Give me carbed or give me death!

[erj-145mech]

As far as the mag timing goes, the mags are not timed to the impluse couplings, they are timed to the point opening. You'll get an impulse click per prop blade rotation on a four banger. Some aircraft engines have two impulse couplings per engine, mine for example does (TCM IO-360) but most Lycomings don't.

When I was working on the Rockwell Commanders, there was a service bulletin out to remove a bus bar from the back of the mag switch that grounds the right mag when you go to the start postion. What this bar did was to ground the right mag during the start (key to the start postition), so with the bar removed, you were getting two start sparks, one just after top dead center and the other at the normal crank position.

The impulse coupling not only retards the spark, but it also speeds up the rotating magnet in the mag to build a higher voltage. The magneto makes its own electricity, but it needs about 300 rpm to do so. The engine may not make that while starting, so the impluse makes up for the low speed.

 

[cforst513]

tried starting it 10 times? what'd your battery juice look like after that? next time, give the starter a rest and just let it cool down for, as mentioned before, 30 minutes or so. i've found if you just let them sit a bit longer there are no problems.

 

[gkrangers]

tried starting it 10 times? what'd your battery juice look like after that? next time, give the starter a rest and just let it cool down for, as mentioned before, 30 minutes or so. i've found if you just let them sit a bit longer there are no problems.

I let the starter rest in between...at one point I had enough, and just chilled watching the planes (and a nice Falcon jet) for 20-30 minutes....took another 2-3 attempts after that break, but it started.

Battery was ok.

So I guess the idea is to just sit and wait if you are vapor locked ?

91W never gives me any problems! I'm gonna start flying that again.

 

[gkrangers]

The fuel injector is on top of the engine. When the engine is run and is sitting there after shutdown, the heat goes up. The fuel in the injector "lines" vaporizes because of the heat. You need to send some "cool" fuel into the lines so you have liquid in there.

Your hot start listed above sounds like a flooded start.

For a normal hot start (engine was running recently), try doing the normal start only without the priming steps. That's the procedure for the 172R (IIRC) and it seemed to work well.

If it doesn't start, just let it cool for 30 minutes (I know the delay sucks but...) and it should start fine for ya.

How'd the DUATS thing go?

-mini

I don't think I have filed since, but I'm sure I'll have no problem.

 

[gkrangers]

It doesn’t matter what starting procedure you use if the mags are out of time and the impulse couplings have gone bad.

What kind of mag drop do you get? To the limit? How much difference when switching between L & R?

Mags were dropping ~100 RPM, both of them.

I attribute it to vapor lock and me bein a dumbass.

 

[DrewBlows]

Vapor lock is a reality of fuel injected engines. When I was instructing we used to purposely flood the engines if it was going to be a hot start. Put the throttle and mixture forward and run the boost pump until fuel is dumped overboard (out the bottom right side of the cowling), then pretty much do a normal start with a little extra throttle. With enough practice you will be able to get a good start every time. I always took pride in having a nice start where the engine stabilizes just above idle. You know you can tell an owner from a renter by how he starts an engine. The owner always starts it on the first or second time with minimal engine run-up during start, the renter takes 3 or more times and runs the engine over 1500 rpm before getting things under control. Of course I've never been an owner but I can pretend.

That said it soulc be something else. Has you always had a hard time starting this particular engine or has it become more difficult since the weather has changed? How does the engine idle after start? How does it idle when brought from running speed to idle (especially if brought to idle quickly by a ham fisted student)? The reason I ask is because the flight school I used to work for had trouble with it's engines any time the weather would change (warm to cold was the worst if memory serves me, which it may not). They even instituted a policy that we couldn't bring the engine all the way to idle during stalls, after one Cessna experienced an engine failure during a stall. They were able to get the engine restarted but they were about 500 feet above the ground with no landing spot below before it did. Anyway, when engines started running rough we wrote it up and the mechanics would adjust the idle mixture and the problem was solved.

Disclaimer: I am not a mechanic, or an expert of anything, any advice you take from me take at your own risk. Always follow your airplanes AFM.

 

[gkrangers]

I fly a different SP almost every time...usually no problem, maybe 3 starts on a rare occasion. This one was the exception for me.

Its Florida...the weather doesn't change.

Idle was fine...runup was fine...ran smooth.

 

[gkrangers]

I fly a different SP almost every time...usually no problem, maybe 3 starts on a rare occasion. This one was the exception for me.

Its Florida...the weather doesn't change.

Idle was fine...runup was fine...ran smooth.

 

[WMUchickenhawk]

In our Cessnas, if the engine temp is in the green we dont bother priming them. Ive never had a propblem starting them this way.

 

[BLing]

The fuel injected Cessnas can be a pain if you dont know how to start them hot. I just do what a few of you have said: Mixture full lean, Throttle full forward, starter engaged, mixture rich and throttle back as soon as it turns over. It works every time. I think that Cessna calls for something different but I cant remember, its been a while since Ive flown one.

 

[aucfi]

Correct me if I am in error, but don't most engines only have one impulse coupling and only utilize one mag for start?

As far as the mag timing goes, the mags are not timed to the impluse couplings, they are timed to the point opening.

See my profile, "still learning" lol. I talked to our mechanic today and he cleared me up on these two things. One of our planes has impulse couplings on both of the mags while the rest only have one.

Thanks for correcting me,

au