Hard starting warm or hot

[SpamPilot]

As helpful as you guys are, I wish I were flying instead of writing to the forum...

 

Since buying my '68 M20F a few months ago, I have learned quite a lot about starting techniques and have tried all of them.  No technique is reliable for me when the engine is hot, or even just warm.  Here's what happens on a typical start:

 

1. First crank will go for six or seven blades, then when I get the first hint of a cylinder firing, the prop stops cold and the starter motor just whirs (disengaged from the ring gear).

 

2. Second crank will go for three or four blades, then a cylinder lights off and the prop stops cold, starter still spinning but no longer engaged.

 

3. Third crank will go for two or three blades, then the prop stops and the starter motor disengages.

 

4. Subsequent cranks go for one or two blades if I am lucky, but usually the starter motor just whirs and doesn't even engage in the first place (as though I have run down the battery).

 

5. If I let it sit for a while, I can get another 3-4 blade crank, and maybe the engine will start successfully.  If I get a jump start, the engine cranks noticeably faster and after 8-10 blades I can usually get it to fire up.

 

I had the battery replaced (RG-35AXC) and the behavior didn't change.  Battery voltage indicates a well-charged battery (12.4V+) even after several starting attempts.  Battery voltage measured at the starter solenoid while cranking does not drop below 10V.  I had the starter solenoid replaced and the behavior didn't change.  Yes, I am using cold start/hot start/flooded start techniques as appropriate.  Often I find excess fuel dripping from the cowl flaps.

 

The problem happens even if the engine hasn't been started yet but the outside air temp is above 90F.  However, if the aircraft has been sitting for two weeks and the OAT is only 75F, she cranks fast and, after a longish crank, she will fire up.

 

I have plenty of evidence to rule out battery self-discharge or an external load draining the battery.

 

TSMOH is 700 hours.  The starter was replaced six years ago, still shiny.  The mags (Slick) were overhauled during the major.  Plugs are new.  On my mag check, I get a 60-70 RPM drop on the right mag and a 80-120 RPM drop on the left mag, EGTs rise on all cylinders for both mags, and I get no rough running.

 

Any thoughts or advice would be appreciated.

 

 

 

[N201MKTurbo]

The method that I have used for the last 30 years, is to leave the mixture at idle cutoff. Open the throttle to the 1000 RPM position. Crank until it starts. Then wait until it starts to die and advance the mixture to full rich. This has worked every time.

 

The fact that you have fuel running out the sump drain indicates the engine is flooded.

[N201MKTurbo]

BTW, go get a Sky Tec starter.

[Bob_Belville]

Sure sounds like a starter issue.

[mooneygirl]

I would get a SkyTec.  I love mine.  When I shut down I make sure the RPM is 1100.  I put the master on, fuel pump on, mixture in, count to ten, pump off, mixture out. Starts every time.  I have NEVER had a problem with hot starts.  Throttle in, no pump, mixture out and go. 

[tomn]

One thing to consider if your starter is OK is your fuel servo. I had a terrible time with hot starts - cold starts were fine - until I had the servo overhauled. Was much better after that. I started getting fluctuations in EGT at altitude of 20-30 degrees up and down. That was the final clue that the servo was not right. I was going to say to check the resisitanc on your plugs until you said they were new -that can make a difference on starts as well.

Tom

[aaronk25]

Plus 1 on sky Tec I paid the labor to have 2 prestolite or whatever the stock starters are changed out in 9 months. Advice to anyone who needs a starter don't replace with cheaper standard equip as it won't be cheaper in long run!!!!!!

[pinerunner]

One thing I notice here is the firing stopping it dead. Mine (64 M20E) makes you turn the key before pushing in to engage the starter. The initial turning of the ignition switch changes the timing (retards it closer to top dead center I believe) to make it better for the low RPM's off the starter. I suspect its stopping dead because its firing too far before TDC and isn't cranking fast enough to make it past TDC into a proper power stroke. Must be hard on the starter. I'd have your mechanic check that timing. Of course my advice is free.

[garytex]

An IO-360 just isn't that hard to start unless something isn't right or is broken.  I don't think that mixture manipulation is going to solve your problem. And when youve got a real puzzler, that usually means that at least two things are wrong.  The prop stopping could be a failure of the retard function of your shower of sparks ignition, the spark then come 24 or 26 degrees before TDC, stops the prop, and throws out the bendix.  You may also have a weak starter, or battery or some lead oxide hiding under the terminals on the battery posts.  You can run the battery traps your self, but don't fool around with a failing spark retard. Things break.  Get to a smart mechanic.  If it turns out you need a new sky tech starter, there are two, get the slightly heavier, and much heavier duty one.

[pinerunner]

Yes it really should be easy to cold start. When first introduced to mine I started it almost like a C-150, 5 sec booster, full rich, start cranking. It started first time. It was 90 degrees near Savanah, Georgia. Cold starting is never a problem requiring interesting tricks. You've got something needing fixing.

 

Dave  

[SkyPilot]

Hey Spam Pilot, I bought an M20F about 3 years ago and had similar hot-start problems not including your stopping dead issue. Sounds like you have either a weak starter or a timing problem.

 

Definitely change the starter out and put a Sky-Tec in. It won't fix bad start procedure or other mechanical issues but it will turn your prop over much faster.

 

I never had problems with cold starts, but the hot starts were completely embarrassing at the fuel pump. The first couple of months I owned the airplane, I'd go for lunch after fueling, just to avoid the "hot start scenario".

 

But with the Sky-Tech starter helping out, I do my hot-starts like this: (Prior shut-down at 1100 rpm) Don't touch the throttle or mixture (assuming they have not been moved), turn the key, advance the mixture once she starts up. That's it.

 

It works every time, sometimes with more blades, sometimes less.

 

Have fun. Don't spend too much on upgrades, avgas is the best way to spend your money

 

SkyPilot

[DrBill]

Here's what I've learned about starting after my last annual. Due to an un-documented AD verification, we had to pull the left mag and inspect some parts to verify they had been replaced (they were). So the A&P had a friend do this for him who was familart with Bendix mags and gave it back.  He put it in and the plane was hard to start hot or cold. Would only start when I let the key off.  So we pulled the left mag and found that:

A: the left mag contains 2 sets of points. One start, one run. The start set is retarded to almost TDC to ease starting. The run set is set at about 20 deg Before TDC. The start set in my case was not opening.  Hence, my starter was cranking and no spart until I let the key off and then the run set took over.   We pulled the mag, adjusted the start set, reinstalled and verified the timing and VOILA.. all was as good as new.

SO.. I suspect your start set is mal adjusted and once you get it straight you'll be AOK.  Of course I too have a skytec starter and I don't think I could have gotten it started at all with the old prestolite.

[Bob_Belville]

Background on Dr. Bill's post:

 

www.donmaxwell.com/publications/MAPA_TEXT/Shower%20of%20Sparks/Shower%20of%20Sparks.htm

 

It should not affect starting, but be sure the timing, 20 or 25 BTC, is set per the engine spec plate. Either could be correct depending upon when it last saw the factory, as I understand it. My factory reman from 2001 is 20 BTC.

[N601RX]

The dwell inside the shower of sparks box has a lot to do with how hot the spark is durring starting. Unfortunately this is usually ignored until the engine will no longer crank reliably. You need the SOS service manual, a adjustable spark gap and an amp meter to adjust it. Here is a video a posted a while back of it firing after adjusting.

http://mooneyspace.com/topic/8019-hard-to-start/?hl=%2Bshower+%2Bsparks

[SpamPilot]

Here's what I know so far after bringing her into the shop...

 

Left mag was timed to about 35 degrees (!).  That means, even with properly working retard points, ignition is still happening something like 10 BTDC.  That explains the prop stopping.  This is probably the root cause of the starting problems.  Both mags are now being overhauled.

 

Additionally, the mag drop with the mixture full rich was found to be 200-300 RPM on either mag, not due to a mag problem but due instead to excessive fuel.  I haven't been doing a mag check at full rich for a long time because I had been told by another A&P that this is not all that unusual.  So I taxi lean, and then when I do my runup, I go a bit rich of peak power (but not full rich) and the mag check is OK.  Haven't thought about it in a while.  It appears that the fuel injection servo needs to be adjusted.  That could have an affect on startability.  Hard starting appeared to be more a function of density altitude than engine temperature, so excess fuel means the mixture would get even worse at high DA.  This may also help explain the fuel dripping out of the left cowl flap (via the intake snifter valve).

[Bob_Belville]

Do you have digital fuel flow? What's you flow full power on climb out with mixture full in? I'm seeing 17.7 (91% power at my 1270' home drome.)

[MB65E]

Holy Crap! 35*!!! Was the mag loose? I can't believe it was running anything close to normal temperature. Glad you found it. +11 or so For the Skytec! If funds don't allow, just clean the terminals off the battery, starter silinoide, and starter. Should start like a champ now! Servo and adjustment I'd leave alone for a while until you put some time on the new mags. The idle mixture will change seasonly. Rpm should rise +25 or so when the moisture is slowly pulled out starting at 900 rpm with a warm engine.

Enjoy the new mags!!

[SpamPilot]

Here's the final verdict on the hard starting predicament...

 

My M20F now starts very reliably, hot or cold.  There were two things wrong.  As previously mentioned, the mag timing was off on one mag, causing firing before TDC during crank and very hard starting.  The second thing was that the mags simply needed to be rebuilt and remagnetized.  They just weren't putting out a hot spark.  Now the mag drop is minimal.  The excessive fuel at full rich turned out to be a red herring.  This aircraft has a Power Flow exhaust, and I have since learned that you can't pass a mag check with the mixture set full rich when running a Power Flow (the motor will bog).  You need to lean it a bit before the mag check.

 

I am using one of two starting procedures:

 

1. Engine cold and zero fuel pressure:  Fuel pump off, crack the throttle, set mixture to lean idle point.  This is the point slightly rich of where the engine begins to stumble at idle.  I have learned to set this reliably by the length of one of my fingers and holding the knob just so.  Crank until the engine fires and comes up to idle.

 

2. Engine warm or hot, or cold with fuel pressure:  Fuel pump off.  Keep mixture in idle cutoff.  If you move the mixture control even slightly out of idle cutoff with pressure in the fuel lines, it will dump a bunch of raw fuel into the intake and likely will flood the engine.  Engine warm or hot: throttle closed.  Engine cold: open the throttle a "big" crack.  Crank until the engine coughs.  At that point, continue cranking and advance the mixture slowly to the lean idle point.  Crank until the engine comes up to idle.

 

I have found that I can reliably start the engine on the first try about 95% of the time using these procedures.  When warm, it fires within 1-3 blades.  When cold, it can take 10 blades.  I have not needed to add a priming step, even down to 25F, but I also preheat at every opportunity.

 

I haven't had to mess with my idle mixture settings as a function of weather

 

Full power full rich fuel flow is 17.0 GPH on my Shadin.