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Dual P Mag carburated starting technique

R

Redbud40

Well Known Member
Several threads on starting technique with injected engines. Anyone care to share their technique that has dual pmags on a carburated engine. Lately it seems my old slick mag technique is not working so great. Battery fully charged
Thanks.
 
Cold start. First start of the day. Subsequent starts warm engine to hot starts fine. Once started runs great.
 
My O360-A4M engine is carbed with dual P-Mags. I do; mixture full rich, throttle about 1/2" open, prime for about 5 seconds and with both mags "ON" it always starts within 1 prop rotation. After the engine starts, I lean the mixture aggressively and set the throttle to around 1,000RPM's for taxi. YMMV

:cool:
 
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Redbud40 said:
Lately it seems my old slick mag technique is not working so great.
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Same thing happened to me recently. I don't have pmags but what I found might apply to you.

In my case my primer line had broken off right at the T fitting, so while I thought I was priming the engine I wasn't, I was priming the inside of the engine cowling.
 
Original builder never put the primer on. I didn't either cause in most cases in warm Texas didn't seem to need it. I would "manual prime " fill bowl with accelerator pump then hand turn prop 6/8 times on cool to cold starts. That has worked well in the past but lately not so good. I have primer in hangar maybe I should look at putting it on. Other thought on primer one more place to leak. IDK.
 
Then check to make sure the accelerator pump in the carb (Marvel Schebler?) is working. If it's working correctly, you should be able to 1st fill the float bowl with the boost pump, then after 5 or 6 full strokes with the throttle, you should see fuel dripping out of the cowl. (Not saying to prime that much; just a quick/dirty way to check acc pump operation.)

I'm assuming you normally run the boost pump to fill the bowl prior to 1st start, right? I'm also assuming that you have a weep hole in the airbox to let excess fuel (and any water that might enter the intake while sitting outside) drain out.

edit: I'm not sure how valuable hand-turning the prop is, to prime the engine. I usually just 'prime' with the acc pump while running the starter.
 
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rv7charlie said:
I usually just 'prime' with the acc pump while running the starter.
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Yep. My carbed O-360 has 2 Pmags, no primer system installed. To start, boost pump on, throttle closed, crank starter. While prop is turning, pump throttle (accel pump) once, then return throttle to just cracked open. Starts on 2-3 blades.
 
rv7charlie said:
Then check to make sure the accelerator pump in the carb (Marvel Schebler?) is working. If it's working correctly, you should be able to 1st fill the float bowl with the boost pump, then after 5 or 6 full strokes with the throttle, you should see fuel dripping out of the cowl. (Not saying to prime that much; just a quick/dirty way to check acc pump operation.)

I'm assuming you normally run the boost pump to fill the bowl prior to 1st start, right? I'm also assuming that you have a weep hole in the airbox to let excess fuel (and any water that might enter the intake while sitting outside) drain out.

edit: I'm not sure how valuable hand-turning the prop is, to prime the engine. I usually just 'prime' with the acc pump while running the starter.
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Sorry, in the interest of safety, I just have to comment. WIth an updraft carb, there is no value in pumping the throttle with the engine not cranking - you just pump fuel into the air box. One backfire and you have an engine fire!

BTW - the carb bowl should still be full from previous engine run, unless you have a heck of a leak. No need to "fill it" with the boost pump. Pump on, leave it on, and you'll have a pressurized system. If not - you have a leak.

Pump the throttle WITH THE ENGINE CRANKING and you'll get a good prime. There is this hard to kill myth that pumping the throttle before cranking doeas something - and it did, with a downdraft carb on a V-8 in your old car. Not with a Lycoming!

My start with dual P-Mags and a Carb is: P-Mags hot, start cranking, two pumps (three if its cold) and the engine is running. Easy.

Paul
 
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Ironflight said:
Sorry, in the interest of safety, I just have to comment. WIth an updraft carb, there is no value in pumping the throttle with the engine not cranking - you just pump fuel into the air box. One backfire and you have an engine fire!

BTW - the carb bowl should still be full from previous engine run, unless you have a heck of a leak. No need to "fill it" with the boost pump. Pump on, leave it on, and you'll have a pressurized system. If not - you have a leak.

Pump the throttle WITH THE ENGINE CRANKING and you'll get a good prime. There is this hard to kill myth that pumping the throttle before cranking doeas something - and it did, with a downdraft carb on a V-8 in your old car. Not with a Lycoming!

My start with dual P-Mags and a Carb is: P-Mags hot, start cranking, two pumps (three if its cold) and the engine is running. Easy.

Paul
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Since you quoted me, were you actually addressing me? If so, please re-read what I wrote. You're preaching to the choir on pumping the throttle prior to engine start. I only said to do it as a troubleshooting method, to be sure that the acc pump is actually working. They do fail, and if his isn't working, he isn't getting the 'priming' action you'd expect.

As to the rest, remember, we're talking about troubleshooting an engine that's hard to start. Assuming that everything is as it should be just isn't a valid assumption, or it wouldn't be hard to start. We don't know whether there's a slow bowl leak, what kind of fuel he's running, how often it runs, etc etc.

Charlie
 
rv7charlie said:
Since you quoted me, were you actually addressing me? If so, please re-read what I wrote. You're preaching to the choir on pumping the throttle prior to engine start. I only said to do it as a troubleshooting method, to be sure that the acc pump is actually working. They do fail, and if his isn't working, he isn't getting the 'priming' action you'd expect.

As to the rest, remember, we're talking about troubleshooting an engine that's hard to start. Assuming that everything is as it should be just isn't a valid assumption, or it wouldn't be hard to start. We don't know whether there's a slow bowl leak, what kind of fuel he's running, how often it runs, etc etc.

Charlie
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Charlie, you are right, and I apologize. I saw the "pumping while not cranking", and actually grabbed the wrong post to quote. Not my intent top impugn you.

We do, however see lots of folks (I had someone I flew with in their plane just the other day!) think that you prime by pumping the throttle, THEN cranking....and we don't need folks catching fire at the fuel pumps (seen that too....).

Sorry I grabbed your quote.

Paul
 
Dual P-Mag Start

I have a carbed O-320 with primers in 3 cylinders. I use switches instead of a keyed switch and start with both mags on. Regardless of outside temp, I prime for 3 seconds and turn the boost pump off. Throttle cracked 1/8" with mixture full rich. Always starts after 2-3 blades. Immediately pull mixture knob out about 3/4" inch to smooth out idle and leave it there during taxi.
 
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