#4 egt drops, engine surges

by James Butcher in 912 / 914 Technical Questions 8 years ago

My 914 has an intermittent problem. As I add throttle around 3500 rpm and 18 in man pressure the engine surges. The rpm drops and mp rises with more throttle. The #4 egt drops rapidly from around 1300 to 900 deg f. i just did the rubber replacement and had LEAF rebuild carbs. Engine ran fine for 10 hours then started this.

Compression is 75/80. No induction leaks. Carbs balanced. Cylinder 2 runs fine. No metal on magnetic plug. Valves appear to operate normally when observed with valve cover off and pulling engine thru.

Need ideas.

Jim Butcher

Re: #4 egt drops, engine surges

by James Butcher » 8 years ago

James Butcher

8 10 5

After talking to other owners with similar problem and Dean at Lockwood, we think the problem is leaking float bowls. We have new ones on the way. Dean suggested to soak the new gaskets in gas for 3 hours and then assemble. Tighten nut to 48 in lbs. wait 24 hours and recheck torque.

I can't find any reference to soaking the gaskets like this. Do others do this? Is it in the manuals somewhere?

Thanks for help.

Jim Butcher

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Re: #4 egt drops, engine surges

by Roger Lee » 8 years ago

Roger Lee

125 5.11k 4.52k

Soaking them is just trying to swell them before installation. Most use them dry. I rub them with white lithium grease and rub the gasket on the top, bottom and sides. Never had a leak yet. If you do rub it down do not leave globs on it. Checking the torque after a week or so is a good idea.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: #4 egt drops, engine surges

by James Butcher » 8 years ago

James Butcher

8 10 5

I wanted to leave an update on this problem.

The new carb bowls and gaskets seem to have solved the surging problem. We had the new parts installed as instructed, soak gaskets in gasoline for 3 hours and then install and torque. Our A&P also used Fuellube on the gaskets. He checked the torque about 6 hours later and found they were slightly loose. He retightened and checked again after another 18 hours. The torque was unchanged.

We have flown about 10 hours since with no surging problems. We do see a little fuel residue in the drip trays, mostly at the front end just under the carb sockets (which were replaced 30 hours ago). Is this normal?

Looking at the old carb bowls, when we hold the mating surfaces of the bowls together, there is a slight gap on all four sides. The corners all touch with no gap. The gap on the sides is very slight, you can barely get a corner of paper in it. I wonder if the old bowls are fine and that the problem was that the gaskets were not properly installed or retightened during the rebuild prior to these problems.

Roger, thanks for your answer about the gaskets. You state you have "never had a leak yet". Are you servicing any 914s? Float bowls seem to be much more critical on 914 engines, especially when operated at altitudes over 12,000 ft.

Jim Butcher

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Re: #4 egt drops, engine surges

by Roger Lee » 8 years ago

Roger Lee

125 5.11k 4.52k

Hi James,

Glad you found the problem. I do agree that once the 914 carb bowl is installed the torque should be checked again a day or two later.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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#4 egt drops, engine surges

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