M20f starting issues

[7thprez]

I have a customer with an m20f, which has recently encountered numerous starting issues. Since the issue has reared its head we have replaced the switch, rebuilt the left mag, and installed a new capacitor in the starting vibrator. He was finally able to fly home and once it sat for a few days he encountered the starting issue again. I have exhausted myself trying to figure out this issue, so any input would be greatly appreciated

[ArtVandelay]

Maybe you can elaborate on the numerous starting issues...
Cold/hot? Okay after starting? I assume you checked all the plugs, and flow tested the injectors?


Tom

[MB65E]

Harness ok? 

Plugs?

Does it fire when you let off the start switch?

how old is the fuel servo?

mixture Ico for start? Does it move full range?

-Matt

 

[Yetti]

Loose nut behind the yoke?

Please elaborate on trouble starting.

Please explain process used to attempt to start.

[MB65E]

Could also be a fault with the seat to yoke interface system.

-Matt

[nightmoves]

I can answer some of these questions (it's my aircraft he's referencing). The symptom is that it cranks and cranks (cold start / hot start / flooded start procedure, doesn't matter). Eventually fuel starts dumping from the cowl after the 4th or 5th attempt. Occasionally when I let go of the key it acts like it wants to fire but never does. One way to get it started is to unhook the left mag (which is brand new). If he does that the plane fires up immediately but runs super rough and is almost impossible to get stopped (I apply full choke and it still runs for 30 seconds until it finally dies).

After he replaced the mag it was started 5 or 6 times over 2 days and fired up each time. As a matter of fact it started more easily than it ever had, maybe 2 revolutions of the prop and off we go. I arrived to fly it to home base, it fired right up, no issues at all. Flew it home and parked it for 2 weeks. Went out to fly it and here we go again, will not start. Just cranks and cranks then fuel starts dumping. Unplugged left mag, starts and runs extremely rough and won't stop until it finally does. As far as more detailed troubleshooting, I'll wait on 7thprez to respond.

[slowflyin]

49 minutes ago, nightmoves said:

I can answer some of these questions (it's my aircraft he's referencing). The symptom is that it cranks and cranks (cold start / hot start / flooded start procedure, doesn't matter). Eventually fuel starts dumping from the cowl after the 4th or 5th attempt. Occasionally when I let go of the key it acts like it wants to fire but never does. One way to get it started is to unhook the left mag (which is brand new). If he does that the plane fires up immediately but runs super rough and is almost impossible to get stopped (I apply full choke and it still runs for 30 seconds until it finally dies).

After he replaced the mag it was started 5 or 6 times over 2 days and fired up each time. As a matter of fact it started more easily than it ever had, maybe 2 revolutions of the prop and off we go. I arrived to fly it to home base, it fired right up, no issues at all. Flew it home and parked it for 2 weeks. Went out to fly it and here we go again, will not start. Just cranks and cranks then fuel starts dumping. Unplugged left mag, starts and runs extremely rough and won't stop until it finally does. As far as more detailed troubleshooting, I'll wait on 7thprez to respond.

I'd venture to guess it's the shower of sparks.   My F had the same issue.   When the engine sometimes starts after you release the starter it's telling you the SOS is failing-weak..... Try this link.  http://donmaxwell.com/shower-of-sparks/

[7thprez]

We have already replaced the capacitor in the shower of sparks box. Points inside were in great shape, so no clue where else to check in the SOS 

[Prior owner]

Perhaps the health of the vibrator and associated wiring can be confirmed by-

disconnecting all leads at the plugs, disconnecting the starter lead, pulling one plug from each cylinder and then engage the vibrator with the ign switch (or jumper current to the vibrator at the back of the ignition switch, if you don’t have a helper) while pulling the prop through slowly by hand. You can place a small piece of card stock or folded paper between each spark lead from the left mag and the cylinder (I just lay the lead next to an exhaust stack with folded paper slid in between). 

You can confirm a few things this way:

1. The retard points are firing the coil at the correct time (~TDC compression stroke)

2. The distributor block and high tension leads are set up properly.

3. That you’re getting a nice, strong, continuous spark from the vibrator.

[EDIT] I just read Maxwell’s article and realized that that is where I had originally got this sequence from.... and it sorted the it my starting issues very quickly! Thanks again Don!

Edited June 25, 2019 by PilotCoyote
LE and realized that

[Guest]

I’m not sure if they still offer it, but Aircraft Magneto Service in Montana would test and repair SoS boxes quite reasonably.

Have you verified that the P leads are correct?  Right lead on right magneto and left lead on left magneto, SoS wire is on SoS terminal on left magneto and not crossed with P lead?

Other simple checks to do, spark plug resistance, ceramic bores are clean, ignition wire ends are clean at both magneto and spark plug ends.

Clarence