Hot start issues

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gwagen
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Hot start issues

#1 Post by gwagen » Sun Sep 24, 2017 9:48 am

My good friend has a champ with an 0-200 in it. Lately it’s been hard to start when hot or say you start up, taxi from the hangar to the fuel pumps at the other end of the field. It will be hard to start.

Just started in the last little while, was generally easy to start hot in the past.

When it’s cold, prime twice the engine barely gets a blade or two by and it’s running like a million bucks.

Mags were overhauled in the last couple hundred hours, new spark plugs 20 hours ago. Compressions excellent valves scoped, zero issues.

Can’t figure it out, ame stumped.

Could it be a mag impulse coupling issue?

Any thoughts appreciated!!
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fish4life
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Re: Hot start issues

#2 Post by fish4life » Sun Sep 24, 2017 9:54 am

Have you tried starting it with full throttle and the mixture full lean? As soon as she fires push the mixture in and pull the throttle back
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Big Pistons Forever
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Re: Hot start issues

#3 Post by Big Pistons Forever » Sun Sep 24, 2017 10:07 am

Had a friend a long time ago that had a similar issues. As I recall it was an ignition switch problem. Try disconnecting the p lead from the mag that does not have the impulse and see if it makes any difference.
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culver10
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Re: Hot start issues

#4 Post by culver10 » Sun Sep 24, 2017 10:17 am

Every small Continental I have worked on uses an impulse coupling on both mags. The great advise given above is for a Lycoming with only one impulse coupling.
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Re: Hot start issues

#5 Post by Big Pistons Forever » Sun Sep 24, 2017 10:30 am

culver10 wrote:Every small Continental I have worked on uses an impulse coupling on both mags. The great advise given above is for a Lycoming with only one impulse coupling.
You are correct the issue I wrote about happened on a Lycoming O 235.

Re dual mags the Contiental Aircraft Engines Operator's manual for the O 200 does say the following.
Impluse coupling is standard on all magnetos used although on the early A and C series the impulse coupling was installed in the left mag
Chances are though the engine has been updated with the dual impulse mag set up so my advice would not apply.
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Re: Hot start issues

#6 Post by jg24 » Sun Sep 24, 2017 10:47 am

Timing? - not a hot start specific issue.... but if nothing else to work with, may as well check it.
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cgzro
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Re: Hot start issues

#7 Post by cgzro » Sun Sep 24, 2017 1:29 pm

- How old is the battery. Sometimes even a small difference in RPM at start can make the difference between easy and hard.

- How old is the starter, again if its dropped a bit in RPM due to being worn that can have an impact.
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Re: Hot start issues

#8 Post by photofly » Sun Sep 24, 2017 1:52 pm

fish4life wrote:Have you tried starting it with full throttle and the mixture full lean? As soon as she fires push the mixture in and pull the throttle back
+1 to this
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JasonE
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Re: Hot start issues

#9 Post by JasonE » Sun Sep 24, 2017 2:07 pm

Check the strength of the impluse coupling in the mags. Flew a 172 that had that problem. Always started cold, but wouldn't hot start. Rebuild mag fixed the problem.
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gwagen
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Re: Hot start issues

#10 Post by gwagen » Sun Sep 24, 2017 7:37 pm

Thanks guys! A few things to try and check into.

The battery is older and could probably stand replacement, she turns over pretty quickly though. Had sky-tec or equivalent installed at overhaul in 2007 approx 700 hrs ago.

Will suggest the full throttle mixture lean, is this with no primer I'm assuming?

Curious to what's involved in checking the impulse coupling?

My theory though perhaps I'm out to lunch is.

When cold the engines turns slower with a weaker battery and more engine friction.

When it heats up a bit and the battery gets a bit of charge, it turns over too quickly and the impulse couplings "disconnect" (I believe it's centrifugal force that causes them to disconnect?) which causes the timing to be not ideal for starting.

After 3-4 attempts at starting, the battery weaker and turning more slowly it catches???

Make any sense? Or just non-sense?

Thanks again!
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Re: Hot start issues

#11 Post by photofly » Sun Sep 24, 2017 7:51 pm

I think you’re overthinking it. Hot start issues are usually mixture related, often due to over-priming. Or maybe the mag timing slipped.
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gwagen
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Re: Hot start issues

#12 Post by gwagen » Sun Sep 24, 2017 7:54 pm

Big Pistons Forever wrote:Had a friend a long time ago that had a similar issues. As I recall it was an ignition switch problem. Try disconnecting the p lead from the mag that does not have the impulse and see if it makes any difference.
On second thought, a new EI digital tach was installed, it picks up rpm info from the P leads and it was attached to the back of the ignition switch, that's the only thing that has changed and co-incides with the hot start issue. Also one mag has a 70rpm drop, the other a 100 they used to be nearly identical......hmmm something to look into, perhaps wrenching on the ignition switch caused it to partially fail or perhaps it's not tightened correctly.

Thanks!
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gwagen
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Re: Hot start issues

#13 Post by gwagen » Sun Sep 24, 2017 7:56 pm

photofly wrote:I think you’re overthinking it. Hot start issues are usually mixture related, often due to over-priming. Or maybe the mag timing slipped.
Probably.

In the past when I've flown this plane, when restarting hot I'd just pump the throttle once or twice and it would restarteasily, no primer ever!

Primer only on the first cold start of the day.

Since the issue developed have tried many different techniques with and without primer.
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Re: Hot start issues

#14 Post by cgzro » Sun Sep 24, 2017 8:15 pm

"EI digital tach was installed,"

That EI tach connects directly to the P-leads where it allows a small amount of current to ground through an "isolator" so that it can measure the pulses and count them. If for some reason the isolator is allowing too much current to flow to ground it will reduce the strength of the spark or I suppose actually ground it so that no spark occurs. If I remember correctly EI wraps them with yellow heat shrink and you put them in-line. There are also two different types and the kit comes with 4 isolators I think. Can't remember how you pick the proper pair. Think it was mag type dependent or something?

You could try disconnecting the tach lead that connects to the impulse mag since thats the one that does most of the work at low RPM to get you started but of course leave the P-lead properly connected to the switch.

You could also try replacing the switch because if there is wear or shorting inside the switch it could also affect the magnetos. Actually there is a special grease in that switch which is supposed to be replaced periodically and it prevents arching or something to that effect.

New switch is not that expensive and may also be worth trying but you could first check with an ohm meter to see how much current is flowing through a P-lead when the switch is on L or R or both and therefore no current should be flowing through the switch to ground from a P-lead.

Also I'd look at the primer and make sure its not leaking a bit even when its shut off. That could give you more prime than you want which is not a problem when cold but a big problem when hot.

Anyway a few things to think about.
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Re: Hot start issues

#15 Post by FOD_Vacuum » Wed Sep 27, 2017 1:47 am

Possibly vapour lock. Look it up. Prime maybe a second. Throttle open all the way and mixture idle cut off, then once it kicks over, throttle idle and slowly enrichen mixture. Each engine reacts a bit differently. Generally speaking, you shouldn't have to prime for a hot start but priming a small amount MAY help.
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Re: Hot start issues

#16 Post by photofly » Wed Sep 27, 2017 3:19 am

I’m trying to imagine where a normally aspirated engine like an O-200 could get a vapour lock. Everything downstream of the carburettor is supposed to be vapour anyway. Isn’t vapour lock exclusive to fuel injection systems?
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