Hi,

Have an O-470R with around 80 Hrs since Fact. Reman.
Wondering if its mixture for S.L. T/O's is rich enough. FF shows Aprox. 20.8 - 21.2, hope its accurate.
Have adjusted the K factor and at least on used fuel / served fuel miss only by around .5 Gls on say a 25 Gls lift up.

Did an inflight lean range/Mixt. Distrib. test.
Wide open throttle, 60% power, mixture full rich, then start leaning out to peak EGT and find the range between them.

Got just 185 Deg. range for Cyl. 1 and 2
All others 250 to 320

What have you gotten?

Understand it should not be below 250 to make sure T/O mixture is rich enough.

Is that what you know?

O-470´s are well known for its uneven Mixt. distribution, that´s for sure. Still more than an excellent engine.

Not that I feel something is unsafe with my engine in the short term here but would like to know your experiences-comments on the subject.
First time I operate a JPI on a carburated engine and want to make the best use out of it mainly to identify things before they start becoming a problem.

Marvel Schebler 4-5 carburator for this Eng. does not have any adjustment to increaseT/O fuel as far as I know, its a jet size, thats it or?


Brgds,

Manuel

Are you actually WOT? As in throttle right to the panel? If you are then you need to pull it out until you see a small drop in MP. At WOT, your accelerator pump is open and bypassing extra fuel. Good for take off and climb, but for cruise and leaning I buggers up your test and makes the fuel distribution worse. Just something to try to get your temps more even. Sometimes a bit of carb heat helps balance flows as well.

Thanks for your comment A-1

Yes, WOT. Radar power as we used to say when the radar was right in front of the throttles. GG

All I am trying to establish is if my Carb is providing enough FF at S.L. T/O. After an anual and a boroscope felt Cyl No1 was probably too lean and started investigating.

Besides FF indications and EGT's I wanted to dig a little more and validate.

Reducing throttle I know will make for a better mixture. Carb heat for some reason on this engine has not shown to be helpfull.
Those things I would consider for cruise but again, my concern is takeoff mixture.
Wonder if reducing throttle to perform the mixture range test if I can call it that way ( between full reach Max FF EGT and peak EGT)
Remember reading that 250-300 range was a good Ref. to make sure take off mixture to be rich enough.

Your or any others help/comments will be appreciated.

To clarify,

The 250-300 range I am talking is not to compare between cylinders and see how uneven the mixture between them is.

In this case its the full rich EGT versus peak EGT on a cylinder.

All I get on No 1 is 185.

Here is a formula to determine fuel flow.

Minimum takeoff fuel flow can be determined by:

(.55# fuel per HP per hour)/6# per gallon

For example:
275 HP
.55*275=141.25/6=25gph

I keep WOT wide open until reaching cruise altitude. This keeps all cylinders around 380 during climb.

Just my $.02 worth.

Thx Rfinkle, yes, the formula gives about 21 Gls FF for 230 HP on the O-470 and that is Aprox. what I am getting.

Wish it was a little higher to still handle the uneven distribution on the O-470 and make each cylinder get what it deserves. Would rader have some Cyl's too rich for T/O than too lean.
Sad to see people removing cylinders with 400 hrs on them...

I don't have any problem with my CHT's and most people say that as long as they are under 380 all is fine with the E. valves but one still can see burned valves on such cases from what I read.

I will keep checking for induction leaks, Thx again.

Induction leaks generally are the place to look on 470's for unequal distribution. You may want to remove the crossover tube and be sure all the metal segments of the induction manifold are in line as you look in from the front. If anyone of them look higher or lower than the others it creates a lot of turbulence which makes the distribution even worse.

Many thanks for sharing that interesting info rfinkle, I will keep that in mind to check it out.