So I got my first airboat, total noob to airboats but have been around boats my whole life. You guys are probably going to roast me for this but how do I start my 320? Is it fuel pump, ignition, mag, mag Or is it fuel pump, mag, ignition, mag? Still learning about mags. After its started can do you turn the fuel pump off or does it stay running.
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Lycoming 320 starting procedure
- Thread starter apg1387
- Start date
Slidin Gator
Well-known member
Welcome to the addiction! :toothy7: Lot's to learn.
I assume it is carbureted? I take it you have an electric fuel pump (mounted on top of or below the tank), but you likely also have a mechanical fuel pump mounted on the front accessory housing (see pic). The purpose of the electric fuel pump is to prime the system, but the mechanical should pull fuel through the electric once the engine is operating.
You also have 2 mags, the STBD side mag should be the "Impulse" mag that is used for starting, the right mag is typically not the impulse type. This is the aviation standard, but it might be different on yours depending on what the prior owners did. With both mags off (see safety info below), if you turn the prop by hand, you should hear a clicking sound every so often, that is the impulse activating. Figure out which mag is making the noise and which switch it is connected to. When operating, both mags should be timed together at 25 degrees BTDC. But, at low RPM during starting, the impulse mag has a spring system that holds the timing back to fire close to TDC for easier starting. Once running this system stops due to centrifugal weights and timing reverts to the 25 degrees advance.
If not installed, add a mixture adjustment cable before running, it is a safety feature, see below.
Procedure is:
- #1, always check that the prop is clear, no one behind boat, no dogs etc...!
- Mixture adjustment to full rich, normally push the cable knob down
- Electric fuel pump on, wait until you hear it load up (a few seconds).
- Hit starter button
- Turn on Impulse mag only
- Engine should start, if not repeat above but add a pump or two of the accelerator to feed some fuel
- Once running, turn on PORT mag
- Confirm oil pressure
- Turn off fuel pump
- Let engine idle and build some temp before putting the hammer down. Usually idle up after a few minutes of idle to build heat.
Safety
The magneto ignition is designed to fail in the running position, no one wants their plane to stop running in the air! To disable, the magneto P lead has to be grounded, this is what the mag switch does. In the run position, the switch is off, in the stop position the switch is on to connect the mag to grounded. This means that a bad wire, switch or ground connection can result in a live mag - the motor may start if turned over, all it takes is one bad mag ground (2 opportunities to fail in the ON position). It also means that when turning the prop by hand there the potential for the motor to spring to life! I have also had a situation where a tree branch broke a mag switch, same thing, I could not turn off the mag.
This is where the mixture adjustment comes in. Normal running is at full rich, but to shut down, do not turn off the mag switches, particularly when hot, the motor may run on. Pull the mixture knob to the lean position. Motor will still idle, give it several seconds and it will stumble, then press the gas and the motor will shut down due to insufficient fuel. Then turn off mag switches. Always leave the mixture in the lean position when off, it prevents run away in the event of a "Ghost" start.
Also, aviation carbs are designed to revert to Wide Open in the event of failure of the throttle return spring. I use 2 springs for this reason, inspect yours. In the event of a WOT runaway, the mixture adjustment is your savior.
If for some reason the mechanical pump fails, you can turn on the electric to feed the motor, but figure out why the failure occurred and resolve first, otherwise you will likely burn up the electric in short order too (hard lesson on my part).
Also consider dual start switches, one latching (or a key switch), the other momentary, so it takes 2 switches to fail to crank the starter.
Always turn off the main battery switch (big red Perko) or disconnect the battery, before entering the cage. Never turn the prop by hand unless ALL plug wires are pulled, or you are trying to hand start the motor and you are prepared for the result. Treat the prop like a loaded gun!
I probably missed some items on the safety list, there are a few threads on the board covering it in more detail, do some searches on "Airboat Safety." Others will probably add.
Stay safe, have fun. Don't be afraid to drive it like you stole it, these things are more likely to sink off plane.
I assume it is carbureted? I take it you have an electric fuel pump (mounted on top of or below the tank), but you likely also have a mechanical fuel pump mounted on the front accessory housing (see pic). The purpose of the electric fuel pump is to prime the system, but the mechanical should pull fuel through the electric once the engine is operating.
You also have 2 mags, the STBD side mag should be the "Impulse" mag that is used for starting, the right mag is typically not the impulse type. This is the aviation standard, but it might be different on yours depending on what the prior owners did. With both mags off (see safety info below), if you turn the prop by hand, you should hear a clicking sound every so often, that is the impulse activating. Figure out which mag is making the noise and which switch it is connected to. When operating, both mags should be timed together at 25 degrees BTDC. But, at low RPM during starting, the impulse mag has a spring system that holds the timing back to fire close to TDC for easier starting. Once running this system stops due to centrifugal weights and timing reverts to the 25 degrees advance.
If not installed, add a mixture adjustment cable before running, it is a safety feature, see below.
Procedure is:
- #1, always check that the prop is clear, no one behind boat, no dogs etc...!
- Mixture adjustment to full rich, normally push the cable knob down
- Electric fuel pump on, wait until you hear it load up (a few seconds).
- Hit starter button
- Turn on Impulse mag only
- Engine should start, if not repeat above but add a pump or two of the accelerator to feed some fuel
- Once running, turn on PORT mag
- Confirm oil pressure
- Turn off fuel pump
- Let engine idle and build some temp before putting the hammer down. Usually idle up after a few minutes of idle to build heat.
Safety
The magneto ignition is designed to fail in the running position, no one wants their plane to stop running in the air! To disable, the magneto P lead has to be grounded, this is what the mag switch does. In the run position, the switch is off, in the stop position the switch is on to connect the mag to grounded. This means that a bad wire, switch or ground connection can result in a live mag - the motor may start if turned over, all it takes is one bad mag ground (2 opportunities to fail in the ON position). It also means that when turning the prop by hand there the potential for the motor to spring to life! I have also had a situation where a tree branch broke a mag switch, same thing, I could not turn off the mag.
This is where the mixture adjustment comes in. Normal running is at full rich, but to shut down, do not turn off the mag switches, particularly when hot, the motor may run on. Pull the mixture knob to the lean position. Motor will still idle, give it several seconds and it will stumble, then press the gas and the motor will shut down due to insufficient fuel. Then turn off mag switches. Always leave the mixture in the lean position when off, it prevents run away in the event of a "Ghost" start.
Also, aviation carbs are designed to revert to Wide Open in the event of failure of the throttle return spring. I use 2 springs for this reason, inspect yours. In the event of a WOT runaway, the mixture adjustment is your savior.
If for some reason the mechanical pump fails, you can turn on the electric to feed the motor, but figure out why the failure occurred and resolve first, otherwise you will likely burn up the electric in short order too (hard lesson on my part).
Also consider dual start switches, one latching (or a key switch), the other momentary, so it takes 2 switches to fail to crank the starter.
Always turn off the main battery switch (big red Perko) or disconnect the battery, before entering the cage. Never turn the prop by hand unless ALL plug wires are pulled, or you are trying to hand start the motor and you are prepared for the result. Treat the prop like a loaded gun!
I probably missed some items on the safety list, there are a few threads on the board covering it in more detail, do some searches on "Airboat Safety." Others will probably add.
Stay safe, have fun. Don't be afraid to drive it like you stole it, these things are more likely to sink off plane.
One Eyed Gator
Well-known member
Look under aircraft power at the top, there is a operation manual and parts manual for that motor.
Slidin Gator
Well-known member
Thanks Waggs, that pic is from a O-320-B2B.
Anyone have a good parts diagram of the marvel 4spa carb? The lean/rich knob seems pretty straight forward, my boat doesn't have one to speak of, i am assuming lean/rich is controlled by a little lever or actuating piece on the carb. Also do people run any kind of air filter on these engines? Mine is currently open, thats the way I bought it, seems sketchy. Appreciate all your help guys.
Slidin Gator
Well-known member
A filter does take away a little power, but once you put one on and see all the stuff the motor would be eating, you'll stick with a filter. It's a custom bracket, flat plate and 4 holes to match carb flange, then a tube with a ridge at end for a K&N style oiled filter.
I am interested to see other pictures of mixture control cable set up's too, but here is what I have:
This is a carb mounted bracket on a O-320-B2B that we just bought recently. Note that the mixture control is tie wrapped to rich as purchased, funny how every boat/engine you buy has that feature!
For another point of reference, here is the set up on my O540. There is a threaded boss on the oil pan on that motor, so I mounted a swivel bracket with a space off the boss. I was concerned about it getting loose, but no issue so far, red loctite helps I think.
Look at Aircraft Spruce, I like the button lock cables. They ship out of Georgia:
https://www.aircraftspruce.com/menus/ap/controls.html
Aircraft Specialties is another source, they are out of Texas, longer shipping to Fla.:
http://www.aircraft-specialties.com
You can get the filter kit (and all of the above and more) from Schmidt Aviation in Pompano, Fla, search "schmidt airboat store" on this site for more info: 954-782-2845 Email: schmidtairboats@yahoo.com
I am interested to see other pictures of mixture control cable set up's too, but here is what I have:
This is a carb mounted bracket on a O-320-B2B that we just bought recently. Note that the mixture control is tie wrapped to rich as purchased, funny how every boat/engine you buy has that feature!
For another point of reference, here is the set up on my O540. There is a threaded boss on the oil pan on that motor, so I mounted a swivel bracket with a space off the boss. I was concerned about it getting loose, but no issue so far, red loctite helps I think.
Look at Aircraft Spruce, I like the button lock cables. They ship out of Georgia:
https://www.aircraftspruce.com/menus/ap/controls.html
Aircraft Specialties is another source, they are out of Texas, longer shipping to Fla.:
http://www.aircraft-specialties.com
You can get the filter kit (and all of the above and more) from Schmidt Aviation in Pompano, Fla, search "schmidt airboat store" on this site for more info: 954-782-2845 Email: schmidtairboats@yahoo.com
Thanks Slidin, going to get that bracket for the filter asap, some good news I got her running this afternoon and got the starting procedure down pat. One thing I noticed though, either I don't have a mechanical fuel pump or it failed. When I shut off the electric pump down in the tank it would quit within a minute or two of me flipping the switch. Going to call the guy I bought it from later and see what he says about it.
Slidin Gator
Well-known member
Post some pictures of your motor so we can figure out what motor you have please. Your mechanical fuel pump should be pretty obvious, in the location shown on the original picture, or on the side of the case towards the prop end (H models as Waggs noted). More than likely you have a failed fuel pump and it is either in the fuel lines (electric pushing through it) or bypassed but still there. But it could have been removed and blanked off too.
You don't have to have a mechanical pump, they will run just fine on a 5-7 PSI electric. But there is nothing more reliable than a mechanical fuel pump and they don't need any battery power to run. They do not offer a rebuild kit (that I am aware of) for the mechanical pumps and it's pretty good coin for a new one, so many folks just bypass them and go electric. If you do that, I highly recommend a spare electric on hand, plus a means to prime it up.
Your electric is submerged in the tank? That is certainly a reliable way to go, no suction issues!
You don't have to have a mechanical pump, they will run just fine on a 5-7 PSI electric. But there is nothing more reliable than a mechanical fuel pump and they don't need any battery power to run. They do not offer a rebuild kit (that I am aware of) for the mechanical pumps and it's pretty good coin for a new one, so many folks just bypass them and go electric. If you do that, I highly recommend a spare electric on hand, plus a means to prime it up.
Your electric is submerged in the tank? That is certainly a reliable way to go, no suction issues!
That was definitely where the mechanical pump was. What are the downsides to putting the mechanical pump back if any? I am considering putting a facet electric pump on there and carrying a Holly Might mite as a backup. Which model of the facet pump do you run on your 320 and do you think the Holly Might mite has enough flow and pressure at 7 psi 32 gph ? I think I have a Holly mighty mite on there now, I didn't get a good look because its mounted under the deck but that's what it felt like, small and plastic.
Slidin Gator
Well-known member
I like mechanical as the primary. They are more reliable, more tolerant of contamination, and don’t have potential for electrical issues. Key advantage is they will pull a good suction so they can suck the tank dry to get every last drop.
Add electric for redundancy.
That Faucet has a built in, easy to clean suction screen. Connect inlet of Faucet direct to tank. Make a loop in the suction line to hold fuel for quick priming.
Feed outlet to a water separating filter and then into inlet of Mechanical. Use electric to prime the system on first start of the day and then leave it off the rest of the day.
One note, had dirt dobbers clog up vent line on me one time. When motor started to stumble I turned on electric without resolving. Destroyed both pumps and ended up with 5 gallon jug in back seat gravity feeding to get home. I now have vent screen and spare electric. Even an el cheapo spare will get you home. Pack it in vac seal bag or other waterproof bag.
https://www.amazon.com/Bang4buck-Un...SX236_SY340_QL65&keywords=bang4buck+fuel+pump
Add electric for redundancy.
That Faucet has a built in, easy to clean suction screen. Connect inlet of Faucet direct to tank. Make a loop in the suction line to hold fuel for quick priming.
Feed outlet to a water separating filter and then into inlet of Mechanical. Use electric to prime the system on first start of the day and then leave it off the rest of the day.
One note, had dirt dobbers clog up vent line on me one time. When motor started to stumble I turned on electric without resolving. Destroyed both pumps and ended up with 5 gallon jug in back seat gravity feeding to get home. I now have vent screen and spare electric. Even an el cheapo spare will get you home. Pack it in vac seal bag or other waterproof bag.
https://www.amazon.com/Bang4buck-Un...SX236_SY340_QL65&keywords=bang4buck+fuel+pump
jopete
Well-known member
I always ran a electric on my lycomings. a Carter brand. I hate electric fuel pumps. I run a 13$ manual fuel pump on my GPU. if I ever get another Lycoming, it will have a manual fuel pump.
anyway.... on a new boat I usually get a label machine and label all the switches and I put a red arrow on the mag switches and power switches so I can glance down and see they are in the right position before I try to start the engine. saves on battery life when u spin and spin with mags off trying to start!! lol
anyway.... on a new boat I usually get a label machine and label all the switches and I put a red arrow on the mag switches and power switches so I can glance down and see they are in the right position before I try to start the engine. saves on battery life when u spin and spin with mags off trying to start!! lol
Reorder your switches whichever way you please but always put the most important 3 to start or stop the motor (pump and mags) on the side you like best by FEEL and just remember what does what. I wouldn't want to be looking for tags on mag switches when my boat is stuck wide open...and it's no race boat.my mags are on the back of my box and it's pretty easy to remember where they are. 
I was going to wire up an outboard style kill switch on the ignition, anyone have one? I have a very newbie question for you guys, i took a look at my alternator this morning and noticed the positive lead is disconnected. Does this wire normally run straight to the positive terminal on the battery? Hopefully thats a good guess, also hoping it still works. How would you guys test this thing? Normally I would just put a multimeter straight on the alternator terminals but thats not really an option with a direct drive airplane engine.
