C-85 high fuel consumption

SFC Hiatt · Post by **SFC Hiatt** » Mon Nov 17, 2008 19:45

tim_chow wrote:Here are my responses to the comments so far:

Carb heat flap: does tend to vibrate open some when flying.

Tim

I had the same problem with the carb heat vibrating out so I added the same spring loaded latch on the carb head that's on the fuel knob

tim_chow · Post by **tim_chow** » Mon Nov 17, 2008 21:34

To 15A and Dusty:

The plane has two 5 gallon wing tanks and the 13 gallon main tank. If I fill up the main and fly it for an hour (keeping the valves to the wing tanks off) it will take 7 gallons to fill it back up. If I was losing a gallon though the gas cap on the main tank I would see and smell it.

I can park the plane for a week with all the valves closed and it will not loose any fuel in any of the tanks.

Tim

MikeB · Post by **MikeB** » Mon Nov 17, 2008 22:05

I still suspect the carburetor although that is a lot of fuel to lose, but if everything else checks out you might try this: run a couple of tanks of 100LL and see if the plugs and pipes still look sooty. If so, it probably indicates trouble in the carburetor that's causing it to run rich. With auto fuel it's pretty hard to diagnose as the plugs and pipes tend to run kind of black anyway. Especially if the engine isn't up to temp or there's been a lot of idling (taxing in and before shutdown, etc. ). I'd be sure to check the timing and carb heat box just to eliminate those possiblities. Eliminate the simple things first before putting out the big bucks. The fact that you never have to prime is a bit confusing

. Do you pull the prop through (with the ignition off) before starting?

Mike Berg

gusc · Post by **gusc** » Mon Nov 17, 2008 22:28

Today's auto fuel makes sooty exhaust pipes, check any newer auto in the parking lot and you will find soot. In the old days it was a sign of an overly rich mixture - no more.

My A65 with Stromberg drips fuel after shutdown also unless the fuel is turned off.

As I remember auto fuel is less dense than avgas but I may have it reversed! If I'm correct auto fuel would make the fuel level in the carb bowl higher

tim_chow · Post by **tim_chow** » Mon Nov 17, 2008 22:36

Mike:

The stacks do seem sootier now than 6 months ago when the fuel burn has less but your right, they were always sooty.

I usually pull the prop through 2-3 times before engaging the starter. It will usually start with the starter after 1 or 2 blades. If I don't pull it through it will still start in 1-3 blades anyway.

Tim

Dusty · Post by **Dusty** » Mon Nov 17, 2008 23:47

Sure someone didn't sneak an O-320 in there?

My old Pacer burned about 7.5 if you babied it.

I'm sure you've overfilled the nose from the wings at some point, and know there's no way you'd not notice fuel coming from the cap.

A leaking tank/gascolator/hose would probably leak on the ground too.

I just don't know how you'd shove that much gas through that little engine and not REALLY know it, but if none of the above.....

I agree with trying avgas at this point. It might do something diagnostic in your engine, and it'll leave blue stains (for a bit) if it's running down your fabric somewhere.

gusc · Post by **gusc** » Tue Nov 18, 2008 23:41

Do you have to advance the throttle more now to get the same power than when you first got it?

That happened to my Stinson once and it was a valve seat that had hammered down because of a failed valve lifter. Supposedly that would affect compression but I don't remember for sure, it was a long time ago. Seems to me it didn't.

tim_chow · Post by **tim_chow** » Wed Nov 19, 2008 11:01

Dusty - I have seen fuel comming out of the nose tank...very noticeable!

Gus - No noticeable difference in throttle postion. I guess the throttle is a little high to get the same cruise rpm since the static rpms are a little lower.

I check the timing and it was ok. I also left the fuel on for 45 minutes to see if it dripped from somewhere in addition to the the carb. It didn't.

Tim

Paul Agaliotis · Post by **Paul Agaliotis** » Wed Nov 19, 2008 11:30

Tim,
If you are buying the gas at the same pump, perhaps the owner has allowed the accuracy of his pump to be off. That is a lot of fuel for such a small cubic engine to use.
Paul

Dennis · Post by **Dennis** » Wed Nov 19, 2008 21:28

Paul,

I am glad you brought that up. Our local airport pump will be off several gallons on a puchase of 25 gallons from the credit card receipt with the credit card receipt being greater. A number of people have complained to no avail. There attitude is "...don't worry, we know what to bill you."

Dennis

Paul Agaliotis · Post by **Paul Agaliotis** » Thu Nov 20, 2008 07:41

Dennis,
California has its Weights and Measures office calibrate the pumps.
We have the privilege of being taxed about 60 cents for a gallon of fuel. Some of the airports also charge a 1 cent per gallon "pumping fee" if you dispense fuel at their airport.
So to California, it's pretty important to have an accurate accounting of the dispensed fuel. Plus it gives 1000 naturalized citizens a place to go and socialize.
Paul

gusc · Post by **gusc** » Thu Nov 20, 2008 21:39

I'm afraid our Ark Weights and Measures people don't spend a lot of time at airports, or gas stations either! They never have enough people!!

At our airports we don't care if you're naturalized or not, or even if you are foreign, just come watch the airplanes and gab.

SFC Hiatt · Post by **SFC Hiatt** » Thu Nov 20, 2008 22:08

Dennis wrote:Paul,

There attitude is "...don't worry, we know what to bill you."

Dennis

Dennis.....next time you pay your runway access fee just short them and tell them not to worry, you know how much to pay...

Paul Agaliotis · Post by **Paul Agaliotis** » Fri Nov 21, 2008 08:14

Gus,
We also get a lot of people coming out to watch the airplanes and gab. But it's usually to get names and N numbers for the complaint.
Paul

WWhunter · Post by **WWhunter** » Fri Nov 21, 2008 20:43

I posted this earlier but I guess it didn't go through.

I had a similar problem when I first bought my Champ. I finally noticed the carb only leaked in the three-point attitude. The carb had been rebuilt before I purchased it and I had the needle/seat check and it was fine. After taking the carb apart for the second time I found out the float had absorbed a minute amout of fuel and it was just enough to keep the needle from seating when the plane was at any angle other than level flight. Since it was a new float Precision sent me a new one.
Just another suggestion.

WW