Hard to start O-360

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Paul B
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Hard to start O-360

Post by Paul B »

My MXT-180 (Lycoming O-360) has become increasingly hard to start when cold. It doesn't have to be very cold either, the first start of the day when below 50 degrees F will take several tries over 5 minutes or so. My usual cold start technique was:

mixture full rich
open throttle slightly
run boost pump until I see about 6lbs
prime 3 to 4 strokes with primer after it is actually pushing fuel
immediately engage starter

A year ago this would usually result in engine start after 4 to 5 seconds of cranking. The engine would run rough for a few seconds, then idle normally @1000rpm. When very cold, the engine would run rough for longer than a few seconds, but eventually would run normally.

This method has gotten less reliable and lately will never work on the first attempt. I have tried more prime, less prime, pumping the throttle after engaging the starter and have not found the magic yet. The engine will fire and sputter but will not run until many attempts have been made. The last couple of morning starts have come close to depleting my battery. This of course, is more than inconvenient if you are not at an airport.

It starts easily when warm and runs normally after starting. Any ideas welcome!

Mountain Doctor
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Post by Mountain Doctor »

Check for broken, leaking, or blocked primer line to one or more cylinders.

Happened to me several years ago.

Also a shot or two off the accelerator pump helps also.
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aero101
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Post by aero101 »

After primer lines and as well as checking the little nozzle in heads at primer line hookup, I would suggest check impulse coupling on mag. Turn prop by hand, see if you hear it snap with crisp snap. Mine would snap, but not crisply, replaced coupler which was slightly corroded, and fixed problem... Another hint coupler not working correctly and retarding timing is that the engine will KICK BACK when starter released, sometimes kicking back even while starter engaged. Very hard on starter as well.
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st8cop166
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Post by st8cop166 »

I don't know if this is the "right" way but was taught to cold start with three shots on the primer, NO boost pump, push throttle all the way in, pull all the way out, push in 1/4 to 1/2, hit starter. Hot start is just one shot of the primer.

I put a Skytec starter on mine the other day and I swear I could taxi on it if I wasn't afraid of over heating it. With that, I cold started with two shots of primer.

They are all different and some engines may be tighter than others I'm guessing. Just as a side note, when I first got the Maule, I noticed I seemed to flood it with the boost pump. That's why an old buzzard told me to keep my hands off the boost pump. :)
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Njacko
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Post by Njacko »

When I first got my MX-7-180 last December it was reluctant to start and when it did condescend to run it would spit, pop and shake to bits. Then the weather got warmer, I changed the bottom plugs for fine wires, unblocked a primer hole, and I learned to use less primer and almost no throttle. Now it starts within a couple of compression strokes and runs smooth as - well, it's still an O-360...

I can't say for sure which of the above made most improvement, but I'm more than willing to try a winter further south. Failing that, fine wire plugs do seem to be worth the $$.

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Post by Mountain Doctor »

The primer is safer than pumping the throttle, less/no risk of intake tract fire. With that said, I use a combination of the two.

Here's another question, what is the boost pump for?

As I recall the only checklist it shows up on is in-flight engine failure. Our engines are fed by gravity and an engine driven mechanical pump, no? I cycle the boost pump as part of the pre engine start checklist but other than that it stays off.
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Hogy59
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Post by Hogy59 »

My O-360 starts on the 2nd or 3rd turn with no primer when cold. I do pump the throttle a time or two, then about a quarter open. Sounds like something not set correctly.

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Post by MauleMechanic »

Mountain Doctor wrote:The primer is safer than pumping the throttle, less/no risk of intake tract fire. With that said, I use a combination of the two.

Here's another question, what is the boost pump for?

As I recall the only checklist it shows up on is in-flight engine failure. Our engines are fed by gravity and an engine driven mechanical pump, no? I cycle the boost pump as part of the pre engine start checklist but other than that it stays off.
Technically in the O-360 it is an aux pump. In the IO-540, it is a boost pump :-) Comes in handy if ya get a vapor lock!! Better chance of winning the lottery though!


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aero101
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Post by aero101 »

Mountain Doc- You got it already, only thing boost pump for in the 180HP O360 is for an engine quitting... I know of one instance where some moisture in fuel, froze to slush, blocked gascolator screen until engine quit, boost pump on restored power, made it home under power. Without that pump, he would have had forced landing out in remote area.

Starting O360= Cold, 4 shots of primer, crack throttle just slightly and crank a couple blades to start... Hot, one or two shots primer, crack throttle, crank couple of blades to start. If not starting easily, you've got something wrong like broken primer line, clogged primer jet at cyl head, fouled plugs, inop or unreliable impulse coupling, these are most common issues though you may also need magneto work, or carb work, but don't see this often....

Don't suggest pumping throttle unless you do it as you're cranking and stop before you quit cranking. If you've ever seen how quickly you can make a pile of ashes, you won't do this as there's no need because it gets you nothing in terms of starting if primer working properly.
Jim
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SlowFlyer
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Post by SlowFlyer »

aero101 wrote:Mountain Doc- You got it already, only thing boost pump for in the 180HP O360 is for an engine quitting... I know of one instance where some moisture in fuel, froze to slush, blocked gascolator screen until engine quit, boost pump on restored power, made it home under power. Without that pump, he would have had forced landing out in remote area.

Starting O360= Cold, 4 shots of primer, crack throttle just slightly and crank a couple blades to start... Hot, one or two shots primer, crack throttle, crank couple of blades to start. If not starting easily, you've got something wrong like broken primer line, clogged primer jet at cyl head, fouled plugs, inop or unreliable impulse coupling, these are most common issues though you may also need magneto work, or carb work, but don't see this often....

Don't suggest pumping throttle unless you do it as you're cranking and stop before you quit cranking. If you've ever seen how quickly you can make a pile of ashes, you won't do this as there's no need because it gets you nothing in terms of starting if primer working properly.
Here in Panama its always a hot start. If I used 2-3 shots of primer I would have to engage starter 5-6 strokes before it would start. If I used 3-4 primer shots then I would get a horrible backfire. There was no sweet spot and the engine would always have hard vibrations the first 10 seconds or so.
I have been using 5 throttle pumps instead of priming and the engine starts in the first stroke with no vibrations, I love the technique.
Now, you mention the dangers of throttle priming but seems much better that over priming with primer or using up the starter when underprimed.
I guess the danger is that fire would come back the induction system to the carb, but how real is this scenario? Does it happen a lot?
I sure don´t wan´t to find out by trial and error.

Teddy

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Post by pilot »

Pumping the throttle causes raw gas to pour out the bottom of the carburetor and leak through the intake filter/hot air box into the engine compartment. It may work for you most of the time, but the slightest backfire will set you on fire - a pretty hot fire at that. I would be standing by with a CO2 extinguisher if I were you.

The primer system keeps the fuel in the manifold, close to the intake valves. No doubt it will catch fire as well, it is just contained.


Don't get me wrong - I hate the primer system design and would much prefer to have NO fuel lines for primer or fuel pressure gauge in the cabin, but it is what it is.
I can't remember if I fired six shots, or only five.....


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bobguhr
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Post by bobguhr »

I have the O-360 and slick mags and I've had what you describe happen twice over the course of my ownership. Both times it was the mags/impulse coupling. First time around 800hrs second time about 600 hrs

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aero101
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Post by aero101 »

Slow Flyer- It's a VERY REAL SCENARIO, Especially if you are priming with carb, then hitting starter... All that fuel used for primer from carb will run thru airbox where it leaks onto cowl, and if primed enough onto ground. Very little makes it into upper induction system unless you're cranking when you're pumping throttle nor does it vaporize well. Doesn't just need backfire, but slight leak on mag lead, bad ground, anything that can generate a spark will make it go WHOOOOSH as cowling full of gas fumes!!! Sounds to me like you have bad impulse coupling that is not retarding ign timing for start (it's really quite common condition and another indication is when you release starter switch, prop will try to reverse direction often as not)!!! You may not burn aircraft to ground, but a fire going from fuel can do A LOT of damage in very short order... When everything functioning properly, an O360 will start just like any other O360 that's starting properly, no vibs, no backfiring, etc, etc.. I've also flown out of Arizona considerably when temps get up over a 100F, you still prime cold engine for a normal start as most components are still well below operating temp!!! I also doubt very much that backfire created by overprime with primer, this is sign of mixture or timing issues, again pointing to bad impulse!!! When overprimed with primer, you'll foul plugs, period. You wouldn't see any backfiring from that unless pulling fairly high RPM... Anyway, after many years in the business, that's my opinion? Could be something else, but odds are as stated, and difficult at best to troubleshoot via forum when acft not in front of you?
Jim
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captnkirk
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Post by captnkirk »

I have read a lot of articles about the electronic ignition systems out there seems like this might be a good reason to consider one. The ability to adjust the timing curve beyond what impulse coupling does should improve power, reduce fuel burn and ease starting. Anyone here have one ?do you like it was it worth the cost etc ????
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Post by Paul B »

Thanks for all replies. Yesterday I checked primer lines, no leaks and they delivered identical amounts of fuel into plastic cups taped to the ends. I removed the primer nozzles from cylinders and checked, they seemed OK but I cleaned them anyway. I rotated prop by hand and could hear distinct "clack" from mag impulse coupler. I put everything back together and have since tried 2 "cold" starts (OAT on 1st one was near 60 F, second was 50 F). I don't believe it is starting any easier.

To be clear, over the last 6 months or so, I have tried everything from 0 to 5 primer strokes; no boost pump, boost pump before cranking, and boost pump during cranking; throttle position all the way out to 1" in and everywhere in between; pumping the throttle while cranking. The only commonly used method to start a cold 0-360 I haven't tried is pumping the throttle before cranking and I really don't want to do this for reasons some of you have mentioned. It always starts easily when warm. One thing I didn't mention before, about every 20 flights or so the engine will backfire on either start-up or shutdown. I have never flown another plane that did this.

So . . . time to call my mechanic and schedule a trip up there. I suspect a mag/impulse coupler problem. Unless someone has another suggestion.

Thanks again!

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