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WindOnHisNose
01-10-2010, 09:16 PM
I flew my supercub up to Park Rapids yesterday, temp there was about 3 degrees, felt warm for what we've seen around here recently. The flight went fine, landed on skis a time or two, put it in the (unheated) barn for 3 hours, put on the engine cover, plugged in the Tanis.

When I came out to fly home I prepared for flight, crawled in and noticed the primer didn't sound or feel quite right, but I primed it the usual 3 or 4 pumps, tried to start the engine...to no avail. Repeated, same result. Primed more without any luck. It was about zero outside and getting a bit dark, and I don't like to fly at night when it is this cold, so I put it back in the hangar, put on the battery charger, plugged in the Tanis, covered the engine and arranged for a friend to bring over one of those propane powered jet heaters this morning.

Put heat on the instrument panel/primer and tested the primer and it felt much more "normal". Pulled the plane out of the hangar, primed 3-4 pumps, the engine started without any delay.

I am assuming I need to replace the little rubber O rings that are on the shaft of the primer plunger (Essex), and Darrel ordered me a couple replacements. Anyone have suggestions on what else might be wrong? Could it have been stuck check valves???

Also, I was thanking my lucky stars that I hadn't just parked it out by my cabin on the lake. Have any of you fellows up north had problems like this, and if so, what have you tried in a pinch to get the engine primed?

I appreciate any feedback. Don't want to be in that position again.

Randy

cubdriver2
01-10-2010, 10:29 PM
If you got stuck and had the right tools you could pull the 2 top plugs on one side and dribble in about a tablespoon of gas into each cylinder after you sumped it out of your fuel tank, make sure you tighten everything before you start up.

Glenn

T.J.
01-10-2010, 10:54 PM
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Darrel Starr
01-10-2010, 11:11 PM
T. J., Randy was telling me about this problem today. I'm thinking that the most likely problem is one of the check valves leaking or stuck with possibly a broken spring because it seems to me that a falty o-ring will result in a dribble of fuel out past the stem, or am I missing something?
Darrel

mike mcs repair
01-11-2010, 12:05 AM
T. J., Randy was telling me about this problem today. I'm thinking that the most likely problem is one of the check valves leaking or stuck with possibly a broken spring because it seems to me that a falty o-ring will result in a dribble of fuel out past the stem, or am I missing something?
Darrel

I would usually do both items (o-rings and pop out inlet check valve ball and clean)since you have fuel shut off already and just drop primer down below panel since you will have it loose, the "inlet" check valve does get gummy and stuck closed...

the o rings can be bad enough to not build a good suction to overcome inlet check valve spring, yet not leak.....

mvivion
01-11-2010, 07:22 AM
I'd follow TJ's advice on "overhauling" the primer.

But, in future, if the engine doesnt' fire right away, WHILE CRANKING, give the throttle TWO (not three or seven) QUICK full travel shots to the stops.

In other words, energize the starter, and while cranking, move the throttle FAST from the normal start position to the wide open throttle position, then quickly back to the normal start position. TWICE. This movement is done basically about as fast as you can move the throttle.

The carburetor has an accelerator pump in it, which this fast movement of the throttle activates, squirting raw fuel into the carburetor.

I don't recommend using the accelerator pump UNLESS your engine is cranking over, because the fuel may drop back down into the air box. While cranking, that fuel is drawn up into the induction, and the cylinders.

In some airplanes with these engines, a primer was a factory option.

I still like using a primer in lieu of the accelerator pump, but....if at first you don't succeed.

MTV

WindOnHisNose
01-11-2010, 09:05 AM
Great suggestions, fellas, thanks very much.

We will replace the o rings and clean the check valves, lube with fuellube.

Mike, I'll keep the throttle accelerator method in the dark recesses of my mind, and will keep the spark plug trick there, also, cubdriver2.

Have a great week!

Regarding the o ring thought...why didn't I smell fuel if the o rings weren't sealing correctly???

rsc

T.J.
01-11-2010, 03:27 PM
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Scouter
01-11-2010, 07:26 PM
How many hrs on the mags? My Scout did the exact same thing in the cold, except I was stuck 100 miles from home. 800 hrs on Slick mags. New mags and it starts excellent at all temps.

Jim

WindOnHisNose
01-11-2010, 11:37 PM
Scouter, only a few hundred hours on the mags.

TJ, your explanation sounds good to me regarding not smelling fuel.

Randy

StewartB
01-12-2010, 10:45 AM
Sometimes when the primer won't pick up fuel on the first suction stroke I can go through a couple of plunger strokes and stop with the plunger pulled out for several seconds. It'll pick up just a little fuel. Once that happens the pump is primed and it works okay. Also try slowing the suction stroke way down. Don't give up too easily.

SB

behindpropellers
01-12-2010, 10:49 AM
Sometimes when the primer won't pick up fuel on the first suction stroke I can go through a couple of plunger strokes and stop with the plunger pulled out for several seconds. It'll pick up just a little fuel. Once that happens the pump is primed and it works okay. Also try slowing the suction stroke way down. Don't give up too easily.

SB

Or you can pull it out, and put a dab of oil off of the dipstick on it.

cubdriver2
01-12-2010, 10:59 AM
Tim, do you mean the one under the cowl or the one in the front seat :lol:

Glenn

badmdcnman
05-06-2010, 10:19 PM
Randy's
I am assuming I need to replace the little rubber O rings that are on the shaft of the primer plunger (Essex), and Darrel ordered me a couple replacements.

Randy,
just curious if your new O rings solved your problem and if so where did you get your O rings or what kind did you use.

Reason I ask is that I have had my O rings replaced in a couple recent annuals and a month or so later especially getting into winter the primer becomes nearly impossible to cycle.

I recently decided to take it upon myself and pulled the Essex primer out of my 12 to see for myself what was going on. The cylinder was perfectly smooth and the check valves were fine, but the black O-rings appeared to be scuffing and leaving a residue on the cylinder walls. Upon cleaning and replacing the O-rings with a green chemical resistant HNBR O-ring we use in air conditioning systems the primer cycles dry (not yet installed) perfectly.

I have some of these O-rings soaking in AvGas for about a week now and have not noticed any degradation. I have yet to install the primer back in the aircraft. A phone call to Univair revealed no overhaul kits available for this primer and I hate to spring $200+ for a new primer that could be fixed for 50 cents.

Would these primers built in the late 40's actually have had rubber or neoprene O-rings or would they have been leather seals of some sorts. I am assuming my mechanic would have used the recommended O-rings when he changed out the seals in previous annuals.

Just curious how you turned out.

Thanks........Rod

Darrel Starr
05-06-2010, 10:41 PM
Rod, I orered the 0-rings for Randy. They came from Aircraft Spruce. Perhaps he will see your post and answer. I saw him a couple of hours ago in his MN Twins uniform dreaming of being called up to save the team. He is probably still taking swings with his favorite bat in the full length mirror at home. So be patient, when he comes back to reality he probably will answer you.
Darrel
http://www.supercub.org/photopost/data//500/medium/Essex_Fuel_Primer.jpg

badmdcnman
05-07-2010, 10:56 AM
Thanks Darrel! I will check that out. My primer is an Essex2406-2 if that makes any difference. I'll check it out with A/S.

Appreciate the tip........Rod

WindOnHisNose
05-07-2010, 06:58 PM
Hi, Rod, the O rings fixed the problem! Very simple to change, as even I could do it!

Unfortunately, the Twins haven't called me up yet, but I am ready when they do. I think it only appropriate for the Twins to have a supercub.org player on their roster.

Take care.

Randy

SteveE
05-07-2010, 07:30 PM
You talkin about the Barbi Twins? I hear they are looking for a Dr. like you.. 8)

texmex
05-10-2010, 08:13 AM
I only wish I could be asking questions about primers, unfortunately I don't have one. It's taken a lot of trouble starting over the years and finally I've worked out the only way to start it is with the throttle closed. I use to pump the throttle a few times and then leave it half open thinking the larger volume of air would drag the pumped fuel into the cylinders, but no. I'm guessing but I now think the closed throttle butterfly valve creates low pressure around the idle jet and drags the fuel in that way. Corrections to my current thinking welcomed!!!!

My father is adamant starting should be on the left mag only. I spoke to a friend who use to rebuild Lycoming 540's who thought this was an old wives tale. What's the general consensus on this?

Temporarily using a "strong arm" starter. One mag, throttle closed and not being in the cockpit to flick the mags to both can be a little tricky.
Denis.

Darrel Starr
05-10-2010, 12:50 PM
The type of mag switch that has "left- right-both-start" positions is wired so that only the mag with the impulse coupler is hot in the "start" position.
Darrel

mvivion
05-10-2010, 02:33 PM
Texmex,

Starting little Lycomings on the left mag only is NOT a wives tale.

The reason is that only the left mag has an impulse coupling the way these engines come from the factory. The impulse coupling changes the timing of the magneto. The right mag, on the other hand, is timed for running, not for the start.

So, if you try to start these engines with both mags on, you will have magnetos with two different timings, both trying to start that engine. The potential for kickback if not an actual backfire are increased, and particularly with the newer lightweight starters, this is a great way to equip your airplane with yet another NEW starter, after the kickback snaps the starter drive.

If you're starting by hand, a kickback can break your arm if you're a little off in your technique.

For hand starts I really like a primer. Makes starting a bit easier.

Working the throttle full open and back a couple times PRIOR TO CRANKING dumps a bunch of gas into the airbox, and combine that with a back fire, and you'll be hunting a fire extinguisher. If I use the accelerator pump (operated by fast movement of the throttle) I like to have the engine cranking FIRST.

If you're hand cranking that thing, and your technique works, keep doing what you're doing. But, I'd start on left mag only. There's no rush to get the other mag engaged, the thing will run fine on the left till you climb aboard and get settled.

Darrel is correct on airplanes that have been modified to have the magnetos controlled by a regular "ignition switch" as opposed to separate mag switches, as Cubs were originally equipped with. In the case of an ignition switch, the "start" position on the switch grounds out the right mag, so you're starting on the left mag only.

Some engines have been equipped with a second impulse coupling, so they can start on one or both mags, no harm no foul. Many of the BIG Lycoming engines were equipped with two impulse couplings.

MTV

texmex
05-10-2010, 07:31 PM
Thanks Guys, I've always wondered why the single mag start was confined to cubs, scouts etc. with individual mag switches. The earthing of the right mag on other aircraft when start selected makes sense.
Any comments on why starting without a primer I have success only with the throttle closed?
MTV- war story only- that accelerator chamber caused me grief when the engine was overhauled. I was up doing stalls, wingovers etc. When I advanced the throttle quickly it became stuck. Trying to free it up I successfully jammed it in the idle position. With some poor piloting decisions I ended up in a very tight paddock surrounded by tall trees. Anyway eventually flew it out of there back to the engine rebuilder where I repeated my trick several times over a huge airfield. Turned out the valve a the end of the accelerator chamber was blocked causing a hydraulic lock in the carby and hence the throttle linkage.
I've another engine "myth" I'd like discussed but I'll start a new thread.
Thanks Texmex.

texmex
05-10-2010, 07:39 PM
Oh yes, kickback while hand starting is murder on the finger tips :oops: