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Rough Running 912 UL Fixed!

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experimental208nd(at)comc
Guest

Posted: Fri Nov 10, 2006 7:48 pm Post subject: Rough Running 912 UL Fixed!

Hi List,

 Well I think it is fixed. I only tried one thing at  a time to narrow down the results and the culprit. Someone sugested moving the  c-clip down a notch to enrichen the carbs as it might be starving in the middle  range. I did it to both by moving the clip to the 3rd groove. I wanted to make  sure I was not going to make it too lean so I ran the plane for a half hour at  diff speeds.

 The EGTS only got up to 1,250 deg F at 4200 RPMS  for about 5 min. CHTS stayed at 180 deg F. 63 deg F OAT.

  

 It ran so much Smoother on start up and it was like  glass trough all rpm ranges, even quick trottle adjustments up and down.It was  great!  I only did the clips , and have not changed the plugs yet so It  seems to be the clip adjustment that helped.

  

 Question is  I have NEVER Had to move it  before in summer or dead of winter, So WHY now??????

  

 I did also do the methanol test of my gas with the  water and it tested out to have 10% methanol in it!   Maybe that is  the reason why I now needed to adjust it as there was not that much over the  summer?

  

 I will report back with the test fight next week  hopfully.

 Thanks to all that helped,

 Jay Fabian

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ddsyverson(at)comcast.net
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Posted: Sat Nov 11, 2006 5:17 am Post subject: Rough Running 912 UL Fixed!

Jay,



If you found that enrichning the mixture solved the problem, AND, you know 

that you currently have 10% alcohol (methanol according to your test) fuel, 

there is a theoretical and logical explanation as to why you now need to 

enrichen the mixture now, but did not need to at some time in the past. The 

reason I say "theoretical" is because we don't have an analysis of the fuel 

you were using before the engine began running rough - that part may be a 

guess at this point.



Consider the chemistry involved with burning  gas versus alcohol.



I provided some if this information in an earlier post when we were discussing 

corn gas on the list (ethanol added to gasoline). Alcohol has less energy per 

gallon than gasoline. Ethanol has approximately 60% of the energy that 

gasoline has - this means that if a person burns pure gasoline and compares 

it to burning pure ethanol, it will work like this (disregarding the factors 

of octane rating and a couple other minor things): If you get 20 nautical 

miles per gallon on pure gas, you will get 12 nautical miles per gallon on 

pure ethanol. - Again, this does not take into account a few other minor 

factors, but it is ballpark for government work. Taking the logic a bit 

further - this means you need to enrichen the mixture for ethanol so you can 

now burn an additional 8 gallons in the same distance IF you are running 100% 

ethanol compared to 100% gasoline. Actually, we do not burn 100% ethanol 

(maybe in cars in Brazil), but the need to enrichen the mixture due to 

additional of alcohol is exactly porportional to the amount of alcohol used 

to dilute the gasoline. Gasoline with 10% ethanol has approximately 94% of 

the energy as 100% gasoline - so the mixture needs to be enrichened to 

account for the missing 6% energy content.



NOW - you mentioned that your current fuel was actually 10% methanol, not 10% 

ethanol - if this is the case, methanol has LESS energy yet per gallon than 

ethanol so the 10% dilution would cause a somewhat greater reduction in BTU 

content than if the 10% was ethanol - not a lot, but some. This is due to the 

shorter chain structure of methanol (less carbon, less haydrogen=less 

energy).



Science trivia - Back during the first energy crisis in the US (the second  

also + during the runup in gas prices this summer) there were all kinds of 

snake oil guys coming out of the woodwork. Some claimed a 200 MPG carburetor 

for a 6000# vehicle was buried in some sort of conspiracy between the 

government and auto companies. This little crock of bull is easily debunked 

since it takes a defined quantity of gasoline to do a defined amount of work 

and there just isn't enough energy in a gallon of gas to push a 6000# vehicle 

200 miles.  I actually have seen a 200 MPG carburetor - it is on a very, very 

tiny radio controlled car which can actually carry four passengers, provided 

the passengers are four hummingbirds. My point of this is the big picture 

(energy needed versus gallons burned) is subject to the laws of chemistry and 

physics and these big picture items will sometimes provide us with answers to 

the puzzling things we observe.



Aside from all this chemistry stuff - give yourself a pat on the back for 

solving your original issue with the rough running; but keep your eyes and 

ears working. The only other thing I will mention is this - if it actually is 

not a difference in fuel, don't forget the possibility that some other 

problem may have it's solution manifest through enrichment (such as a vacuum 

leak, induction air temperature to name a few) Engine systems have several 

factors which affect the ideal mixture for smooth running - sometimes one 

change masks another issue. Or, you might have the problem solved and it 

might be that simple.



Please conside that my experience has been more involved with auto 

applications than aircraft engines. Some things transfer and some things 

don't; But, basic chemistry and physics doesn't distinguish what vehicle an 

engine is mounted on.



Sincerely,



Dave S

St Paul, MN



DO NOT ARCHIVE





On Friday 10 November 2006 9:47 pm, Jay Fabian wrote:

 	  Quote: 	
		   Hi List,

 Well I think it is fixed. I only tried one thing at a time to narrow down

 the results and the culprit. Someone sugested moving the c-clip down a

 notch to enrichen the carbs as it might be starving in the middle range. I

 

 Question is  I have NEVER Had to move it before in summer or dead of

 winter, So WHY now??????



 I did also do the methanol test of my gas with the water and it tested out

 to have 10% methanol in it!   Maybe that is the reason why I now needed to

 adjust it as there was not that much over the summer?

 
	


 	  Quote:

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Fox5flyer
Guest

Posted: Sat Nov 11, 2006 7:26 am Post subject: Rough Running 912 UL Fixed!

Great primer Dave.  Thanks.

Deke



do not archive



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