Longer starting

[Stan]

I have a 1989 J model and just got my Dual Magnetos rebuilt.  The mag drop and difference are fine.  However, my normal start of 2 to 3 engine blades now takes over 10 to 15 blades with 2 cycles of 10 to 15 blades before it starts.  Once started it runs fine with no issues.  A hot start is fine with 2 to 3 blades.

 According to the engine data plate, the engine's timing is 25⁰ BTC.  But according to the “Lycoming Operator’s Manual, O-360 And Associated Models,” Page 2-3, Revised March 2009, for my serial number L-27655-51A, the timing for the mags is 20⁰ BTC, with the caveat, “Consult nameplate before timing magnetos.”  So, it was timed according to the data plate.

 Does anyone have any thoughts or experience with a longer blade count?

[PT20J]

The dual mag can only be timed to 25 deg BTDC.

Can you hear the impulse coupling click when you rotate the prop by hand?

Was any other word done to the ignition or fuel system?

[A64Pilot]

I think the reason why you can only time the dual mag to 25 as opposed to 20 is there isn’t a 20 deg impulse coupling available, so if you timed it to 20 then the mags would fire 5 deg late, which won’t hurt anything but it would make it harder to start.

If an impulse fires early it can kick back and break things but late won’t cause a kick back.

[Stan]

We heard the impulse coupling so they were timed to 25⁰ BTC. 

Checked the fuel flow at the injectors and the bottom plugs, the engine is getting fuel.

Nothing was done to the ignition system at all.  The battery shows 24 volts on start.

Going out tomorrow and will play with the boost pump and throttle settings

[Joe Linnebur]

That’s weird, our ‘79 had the dual mags overhauled recently as well and I’m seeing the same thing. 

[EricJ]

Who overhauled the magneto?

[PT20J]

Just to be clear, hearing the impulse click just means that the impulse coupling is working. The only way to tell that the mag is timed correctly is with a magneto synchronizer.

When priming, the throttle position has an effect on fuel flow. It should be well open to make sure that the idle valve has fully opened the main jet. Then it should be closed to maybe a quarter inch open for starting. 

With two single mags, only one has the impulse coupling and so only one is firing for starting. The impulse coupling on the dual mag fires both mags, so it should start easier than with single mags. To take advantage of this, the ignition switch should be wired according to SIM20-59A.

Did you get the mag maintenance done because something was wrong, or just because it was due? If nothing was wrong and it started fine before the mag work, I would suspect the mag maintenance. Maybe the E-gap is set wrong and the spark is weak.

[N201MKTurbo]

I would agree, you should check the internal timing. It can be checked with no special tools except a mag timer. It is kind of tough to get the e-gap and point gap in range and both working the same. I always re-time mine after overhaul, they are never right.

[Stan]

The mags were timed with a synchronizer and were overhauled because they were due.

As an aside: if there isn't a  20⁰ impulse coupling, why would Lycoming say time it to that in their Operator's Manual?

Again my mechanic timed it to 25⁰ as referenced on the dataplate. 

[jetdriven]

Who did the magneto? What kind of spark plugs do you have and how old are they? How much are you priming it?

[201er]

Could it be that the mag is perfect now but the timing was off before… so the priming method used before was to help compensate for the issue, but now it requires less fuel during priming for a quicker start? Just thinking out loud.

[PT20J]

3 hours ago, Stan said:

As an aside: if there isn't a  20⁰ impulse coupling, why would Lycoming say time it to that in their Operator's Manual?

Single mags from Bendix and Slick are available with 15 degree lag angles, which means that when the mag is timed to the engine at 20 deg the impulse coupling will fire at 5 deg BTDC. The Bendix dual mag is not available in different lag angles and was designed for mag to engine timing of 25 deg BTDC. Here is the original Lycoming Service Instruction.

SI 1325 Timing Change for IO-360 Series Engines.pdf

Also, the note in the Operator's Manual begins, "On the following model engines..." The first engine listed is "IO-360-A Series (Except -A1B6D)". You have an -A3B6D. The difference between the 3 and the 1 is just the propeller indexing, so the parenthetical note applies to your engine. The D signifies dual mags.

[thomas1142]

18 hours ago, 201er said:

but now it requires less fuel during priming for a quicker start?

I had starting issues after rebuilt mags. Mags were sent back and some issues were corrected. After reinstalling I still had some issues starting whereas before it would start perfectly all the time. Two things were adjusted. It was determined that the fuel mixture was a bit lean, annnnd I adjusted how I primed before starting. Before on a cold start I would prime 7-8 seconds, and do nothing for a hot start. Now about 3 second prime for cold, and just a bump on the prim for hot start.

[PT20J]

My two M20Js both required about 4 seconds of prime when cold. Make sure the throttle is open when priming - it affects the fuel flow when near idle.

[Ragsf15e]

1 hour ago, PT20J said:

My two M20Js both required about 4 seconds of prime when cold. Make sure the throttle is open when priming - it affects the fuel flow when near idle.

As @PT20J said, throttle and mixture full in when priming.  ~4 seconds when cold, a little less when it’s warm outside.  After prime, reset mixture to cutoff, throttle just open enough so you get 1000 rpm when it starts.

[MikeOH]

42 minutes ago, Ragsf15e said:

As @PT20J said, throttle and mixture full in when priming.  ~4 seconds when cold, a little less when it’s warm outside.  After prime, reset mixture to cutoff, throttle just open enough so you get 1000 rpm when it starts.

Exactly what I do....except it's only 3 seconds prime here in 'cold' southern California

[Stan]

A 3 count on the prime solved (hopefully) my starting issue.  I went flying yesterday and the 3 count worked for me, it was in the high 80⁰ F. 

I was over-priming it before.

Thanks for the help and discussion!

[Fly Boomer]

4 hours ago, Stan said:

A 3 count on the prime solved (hopefully) my starting issue.

I think it was Mike Busch who said "if you are having starting issues, and it's hot, you have probably over-primed -- if it's cold you have probably under-primed".

[MikeOH]

I also wait 10 to 30 seconds after prime before cranking...10 seconds when a hot day, 30 seconds if it's a cold day.

[DCarlton]

5 hours ago, MikeOH said:

I also wait 10 to 30 seconds after prime before cranking...10 seconds when a hot day, 30 seconds if it's a cold day.

I’ve never tried waiting that long.  I may give it a try.  My engine usually starts on the first try though.