Primer issues

aftCG

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Apr 3, 2018
Messages
274
Location
Tacoma, WA
#1
Anyone here every have a primer stop working with little notice?
Looking back I probably had a warning I ignored. My plane has typically always started cold with three pumps.
The past few months it has taken four but I wrote it off to cold weather.
Last week I went up to abuse the pattern and had a hell of a time getting it started. I added a fifth and sixth pump and then concluded that I must have flooded it.
I got out and looked for gas running out of the cowl (none), let it rest and then went through a flooded engine procedure. Not a cough.
More primer (a lot more) and it eventually it stumbled to life. Ran perfectly after that.
Well the same thing happened two days ago. I went through the same logic of suspecting it was flooded. It wasn't.
Real sure my primer isn't priming now. Is that common?
One thing my IA pointed out was that the Citabria has the primer line come off the fuel shut off valve up stream of the actual shut off which means I might have to drain the fuel system before opening the primer mechanism.
Any thoughts appreciated.
 

Bob Turner

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Apr 4, 2018
Messages
643
#2
What kind of carb? What temperatures are you starting in?

I have all Strombergs, and they start cold down to about 55 degrees F by pulling seven blades with the throttle completely closed.

If you have a starter, the M-S carb can be used as a primer - while cranking, sharply go between idle and full throttle three times. Don't do that unless you are cranking; you do not want fuel dribbling on the ground.
 

aftCG

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Apr 3, 2018
Messages
274
Location
Tacoma, WA
#3
Bob,
I have a Marv Schebbler (or however that's spelled) and one of those new fangled starter things you mention.
I'm not talking Minnesota cold. 50-65 degrees.

Great tip on the throttle. I wasn't sure if it had an accelerator pump, and the other engine I fly (R985) says to NEVER pump the throttle.
 

Bob Turner

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Apr 4, 2018
Messages
643
#4
The problem is when you pump while not cranking. The Marvel Schebler does have a pump, but at 60 degrees you really shouldn't need prime. With the butterfly completely closed you should hear fuel being sucked in there when pulling the prop through.

We start the Stearman that way - get it cranking, three sharp jabs all the way from idle to full, and off we go. If it floods, crank wide open and it goes on the third blade.

I don't know how to fix primers. Mine is a Lunkenheimer, and has a leather plunger. Been on the shelf since 1969.
 

aftCG

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Joined
Apr 3, 2018
Messages
274
Location
Tacoma, WA
#5
What kind of carb? What temperatures are you starting in?

I have all Strombergs, and they start cold down to about 55 degrees F by pulling seven blades with the throttle completely closed.

If you have a starter, the M-S carb can be used as a primer - while cranking, sharply go between idle and full throttle three times. Don't do that unless you are cranking; you do not want fuel dribbling on the ground.
Damn if that trick doesn't work perfectly. The first time I tried it I probably had to do an extra pump or two before it caught. Then I realized that if I do three pumps and the all the way back it catches instantly (more vacuum sucking the fuel upward where it belongs I suspect). Starts smoother than if I used the primer.
I've got O-rings on the way but not sure I'm in a hurry to do the job.
 

Bruce

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Dec 22, 2018
Messages
166
Location
Knoxville TN
#6
Great timing just went through this in my Warrior usually 4 prime and 2 blades came to life but lately it's been 5 to 6 this week it wouldn't start thought I flooded it so pulled some plugs no fuel 9 prime and it stumbled to life mines an Essex so some new o rings yesterday was very easy one ring nut and it slides out 2 o rings a little lube and done. Happy flying
 

aftCG

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Joined
Apr 3, 2018
Messages
274
Location
Tacoma, WA
#7
I just realized I never circled back on this subject. After adopting the throttle pumping technique I decided it was a better way to start the engine and decided I didn't need a primer. It starts so much more gently than with the primer. Cylinders come to life gradually without that sudden flare of rpms that always makes me cringe, and it's possible to smoothly bring it up to 1000rpm.

By comparison, with the primer I get about four blades across the cowl and Vroom! The shake was always so abrupt I was picturing it breaking a motor mount some day.

But I still wanted the plane to work as designed, so I swapped out the O-rings using the supplied grease and instructions.

For sake of thread usefulness I'll answer my own question from above regarding the need to drain fuel:. No need to drain the aircraft. I could see some fuel pooling in the bottom of the primer housing but that was it.

Well. It still didn't work. For my annual in July I gave my IA my extensive squawk list:
Primer INOP

I told him about the symptoms and the technique I learned from the internet (here). I can tell he takes most of that like someone going to their doctor saying they think they have Lupus because of something they read on the internet.

Well he and his assistant discovered that I did indeed have a broken primer line and that no gas was getting to the engine regardless of how many pumps you gave it. So odd to me that there was no smell or gas running out the bottom, and I've got the old style cowl that opens wide on both sides.

I've put about 40 hours on the plane since annual and while I've verified that the primer operates "correctly" I prefer to wake the plane up gently by pumping the throttle while cranking.