MVVS .91 Quits
08-25-2004, 05:31 PM
#1
MVVS .91 Quits
I have an MVVS 91. which is fairly new and really powerful but it quits after about 5 minutes of flight. I think it's due to the fact that it's mounted inverted in the plane and the tank is about 1/2 inch higher than the needle valve. Lowering the tank is going to be difficult but possible. Do you think this is why it won't keep running?
08-25-2004, 06:08 PM
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RE: MVVS .91 Quits
The tank outlet is 1/2" above the needle valve? That shouldn't make it quit.
Does it run OK on the ground? What kind of fuel are you running? Too much nitro will make these engines a little grumpy - if you can, try some 5% fuel.
When it dies, does it sag an die, indicating a lean condition or does it just quit all of the sudden?
Does it run OK on the ground? What kind of fuel are you running? Too much nitro will make these engines a little grumpy - if you can, try some 5% fuel.
When it dies, does it sag an die, indicating a lean condition or does it just quit all of the sudden?
08-25-2004, 07:26 PM
#3
RE: MVVS .91 Quits
I am using 10% fuel. It is very powerful at full throttle but quits for no reason and after idling for a short while. In flight it runs like mad then quits after about 5 minutes. Is this too lean? I have tried to richen the needle valve , it does seem to be somewhat hotter than normal when I touch the head after it should be cooled down. About 1/4 of the head is exposed to the slipstream so I don't think it's overheating for that reason. This is my first MVVS (and my last) Thanks
08-25-2004, 10:19 PM
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RE: MVVS .91 Quits
Yup common mistake with these engines. They are designed with a higher compression ratio to allow for the use of low nitro fuels. They get hot, and start to pre-ignite. Switch to 5% fuel and your engine will run MUCH better. Unfortunatley this is not stated clearly (if at all) in the manual. The 91 is a great power plant, stick with it!
08-25-2004, 11:08 PM
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RE: MVVS .91 Quits
Skip:
I was having exactly the same problem with my .77 - followed David's advice and went down to 5% fuel and the problem has been corrected.
I was having exactly the same problem with my .77 - followed David's advice and went down to 5% fuel and the problem has been corrected.
08-26-2004, 04:14 AM
#7
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RE: MVVS .91 Quits
Skip,
While a defective engine can come out from time to time, what you describe is more likely to be a technique problem. No specific defect can reproduce what your engine is doing.
First, as was said already, do not use fuel with any more than 5% nitro in this engine.
If you fly in a very hot region, make that 3%.
No buts. Just do it!
Unless you live on an island, with only one hobby shop, stocking only 10% nitro, there is no excuse for not getting the needed fuel.
If your motorcar needed premium gas, you would not force it to run on regular, because your LGS (local gas station) only has that. You'll drive further to get it. Do the same with the fuel for your MVVS.
The detonation is not always evident from the initial behavior of the engine.
It can soak heat gradually and quit for 'no reason at all' after a few minutes.
Cooling; you would want the fins above the exhaust stack all exposed to direct airflow, in addition to the head.
The MVVS makes a lot of power and extra heat is the unwanted by-product. Good cooling airflow is required to get rid of it.
To err is human. To blame your engine for it is even more so...
While a defective engine can come out from time to time, what you describe is more likely to be a technique problem. No specific defect can reproduce what your engine is doing.
First, as was said already, do not use fuel with any more than 5% nitro in this engine.
If you fly in a very hot region, make that 3%.
No buts. Just do it!
Unless you live on an island, with only one hobby shop, stocking only 10% nitro, there is no excuse for not getting the needed fuel.
If your motorcar needed premium gas, you would not force it to run on regular, because your LGS (local gas station) only has that. You'll drive further to get it. Do the same with the fuel for your MVVS.
The detonation is not always evident from the initial behavior of the engine.
It can soak heat gradually and quit for 'no reason at all' after a few minutes.
Cooling; you would want the fins above the exhaust stack all exposed to direct airflow, in addition to the head.
The MVVS makes a lot of power and extra heat is the unwanted by-product. Good cooling airflow is required to get rid of it.
To err is human. To blame your engine for it is even more so...
08-26-2004, 06:07 AM
#9
Senior Member
RE: MVVS .91 Quits
Skip,
Also do something about the cooling.
You can set up baffles inside the cowl, to route air into the cooling fins.
Make sure there is plenty of place for the air to exit; twice as much as for entry.
Also, how did you do the break-in?
If you did not do it as described in [link=http://www.rcuniverse.com/forum/Tapered%2DBore_Engine_Break%2Din_%2D_Upgraded/m_1850473/tm.htm]this RCU thread[/link], repeat the process.
Also do something about the cooling.
You can set up baffles inside the cowl, to route air into the cooling fins.
Make sure there is plenty of place for the air to exit; twice as much as for entry.
Also, how did you do the break-in?
If you did not do it as described in [link=http://www.rcuniverse.com/forum/Tapered%2DBore_Engine_Break%2Din_%2D_Upgraded/m_1850473/tm.htm]this RCU thread[/link], repeat the process.
