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Old Sep 25, 2012, 01:49 PM
MY DREAM: FLYING
jimmymugurel's Avatar
LUGOJ Romania
Joined Dec 2006
732 Posts
Carburetor problems

Hi,
I had a lot of problems with the original carburetor. Also the pump. Finally I installed a Walbro carburetor. Now the engine runs very well, although it does not look the same.
Until winter comes, I hope to try it and a model airplane in flight.
Mechanical engine is very good, I very much run at very high temperatures without any problems. The problems seem to not like all carburetors.

Regards
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Old Sep 25, 2012, 10:10 PM
no no no, a music gig
Chophop's Avatar
Pleasant Valley Modelport
Joined Sep 2006
8,605 Posts
Have any of you used an exhaust gas temperature probe to set these up ? Usually on larger ultralight engines we see 1000 to 1200* F. It gives a good indication of mixture. Any higher means melting and blow-away of metal in the flame path.
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Old Sep 26, 2012, 12:28 AM
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Istanbul, Turkey
Joined Aug 2004
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Quote:
Originally Posted by Gary Cee View Post
It seems at some point there was an indication that delivery was an issue . Maybe Greg sees it differently ?
Hi Gary, the issue is delivery volume is reversal against the RPM rate/acceleration.If anybody can deliver a constant-enough for WOT- volume/pressure fuel to carb, carb design is great to have a good adjustment.The problem is to deliver the fuel without making carb to confuse.An electrical,constant delivery pump is ideal for this carb.(Maybe LSN will be needed to retapering because I saw this problem on much Chinese glow type carb)
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Old Sep 26, 2012, 04:21 AM
Glow is Great !
Gary Cee's Avatar
United States, MI, Marysville
Joined Apr 2010
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Quote:
Originally Posted by turk1 View Post
Hi Gary, the issue is delivery volume is reversal against the RPM rate/acceleration.If anybody can deliver a constant-enough for WOT- volume/pressure fuel to carb, carb design is great to have a good adjustment.The problem is to deliver the fuel without making carb to confuse.An electrical,constant delivery pump is ideal for this carb.(Maybe LSN will be needed to retapering because I saw this problem on much Chinese glow type carb)
That is pretty much the same as I took it . The issue with the too small signal hole in the pressure fitting seemed to reinforce that element .
The best thing at this point is to try it rather than discount and walk away .
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Old Sep 26, 2012, 11:51 AM
UAS Pilot/Tech Instructor
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United States, CA, San Diego
Joined Apr 2000
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Quote:
Originally Posted by turk1 View Post
Hi Gary, the issue is delivery volume is reversal against the RPM rate/acceleration.If anybody can deliver a constant-enough for WOT- volume/pressure fuel to carb, carb design is great to have a good adjustment.The problem is to deliver the fuel without making carb to confuse.An electrical,constant delivery pump is ideal for this carb.(Maybe LSN will be needed t
ao retapering because I saw this problem on much Chinese glow type carb)
Soooo...... a calibrated fuel delivery system?

OH wait, Greg already said that.

An "electrical, constant delivery pump"........? Are you freakin kidding me? For this engine? When was the last "electrical, constant delivery pump" seen on any production "Model Airplane" engine? If your gonna do that then hey.... why not fuel injection, watercooling, and twin turbos?

How 'bout back to reality. The problem is the carb is a complete pile of doo. The front plate covers a chamber that does NOTHING! I don't know how Michael Chow got this carb but it looks suspiciously like the carb for the Magnum .52 gasser project that Magnum has apperantly shelved. Chow didn't even change the parts breakdown drawing to take out the parts he left out. He then raped part of Walbros design and called it good.

Granted, "calibrated" is a pretty broad term but fuel delivery is NOT the issue. It gets fuel to the carb just fine. Tweek the pump if necessary but what is needed is a carb that works TOGETHER with the pump in a "calibrated" system instead of two pieces hodge-poged together and called good. I think this is what Greg is refering to and understand why he is so frustrated that some people on here cannot grasp that concept.

Mike
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Old Sep 26, 2012, 03:11 PM
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Istanbul, Turkey
Joined Aug 2004
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Quote:
Originally Posted by CryHavoc View Post
Soooo...... a calibrated fuel delivery system?

OH wait, Greg already said that.

An "electrical, constant delivery pump"........? Are you freakin kidding me? For this engine? When was the last "electrical, constant delivery pump" seen on any production "Model Airplane" engine? If your gonna do that then hey.... why not fuel injection, watercooling, and twin turbos?

How 'bout back to reality. The problem is the carb is a complete pile of doo. The front plate covers a chamber that does NOTHING! I don't know how Michael Chow got this carb but it looks suspiciously like the carb for the Magnum .52 gasser project that Magnum has apperantly shelved. Chow didn't even change the parts breakdown drawing to take out the parts he left out. He then raped part of Walbros design and called it good.

Granted, "calibrated" is a pretty broad term but fuel delivery is NOT the issue. It gets fuel to the carb just fine. Tweek the pump if necessary but what is needed is a carb that works TOGETHER with the pump in a "calibrated" system instead of two pieces hodge-poged together and called good. I think this is what Greg is refering to and understand why he is so frustrated that some people on here cannot grasp that concept.

Mike
Hi Mike,
Carb has no flaw but designed like glow type.You should think again the main difference between a Walbro type venturi system suck and glow type carb suction.So, calibrated pump cannot work properly with glow type carb.
If one can supply proper fuel to carb than that carb will work flawlessly.
But unfortunately that "calibrated pump" can not deliver fuel to carb like you said.Because there is a f...g spring /needle assembly which waiting for demand(sucking) from carb side to work.Pls. think again how a glow carb creates suction under RPM spectrum.
Haa, "electrical delivery pump" was not my imagine but SBP said in #895.
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Old Sep 30, 2012, 03:06 PM
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Joined Sep 2012
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GT-9 experience, carb surface

Hi,

I just want to add my experiences regarding the carb problem. I am running the GT-9 in a Phoenix Decathlon. At first I had the pump installed about 1" lower than the carb. Suction was high enough to allow the engine run at throttle full open, but I was wondering that the pump does not deliver much fuel when turning the engine by hand. Idle speed was quite high and when the engine was running at idle speed for a few seconds it died even when the throttle was opened carefully.
I changed the position of the pump and turned the carb 180 so that the conneting hose is now less than 2" long. But the abovementioned problem still existed.
While flipping through these pages I read about the various hints, especially the expected perforation of the diaphragma, the use of walbro parts, the bore of the vacuum connector in the crankcase and remaining particles from manufacturing.
I found out that there WERE particles in the chamber where the little rocker arm controls the fuel flow, but removing those particles did not solve the problem.
But I also found out, that the surface of the pump side (that is where the pump diaphragma rests on) has only been treated by a lathe. The surface still shows significant grooves from turning, you can feel them with your fingernail.
It is impossible to achieve tight valves (and this is one task of the diaphragma) as long as there are grooves in the surface. You can slightly improve the functionality of the pump by using different materials or increasing the actuation using higher air flow but this does not remove the reason.
I smoothed the surface through grinding and polishing and now the pump produces proper fuel pressure even at idle speed.
The engine starts right away at idle throttle with low revs like a proper chainsaw. You can open the throttle to full with immediate response without any indications of running it lean. I already had some nice flights

Regards
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Old Oct 02, 2012, 04:43 AM
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brace's Avatar
Australia, NSW, Ashby
Joined Jul 2011
219 Posts
C_Groth, Had a look at my pump and noticed the grooves as well, quickly removed them to a nice shine with a good stone and then rebuild the unit with a B1WK20WAT kit that fit just fine. the pump works well now and the motor starts straight away. Still having tuning issues so could you pass on what needle settings you have and how you achieved this. Most grateful for your help. Oh yes I also put the larger nipple on the crankcase and used viton tubing to run to the pump, it has less flex than the tygon.
Glenn
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Old Oct 03, 2012, 04:34 PM
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brace's Avatar
Australia, NSW, Ashby
Joined Jul 2011
219 Posts
Tricky little motor to tune but I think I have it sorted and will be able to fit into the plane soon. Idle is about 2300 and WOT is looking around the 10500, seems to transition fine and now with the new gasket kit in there are no air bubbles in the fuel line with a lot better pumping pressure.
Will still change the metering lever spring when it arrives and with that I may be able to drop the idle rpm a bit more. Running 20:1 fuel oil mix. Have
to keep reminding myself that this motor is still only running in so hopefully it will just get even better. Oh yes running a APC 10.5 x 6 prop.

Glenn
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Old Oct 03, 2012, 07:08 PM
A few Models is not enough Hon
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Australia, WA, Noranda
Joined Mar 2007
173 Posts
Quote:
Originally Posted by brace View Post
Tricky little motor to tune but I think I have it sorted and will be able to fit into the plane soon. Idle is about 2300 and WOT is looking around the 10500, seems to transition fine and now with the new gasket kit in there are no air bubbles in the fuel line with a lot better pumping pressure.
Will still change the metering lever spring when it arrives and with that I may be able to drop the idle rpm a bit more. Running 20:1 fuel oil mix. Have
to keep reminding myself that this motor is still only running in so hopefully it will just get even better. Oh yes running a APC 10.5 x 6 prop.

Glenn
Can you tell me how many turns out you are running the high and low mixture screws
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Old Oct 03, 2012, 07:29 PM
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brace's Avatar
Australia, NSW, Ashby
Joined Jul 2011
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LSN a touch more than 2 1/2
HSN just under 1

Engine is still hunting a bit I think due to the excess fuel spitting out of the carb, It seems to suck in more fuel that is spitting and pooling about the carb. No way to stop the fuel spitting out unless a velocity stack fitted may work?
Will still fit the new spring when it arrives and see if I can improve on the control. At present if I fitted it into a model I would fly it now.
However I am off to work tomorrow for another four weeks so will have to wait for my return. Happy that is running a lot better though.

Glenn
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Old Oct 05, 2012, 03:19 PM
SBP
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United States, PA, Waynesboro
Joined Aug 2011
97 Posts
My slightly used GT9 arrived today so it's time to work on getting it to run properly. With all the info in this thread, I believe my chances are pretty good.We've been flying electrics for a year and a half and this will be our first gasser. I'm unsure of exactly what plane we should look for, something stable and easy to fly as the grandchildren will want to fly it too. I'm thinking maybe a .40 piper pawnee with the 80 in wing span. Suggestions and opinions would be welcome. Thanks
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Old Oct 05, 2012, 09:40 PM
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brace's Avatar
Australia, NSW, Ashby
Joined Jul 2011
219 Posts
I picked this up the other day, looks like it will work well for the NGH 9
http://www.hobbyking.com/hobbyking/s...40mm_ARF_.html
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Old Oct 06, 2012, 04:23 AM
A few Models is not enough Hon
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Australia, WA, Noranda
Joined Mar 2007
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Quote:
Originally Posted by brace View Post
LSN a touch more than 2 1/2
HSN just under 1

Engine is still hunting a bit I think due to the excess fuel spitting out of the carb, It seems to suck in more fuel that is spitting and pooling about the carb. No way to stop the fuel spitting out unless a velocity stack fitted may work?
Will still fit the new spring when it arrives and see if I can improve on the control. At present if I fitted it into a model I would fly it now.
However I am off to work tomorrow for another four weeks so will have to wait for my return. Happy that is running a lot better though.

Glenn
Interesting. I set my needles up like this but could get very little fuel through the pump. I pulled the pump off and disasembled it to see if I could spot anything wrong but not anything I could see. I had the motor mounted on a test stand. While I was playing about with the pump my friend hooked the line from the back plate or crankcase to the tank vent and tank outlet dirrect to the needlevalve without a pump and it sucked the fuel up and ran quite well. This is the first time that this engine has ran for more than a second before it ran out of fuel.

I disconected the Crankcase to fueltank vent line and it ran but would not idle verry well. I then used a full metre of fuel tubing from the crankcase to the fueltank vent and half filled it with fuel so there was a big bubble of fuel in it. When I started the motor all the fuel in this line was pushed into the tank as you would expect a pressure feed from a muffler.

My conclussion is that this motor does not have much if any pulse from the crankcase to work the pump.

I have run 2 litres of fuel through my pumpless engine and it is comming up OK but the needles are very sensitive and its easy to over do the adjustments but the top end is good but I am still not happy with the bottom end.

This engine is modified with the 4mm fitting in the crankcase. I am thinking of trying to restrict the size/flow to see if it helps the idle but havent deceided how yet.
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Old Oct 06, 2012, 05:28 AM
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brace's Avatar
Australia, NSW, Ashby
Joined Jul 2011
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Originally Posted by GadgetEric View Post
Interesting. I set my needles up like this but could get very little fuel through the pump. I pulled the pump off and disasembled it to see if I could spot anything wrong but not anything I could see. I had the motor mounted on a test stand. While I was playing about with the pump my friend hooked the line from the back plate or crankcase to the tank vent and tank outlet dirrect to the needlevalve without a pump and it sucked the fuel up and ran quite well. This is the first time that this engine has ran for more than a second before it ran out of fuel.

I disconected the Crankcase to fueltank vent line and it ran but would not idle verry well. I then used a full metre of fuel tubing from the crankcase to the fueltank vent and half filled it with fuel so there was a big bubble of fuel in it. When I started the motor all the fuel in this line was pushed into the tank as you would expect a pressure feed from a muffler.

My conclussion is that this motor does not have much if any pulse from the crankcase to work the pump.

I have run 2 litres of fuel through my pumpless engine and it is comming up OK but the needles are very sensitive and its easy to over do the adjustments but the top end is good but I am still not happy with the bottom end.

This engine is modified with the 4mm fitting in the crankcase. I am thinking of trying to restrict the size/flow to see if it helps the idle but havent deceided how yet.
I would definitely look at cleaning up the pump faces as c_groth did and replacing the pump with the kit as mentioned before. Made a world of difference to my motor and I am looking forward to seeing what a new spring will do under the metering lever.
I too would like the low speed to be a bit smoother but I am not too sure we will be able to achieve this.
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