To prime or not to prime? Engine primer that is

[N941WR]

Simple question.

Should I install an electric engine primer for my carbureted Lycoming?

Please provide me with pro?s and con?s

[robertahegy]

I live in Wisconsin and I never used the primer in my Cherokee (0-360) and I did not install one on my 7A with 0-360-A1A. The accellerator pump in the carb provides enough enrichment for fast, easy starts in weather to 30 deg. F. for me.

Roberta

[penguin]

An awful lot of professional mechanics don't like the accelerator pump method of priming as it can lead to induction fires following a back-fire. A proper primer is much less likely to lead to pooled fuel in the intake box. Clearly, RV builders and more knowledgeable that spam can renters, and are more likely not to over prime with the acceleator pump, or only use it when already cranking the engine.

Pros: - Much reduced likelyhood of intake fires
- Easier starting because of better fuel distribution (assuming at least 3 of 4 cylinders are primed, all 4 is much better).

Cons: - Additional expense
- Additional time to engineer
- Additional hassle to build

The other day I say a builder who used a small block of aluminium bolted to the top of the case as a primer distribution block to send the priming fuel to primer nozzels installed in the fuel injection ports - I thiught it was fuel injection for a moment. Seemed like a great idea and a relatively simple way of running the primer lines.

[gmcjetpilot]

Originally Posted by N941WR

Simple question.
Should I install an electric engine primer for my carbureted Lycoming? Please provide me with pro?s and con?s

I have a O-360-A1A, I am going without, but you can always add it later. Consider NOT installing it, but plan for future installation, like leave room for the solenoid near the gascolator and so on.

If you decide to go with a primer, I like the semi fuel injection approach, as was mentioned. A distribution block on top of the engine or a "T" fitting feeding at least 2 cylinders is a clean way to run the primer lines. Bottom line a pump of the throttle usually does the job. Yes that is raw fuel in the throat of the carb and likely in the bottom of the air filter. If you over prime even with a dedicated primer system, fuel can run down into the sump and even out the carb. It's all down hill.

Here is an aside, a story or tale if you will. I have heard of a primer saving the day. I can't back-up the story, but as the legend goes the Carb had a failure and the engine was starved for fuel. The primer was manipulated to get momentary bursts of sporadic power to save the day....blaaa blaaa. Don't know if it is true but sounds cool. My guess a primer system might causes more problems than solve.

The opposite is if a primer leaks or fails you can get a very rough running engine. KEY is primer fittings with a restrictor orifice. If you price all the parts the whole system is not cheap, but than what is on a plane.

[13brv3]

FWIW, my local RV-8 buddy and I both left off the primer on our O-360's, because we didn't see why we really needed them. By the end of the first winter, we had both added the primer. Keep in mind that we are in the FL panhandle, so not exactly what most people call winter.

I'm building a new RV-8 now. Do you think it will have a primer

Cheers,
Rusty (correct, the answer is YES)

[redbeardmark]

You can start a cold engine with a priming system even when the engine is very cold, which I've been told is not a good thing to do. Your money would be better spent on an oil sump preheater. During the ND winter, I fly when the OAT rises to +5 or +10F using the preheater(plugged in the night before, cowl plugs poked in front, and a blanket over the top of the cowl for a little insulation) and a single stroke on the accelerator pump. After one pump of the throttle, let it evaporate for 20-30 seconds and then crank. Works like magic.

[Kyle Boatright]

I installed a primer when I built my airplane. I could never tell that it helped much.

IMO, a better solution is a sump heater. With a warm sump, you don't need a primer. Of course, you will need access to electricity.