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Fuel Primer Installation for O-320

dbaflyer

Well Known Member
I have the kit from Vans, but am considering soldering the discharge end at the port or going completely SS. I know how much the SS route is going to cost and would like to first consider the solder method. I also think trying to get the length right on the SS lines is going to be difficult.

My engine came with two AN4022-1 discharge ports that would fit into the primer port on each cylinder. Looking at them the discharge hole is very tiny compared to the AN816 fittings that came with the Vans kit. Is that correct? Does't seem like much fuel would get through there.

My engine also came with a 3 way brass splitter, AN795-2.

This fittings are not the same thread as the blue fittings that Vans supplied in the kit. So those coupler nuts are not good here, but I would need AN805-2 intstead? And AN800-2 union cones which are soldered to the copper line? What do I need to purchase to perform that soldering?

Then how do I transition off the primer pump using the blue AN fitting sizes into the brass splitter? These are going to have different sizes on either end of that line which I would like to have as SS.

Finally I am struggling a bit how to route all this to my front two cylinders and keep it secured. I am considering attaching an adel clamp to the bottom screw on the #1 cylinder valve cover and securing the 3-way splitter to that. That would make a pretty short run of copper to the primer port on that cylinder. Then running down and across the engine (near the sump) and securing the line using another adel clamp attached to the case mounts next to my alternator and then up to the #2 cylinder.

I've managed to find one set of photos of other peoples routing but I figured there should be way more out there somewhere. Anyone have some sites or photos to share?

Denis.
 
Denis,
I have a O-320 D2A engine that came with a primer system. It is copper. I did have to get a couple weird fittings to make it work, but I think it is installed properly. I will be doing my first engine start next week, so I guess I will find out.

I can get a couple pictures if you want. Email me and I will get them tomorrow at the hangar.
 
You don't need a primer and could consider removing it. Especially with impulse mags or dual impulse mags. My -9A O-320 has no primer and haven't had any issues starting it down to 0 degrees. Same with my 0-360 Mooney. Just a few pumps of the throttle, let it vaporize and crank. 2 pumps, with 4-5 seconds in between on the RV is usually sufficient. Now with a pmag one pump would probably suffice. The mooney needed 3-5 pumps. My 182 with an O-470 continental had a primer and it was definitely needed to start that beast. I'd bet that most carb RV's dont have a primer.
 
+1 for skipping the primer, at least if you are using an electronic ignition system. My airplane has a O-360 with dual PMags and no primer, and has always started immediately. I do preheat when it's cold, which may help. Having a good, strong starter also helps - I've got the PP starter from the Vans FWF kit.

On the other hand, I've flown a few spam cans with mags, really anemic starters, and probably somewhat fouled plugs from students flying and always running full rich. One in particular always needed several shots of primer to start.
 
My engine came with two AN4022-1 discharge ports...
I have one of those installed in my #1 cylinder only and it works just fine. You'll save a lot of plumbing (and possible leaks) by only doing one cylinder. My plane won't start in cold weather by pumping the throttle because I have the accelerator pump linkage set to minimum (long story). Three or four pumps on my Essex primer and the plane starts right up on a cold day. (I do have an oil pan heater for really cold days.)

I used 1/8" copper tubing for my primer line from the firewall to the cylinder, with the "Union Cone" soldered to the line with standard silver-bearing plumber's solder. I did as you mentioned and supported the tubing with an Adel clamp mounted on the bottom rocker cover screw under the #3 cylinder. The firewall end of the tubing is flared to mate with a standard steel AN-2 fitting.

It's really a PITA to get a tool in there to tighten the fitting. As you can see, I had to nibble away the baffle for access:

e2RsuY.jpg
 
If using the "pump the throttle" method, please have someone nearby with a fire extinguisher. A back-fire will light the fuel and they'll be busy. :D If a fire does start, keep cranking until it goes out (hopefully).
 
Just a few pumps of the throttle, let it vaporize and crank. 2 pumps, with 4-5 seconds in between on the RV is usually sufficient. Now with a pmag one pump would probably suffice. The mooney needed 3-5 pumps.

As Raymo stated above, pumping, waiting, then cranking is not a great idea due to the fire hazard; a perhaps better technique is to pump the throttle while cranking as the atomized fuel is sucked into the engine as opposed to pooling in the airbox.

A few years ago I watched a hangar neighbor start a cowl fire in a carbed 150hp Cardinal using the pump/wait technique. Oops!
 
I was also wondering whether there is any reasoning to which cylinders you use. It would certainly be easier to do #1 and #3 for example as there would be no need to route over to the other side and the gascolator and primer pump are mounted to the right side of the FW. It's also going to be easier for me to use #4 for my manifold pressure.

Thanks all for your suggestions and good photos.
 
Primers

I was also wondering whether there is any reasoning to which cylinders you use. It would certainly be easier to do #1 and #3 for example as there would be no need to route over to the other side and the gascolator and primer pump are mounted to the right side of the FW. It's also going to be easier for me to use #4 for my manifold pressure.

Thanks all for your suggestions and good photos.

Glad to see you are moving forward with a real primer system over using the accelerator pump as a makeshift one.
As far as which cylinder goes if you are doing less than all of them, it doesn't matter to the engine that I know of. Do understand how it works. The primer system puts fuel into the intake manifold just outside the intake valve. If the valve happens to be closed, which in the 4 stroke cycle it is 75% of the time. The fuel coats the area behind the valve and excess, if there is any, runs down the intake tube and vaporizes while waiting for the intake stroke. If you hapen to catch the valve open, well , you hit the jackpot and you get some fuel in the cylinder.
So clearly the more cylinders are primed, the better the primer system will work. You mentioned the MP line on the #4 cylinder, this is why most systems use 3 or less cylinders for priming. You also mentioned the complexity of dividing the lines and taking one or more to the other side. These are all good points to consider. Also every fitting is a possible fuel leak while priming and intake air leak while flying, and yet, the normal seems to be to use copper or believe or or not aluminum. Another point to mention is all this tiny tubing is routed around the bottom of the engine, along with electrical wires and cht and egt wires and next to exhaust pipes which makes it harder to install and inspect.
Do understand your system, if you are using the Van's primer system,you do not actually have a primer pump. The larger heavy metal part is a solenoid valve, not a pump. When energizerd, it opens to allow fuel to flow. The pressure to deliver the fuel comes from the engine system boost pump. That is right, you first turn on the boost pump, then switch open the solenoid valve to allow fuel to flow to the primer lines and squirt or spray out the terminations in the intake manifold. That is why you count....1,2,3.
Sorry for the long post. This journey is all about learning. It is your airplane, do what you think is best for you.
 
As Raymo stated above, pumping, waiting, then cranking is not a great idea due to the fire hazard; a perhaps better technique is to pump the throttle while cranking as the atomized fuel is sucked into the engine as opposed to pooling in the airbox.

A few years ago I watched a hangar neighbor start a cowl fire in a carbed 150hp Cardinal using the pump/wait technique. Oops!

I take this warning seriously so I've been trying to do this with my carbed O-360 A1A.

I start the engine and then pump the throttle at about the same speed as I do when I used to pump first and then crank.

It NEVER starts. Good thing I have a strong battery.

I don't know what I'm doing wrong:

I never bring the throttle all the way back to closed - but to the cracked position

I pump about once a second.

Yet if I then pump the throttle without cranking 2-3 times it starts right up.

If there's a bit of technique here I'd love to learn it - I'd much rather pump while cranking.

Thanks
 
I take this warning seriously so I've been trying to do this with my carbed O-360 A1A.

I start the engine and then pump the throttle at about the same speed as I do when I used to pump first and then crank.

It NEVER starts. Good thing I have a strong battery.

I don't know what I'm doing wrong:

I never bring the throttle all the way back to closed - but to the cracked position

I pump about once a second.

Yet if I then pump the throttle without cranking 2-3 times it starts right up.

If there's a bit of technique here I'd love to learn it - I'd much rather pump while cranking.

Thanks

No "technique".......but some thoughts.
Does your A1A setup use a standard carb?
If it does, is the accelorator pump working? This is easily checked by removing the airbox and looking up into the throat of the carb while someone is stroking the throttle , you will see a strong squirt of fuel shooting up the throat toward the engine, then it will fall back in your face! So be careful.
FYI the accelorator pump is there to help supply the engines fuel needs when rapid advancement of the throttle is done.
Understanding how this works will help you understand just what you are doing when your use the accelorator pump for a make-shift primer.
 
Hard starting issue and my fix(?)

My carbed 0-320 without primer would never start on first attempt of the day
even when I added a pmag, and even then after only what I felt was prolonged cranking. I tried pumping throttle dUring cranking and it got a little better but sometimes the engine would roar to life with way too many rpm's.
I considered adding a primer but first I tried before preflight turning on the electric fuel pump, waiting for fuel pressure and pumping the throttle once or twice. Then I turn everything off, do my preflight, 10 min or so, get in crack the throttle and she starts right up and I usually have to add throttle to keep it running. No more high rpm starts and blasting everything on the ramp.
My theory and wishful thinking perhaps is that I am minimizing the fire risk from pumping the throttle just before ignition by allowing the fuel in the carb to vaporize while I preflight. I think the important thing is to keep the fuel pumped in to a minimum, 2 full pumps seem to be working well along with preheat in temps below 40f.
 
Six pumps

I think the important thing is to keep the fuel pumped in to a minimum, 2 full pumps seem to be working well...
Many years ago I did a test to see how many pumps it would take before fuel ran out of the carburetor into the airbox. It took six pumps. I only had a primer line to cylinder #1, so clearly your results might be different. It would be best to run this test for yourself to be sure.
 
+1 Primer not required

You don't need a primer and could consider removing it. Especially with impulse mags or dual impulse mags. My -9A O-320 has no primer and haven't had any issues starting it down to 0 degrees. Same with my 0-360 Mooney. Just a few pumps of the throttle, let it vaporize and crank. 2 pumps, with 4-5 seconds in between on the RV is usually sufficient. Now with a pmag one pump would probably suffice. The mooney needed 3-5 pumps. My 182 with an O-470 continental had a primer and it was definitely needed to start that beast. I'd bet that most carb RV's dont have a primer.

Running an O-320 with two impuls mags an have not had the engine go more than a cylinder or two to start. Even hand propped a couple time when in the NWT and Yukon when my battery was going.
 
Yet if I then pump the throttle without cranking 2-3 times it starts right up.


Thanks

Nobody is saying it is an ineffective technique. Your procedure dumps a bunch of liquid fuel into the air cleaner assy. Evaporation starts quickly, creating a good ratio of air / fuel that you suck up when you crank and it gets the combustion going (dumping fuel in the intake with the primer does the same thing). The problem is that almost all of the liquid fuel remains in the air cleaner assy and the vacuum is not strong enough to suck up the liquid). If you have a backfire, you now have a good solid source of fuel to ignite and burn for some time. Possibly you have never seen a backfire during a botched start sequence. It produces a large and impressive plumb of flames.

When I had a carb, the second I hit the starter I started pumping rapidly. It usually took three full strokes. Then quickly pull the throttle back to 1/4" and give it a chance to catch. If it doesn't, give it another shot or two. I could get three strokes and start well within 10 seconds. If your starter can't do that, it's time to look at replacing your battery.

The reason that the primer is easier is that you can shoot in the fuel (without backfire risk) and let it evaporate, just like your current technique. This is a time tested mehod that works well, you just need a way to do it without the backfire risk. When I used my primer, I always waited 15 seconds before starting to let some fuel evaporate.

Larry
Larry
 
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Many years ago I did a test to see how many pumps it would take before fuel ran out of the carburetor into the airbox. It took six pumps. I only had a primer line to cylinder #1, so clearly your results might be different. It would be best to run this test for yourself to be sure.

The previous poster is talking about pumping the throttle in an updraft carb. In that case, every drop ejected from the accel pump goes to the air box. In your case, you're using a proper primer circuit and the fuel is going straight to intake chamber of the cylinder head, so 6 pumps sounds about right before seeing fuel in the air box.

Larry
 
Nobody is saying it is an ineffective technique. Your procedure dumps a bunch of liquid fuel into the air cleaner assy. Evaporation starts quickly, creating a good ratio of air / fuel that you suck up when you crank and it gets the combustion going (dumping fuel in the intake with the primer does the same thing). The problem is that almost all of the liquid fuel remains in the air cleaner assy and the vacuum is not strong enough to suck up the liquid). If you have a backfire, you now have a good solid source of fuel to ignite and burn for some time. Possibly you have never seen a backfire during a botched start sequence. It produces a large and impressive plumb of flames.

When I had a carb, the second I hit the starter I started pumping rapidly. It usually took three full strokes. Then quickly pull the throttle back to 1/4" and give it a chance to catch. If it doesn't, give it another shot or two. I could get three strokes and start well within 10 seconds. If your starter can't do that, it's time to look at replacing your battery.

The reason that the primer is easier is that you can shoot in the fuel (without backfire risk) and let it evaporate, just like your current technique. This is a time tested mehod that works well, you just need a way to do it without the backfire risk. When I used my primer, I always waited 15 seconds before starting to let some fuel evaporate.

Larry
Larry

Hi Larry,

No need for the full repetition of the reasons why you don't want to pump without cranking...I understood all of that.

My problem is that it's not starting when I pump while cranking and I need to understand why.

I have a great battery and it can crank all day.

Is it possible it's being flooded? You mention "...the second I hit the starter I started pumping rapidly"...Can you give me an idea how fast? As fast as you could?
 
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Hi Larry,

No need for the full repetition of the reasons why you don't want to pump without cranking...I understood all of that.

My problem is that it's not starting when I pump while cranking and I need to understand why.

I have a great battery and it can crank all day.

Is it possible it's being flooded? You mention "...the second I hit the starter I started pumping rapidly"...Can you give me an idea how fast? As fast as you could?

Didn't mean to insult your knowledge. It seemed like a lot of folks still do this and thought a detailed answer might help convince them why it is bad and not to take the risk.

You may be flooding it. In warmer weather you should need very little priming; maybe one half to one pump. It's been a couple of years since I had the carb and I used the primer more often than pumping.

I can tell you that the fuel required is not linear with temps. At 70+* you might need one pump, maybe less. At 30*, you might need three or four pumps. With the warm weather, I would not over do it. 98% of the 2-3 pumps you do before cranking are just sitting in the air cleaner and have nothing to do with starting the engine, so don't use that as a guide. When you pump with the starter turning, all of that fuel is going into the engine.

Start with a minimal amount and keep adding to it until it kicks. On your next start over 70*, give it half a shot as you start cranking and let it go a bit if it doesn't catch. It would also be wise to try starting with no priming. It may take a few extra seconds, but might start. You need to do some experimentation to learn your engine. Start on the lean side and keep adding more each time and observe the behavior. Then remember that more priming is required as it gets colder.

Rapid is relative. I pump as fast I feel comfortable with the seals. In theory, you want to be relatively quick about it, as your engine isn't likely to start with the throttle open beyond 1/2" unless your flooding it. However, you want to avoid damaging your accelerator pump seal by being too agressive. I doubt I was taking a full second for each pump.

I would often give it two pumps (sorry, should have mentioned this was my protocol in the winter) and give it a bit to start, then give it the third if it didn't catch all without relasing the start button. You can also do multiple 1/4 or 1/2 pumps and back to 1/4" while cranking.


Larry
 
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Didn't mean to insult your knowledge. It seemed like a lot of folks still do this and thought a detailed answer might help convince them why it is bad and not to take the risk.

You may be flooding it. In warmer weather you should need very little priming; maybe one half to one pump. It's been a couple of years since I had the carb and I used the primer more often than pumping.

I can tell you that the fuel required is not linear with temps. At 70+* you might need one pump, maybe less. At 30*, you might need three or four pumps. With the warm weather, I would not over do it. 98% of the 2-3 pumps you do before cranking are just sitting in the air cleaner and have nothing to do with starting the engine, so don't use that as a guide. When you pump with the starter turning, all of that fuel is going into the engine.

Start with a minimal amount and keep adding to it until it kicks. On your next start over 70*, give it half a shot as you start cranking and let it go a bit if it doesn't catch. It would also be wise to try starting with no priming. It may take a few extra seconds, but might start. You need to do some experimentation to learn your engine. Start on the lean side and keep adding more each time and observe the behavior. Then remember that more priming is required as it gets colder.

Rapid is relative. I pump as fast I feel comfortable with the seals. In theory, you want to be relatively quick about it, as your engine isn't likely to start with the throttle open beyond 1/2" unless your flooding it. However, you want to avoid damaging your accelerator pump seal by being too agressive. I doubt I was taking a full second for each pump.

I would often give it two pumps (sorry, should have mentioned this was my protocol in the winter) and give it a bit to start, then give it the third if it didn't catch all without relasing the start button. You can also do multiple 1/4 or 1/2 pumps and back to 1/4" while cranking.


Larry

Hi Larry,

You weren't insulting my intelligence. It's just that the admonition has been repeated in the thread already plus numerous times in other threads.

Thanks for the info on technique. Right now I suspect I'm flooding it. There was one attempt where I stopped pumping and kept cranking and then it almost started.

I think the next experiment will be half a shot while cranking.

thanks!
 
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