper).Better should be a sharp tapering.
Another suggestion from me;to remove completely regulator needle,making pump works directly against carb needles.And modifying carb needles accordingly.(No need any mod. for HSN but a radical taper change on LSN).Also maybe Flypaper s additional notch too.

Ray I dont think Michael has such a mind but I think they decide all is OK after ground tests but not by flight.On ground, engine seems running not bad but on a plane, system lacks.
I still wonder if exhaust pressurized tank system will work better or not.Michael said that doesnt work on gasoline.Anybody test it though?Engine has standart 46/55 glow type exhaust bolt spacing.
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Old Sep 02, 2012, 09:45 AM
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Turk, why aren't you testing your ideas?
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Old Sep 02, 2012, 02:18 PM
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Originally Posted by turk1 View Post
Bill,I simply cut the LSN to change the taper profile at mentioning glow carbs above but not a perfect solution.(Because low taper).Better should be a sharp tapering.
With the 30psi pop-off spring, needle changes are not necessary.


Quote:
Originally Posted by turk1 View Post
Another suggestion from me;to remove completely regulator needle,making pump works directly against carb needles.And modifying carb needles accordingly.(No need any mod. for HSN but a radical taper change on LSN).Also maybe Flypaper s additional notch too.
The original carb had a fuel pump incorporated into the carb. And many people have tried exhaust, and other ways to supply fuel to
the carb without success.

Quote:
Originally Posted by turk1 View Post
I still wonder if exhaust pressurized tank system will work better or not.Michael said that doesnt work on gasoline.Anybody test it though?Engine has standart 46/55 glow type exhaust bolt spacing.

The NGH fuel pump puts out 7 psi to the needle and seat, at wot, with the small fittings.


Greg, on post #533, you were right. It is only a slight negative pressure difference.



Bill M.
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Old Sep 02, 2012, 09:13 PM
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Well my flight tests went pretty well today. Using a NGH 9cc engine on my Great Planes Escapade turned out really well. I used a stock carb and stock pump/regulator and the only modification was to use 8x32 fittings and 1/8 inch tubing to connect the engine crankcase to the pump. The maiden flight turned out well even though I had to dead stick the plane in. The fuel tubing inside the fuel tank is a little stiff still, until it softens some from the gasoline and it sucked some air when I did a couple of loops. Hopefully that will clear up soon. I'll post a video shortly, it takes seemingly forever to convert and upload a video to Youtube. But anyway the engine was running really well. I flew the plane five times today, and it got better and better. The last two flights were without a tailwheel as it came off on the third flight. The plane just was a little crummy at taxing around like that. When I get the video posted you'll be able to glimpse how well the engine performed then. When I figure out something for the tail wheel, I'll have it out tomorrow too. It flew really well today.

Getting all the stuff into the Escapade model was a challenge. I wound up putting the CDI module under the engine, as there wasn't any other place to put it that I could find. Of course the fuel pump/regulator is always a challenge to place it someplace near the carb.

I also flew the Ugly Stick plane with the NGH 9cc engine sporting a Walbro carb, and it ran well too. I made five more flights with it too. It has been working out really well even though it doesn't look all that good with a carb almost as big as the engine.







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Old Sep 03, 2012, 01:42 AM
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Istanbul, Turkey
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Originally Posted by gkamysz View Post
Turk, why aren't you testing your ideas?
Good question,I was waiting for it.
I m not into gas at all.So I dont have necessary accessory/equipment /fuel for it.All I am involving gas with friends engines only because asking help from me.
Those 2 GT 9 were not for me but friends also.But after failure they drop down them to me.I was only testing on bench.
Also I dont think to mount any plane because;
I dont want to spend money for equipment/fuel only to engine test ,
My field have some disadvantages that any deadstick means a lost plane.
But maybe I can have tests on bench again if I feel energetic myself for it.
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Old Sep 03, 2012, 01:50 AM
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Good work Earl.Cudos.
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Old Sep 03, 2012, 07:10 AM
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Australia, WA, Noranda
Joined Mar 2007
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Super Sportster 40

Well I squeezed mine in to. I am pretty happy with the way it looks.
Had to make a muffler extention and a few right angle nipples

Pitty I cant get it to run
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Old Sep 03, 2012, 07:42 AM
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Thanks guys,

Here is a video clip of the maiden flight of my Escapade .40 plane with the NGH 9cc gas engine installed on it. I think I figured out the problem with the engine stalling out in the loops, in that the fuel pump/regulator moved down from the Gee forces causing the engine to lean out a little too much. I'll fix that and flight test it some more today. The carb needle is sensitive to the fuel pump/regulator changing position too much, a little movement is OK, but not a whole lot.

I thought my camera was recording but it wasn't. So I only got this one video made from yesterday. The flights after the first one were much better. The grass is lush and thick, so it winds up going longer on the take off roll to get it out of the grass to fly. I also tend to go for longer take off roles versus the force it off the ground approach too.
Great Planes Escapade with 9cc NGH engine Maiden Flight (5 min 11 sec)
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Old Sep 03, 2012, 07:59 AM
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Originally Posted by GadgetEric View Post
Well I squeezed mine in to. I am pretty happy with the way it looks.
Had to make a muffler extention and a few right angle nipples

Pitty I cant get it to run
Please tell us what your engine was doing. Your plane setup looks pretty good with everything all put back to keep it all clean and sanitary like that.

I have found that the fuel pump/regulator outlet ought to be as close to the carb fuel inlet as is possible, it seems to work best for me like that. The Cline Regulator instructions is where I got that idea from. The Cline regulator is basically the fuel pressure regulator from a Walbro carb. Also the fuel pump/regulator is sensitive to engine vibration, so you can't just bolt it to anything directly either. It needs to have some vibration isolation. When the temperatures are around 100 degrees F or more the gasoline tends to start to vaporize inside the pump/regulator resulting in bubbles going to the carb. Also the vibration sensitivity results in bubbles too, if the unit is mounted solidly without some vibration isolation. Then the stock OEM small single barb fittings have too small of a hole in them to allow for good pressure pulses to operate the fuel pump diaphragm, which results in poor engine running conditions. If I let the engine run the fuel out of the pump/regulator, then I need to work the engine and plane for a while to get the air bubbles out of the pockets inside the unit. Once done it stays like that OK, but it can be a hassle at first. I need to move the plane and engine around to get any lingering air bubbles caught inside out before I try flying it.

Michael Chow stated a while back in the thread that the low speed needle should be set to about 6 turns out and the high speed to about 1 and a half turns out for initial running. That turned out to be pretty close, and I haven't touched the LSN, and I only needed to tweak the high speed needle some. The carb does spit fuel making it appear to be too rich, but that seems to be normal for the carb design. Also idle speed is about 1/2 open on the throttle, the throttle doesn't close up like we normally expect.
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Old Sep 03, 2012, 09:01 AM
A few Models is not enough Hon
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Australia, WA, Noranda
Joined Mar 2007
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Super Sportster 40

Thanks Earl

To start with I had the bubbles in the fuel and overfueling - Found a bit of crud under the needle in the pump and that seemed to solve the bubbles but then it wouldnt pump fuel. I tried playing with the tension on the needle by bending the little bracket that holds it in and then by cutting the spring but that just got it flooding again. I have ordered a new pump to start again and have bought the larger nipples localy to do your mod when the pump arrives.
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