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larry(at)macsmachine.com
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 Posted: Sat Mar 25, 2006 1:56 pm Post subject: Color tune plug for Idle mixture |
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Hi guys,
About 2-years ago, I wrote a lengthy post here on jetting the Stratus
Subaru with Bings and I had maneuvered thru mixture adjustments using
EGT sensors and a Grand Rapids Technologies Engine Information System.
It was intended that further mixture corrections would be resolved by
simply reading the EGT temps. I forgot that Id purchased a Color-Tune
plug that enabled seeing the actual flame within the chamber. Seemed
redundant with engine running fine of late. Today the color tune plug
was used and I was surprised to be so mistaken.
Spark plugs have always seemed sooty at idle rpms, so this afternoon, I
removed the prop, replaced the front #1 plug with the Color-Tune plug
and connected the plug wire. The engine had been warmed a few minutes
earlier so it fired and ran a little roughly at 1000 rpm. I saw the
orange glow thru the glass in the plug and began turning the idle
mixture screw until the glow had changed to a bright blue. The engine
seemed to run a little better at the low rpm. This was repeated on the
opposite front plug as it also was unsteadily flashing orange and I
adjusted the idle mixture screw to a steady blue flame.
Again, on the rear plug, the process was repeated and I was surprised to
see a bit of orange flashing in the chamber. A slight adjustment brought
the rear plug to a constant blue fire. The opposing rear plug was done
the same way with the same results. The front plugs were checked again
and all were blue and the engine was ticking along smoothly even better
than its ever run at idle. What a difference!
Anyway, the first of this series was a 1000-rpm test for setting idle
mixture and Im awaiting a 2.78 one-size larger mid range jet for the
2000-rpm test and a #178 one size larger main jet for a 3000-rpm test.
Ive been comfortable that EGT temps have stayed near 1400, but now Im
convinced the engine EGTs might be able to run even cooler.
Will post again when the jets arrive and the next set of rpms are run.
Fly safe,
Larry McFarland 601HDS at www.macsmachine.com
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frank.hinde(at)hp.com
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larry(at)macsmachine.com
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frank.hinde(at)hp.com
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d3dw(at)msn.com
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| Posted: Sun Mar 26, 2006 5:21 am Post subject: Color tune plug for Idle mixture |
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Larry and Frank,
I am surprised, too, that the rear plugs, which usually run a little leaner than the front, were still orange. (I don't have a color-tune and I guess the orange is a too rich mixture). From what you are saying, Larry, this contradicts the old method of adjusting both carbs at idle until the rpm max out, then lean a hair. Yours looked right by color at a little lower rpm...correct?
Next question. time for bungees. Mine are now now 13 years old counting shelf life (holy cow). With the Stratus are you guys okay with the 1080 on the mains or are you using something heavier...like an HD or something.
Third, have any of you tested your cog belts past three years and 36.000 miles? Mine second is now four years old but I haven't gotten to the 250 hours yet. Not an item to take risks on, but the old one I took off still looks good, now seven years old. Don Walker
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larry(at)macsmachine.com
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| Posted: Sun Mar 26, 2006 6:51 am Post subject: Color tune plug for Idle mixture |
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Don,
I'm not sure it contradicts the old method as the rpm did increase with
smoothness and I did have to reset rpm each time.
The flame color runs from orange (rich) to blue (just right) to white
(too lean). The initial color at the front plugs was orange and
a turn of adjusted idle-mixture brought that to blue. The rpm did
increase and smooth out. I reset the 1000-rpm each time
before reading the flame color and the rear ones were not so pronounced
an orange, but went blue with a lesser adjustment.
The color was correct at 1000-rpm and appeared not to change 200-rpm
either way.
I don't think I've enough time on my bungees to evaluate them. I'm
using 1080s and have 3/8ths inch cap above the wing. Not looking
forward to changing them. Considering they are 4-years on the gear and
probably 10-years from manufacture they look good.
The 300 hour change out for the cog belt is probably half the actual
service life expectancy. Even for an aircraft, the
recommended 300 hours is what I'd call pessimistic and others would call
it prudent. I believe Kelly Meiste sent a document that I've stored
somewhere in here about belt life expectancy and my opinion is held from
reading that article. Not sure how to test my belt, but it gets a good
examination each time the cowl is off. These things don't seem to crack
or age predictably. I think the failures we've seen were the result of
poor adjustment, objects fed thru the belt or poor handling during
removal and replacement. There's lots of room for error in all of these.
I will comply with the 300-hour change out because the belt is not as
expensive as having one fail in flight.
Larry McFarland
Don Walker wrote:
| Quote: |
Larry and Frank,
I am surprised, too, that the rear plugs, which usually run a little leaner than the front, were still orange. (I don't have a color-tune and I guess the orange is a too rich mixture). From what you are saying, Larry, this contradicts the old method of adjusting both carbs at idle until the rpm max out, then lean a hair. Yours looked right by color at a little lower rpm...correct?
Next question. time for bungees. Mine are now now 13 years old counting shelf life (holy cow). With the Stratus are you guys okay with the 1080 on the mains or are you using something heavier...like an HD or something.
Third, have any of you tested your cog belts past three years and 36.000 miles? Mine second is now four years old but I haven't gotten to the 250 hours yet. Not an item to take risks on, but the old one I took off still looks good, now seven years old. Don Walker
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frank.hinde(at)hp.com
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| Posted: Sun Mar 26, 2006 4:21 pm Post subject: Color tune plug for Idle mixture |
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Hello Don,
My bungees seem just fine with the standard ones that were in the
kit..Whatever they were.
Over rough grough the nose is a little too bouncy sometimes but just
slowing it down cures that usually.
I have not changed my bungees in 6.5 years and they seem just fine. Not
sure if there is a recommended change interval on these? I think as long
as they don't get exposed to UV they should last a long time.
As to the belt, changed mine a couple of years back at around 300 hours
and it looked perfect. I also changed the bearings at the same time cus
its easy to do and cheap...Bought all bearings and belt from my local
bearing suplier
Frank
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