Tuning Problems
11-14-2008 | 11:47 PM
#1
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From: Newcastle, AUSTRALIA
Tuning Problems
Hi all I have the 90 size SK engine. My satisfaction with this motor has been very mixed. Break in on the bench seemed to be a non event, but once put into my plane, a Sportsman Aviation Paramount 60 I have had no end of trouble with tuning. The motor is mounted inverted, but I have never had a problem with inverted motors before. The low speed needle has been wound in quite a fair way to maintain a reliable idle but in doing this I cannot get the high speed needle set rich enough, after turning high speed needle out approx 4 1/2 to 5 turns the engine to try and get rich enough it all of a sudden goes lean and just dies. Now looking through the top of the carb my low speed needle has nowhere near a 1mm gap it actually has no gap and is in the spray bar if that makes sense. I am running a 14X8 APC prop and would run a 15X6 but I do not have the ground clearance. Oh also when flying when dropping back on throttle the engine makes a ring ding ding noise like a 2 stroke motor bike which some would say indicates too lean a setting on the low speed needle but if I try to richen it, it just loads up and stalls. Please any help would be appreciated
Cheers
Scott
Cheers
Scott
11-15-2008 | 12:26 AM
#2
Senior Member
RE: Tuning Problems
Scott,
Is your plane's fuel-tank set at the right height?
The correct setting is: tank center-line level must be identical to that of the carburettor's jet, with the model in level flight attitude.
Also, is the tank as close as possible to the engine and is fully isolated from any airframe vibration, using at least ¼" thick Latex foam?
If any reply is negative then you had just found the cause of your misery...
And as to the 'ring ding' sound on over-run... Just ignore it.
Detonation could damage your engine, but it will happen at high-throttle setting, if you are running the engine too lean, or with too large a prop.
This is what is popularly called a 'lean run', which in essence is excessive 'ignition advance'.
It is more often described as 'frying egg' sounds...
In any glow engine; since a leaner mixture will ignite sooner and will combust more rapidly, compared to a richer mixture; the needles are actually the 'ignition timing control'...
Is your plane's fuel-tank set at the right height?
The correct setting is: tank center-line level must be identical to that of the carburettor's jet, with the model in level flight attitude.
Also, is the tank as close as possible to the engine and is fully isolated from any airframe vibration, using at least ¼" thick Latex foam?
If any reply is negative then you had just found the cause of your misery...
And as to the 'ring ding' sound on over-run... Just ignore it.
Detonation could damage your engine, but it will happen at high-throttle setting, if you are running the engine too lean, or with too large a prop.
This is what is popularly called a 'lean run', which in essence is excessive 'ignition advance'.
It is more often described as 'frying egg' sounds...
In any glow engine; since a leaner mixture will ignite sooner and will combust more rapidly, compared to a richer mixture; the needles are actually the 'ignition timing control'...
11-15-2008 | 02:13 AM
#3
My Feedback: (26)
RE: Tuning Problems
I also suspect your tank is too high, giving gravity feed to your carb. To compensate for the forced flow of fuel, you have leaned down the low speed mixture to the point that your high speed setting cannot possibly supply enough fuel for full throttle runs. If you cannot lower your fuel tank so center line of tank is even or slightly lower than spray bar of carb, you could either change the engine mount to 90 degree/side mount or you could use a regulator like Cline.
11-15-2008 | 04:15 AM
#4
Senior Member
RE: Tuning Problems
ORIGINAL: FlyingPilgrim
...If you cannot lower your fuel tank so center line of tank is even or slightly lower than spray-bar of carburettor, you could either change the engine mount to 90º side mount or you could use a regulator like Cline.
...If you cannot lower your fuel tank so center line of tank is even or slightly lower than spray-bar of carburettor, you could either change the engine mount to 90º side mount or you could use a regulator like Cline.
The 90º mounting is OK, but I have a reservation regarding the Cline regulator.
Yes, it does work very well, I am told; but even though it is constructed from pretty inexpensive components, it costs nearly as much as the whole SK .90 engine...
11-15-2008 | 04:36 AM
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From: Newcastle, AUSTRALIA
RE: Tuning Problems
So then if the prop is too big if I was to use a 14x6 or 13x8 would this help if if so can u please explain how it would help?
Cheers
Scott
Cheers
Scott
11-15-2008 | 07:57 AM
#6
Senior Member
RE: Tuning Problems
ORIGINAL: buddy072
Hi all I have the 90 size SK engine. My satisfaction with this motor has been very mixed. Break in on the bench seemed to be a non event, but once put into my plane, a Sportsman Aviation Paramount 60 I have had no end of trouble with tuning. The motor is mounted inverted, but I have never had a problem with inverted motors before. The low speed needle has been wound in quite a fair way to maintain a reliable idle but in doing this I cannot get the high speed needle set rich enough, after turning high speed needle out approx 4 1/2 to 5 turns the engine to try and get rich enough it all of a sudden goes lean and just dies. Now looking through the top of the carb my low speed needle has nowhere near a 1mm gap it actually has no gap and is in the spray bar if that makes sense. I am running a 14X8 APC prop and would run a 15X6 but I do not have the ground clearance. Oh also when flying when dropping back on throttle the engine makes a ring ding ding noise like a 2 stroke motor bike which some would say indicates too lean a setting on the low speed needle but if I try to richen it, it just loads up and stalls. Please any help would be appreciated
Cheers
Scott
Hi all I have the 90 size SK engine. My satisfaction with this motor has been very mixed. Break in on the bench seemed to be a non event, but once put into my plane, a Sportsman Aviation Paramount 60 I have had no end of trouble with tuning. The motor is mounted inverted, but I have never had a problem with inverted motors before. The low speed needle has been wound in quite a fair way to maintain a reliable idle but in doing this I cannot get the high speed needle set rich enough, after turning high speed needle out approx 4 1/2 to 5 turns the engine to try and get rich enough it all of a sudden goes lean and just dies. Now looking through the top of the carb my low speed needle has nowhere near a 1mm gap it actually has no gap and is in the spray bar if that makes sense. I am running a 14X8 APC prop and would run a 15X6 but I do not have the ground clearance. Oh also when flying when dropping back on throttle the engine makes a ring ding ding noise like a 2 stroke motor bike which some would say indicates too lean a setting on the low speed needle but if I try to richen it, it just loads up and stalls. Please any help would be appreciated
Cheers
Scott
With this engine, be sure to use an OS-F plug. It is about the only plug that works well.
What if you are using too much nitro?
11-15-2008 | 02:34 PM
#8
RE: Tuning Problems
Hi!
Yes! How much nitro do you use??
Don't make any engine modifications before you have set everything right first. That is: Tank hight , tank size , type of tank, fuel, glow plug etc.
A 14x6 or 15x6 APC prop will work just fine!!
Here is my choice:
Tank size: 10-12oz if you use a large slow rewing 15x6 APC prop. 12-14oz if a 14x6 or 13x8 prop is used.
Best tank is a Tettra "Bubbleless"! Second..an ordinary R/C tank like Kavan ,Sullivan or Du-Bro... with Uni-flow set-up (Two clunks).
Tank position: Center of tank inline with carb fuel intake orifice when airplane sits horizontal...This is very important!!!
Glow fuel: 5-10% nitro.
Glow plug: Nova Rossi / Rossi 3, 4 or 5. Enya 3, 4 or OS 8...there are many others too.
Yes! How much nitro do you use??
Don't make any engine modifications before you have set everything right first. That is: Tank hight , tank size , type of tank, fuel, glow plug etc.
A 14x6 or 15x6 APC prop will work just fine!!
Here is my choice:
Tank size: 10-12oz if you use a large slow rewing 15x6 APC prop. 12-14oz if a 14x6 or 13x8 prop is used.
Best tank is a Tettra "Bubbleless"! Second..an ordinary R/C tank like Kavan ,Sullivan or Du-Bro... with Uni-flow set-up (Two clunks).
Tank position: Center of tank inline with carb fuel intake orifice when airplane sits horizontal...This is very important!!!
Glow fuel: 5-10% nitro.
Glow plug: Nova Rossi / Rossi 3, 4 or 5. Enya 3, 4 or OS 8...there are many others too.
11-17-2008 | 02:16 AM
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From: PerthWA, AUSTRALIA
RE: Tuning Problems
Hi Scott, I have just PM'd you with some details.
As the others have posted - tank height is critical.
A couple of points.
I always seal the carbs with high temp silicone around the carb barrel where it mounts into the engine. It is possible for an air leak to exist around the carb retainer which is below the o'ring seal. This can cause a lot of weird needle settings to be made. I have asked the factory to change the sealing arrangement to a lower o'ring but who knows if or when that will happen.
These carbs are finicky about needle settings, More so than a lot of other brands - the needles do react to each other. I suggest starting back to the factory settings - about 1 - 1.5 turns out on the high speed and the low speed about 1.5mm below the face of the throttle arm (about 3 - 3.5 turns out with the carby closed). The high speed needle is more coarse than some of the other carbs such as OS use.
Then follow the usual routine of set the high speed for max rpm minus a few clicks, set the low speed for good idle and transition, reset the high, double check the low, reset the high and go fly.
As the others have posted - tank height is critical.
A couple of points.
I always seal the carbs with high temp silicone around the carb barrel where it mounts into the engine. It is possible for an air leak to exist around the carb retainer which is below the o'ring seal. This can cause a lot of weird needle settings to be made. I have asked the factory to change the sealing arrangement to a lower o'ring but who knows if or when that will happen.
These carbs are finicky about needle settings, More so than a lot of other brands - the needles do react to each other. I suggest starting back to the factory settings - about 1 - 1.5 turns out on the high speed and the low speed about 1.5mm below the face of the throttle arm (about 3 - 3.5 turns out with the carby closed). The high speed needle is more coarse than some of the other carbs such as OS use.
Then follow the usual routine of set the high speed for max rpm minus a few clicks, set the low speed for good idle and transition, reset the high, double check the low, reset the high and go fly.
11-24-2008 | 05:12 AM
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From: Newcastle, AUSTRALIA
RE: Tuning Problems
Hi all thanks for all the posts, I changed the glow plug from an OS 8 to an OS F as suggested. I was then able to richen up the bottom end which then allowed the top end to richen. So no more lean runs. I would like to be able to lean off the bottom more but it will affect the top too much. Could someone explain to me the mod with the 1.5mm drill bit?
Once again thanks for all the helpful info.
Cheers
Scott
Once again thanks for all the helpful info.
Cheers
Scott
