mvvs 58 leaning out
05-04-2006, 07:46 AM
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mvvs 58 leaning out
Hi Everybody
I have a MVVS 58 that is still very new, The problem I have is that it seems
to lean out after it has been in the air for a few minutes, I found that after it
landed the prop hub had movement , when it cools down the movement goes
The motor is in a (wild hair) pro-built in AUS 84" extra 300 with a pitts type
muffler, fuel is 30:1, prop 22-12, 23-10. I first thought it was a carb problem
but now not so shaw, I have it 4 stroking in mid range and also at top end
when it leaves the ground a few minutes into the flight it starts to run realy
nice. I have been told these have a 2 peace grank, and that the come loose
I have tried to tighten the front hub, but will not move, I feel that it is sucking
air and leaning it out, Any thoughts on this would be of much help
Many thanks Lindsay
I have a MVVS 58 that is still very new, The problem I have is that it seems
to lean out after it has been in the air for a few minutes, I found that after it
landed the prop hub had movement , when it cools down the movement goes
The motor is in a (wild hair) pro-built in AUS 84" extra 300 with a pitts type
muffler, fuel is 30:1, prop 22-12, 23-10. I first thought it was a carb problem
but now not so shaw, I have it 4 stroking in mid range and also at top end
when it leaves the ground a few minutes into the flight it starts to run realy
nice. I have been told these have a 2 peace grank, and that the come loose
I have tried to tighten the front hub, but will not move, I feel that it is sucking
air and leaning it out, Any thoughts on this would be of much help
Many thanks Lindsay
05-04-2006, 08:01 AM
#2
Senior Member
RE: mvvs 58 leaning out
Chris,
With the Walbro carburettor that has its own pump, fuel supply should be unaffected by fuel level.
Having its own virtual float chamber should preclude bubbles from having much affect.
Heating of the crankshaft should not produce an air-leak either.
Maybe Pe has encountered something that could bring a solution to you.
With the Walbro carburettor that has its own pump, fuel supply should be unaffected by fuel level.
Having its own virtual float chamber should preclude bubbles from having much affect.
Heating of the crankshaft should not produce an air-leak either.
Maybe Pe has encountered something that could bring a solution to you.
05-04-2006, 10:42 AM
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RE: mvvs 58 leaning out
Have you tached yor engine? A 22 or 23 inch prop seems small for your MVVS 58. With a 24/12 on my MVVS 58 it ran above manufacturers rpm reccomedations and I went to a 24/12 to keep it within the manufactures recomended rpm range. I use this engine in a wild hare 300 and it is way more power than it's needs. Also extreme leaning out can be caused from a crankcase air leak.
05-05-2006, 06:29 AM
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RE: mvvs 58 leaning out
Wild Hare shows a nice muffler install for the MVVS 58. They do however not say anything about proper engine cooling.
I have the feeling, that your engine gets extremely hot in flight. This may cause (partly) vapour lock in the carb and disturbed pump action. It also may cause the crankcase pressure line to leak.
How is your engine baffled for forced airflow through the cylinder fins? It should be.
Imagine how the engine can get rid of about 4000 Watts heat. In a glow engine, much of that goes into fuel evaporation. Not so with a gasoline engine, so all heat has to be carried away by the coolant (air). This air rather goes around the fins than through them, so you have to force the airflow by baffling.
I have the feeling, that your engine gets extremely hot in flight. This may cause (partly) vapour lock in the carb and disturbed pump action. It also may cause the crankcase pressure line to leak.
How is your engine baffled for forced airflow through the cylinder fins? It should be.
Imagine how the engine can get rid of about 4000 Watts heat. In a glow engine, much of that goes into fuel evaporation. Not so with a gasoline engine, so all heat has to be carried away by the coolant (air). This air rather goes around the fins than through them, so you have to force the airflow by baffling.
05-06-2006, 09:56 PM
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RE: mvvs 58 leaning out
HI Pe
I do agree that the engine is getting hot, the head is almost entirely out of the cowl
I have looked at a lot of other motor installations and they are not much different to mine
when it lands you can put your hand on head & it's not hot, but the crank has movement
How does the crank come apart , I suspect I have a problem there, because once the
motor cools there's no movement.
Many thanks icicles
I do agree that the engine is getting hot, the head is almost entirely out of the cowl
I have looked at a lot of other motor installations and they are not much different to mine
when it lands you can put your hand on head & it's not hot, but the crank has movement
How does the crank come apart , I suspect I have a problem there, because once the
motor cools there's no movement.
Many thanks icicles
05-07-2006, 03:00 AM
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RE: mvvs 58 leaning out
The crank of the 58cc is a solid one piece affair, and cannot be disassembled. The only piece you can take off is a plastic crankcase filler piece which increases internal pumping efficiency of the engine.
The crank has a seperate front seal, which is not integrated in the bearing, so your engine is not bypassing air. If it would do that, idle rpm would skyrocket.
Midrange burble like you have is probably due to the small prop you are running. 24" diameter x 10 or x12 is better. This burble also is dependent on how you balance the low and the high needles. If the balance shifts to more main needle opening and less idle needle opening, with the right prop you can make the midrange richness go away. I have described this on my forum.
The crank has a seperate front seal, which is not integrated in the bearing, so your engine is not bypassing air. If it would do that, idle rpm would skyrocket.
Midrange burble like you have is probably due to the small prop you are running. 24" diameter x 10 or x12 is better. This burble also is dependent on how you balance the low and the high needles. If the balance shifts to more main needle opening and less idle needle opening, with the right prop you can make the midrange richness go away. I have described this on my forum.
05-08-2006, 05:59 AM
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RE: mvvs 58 leaning out
Hi Pe,
I have the same problem with icicles my IRS 45MG. It leans out in the idle range during flight making the landing real pain. I use an idle down switch, which completely closes
the Walbro (This should "kill" the engine in normal conditions) but even this is not enough sometimes. The problem is partialy cured riching the low needle
but this makes the engine to four-stroke unacceptably in the mid-range. In ground tests the engine has variable idle RPM after throttling up and then down.
Some times throttling down results in a lower that the intended RPM and flame out but most of the times throttling down results in a higher (2800 - 3400RPM).
This idle may "dive" to the intended idle RPM (or a lower) after a few seconds of even after 1-2 minutes. Richening the low needle makes this time shorter.
But in the air the engine always increase its idle RPM.
At first look seems like there is a mechanical advantage problem in the throttle linkage but this is NOT the case. I have lengthen the Walbro throttle arm to about 3cm
to mininize the effects of any mechanical advantage. Also, I installed a spring to preload the linkage during idle moving any mechanical advantage to the same direction
always but with no effect . Guys with many years of experience in gas engines agreed that definitely this is NOT a tunning problem. Also I checked extensively the Walbro for leaks and even run a pressure test.
The (funny ?) coincidence is that I had another MVVS 26cc gas with exactly the same problem. We had a very long discussion over RCU then.
Whatever I 've done with MVVS 26cc, it was impossible to resolve the problem, so, I sold it and forget about it.
The only common parts between these engines, is that both had BCM in cowl mufflers and Multiplex Digital servos in throttle.
The engine is installed on a WM Ultimate with lot of opening in the cowl, and the engine head is almost completely out of cowl. I have also an intake trumpet installed on carb.
The propeller I use is Menz 22x8. This gives me 6800RPM after 6-7 litters of gas. The engine runs very well in the mid and top range.
Is it possible to have this problem cause of the in cowl muffler? How can I check this? How can I check if I have fuel evaporation problems?
Another idea was that something goes wrong with the digital servos during engine operation - I will try a simple analog but I don't think is the case.
Any ideas ?
Angelo
I have the same problem with icicles my IRS 45MG. It leans out in the idle range during flight making the landing real pain. I use an idle down switch, which completely closes
the Walbro (This should "kill" the engine in normal conditions) but even this is not enough sometimes. The problem is partialy cured riching the low needle
but this makes the engine to four-stroke unacceptably in the mid-range. In ground tests the engine has variable idle RPM after throttling up and then down.
Some times throttling down results in a lower that the intended RPM and flame out but most of the times throttling down results in a higher (2800 - 3400RPM).
This idle may "dive" to the intended idle RPM (or a lower) after a few seconds of even after 1-2 minutes. Richening the low needle makes this time shorter.
But in the air the engine always increase its idle RPM.
At first look seems like there is a mechanical advantage problem in the throttle linkage but this is NOT the case. I have lengthen the Walbro throttle arm to about 3cm
to mininize the effects of any mechanical advantage. Also, I installed a spring to preload the linkage during idle moving any mechanical advantage to the same direction
always but with no effect . Guys with many years of experience in gas engines agreed that definitely this is NOT a tunning problem. Also I checked extensively the Walbro for leaks and even run a pressure test.
The (funny ?) coincidence is that I had another MVVS 26cc gas with exactly the same problem. We had a very long discussion over RCU then.
Whatever I 've done with MVVS 26cc, it was impossible to resolve the problem, so, I sold it and forget about it.
The only common parts between these engines, is that both had BCM in cowl mufflers and Multiplex Digital servos in throttle.
The engine is installed on a WM Ultimate with lot of opening in the cowl, and the engine head is almost completely out of cowl. I have also an intake trumpet installed on carb.
The propeller I use is Menz 22x8. This gives me 6800RPM after 6-7 litters of gas. The engine runs very well in the mid and top range.
Is it possible to have this problem cause of the in cowl muffler? How can I check this? How can I check if I have fuel evaporation problems?
Another idea was that something goes wrong with the digital servos during engine operation - I will try a simple analog but I don't think is the case.
Any ideas ?
Angelo
