Carbed Lycoming Starting Issue

Skymac

Skymac

Pre-takeoff checklist
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Justin
I’ve got a new, carbed O-360 with about 50 hours on it. It’s got to where it doesn’t want to start vary easily, cold or hot. I’ve got a hot battery and fresh starter.

Im starting to think I might have an ignition key issue? It seems like many times as soon as you let off the starter switch, it will fire. It is an ACS style switch in a later model C172.

When pulling the mixture to lean cut off, it is adjusted for roughly 50 rpm rise before stopping.
 
Skymac said:
Im starting to think I might have an ignition key issue?
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Could be several issues. Even with a good battery and starter you could have a large voltage drop. I say this because it wants to start when you release the start switch. Maybe check voltage at the starter/relay during a start attempt to see what you have then troubleshoot from there?
 
Bell206 said:
Could be several issues. Even with a good battery and starter you could have a large voltage drop. I say this because it wants to start when you release the start switch. Maybe check voltage at the starter/relay to see what you have then troubleshoot from there?
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What does a voltage drop have to do with starting other than spinning up the starter? I'm missing something here...
 
It turns over good, with new solenoids, and such so I don’t think it’s going to be that, but may be.

The old engine had 5000 hours on it, and didn’t care wether it was hot or cold. It’s a Lycoming factory engine, new carb, new mags, etc. Seems to be progressively getting worse though, when we first did the swap, the cold starts were first or second blade.
 
kyleb said:
What does a voltage drop have to do with starting other than spinning up the starter?
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I've found in some cases when a starter draws excessive amps and causes a voltage the starter keeps the start RPMs low or puts a "bind" in the system which leads to start issues. Most of the start problems I've dealt with were wiring related either with the starter or P-lead system. The start voltage check is an easy first T/S step. A given they just replaced the engine and disturbed both of those systems I would check that first before looking into a fuel issue.
 
Check ignition switch at P leads to be sure it is working properly...like almos5 all have suggested.
 
After priming the normal amount, try filling the primer and shooting it in just as you hit the starter. O360A4K here, and I couldn't get the engine to start reliably since I bought it. Once I started using this technique, it starts on less than one blade.

The effectiveness of this will depend on your primer set up. Some set ups put a primer in one cylinder, others prime two or more. The more primer lines you have, the better this will work.
 
Did it start better with fewer hours on it? So a gradual change? Or did something change all at once? Or has it been a hard starter all 50 hours?

most of us have an impulse coupling on one mag only and have the ignition switch grounds out the non-coupled mag when in the start position, so you start it on one mag only. If yours fires once you let off the start position, I’d think that’s a hint to look at the switch or the coupled mag.
 
Your description seems like it is actually starting on the RIGHT mag.

My guess is “Starting “ ( not Running ) Timing. This is set by the the relationship between the Impulse Coupling, E-gap and Starter Speed. Improper lube of the Contact Point Cam can result in retarded timing where combustion is trying to catch up with the retreating Piston.

There are issues with some components described a Slick Mag Alert thread pertaining to both mfg. that could be the issue.

The Impulse Coupling retards the spark until approximately TDC. Later firing will result in hard starting. Observing safety precautions; see if the Impulse clicks at TDC. Timing Marks are on the Flywheel ( Support). A late click can be caused by mag/ engine timing retarding (loose nuts?) or the E-gap issue.

Get back on this.
 
That’s a good thought! I have 2 new mags in the box, I could always try another impulse mag. We have checked the timing at the first oil change and it was still spot on. I was just reading through the slick mag issue. I’ve seen more new mags fail then mags with a few hundred hours on them.

It’s slowly got worse I believe, as it was cold starting very good.
 
If it slowly got worse, have you pulled/inspected your plugs?
 
If you’re starting on BTC timing you probably would have seen some false start kick-backs. Those can do damage very quickly. I destroyed a ring gear from it. Somehow the Skytec starter survived.
 
Before a swap consider:

Disconnect P-lead at the mag. Now it’s HOT. You don’t need switch to start.

If issue continues the timing about 10 degrees. ( to 35ish) . If it starts better E-gap is the likely culprit. GROUND RUN LOW RPM ONLY.

The Primer System is often ignored at o/h time. Cessna usually have better lines than the work hardened copper Piper items.

Activate the Primer and check for external leakage to check.

Soaking the nozzles in Hoppes #9 is good to do at o/ h time. Fuel cokes up and eventually blocks them.

To check ; disconnect the Line and remove nozzle. Reconnect outside of cylinder and observe to spraying well.

Still thinking ignition though.
 
Magman beat me to it. I’m thinking an Egap issue. Check the timing. I’ve started making log entries for advance and retard adjustments. This way I’ll know if it’s walking off one way or the other over time.
Voltage drops, like Bell described, is also super likely. Not uncommon to have both issues actually.
Switching to Bogart cables and skytec starter does wonders for starting the old 172s. The interesting thing about the Bogart kit is that it adds a dedicated starter ground cable. So instead of the starter having to find a ground through the engine and engine ground, it has an additional grounding cable right at it’s mounting stud.
 
OP’s comment “It turns over good” seems to imply normal Starter operation.

You don’t need to spin FAST but you need good SPARK.
 
I’ll report back. I just wanted a good pool of thoughts as I’ve thought of many of the basics as well as my other mechanic and it’s good to think outside the box…. This is going to sound horrible, but I’m going to double check the P-Leads, being reversed may also be the issue.
 
Skymac said:
This is going to sound horrible, but I’m going to double check the P-Leads, being reversed may also be the issue.
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That's what StewartB suggested. If they're reversed, the impulse mag is dead during cranking, and the non-impulse mag turns too slowly to do anything useful (other than to cause kickback sometimes if it's not grounded).

Remember that the ignition switch grounds the left mag when it's on R, and grounds the right mag when it's on L. Checking the P-leads with an ohmmeter can get things mixed up if one isn't thinking about that.

And is that ACS switch in compliance with the AD against it? https://rgl.faa.gov/Regulatory_and_...B8ABD56539B4684886256A3E00759DBF?OpenDocument
There should be a diode between the starter contactor coil terminal and ground, to protect the thin contact plates inside the switch. Without that, and the 2000-hour servicing, the switch can cause problems.
 
The ACS switch kit was only 18 bucks if I remember right?
IMG_8416.JPG

There was nothing wrong with this switch as it was working normal except it needed lube.
IMG_8423.JPG

Preventive maintenance and is cheap and easy to do. Diode was installed also across the starter relay coil.
If your see a blue switch plate and red screw heads you know it has been serviced at least once before.
IMG_8431.JPG
 
Magman said:
OP’s comment “It turns over good” seems to imply normal Starter operation.

You don’t need to spin FAST but you need good SPARK.
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I know you’re right, and I just noticed that he already has a new starter, so it’s probably not that. I’m still thinking it’s a mag gap problem, but cranking speed can be deceiving. I’ve had engines that I thought was turning over good but they were not. With a voltage issue it can be insidious. We tend to get used to things as they are gradually changing over time.
 
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This is a simple, free, quick check of your impulse coupling.

Check the P-Leads first to ensure they are properly configured.
Turn off the ignition, master, and everything else. Consider pulling the battery ground.

Gently pull the prop through. You should hear the impulse coupling "snap" as you make a prop revolution. If no "snap" your impulse coupling spring has likely broken. Starting at ignition let off is a common symptom of a broken IC spring (not definitive but suggestive).
 
If you followed Dom’s suggestion you may find another phenomenon has occurred.

They IC can become magnetized and the Flyweights will not engage the Stop Pin.
Not surprising as the IC is a chunk of steel on the end of the magnet. Not easy to identify but de-magnifying the IC is easy but requires removal from the mag.

The same condition can cause “ Kick - back” when starting as it provides a weak, advanced spark.

A Starter that turns too fast can actually result in what I call a “ Hung Start”. The early C-152 with Lyc O-235 L2C was infamous for this. Hand prop fine though. A switch to a lower speed Starter, reduced retard IC and other changes improved the condition.

Lycoming /Slick has a graph showing how Ignition Timing is retarded with increased Starter speed.
 
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Skymac said:
It’s a Lycoming factory engine, new carb, new mags, etc. Seems to be progressively getting worse though, when we first did the swap, the cold starts were first or second blade.
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That implies a failing impulse mag. There have been some defective Slicks delivered recently. Bad points.
 
I experienced a similar problem, but the problem was contained in the ignition switch. This was in an Archer II. The engine wouldn’t start except when you gave up and released the switch. Then it fired and ran normally.

Turns out this is (was?) a known problem with the switch. If you turned the switch ‘too far’ and held it against the stop, the P-lead on the impulse coupling would be grounded, I.e. no or difficult start. Same thing on shut down in reverse: turn the key off and hold it against the off position stop, the engine would in fact stop, but if you released the key and the spring moved it to the center of the off position, the engine would continue to run.

A new switch solved the problem. The A&P said this was a known problem with the switch which was a Bendix IIRC. -Skip
 
Looks like it probably had something to do with the impulse coupling, swapped the mag out and all is well with the world!

In good old fashion Aviation fashion though, fix one problem and get another. The old trusty Garmin 430 Decided it wanted to not read the aviation database anymore and after trying another known good card, I believe I’ve chalked it up as needing to head to the shop for a flat rate repair. :)
 
Skymac said:
The old trusty Garmin 430 Decided it wanted to not read the aviation database anymore and after trying another known good card, I believe I’ve chalked it up as needing to head to the shop for a flat rape repair. :)
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Fixed your typo
 
I had the EXACT same thing wrong with my airplane… hot or cold, I would crank and crank no start. Various throttle positions, priming, etc. like you described, it would seem to almost start as I let go of the ignition key. I could eventually get it to start, but ran the battery down a time or two.

I struggled with this problem a whole summer of flying. It made my wife scared of the plane…

Then one day it would not start at all. Old timer A&P pulled the left mag showed me the broken impulse coupling. He told me it had been getting weak for a while and finally the spring broke completely. Fortunately it was a clean break and there were no pieces of steel in the sump.

Replaced the impulse coupling and I never had an issue again, for the next 250+ hours it was super quick and easy to start.
 
Kevin Holbrook said:
I had the EXACT same thing wrong with my airplane… hot or cold, I would crank and crank no start. Various throttle positions, priming, etc. like you described, it would seem to almost start as I let go of the ignition key. I could eventually get it to start, but ran the battery down a time or two.

I struggled with this problem a whole summer of flying. It made my wife scared of the plane…

Then one day it would not start at all. Old timer A&P pulled the left mag showed me the broken impulse coupling. He told me it had been getting weak for a while and finally the spring broke completely. Fortunately it was a clean break and there were no pieces of steel in the sump.

Replaced the impulse coupling and I never had an issue again, for the next 250+ hours it was super quick and easy to start.
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That's a symptom that the impulse mag was also weak. Letting go of the key puts the other, non-impulse mag back to work, and the engine fires because that mag isn't weak.

A broken spring takes the mag's timing to TDC, and that would show up as a huge mag drop in the runup.
 
As Dan said; a broken IC spring provides a huge drop; except on engines with a D- mag. Then the engine gets quiet.

From what I’ve seen; IC Springs tend to function normally and break suddenly.
In my book; the biggest culprit is rust from inactivity. Starting the engine puts a fresh coat of oil on internal components. Much better to fly though. I’ve seen springs fail on hangar queens with only minutes of operating time but years of sitting.
 
In my case, the mag check at various RPM’s was satisfactory, as well as an in air check. We didn’t disassemble the mag, just box up it up as a core and swapped it out. It did take care of it though. Thanks for all of the comments!
 
Skymac said:
In my case, the mag check at various RPM’s was satisfactory, as well as an in air check. We didn’t disassemble the mag, just box up it up as a core and swapped it out. It did take care of it though. Thanks for all of the comments!
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Impulse spring couldn't have been broken, then. Maybe broke after mag removal.
 
Dan Thomas said:
Impulse spring couldn't have been broken, then. Maybe broke after mag removal.
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I wondered the same. Then I noted Kevin had the broken spring and Skymac just boxed with no disassembly.

Magnetized coupling for Skymac?
 
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