BlackRV7

BlackRV7

Well Known Member
OK, I've been sitting on the fence with this primer install deal. Basis here, O-360 A1A configuration, carb, dual mags, standard vans electric fuel pump with mechanical. Primer or no primer installed on panel???? Care to throw out your thoughts and experiences?? I have a new primer I bought at SNF still sitting in it's box. Complexity (can't be much), photos of install would be helpful.
 
To prime or not to prime that is the question?

BlackRV7 said:
OK, I've been sitting on the fence with this primer install deal. Basis here, O-360 A1A configuration, carb, dual mags, standard vans electric fuel pump with mechanical. Primer or no primer installed on panel???? Care to throw out your thoughts and experiences?? I have a new primer I bought at SNF still sitting in it's box. Complexity (can't be much), photos of install would be helpful.
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I have a O360A1A for my RV7 project and plan on going with out a primer system to start. I have flown O360's without the primer system and had no problem starting them. My O320 RV-4 had an electric primer and did use it on first start of a cool or cold day. Sometimes I did not use the primer.

As you probably know the carbs on O320's do not all have an accelerator pump like the larger O360 carb. The MA4-5 has an accelerator pump to feed the larger engine when going from idle to WOT, like on takeoff. This circuit squirts extra fuel in the carb throat by fwd movement of the throttle.

I assume you're talking about the electric solenoid type primer. Not many are using the manual pump much these days. I can speak for the electric method, since I used it on my RV4. Unlike the hand pump on a Cessna, you can over do it. I used my electric primer very sparingly, pushing the button for just a second before cranking. Sometimes I'd jab it during cranking. You can over do priming with any system; if you do, fuel will drain down the manifold, into the air box, just like the pump prime method. There is some small fire danger with primer lines. A damaged primer line could pump raw fuel into the cowl and start a fire. Unlikely, but its a maintenance item and not unheard of.

With a priming system you're pumping raw fuel right into the intake ports, so raw fuel can get directly into the cylinders. This can wash oil off the jugs, causing extra wear. I don't know if using the upper primer port is worse than the lower ones for getting raw fuel into cylinders. I know some guys are using the upper ports for priming because the routing of the lines is nicer.

Complication of a primer system? Well its all those little primer line runs to each cylinder. Metal lines (usually 1/8" copper), fittings at each cylinder port and some kind of distribution block or "Tees" does make it more complicated. Running little primer lines from the lower ports across or near the intake and exhaust pipes is a pain. It also looks bad and is hard to support. Go out and price all the little special primer fittings and AN fittings; they are expensive, but the copper line is cheap. The special primer fittings have a reduced orifice. If a primer line breaks in flight the engine can run rough. If you used AN fittings with out the reduced openings, the engine would run scary rough, since a vacuum leak causes a lean condition.

Maintenance? Something more to go wrong. You have to wire the solenoid, wiring, circuit protection and a button. The little primer lines look terriable and can be a maintenance issue. Going with out a primer system is lighter, cheaper and there is no maintenance.

Down side of not putting a primer system on? Well it may be harder to start?

From my experience and what I hear, that's not the case, at least if the temps are not sub frigid. I have always lived in temperate climates, so that is my perspective. If you go on the advice of one of Van's senior guys and RV builder, he said he wished he would not have put the primer on and ended up removing it. This was documented in the RVator.

This debate goes on and on. People with out primers seem satisfied. People who opt to install the primer are also happy. The primer system is a fairly complicated system. By leaving it off I save parts, cost, weight which are fairly significant. Solenoid, wiring, CB/Fuse, switch, AN fittings, primer fittings, lines, brackets, clamps, nuts and screws, I'm sure I am missing something, all adds up. That's my story and I am sticking to it. :D If you want pictures email me I'll send you some pics of primer line installations. It is not horrible and if you want to jump off the fence onto the primer system side, that's OK. A lot of builders do install the primer.



PS: So what is priming like with out a primer?

The technique of priming the O360 using the accelerator pump, is pretty simple, pump the throttle once or twice before starting or during cranking. Two things people do wrong is pump the throttle too many times, once or twice max, at least at first. Since raw fuel can build up in the air box, don't over do it. The other technique is waiting a short period of time after priming before cranking. I usually prime while I'm finishing pre-flight, letting it set for 10-60 seconds, say while I close the canopy or copy ATIS. This allows the fuel to vaporize, which is really key in cold weather. The colder it is the longer you should wait. The time allows the fuel sitting in the air box to vaporize. If it's NOT COLD you can skip priming before cranking and see if its starts or pump once during cranking, if it does not catch. Remember to always go back to cracked open throttle while cranking.

Don't over do the priming because you could make a fire. When you move the throttle don't be abusive and just move it steady but not super fast or abrupt. If you have never seen what or how it works, take the airbox off, look under (not directly of course) and move the throttle slowly. If the carb has fuel in the bowl, you do NOT need the electric fuel pump. You will see a stream of fuel injected into the carb throat. Its pretty impressive amount of fuel. If you get too close you will get fuel injected into your throat. :rolleyes:

A primer system may be handy in really cold weather? I rarely fly when it's that darn cold. If I do fly on a crisp day, its from my hanger and I have heated the engine compartment. I don't plan on doing winter time X-C's to cold climates, leaving the plane tied down on a ramp in a snow storm in sub freezing temp. If I fly in the winter its South. Even than, in cold weather, I don't think the O360 is impossible to start without a primer. The trick as I mentioned is to pump, pump and wait to let the fuel vaporize a little. It takes a minute or so to let the fuel vaporize in cold weather. Really that applies to a primer system as well. You want vapor not raw liquid fuel.

One thing people worry about using the carb to prime is there's a possibility of a stack fire. It's not a bad thing to worry about, but I don't think its a big deal. When was the last back-fire you had? You do have to be very careful not to pump gobs of raw fuel into the air box, where it drains into the cowl and puddles under the plane on the ramp. Just use common sense. My engines have never been that hard to start. I guess that is a good point. The engine has to be in good repair, good battery, starter, ignition and fuel system. May be a primer system may help a weak starting engine.

I am going with out at first and plan on not looking back. If I need to add I will do it later.
 
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If you ever plan to fly in cold weather put the primer in. Trying to start in cold weather using the accelerator pump method will almost guaranty an airbox fire at minimum and a burned up hulk at the worst. I always use the primer on a carburated engine hot or cold. Don
 
One word of caution if you are planning to use the accelerator pump as primer. Only pump while the starter is turning. If the engine is not turning, there is no vacuum in the intake sysem and the fuel will just run out into the airbox. The updraft intake system on aircraft engines is not conducive to using the accelerator pump as a primer. I have the old standard manual primer and it's been working great for almost 14 years. Of course I also have manual flaps and manual trim.
 
Cold weather a must?

Mel said:
One word of caution if you are planning to use the accelerator pump as primer. Only pump while the starter is turning. If the engine is not turning, there is no vacuum in the intake system and the fuel will just run out into the airbox. The updraft intake system on aircraft engines is not conducive to using the accelerator pump as a primer. I have the old standard manual primer and it's been working great for almost 14 years. Of course I also have manual flaps and manual trim.
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U da man, the manual man. The electric primer is a little finicky. Except for a little more fuel line work the manual primer pump is cool. Manual flaps also cool. You don't need battery power to make it work.

With the electric primer you have to turn the fuel pump on and you really never know exactly how much you are pushing into the engine, but you get the timing down. The manual primer pump is a little more controlled.

I agree that cranking while you uses the carb prime method is best and safer. However if its real cold one pump and waiting a minute or two. 1 Oz of fuel is not super critical. If you have a back fire (and you should not), go to lean and keep cranking for a few seconds. That will suck any possible fire out.

I don't agree that fire is guaranteed or that cold weather starting is impossible if done properly. I hate cold soaked starts, its hard on the engine. On the other hand the reason planes don't start in the winter is not due to lack of fuel. Some times it's too much fuel, i.e. flooded.

Timing, spark intensity, compression and spin (fast enough) all have to be right to start, especially in cold weather; it does not really take much fuel to start. In cold weather all these things suffer. When the oil is like molasses and fuel does not vaporize, starting is difficult, even with a primer system, but if I lived in the cold states (ND, Minnesota, Colorado), I'd put a primer system on.

I don't like starting below 40-ish with out preheating. Below 40F I many not go flying at all.

Click here: Lycoming's cold weather operation recommendations

When I flew with out a primer system most of the time I did not prime at all, even in the 50's, and if the engine did not seem to catch on the first blade or two, I'd give it a quick 1/2 pump, which usually resulted in an immediate start. Lycoming talks about 25F as requiring pre-heat for some engines, but hint at 40-45F. The pre-heat is by pilot discretion according to Lycoming but they say at 10F its needed.

Having a primer is better for cold weather, no doubt, because its better for priming before cranking, since the fuel puddle is further up in the induction, not pooled in the airbox. Vapors that form will not float off either. Still a back fire can cause a stack fire either way. A back fire blows any liquid fuel OUT regardless where it is. Regardless continue cranking with cutoff mixture.


I hear in "cold weather" you can't start with out a primer. Trust me you can, but again I admit a primer system is better for real cold temps. Planes that are hard starting cold weather often have a weak battery, starter, ignition or miss timed ignition, usually from poor maintenance condition.

Fuel is less likely to vaporize when cold. Be careful in the winter, since you can flood the engine easily, especially with a solenoid primer system. Regardless, when its real cold, prime and wait a minute, allowing the gas to vaporize. You don't want gobs of liquid fuel drops going into the cylinder, it just floods the engine, soaks and fouls the plugs.

The high vapor pressure of Aviation fuel is a plus in the summer, resisting vapor lock, but its a negative in the winter. That's why the auto gas has winter and summer blends. Winter has lower vapor pressure and burns better at cold temps, helping cold starting.

Pooling of gas in the air box with throttle priming is not desirable, as Mel said, but it can be done safely. An ounce of gas is not going to start a huge fire. Besides its needed only when real cold; usually you pump the throttle while cranking. Now pump the throttle 10 times you have a potential fire hazard.

To be fair you can do bad things with a primer system. Liquid fuel runs down hill, down the induction tubes and into the air box one way or another. You can over do it and foul plugs and put fuel in the air box.

Cheers

"If palm trees are not growing you are too far north in the winter time."
(Any one from Canada, please take no offense, its all in fun and I love skiing, I love the snow, I love to visit it and than love leaving it for shorts and T-shirt weather. :D )
 
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Engine priming / starting

I have (nearly) decided not to install any priming circuit on my RV4 O-320. (Less weight, complexity, bits to go wrong.) I decided to poke arround the archives, and in support of this, found a post from Sam Buchanan saying he did not have a primer on a similar setup, and also the previous post to this where GMC points out that unlike the O-360, the 320 does not have an accelerator pump in the carb. This last fact was news to me.

All my experience of starting without a primer is on an O-540/Pawnee; 4 strokes of the throttle (3 in summer), hit the tit, and up she fired. I do occasionally start my Supercub this same way, and have always (erroniously?) assumed there is a throttle pump there. (It also has a primer which I normally use.) Are the throttle strokes doing nothing?

Presumably, if there is no throttle pump, the much talked about elevated fire risk is a non issue?

So my questions:
1) With an O-320, what is the correct way to start without a primer? Crack the throttle and press the starter?

2) Those that fly O-320 without primer, how hard to start?

I should add that while there are no palm trees around here, its never below 20F, and that is quite exceptional.
 
My O-320 has an accelerator pump. I believe it was the 0-235 that never had an accelerator pump. Saved Lycoming $10 bucks a copy or thereabouts.

I've removed the electric priming system from my 0-320. I never got calibrated to the priming system - i.e. how long to prime, so it never helped me, and I saw it and all those primer lines as another maintenance point/failure point.

My non-preheated engine cold weather starting procedure is to pump the throttle once right before I climb into the plane. Then I check for switches cold and flip the prop over 3 or 4 blades by hand. Then I climb in, crack the throttle, flip the ignitions to hot (one mag, one electronic), and hit the starter button. The airplane usually starts after a couple of blades.

I prefer to use my preheater, though. If I'm smart and dilligent, I will go by the airport a few days before a cold weather start and set the timer to give me a 2-4 hour preheat (reiff sump strip). With a preheated engine, I climb in the plane, cycle the throttle once, let it sit for long enough to buckle the belts, etc., then crack the throttle, go ignition hot, and crank the engine. Again, the engine usually starts on 2-3 blades.

One thing about the preheater in my (Atlanta) climate. Even on a 30F morning, a 15 minute preheat makes a difference for starting. No, the engine isn't warm, but the oil is *warmer*, and so are the carb and induction tubes. That makes the engine turn over much more easily and helps the fuel vaporize.

By the way, a strong battery really helps for cold starting. I use a battery tender to keep the battery topped off. Even an extra 0.1 or 0.2 V on the battery gives you an advantage on a cold morning.
 
Never seen an O-320 without an accelerator pump. My old Continental 65 didn't have one but anything bigger should have one.
 
I have been thinking of installing a primer too, but so far haven't needed it. Down to about 30 so far (maybe high 20's, MILD winter here in Chicago) I can hit the throttle a couple of times, wait perhaps 15-20 seconds and rarely does the prop make a full revolution before it's running. Still pondering putting one in though for really cold.

Scott
RV-9A - N598SD Flying - ~90 hours
 
Certified planes

Interestingly enough, a neighbors certified 1976 Kachina Varga was delivered without a primer - It has a 150 HP O-320 in it...

I'll ask him what the Pilot's Handbook gives as a cold weather starting procedure.

The Varga was designed and built in Phoenix though..... :)

Does anyone know if any other certified planes were delivered without a priming system??


Gil in Tucson
 
Dana:

Living up in the "Great White Nort", I opted for a primer. You being located in warmer climes, its installation may not be as much of a factor. Other posts have mentioned the increased complexity and added weight, both of which IMHO are minor.

I must add that I purchased a midtime 0320-E2D that had primer lines to three cylinders, so my install was made easy for me. So my opinion may be a bit clouded ;)

One thing to consider that has not been mentioned here. If you have some sort of fuel draw problem causing an engine failure, you MAY (I must emphasise MAY) be able to limp along just enough by hitting your primer switch intermittantly. It would take a bit of finesse, I assume, but still might save the day. At least that is what the old salts at the airport tell me.

Regards,
 
A few of the O-235's have accelerator pumps and a few don't. The Cessna 152's I fly have them. As does the 152 (O-200). Pretty standard start procedure in warm weather is 2 pumps and then crank for all the lyc's i've started. Three pumps and crank worked fine last night in the FRIGID (for LA) 34?F night air in the Cardinals O-360A1A. Never used the primer in the Cardinal since we got the Carb rebuilt (Accelerator pump wasn't working before).
 
Have Primer - still haven't used it....

I built the Val with a primer (electrical solenoid type), but have still never had a need to use it. Yeah, I'm living down here in the south, but didn't use it when I was in Minnesota last month either.

For many years, I have used two pumps on the throttle to start my various airplanes that had accelerator pumps in the carbs, and it always works. One caution and caveat I always add however - I NEVER pump the throttle without the engine cranking and creating a vacuum to pull the fuel into the cylinders. I was always taught (and it makes sense to me), that if you pump the throttle without cranking the engine, you just make a pool of gas in the airbox, and a backfire can start a fire.

Just my expereince...

Paul
 
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I have also never needed to prime my 0-360's in Wisconsin. I normally don't fly in ground temps below 25 deg. F. I did not install a primer in my 7A.

Roberta
 
I wont install a primer.

Thanks for all the replies to my question. With all those +ve answers I wont install a primer.

[That will save 8 joints, a switch and at least 4 electrical connections.]

Thanks again,
 
primer? whats that?

I've flown in AZ my whole life mostly in Pipers, and I seem to remember having to check that the silver knob on the bottom of the panel was in and locked. Never used it. I don't expect to need one in my RV. My thin AZ blood would be frozen befor the accelerator pump became ineffective. ;)
 
I finally tried it!

I decided to get in a quick flight this afternoon (before the predicted freezing rain hits Houston) and call it a "cold weather test". It was right at 36 degrees OAT, so I decided to try the primer switch. Unfortunately, I really have no idea how long to hold the switch for....(carb'ed engine, so low pressure electric pump). I gave it a few seconds, and still had to pump the throttle while cranking a number of times for the engine to catch...

Test - inconclusive....will have to fly more to test it again! :D

Paul
 
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