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Increased fuel consumption

SimonK

Registered User
Nome
Hi Guys

Tried searching on this topic, didn't come up with anything.

After I got through the annual from Hell in May (my first one, and the 14's first "real" one since the previous owner bought it in '86) I had a nice shiny upgraded 160 hp with 500-some hours smoh. I was burning about 8.2 gph during break-in and not much changed after the 50 hours, still burning right there at 8.2 - 8.3. At the advice of my shop I was not leaning to keep the engine temp down, and after the initial 25 hours I would cruise at 2400 rpm.

So here's the problem: After about 60 hours or so the fuel consumption jumped to 9.4 gph. I have tried to think of any changes, but haven't come up with any. Same RPM, same fuel, same outside temperature (approximately), same mixture (full rich),... I also checked it on different tanks to rule out a leaky tank.

I called the shop and was told that 9.4 was still within the specified fuel burn for a 160, but:

1) That seems high to me (might as well run a 180 horse);
2) Why the sudden increase of 1.2 gph?

I know guys who run a 160 burning in the mid 7- range.
Does this sound like a carb problem? Any other thoughts?

Help! Thanks!
Simon
 
Simon,

First, borrow a digital tach checker from a mechanic and verify that the tach is accurate, or at least how inaccurate it is. My experience with mechanical tachs is that they are more frequently than not in significant error.

If the tach is off, its' possible that the tach error changed, I suppose, but in any case, I'd start by verifying the actual rpm (at cruise and full power) that your engine is running.

Then, there are probably a bunch of reasons your fuel flow could have gone up.

MTV
 
Simon

Check to make sure the bolts on the carb have not backed off(float bowl) before you fly again. This is one of the symptoms. Would explain more but in a hurry. Might not be it, but worth a check.

Mark
 
On the other hand, if something in the engine has changed and the result is a subtle reduction in horsepower, the natural thing for you to do to maintain 2400rpm is open the throttle a little more. What conditions can rob horsepower? Constricted muffler? Low cylinder?

I don't think I'd notice if my fuel consumption varied by 1.2 gph.

SB
 
Thanks guys, will check those things out. Would hate to think that I'll spend the rest of this airplane's life burning nine and a half gallons per hour.
 
WAS THERE ANY RESULTS OR RECOMMENDATIONS TO HELP THE FUEL CONSUMPTION SITUATION . I HAVE A 0320 160 hp in a Super cub and is basically burning 9.5 gal / hr. Any help would be appreciated!!
 
One of the first things to check when fuel consumption goes up is a open or leaking primer. It's quick just disconnect the primer pick up line cap the pick up and go fly a couple of hours.

Si
 
My primer slips so easy that I am sure it does not function. I don't use it much here in Texas. I have it screwed down tight, but could it still cause me trouble? Thanks Mark
 
AkPA/18 said:
Simon

Check to make sure the bolts on the carb have not backed off(float bowl) before you fly again. This is one of the symptoms. Would explain more but in a hurry. Might not be it, but worth a check.

Mark
Hi Mark,

This morning I departed for prescott ( about an hour away) I noticed right away that my mixture was farther out (leaner) than normal, given temps altitude etc... in order to maintain my standard cht/egt. Also I noticed that I could almost "put the fire out" if I went to full rich.

At Prescott I coudn't see anything obvious wrong, and to be honest after a short bit I forgot all about it On the way home I noticed it getting a tad worse and also noticed the "range" of mixture I could use was getting smaller.

Upon landing at my home the cub actually momentarily quit on roll out and was running pretty rough taxing back to my parking.

After I got stopped I looked under the hood again and what I saw spooked me. My float bowl was just about ready to fall off! The nuts/ bolts are all still there but bearly.

Since you had suggested Simonk check for this situation I am presuming you have seen this before? Is it common, like should I watch for this again? My mech is in Willow right now, so I am thinking to just tighten it up and fly. I did watch the temps, pressure etc... and it never got out of line, just got harder to manage. Is there anything you can suggest to look for?

Somone local had suggested I check this out before but I dissmissed it thinking it would get leaner running. This seemed to get richer. I am presuming that was a result of raw fuel just boiling over and geting sucked into the intake?

Any insight would be greatly appreciated,

Thanks, Rob
 
SimonK said:
Hi Guys

I called the shop and was told that 9.4 was still within the specified fuel burn for a 160, but:

1) That seems high to me (might as well run a 180 horse);

Help! Thanks!
Simon

I want to dispel some myths about the O-360 fuel burn. My O-360 burns about 10% less fuel the an O-320 Cub. I got the same comment from Christina when I met up with her in Bettles. We got to Kotzebue and I took 5 gallons less then her 150 hp O-320 Cub. Got to Nome and I took 8 gallons less to fill up. Picked up another friend with a 160 hp Cub the next week and the same thing. My 180 hp Cub burns less fuel then either the 150 or 160 hp Cubs. The big difference is how hard you have to run the engine. Running with them I am turning 2250 while they're wound up to 2450 and higher. But if I turn up to 2450 then I am 10 to 15 mph faster and get to the destination quicker and shut down sooner, so again, less fuel burn. So any time some one tells you an O-360 in a Cub burns more fuel then and O-320 take it with a grain of salt. They just don't know what they're talking about. Ask Christina or Slowgo. Crash

P.S. I installed my new Alph Omega hydrasorb replacements today (only been sitting on the work bench in the box for 6 months). Took the plane out and purposely did some hard drop landings to feel how it would bounce. They REALLY work. One small bounce when the tires hit and then you're planted. Be careful about using brakes too much. Your tires never leave the ground after the first bounce so you have maximum braking if you need it. Not like hydrasorbs where you get braking between the bounces. I think they'll really help with getting into tight places.
 
fuel

Simon, I agree with the small power loss theory. Could be something as simple as your {new} points wore in and now you need to retime it although it seems that worn points would make it advanced to much and that shouldn't effect power unless it was quite a bit early. I had a carb bowl come loose once and that will loose you quite a bit of power easiest way to check that is to wiggle the air cleaner dome while looking at the carb through the side door for movement. What prop/pitch are you running? Good luck
Dave
 
Have seen loose carb bowls several times in the past and one just recently. Lock tabs where bent over and everything. I think the gasket must shrink.
 
Carb bowl

This same thing happened to me. Now I always give my air cleaner filter cover a shake to see if bowl is loose. Like Steve says the gasket will shrink. You can re tighten the screws and go fly but it will probably still seep a little. Replacement with a new gasket is necessary. Seems like you are suposed to tighten down then re check the screws again. Steve probably knows the routine,somthing about compressing the gasket.

As for the primer lines I capped mine off and did not use anymore with the replacement of cylinders.I know its not too cold here so it still starts ok.
 
Re: Carb bowl

PA-18 said:
This same thing happened to me. Now I always give my air cleaner filter cover a shake to see if bowl is loose. Like Steve says the gasket will shrink. You can re tighten the screws and go fly but it will probably still seep a little. Replacement with a new gasket is necessary. Seems like you are suposed to tighten down then re check the screws again. Steve probably knows the routine,somthing about compressing the gasket.

If it goes on long enough for the bowl gasket to be completely worn through, the two mating halves will gall a bit - check carefully for that; just replacing the gasket sometimes won't do the trick.
 
I also had my float bowel loosen, to the point the engine started to run better with a little carb heat. The change in engine performance came on relatively suddenly, so it was rather obvious. I flew on to my destination, landed, then looked under the cowling and noted streak-marks extending down from my float bowel gasket. I removed the carburetor, and took it to BJ's in Palmer where it was rebuilt.

According to the mechanic who overhauled my carburetor, he had seen several similar carburetors with the same problem in the preceding 3 months. He said a special gasket had to be re-torqued several days after being put in new (the material must crush down with time). Anyway, scary thought having raw gas exposed under your cowling, flying along at 3,000 ft!

My 160 (0320-B2b) uses 7.4 gph leaned at 2400 with a borer prop with 41 inch pitch. If I don't aggressively lean at every opportunity, I burn 8 gph at 2400 RPM.

Bill
 
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