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Primer wars of a different flavor

Sam_B

Well Known Member
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I’m at the part of the project where I keep saying I’m close to done with wiring, until I remember one more thing I forgot to account for on my wiring schematic. One of those things is the primer.

The primer on my continental O-300 powered 172 hasn’t worked since I’ve owned it, and though I have the parts to fix it, and an A&P friend to supervise my work, I just pump the throttle a few times and it starts up in 2 blades, so I’m not motivated to fix it.

That said I’m thinking I can do the same on my Lycoming O-360 A1A on my RV-8, and save the trouble of one more thing that can break. I’m looking for advice from the collective on why that’s a good idea or why that’s a stupid idea. I live in Wisconsin, but my hangar is heated, and I plan on preheating if I’m away from home for a long period of time in cold weather. Other threads seem to be a mixed bag of “install one” and “don’t bother”, so I’m hoping to get a few fresh opinions and more importantly, the WHY behind them.

Thanks,
Sam
 
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Engine needs to be turning to create vacuum.

Pumping the throttle for purpose of priming is not good unless the engine is turning. With an updraft carburetor, pumping the throttle without the engine turning just pours raw fuel out of the engine into the airbox.
 
I've heard of engine backfires igniting the fuel in the airbox and burning the plane to the ground. Apparently it was a pretty risky practice in Cessna 180s with the O-470.
 
I suppose I should word that more clearly

Yes, doing so while cranking, kind of a quick dance I do to not start at full throttle, and it usually pops once or twice after about two blades after the 2nd pump of the throttle, then dies for a bit until I push the throttle back in a touch to a decent idle. That said, I should probably find the service manual and fix it. But that’s not an RV and my original question still stands... is a primer worth the trouble and why or why not? After typing all of that, I’m beginning to think so, but it really isn’t hard to start my other plane, so I’m wondering what the others have found on Lycomings. I’m trying to avoid bolting everything but the kitchen sink to my plane, but I’ll pay the weight penalty if it’s going to annoy the heck out of me.
 
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But that’s not an RV and my original question still stands... is a primer worth the trouble and why or why not?

Sam, I have the same engine on my -8 and -4 and have never used or had to use the primer. Both planes start on the 2nd blade with a short pump of the throttle while cranking. I say it is not worth the trouble.

Btw, Boyceville is my favorite place to get cheap gas when I am in MN for the summer.
 
I'm in KATW, unheated t-hangar, oil-sump preheater only. I was concerned as you were.

No primer...not needed. Waste of space, and adds risk (air/fuel leaks).

Crank...then pump 2x just like your 172 and bring the throttle all the way to IDLE to choke off air and she'll light off when the mixture is just right (2-3 blades). When engine starts, smoothly bring up to 1000 rpm, and laugh at the people who over prime and throttle during the start causing an un-lubricated race to 2000 rpm.

It helps if you have electronic ignition, but I used this same technique with Slicks and it works flawlessly.
 
So long as I preheat to 45F or better, a single pump of the throttle while engaging the starter is usually sufficient, even with two mags.

I used to have a primer installed but didn't really get a warm and fuzzy feeling when I found the primer line cracked right above the cylinder priming port during a routine inspection. I promptly removed the whole system. That was about 8 years ago and I've never seen the need for a primer since.

As others have noted above, however, be absolutely certain that you are cranking before you pump the throttle.

Good luck.
 
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No primers on any of our Lycomings powered planes here in western Nevada - doesn’t get as cold as Wisconsin, but the “pump while cranking” (for the carbed engines) works every time and the primer can’t fail since it’s not installed.
 
I used to have a primer installed but didn't really get a warm and fuzzy feeling when I found the primer line cracked right above the cylinder priming during a routine inspection. I promptly removed the whole system. That was about 8 years ago and I've never seen the need for a primer since.

That’s one of the reasons I was leaning towards not. Those lines just don’t strike me as very robust in the vibrating environment of an airplane.

As for the cold, my hangar is heated and I’m always planning to keep it heated, so that doesn’t bother me that much. There may be times away from home that it becomes more of a concern, but I think preheating is a good practice.

Thanks guys, I think I’ll skip the primer.
 
FWIW, the manual primer that was installed on my RV-6 when I bought it rarely seemed to work. It even leaked occasionally, and with the lines running fuel into and back out of the cockpit it just seemed like a potential failure point that could only have bad consequences if it did let go somehow in flight.

I removed all of the lines into and out of the cockpit, and instead plumbed the primer lines back to the high-pressure side of the fuel line, inside the engine compartment, with a solenoid valve to actuate it. Now I can prime by turning on the electric fuel pump, and pushing the "prime" button for a few seconds. 3 seconds in summer, and 5-6 seconds in winter seems to do it.

Before I did the switch, I experimented with the pump-while-cranking method, but I found I had a hard time balancing the not-enough-to-fire and too-much-now-its-flooded points. I didn't have anyone guiding me on the best methods though, so maybe I could have done better on that front. If I could have dialed that process in, I may have forgone the primer entirely.
 
I also used the solenoid type.

I also have the solenoid primer system Vans sell's, with lines to 3 cylinders. Works like a charm and the copper lines are supported well with coil loop at the end run. Nothing to leak in cockpit. I respect the simplicity with accelerator pump technique, however, I have had a fire in a C-150 doing that and watched a fellow RV-4 friend end up with fuel running out of his cowl recently..just a backfire away from a fireball..It can happen.
 
More good data points

I’m still leaning towards going without, but maybe I’ll run the wires through the firewall to operate one just in case I want to install one at a later point.
 
Firewall forward primer

I had a Cessna 182 and had an engine fire start while priming with the throttle and blades turning. It was a very cold day here in Canada.

I have used a solenoid operated primer into cyl 1 and 4 in my RV 7 and put the switch on the panel under a red lock tag. I think it better to use then the throttle as I almost lost my C182 using it. Of course we are historically colder than our southern brothers.

Dave
 
Primer

I have the solenoid style primer and use it on every cold start. 3-4 seconds on the button and it starts consistently.
I learned about it from a friend who ferried a 7 to the SW with a cold overnight in Nevada. Couldn’t get it started.
Recommended the primer.
I figure it gives me a foolproof systematic starting procedure without extra manipulation.
I vote for the primer. Simple to install and worth the effort.
 
No Primer - No Problem, yet

We have an -8, O360 with a carburetor and give it about 1/4 stroke on the throttle as the engine begins to turn. Starts easley.
This airplane lives in a heated hanger which makes a huge difference. When traveling in cold climates, I use a very small forced air heater overnight.
Without a warm soaked engine on a cold morning, I may be wishing for a primer...
 
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