MOKI RADIAL Care and Maintenence
#4176
tmac46.
#4177
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the diaphragm you are all talking about is in the metering section of the Walbro carb. The metering section will not allow any fuel to flow through the carb unless and until you close the choke and flip the prop. Thi s causes a partial vacuum in the carb which sucks the diaphragm down thus opening the metering needle. also, when the engine is running, a partial vacuum exists in the venture which keeps the diaphragm in and the fuel flowing.
#4178
My Feedback: (2)
The vacuum is actually in the crank case. The pulse (change in pressure) is transfered to the carb and that is what moves the inlet needle.. Both diaphragms move in concert. One moving in the opposite one moving out.. Then they change direction.during each pulse.
Works pretty well.
Works pretty well.
#4179
My Feedback: (156)
The vacuum is actually in the crank case. The pulse (change in pressure) is transfered to the carb and that is what moves the inlet needle.. Both diaphragms move in concert. One moving in the opposite one moving out.. Then they change direction.during each pulse.
Works pretty well.
Works pretty well.
The Moki uses a small air pump driven by the camshaft. Because the cam follower that drives the pump must remain lubricated, Moki packs the area with molybdenum grease. As the grease gets hot it liquefies and gets pushed into the air tube that connects the air pump at the front of the engine to the carburetor. When the tube becomes blocked by grease, it no longer provides reliable pressure pulses to the carburetor and the engine can be starved for fuel. This is why so many no longer use the air pump and have switched to an external electric fuel pump.
#4180
Guys, the Walbro carburetor pump on a Moki is not activated by crankcase pressure. Because a four stroke crankcase is vented to the atmosphere, there are no positive/negative pressure pulses... whereas a two stroke case is sealed and does generate positive and negative pressure that can be used to move the carburetor pump diaphragm.
The Moki uses a small air pump driven by the camshaft. Because the cam follower that drives the pump must remain lubricated, Moki packs the area with molybdenum grease. As the grease gets hot it liquefies and gets pushed into the air tube that connects the air pump at the front of the engine to the carburetor. When the tube becomes blocked by grease, it no longer provides reliable pressure pulses to the carburetor and the engine can be starved for fuel. This is why so many no longer use the air pump and have switched to an external electric fuel pump.
The Moki uses a small air pump driven by the camshaft. Because the cam follower that drives the pump must remain lubricated, Moki packs the area with molybdenum grease. As the grease gets hot it liquefies and gets pushed into the air tube that connects the air pump at the front of the engine to the carburetor. When the tube becomes blocked by grease, it no longer provides reliable pressure pulses to the carburetor and the engine can be starved for fuel. This is why so many no longer use the air pump and have switched to an external electric fuel pump.
tmac48
#4181
My Feedback: (156)
Yes but this does not explain why when I first turn my pump on it takes for ever to push the fuel the last 40mm into the carby. Some one suggested pumping the prop to promote fuel flow but with no crank case pulse or in this instance air pump I fail to see how this would help in the flow of fuel.
tmac48
tmac48
Have you tried applying the choke, cracked throttle, and flipping the prop to see if this then enables the fuel to travel into the carburetor?
#4182
tmac48.
#4183
My Feedback: (156)
Tanks are high in the fuselage pump is below tanks.the question is, with no crank case pump connected to carby what is the thinking behind pumping or flipping the prop? Another question to those that have electric pumps that are having success are you disconnecting the Moki standard pump and do find that fuel gets to the carby without having to flip the prop?
tmac48.
tmac48.
There is no reason to flip the prop if the goal is to make the carb "pump" - once the air line has been disconnected from the engine air pump, the carburetor no long pumps fuel.
CLOSE the choke and flip the prop. This creates a vacuum that will pull fuel in the fuel line into the carburetor.
#4185
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tmac48, you still don't get it. The metering section of the Walbro has cut off all flow of fuel. It will allow fuel to flow only when the choke is closed and the prop is flipped. When the choke is closed and prop flipped , (or when the engine is running under its own power), there exists a low pressure area within the carb, the metering diaphragm is deflected by this low pressure (downward/inward) opening the metering needle and allowing fuel to flow. You can leave the pump on until the cows come home but no fuel will flow until a low pressure in the carb deflects the diaphragm which opens the needle allowing fuel to flow.
Remember, this type of carburetor was designed primarily for yard implements, weed eaters, chainsaws, leaf blowers, etc. The primary function of the metering section is to prevent fuel from leaking from the implement regardless of the position the implement is stored in. Hung on a wall or thrown in the back of a pickup or tossed on the floor, no fuel can flow to the carb until a low pressure exists in the throat of the carburetor.
Remember, this type of carburetor was designed primarily for yard implements, weed eaters, chainsaws, leaf blowers, etc. The primary function of the metering section is to prevent fuel from leaking from the implement regardless of the position the implement is stored in. Hung on a wall or thrown in the back of a pickup or tossed on the floor, no fuel can flow to the carb until a low pressure exists in the throat of the carburetor.
#4186
tmac48, you still don't get it. The metering section of the Walbro has cut off all flow of fuel. It will allow fuel to flow only when the choke is closed and the prop is flipped. When the choke is closed and prop flipped , (or when the engine is running under its own power), there exists a low pressure area within the carb, the metering diaphragm is deflected by this low pressure (downward/inward) opening the metering needle and allowing fuel to flow. You can leave the pump on until the cows come home but no fuel will flow until a low pressure in the carb deflects the diaphragm which opens the needle allowing fuel to flow.
Remember, this type of carburetor was designed primarily for yard implements, weed eaters, chainsaws, leaf blowers, etc. The primary function of the metering section is to prevent fuel from leaking from the implement regardless of the position the implement is stored in. Hung on a wall or thrown in the back of a pickup or tossed on the floor, no fuel can flow to the carb until a low pressure exists in the throat of the carburetor.
Remember, this type of carburetor was designed primarily for yard implements, weed eaters, chainsaws, leaf blowers, etc. The primary function of the metering section is to prevent fuel from leaking from the implement regardless of the position the implement is stored in. Hung on a wall or thrown in the back of a pickup or tossed on the floor, no fuel can flow to the carb until a low pressure exists in the throat of the carburetor.
tmac48
#4187
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tmac48, good for you!
I,ve just-about given up on the Walbro and am in the process of adapting a two-stroke nitro carb to the engine. 13 flights on my comparf Corsair with a half-dozen engine shutdowns, one in-flight, has left me with little confidence in the factory set-up. In my opinion, the Walbro carb is way oversized for this motor (the moki 250). The engine's demand for air is much smaller than the carb was designed for thus creating a marginally small pressure differential in the carb throat. I have been running my engine with the choke 60% closed with no power loss.
I,ve just-about given up on the Walbro and am in the process of adapting a two-stroke nitro carb to the engine. 13 flights on my comparf Corsair with a half-dozen engine shutdowns, one in-flight, has left me with little confidence in the factory set-up. In my opinion, the Walbro carb is way oversized for this motor (the moki 250). The engine's demand for air is much smaller than the carb was designed for thus creating a marginally small pressure differential in the carb throat. I have been running my engine with the choke 60% closed with no power loss.
#4188
My Feedback: (156)
So, this may ruffle some feathers but here goes... I flew my CARF P-47 with Moki 250 many times. Used Red Line 50:1 and no air baffles. Stock "top hat" ignition and stock air / fuel pump (NO auxiliary electric pump). In other words, by today's conventional wisdom, I was doing almost everything WRONG... Even though at the time, I was following Moki's instructions (with the exception of NO baffles) and using the factory engine accessories. The engine ran perfectly with only a couple exceptions, both of which can be attributed to flying in exceedingly hot weather (engine getting too hot), and the air tube to the carb pump clogging with grease and needing to be flushed out.
It never once quit, but would run slightly rough.
The engine always started using exactly the same choking and starting procedure as every other gasser I have ever run.
The Solo 4-blade prop was tuned to produce 3900 rpm on the ground and absolutely HOWLED in the air.
Was I lucky? Don't know.
But I do believe some tend to over-complicate things by trying to solve simple problems with complex solutions.
Switched to Amsoil Dominator 40:1 at the behest of the Moki retailer who will honor the warranty
Added the baffle to keep the engine running cool
These engines are superbly designed and thoroughly tested to run properly right out of the box.
It never once quit, but would run slightly rough.
The engine always started using exactly the same choking and starting procedure as every other gasser I have ever run.
The Solo 4-blade prop was tuned to produce 3900 rpm on the ground and absolutely HOWLED in the air.
Was I lucky? Don't know.
But I do believe some tend to over-complicate things by trying to solve simple problems with complex solutions.
- The most common problem is that too many do not understand how to properly tune the carburetor
- Some are using inferior wiring and connectors (high resistance) which drop voltage to the ignition
- Some are getting the engine too hot and not using the proper oil or oil mix
- Some have overheated the engine so frequently that engine components no longer have the proper fit and the engine will never run evenly
Switched to Amsoil Dominator 40:1 at the behest of the Moki retailer who will honor the warranty
Added the baffle to keep the engine running cool
These engines are superbly designed and thoroughly tested to run properly right out of the box.
Last edited by RichardGee; 09-14-2018 at 08:55 AM.
#4189
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RichardG, I am happy you are having good luck with your motors. And I agree with you that usually simple fixes are best. However, due to my bad experience with the motor I have read every post on this forum since 2009 and have found that many have had similar problems. The Walbro type fuel pump couldn't be simpler and millions of them are in operation round the world, yet "the experts" recommend and the factory offers a substitute electric pump, why?. I have been in modeling for 60yrs. and have never heard of an application requiring an electric fuel pump.
I agree with you, these engines are superbly designed. But thoroughly tested, I don't think so. Remember the brass cam gears?, the grease in the cam compt. getting into the pump pulse line? The pushrods that fell into three pieces when they were removed? The fact that the cam lobes differ in height so that one must adjust each valve's lash on every lobe, or risk picking the lowest lobe and possibly suffering a burnt exhaust valve.
I agree with you, these engines are superbly designed. But thoroughly tested, I don't think so. Remember the brass cam gears?, the grease in the cam compt. getting into the pump pulse line? The pushrods that fell into three pieces when they were removed? The fact that the cam lobes differ in height so that one must adjust each valve's lash on every lobe, or risk picking the lowest lobe and possibly suffering a burnt exhaust valve.
#4190
So, this may ruffle some feathers but here goes... I flew my CARF P-47 with Moki 250 many times. Used Red Line 50:1 and no air baffles. Stock "top hat" ignition and stock air / fuel pump (NO auxiliary electric pump). In other words, by today's conventional wisdom, I was doing almost everything WRONG... Even though at the time, I was following Moki's instructions (with the exception of NO baffles) and using the factory engine accessories. The engine ran perfectly with only a couple exceptions, both of which can be attributed to flying in exceedingly hot weather (engine getting too hot), and the air tube to the carb pump clogging with grease and needing to be flushed out.
It never once quit, but would run slightly rough.
The engine always started using exactly the same choking and starting procedure as every other gasser I have ever run.
The Solo 4-blade prop was tuned to produce 3900 rpm on the ground and absolutely HOWLED in the air.
Was I lucky? Don't know.
But I do believe some tend to over-complicate things by trying to solve simple problems with complex solutions.
Switched to Amsoil Dominator 40:1 at the behest of the Moki retailer who will honor the warranty
Added the baffle to keep the engine running cool
These engines are superbly designed and thoroughly tested to run properly right out of the box.
It never once quit, but would run slightly rough.
The engine always started using exactly the same choking and starting procedure as every other gasser I have ever run.
The Solo 4-blade prop was tuned to produce 3900 rpm on the ground and absolutely HOWLED in the air.
Was I lucky? Don't know.
But I do believe some tend to over-complicate things by trying to solve simple problems with complex solutions.
- The most common problem is that too many do not understand how to properly tune the carburetor
- Some are using inferior wiring and connectors (high resistance) which drop voltage to the ignition
- Some are getting the engine too hot and not using the proper oil or oil mix
- Some have overheated the engine so frequently that engine components no longer have the proper fit and the engine will never run evenly
Switched to Amsoil Dominator 40:1 at the behest of the Moki retailer who will honor the warranty
Added the baffle to keep the engine running cool
These engines are superbly designed and thoroughly tested to run properly right out of the box.
Bob
#4191
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Moki 150 problem
Hi,
I just fire up for the first time my 150. Engine don't start without the choke on it. With the choke even at idle the rpm is high and throttle play don't vary the rpm. The only way to stop it is by cutting the ignition.
Both needle are at factory setting.
The tank is at about the same level as the carb and approx. 10 inch from the engine.
Ignition battery are fully charge two 2s life 2100mha regulated the 5.5v
Any clue? Too lean?
Thanks for your help
I just fire up for the first time my 150. Engine don't start without the choke on it. With the choke even at idle the rpm is high and throttle play don't vary the rpm. The only way to stop it is by cutting the ignition.
Both needle are at factory setting.
The tank is at about the same level as the carb and approx. 10 inch from the engine.
Ignition battery are fully charge two 2s life 2100mha regulated the 5.5v
Any clue? Too lean?
Thanks for your help
Last edited by 009; 09-15-2018 at 03:15 PM.
#4192
So, this may ruffle some feathers but here goes... I flew my CARF P-47 with Moki 250 many times. Used Red Line 50:1 and no air baffles. Stock "top hat" ignition and stock air / fuel pump (NO auxiliary electric pump). In other words, by today's conventional wisdom, I was doing almost everything WRONG... Even though at the time, I was following Moki's instructions (with the exception of NO baffles) and using the factory engine accessories. The engine ran perfectly with only a couple exceptions, both of which can be attributed to flying in exceedingly hot weather (engine getting too hot), and the air tube to the carb pump clogging with grease and needing to be flushed out.
It never once quit, but would run slightly rough.
The engine always started using exactly the same choking and starting procedure as every other gasser I have ever run.
The Solo 4-blade prop was tuned to produce 3900 rpm on the ground and absolutely HOWLED in the air.
Was I lucky? Don't know.
But I do believe some tend to over-complicate things by trying to solve simple problems with complex solutions.
Switched to Amsoil Dominator 40:1 at the behest of the Moki retailer who will honor the warranty
Added the baffle to keep the engine running cool
These engines are superbly designed and thoroughly tested to run properly right out of the box.
It never once quit, but would run slightly rough.
The engine always started using exactly the same choking and starting procedure as every other gasser I have ever run.
The Solo 4-blade prop was tuned to produce 3900 rpm on the ground and absolutely HOWLED in the air.
Was I lucky? Don't know.
But I do believe some tend to over-complicate things by trying to solve simple problems with complex solutions.
- The most common problem is that too many do not understand how to properly tune the carburetor
- Some are using inferior wiring and connectors (high resistance) which drop voltage to the ignition
- Some are getting the engine too hot and not using the proper oil or oil mix
- Some have overheated the engine so frequently that engine components no longer have the proper fit and the engine will never run evenly
Switched to Amsoil Dominator 40:1 at the behest of the Moki retailer who will honor the warranty
Added the baffle to keep the engine running cool
These engines are superbly designed and thoroughly tested to run properly right out of the box.
Great info. Do you have any specific advice on timing the carb that might save me reading through dozens of pages?
#4194
Join Date: Nov 2005
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009, has the engine been sitting for a long time? I had to rebuild the carburetor before the engine would run correctly. You also may want to richen the high side and see if that helps.
#4195
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Hi,
Yes this engine sit there for more than 5-6 years. I will retry to enrich the high side and see. It's weird with choke on throttle at idle I get 3000 rpm if a push it to full throttle the rpm drop a bit. Than if I close the choke when the engine is running the rpm rise but the throttle play have no effect. I can't cut the engine by the throttle but just by cutting the ignition.
Yes this engine sit there for more than 5-6 years. I will retry to enrich the high side and see. It's weird with choke on throttle at idle I get 3000 rpm if a push it to full throttle the rpm drop a bit. Than if I close the choke when the engine is running the rpm rise but the throttle play have no effect. I can't cut the engine by the throttle but just by cutting the ignition.
#4197
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009 in addition to Bob H suggestion, are you sure that the throttle blade is closing all the way? You may want to check to see that the idle adjustment screw is not holding the throttle blade open.
#4199
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Two years ago I bought a Moki 250 for a comp arf F4-U i was building. Initial test running on a test stand was not satisfactory. it wasn't possible to get the high speed mixture rich enough (turn the needle out three or more turns no drop in rpm). I settled for this, finished the airplane and installed the engine and test flew. However, the Moki quit frequently, once in flight, and was just very temperamental. I started reading others comments in this forum and found out that many were having similar problems. At one point V.A. came out recommending an electric fuel pump. To me, this was an admission from the factory rep. that the engine had issues. Finally, out of total frustration, I discarded the factory Walbro carb. In it's place I used an O.S. Max 8B carb I had in my "junk box" (I believe O.S. used this on their 108 motor). GUESS WHAT! All problems disappeared. I use no pump of any kind, not even muffler pressure. The throttle response is much more linear and CH temps have dropped from somewhere around 250F to less than 200F (Jeti telemetry). I've had many flights on the Corsair since making this change and I no longer have any concerns about the engine stopping in flight or any other time.