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New Hot Start Problems

odens_14

Well Known Member
I fly an RV-7 with the IO-360 w/ slick mags it has about 400 hrs on it. Recently, I've had trouble with hot starts. I use the full throttle mixture cut-off dance; which up until this summer has worked without fail relatively quickly. Lately it's been much more difficult to start hot, or even warm after it sits for an hour or so. Every time except once I was able to get it started eventually but took a fair amount of cranking which is not normal (and to be honest slightly embarrassing when you're at a fly-in with people watching :p). Cold starts are no issue and it usually fires after 3-5 blades. No other anomalies once started.

I guess my question is where to start looking, it feels like ignition but I'm not sure. Spark plugs looked fine in May, mags haven't been touched. second option is I'm just out of practice with the dance and its pilot error, but it doesn't feel like I've changed anything.
 
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Agree - I?d first look at the igntion starting with cleaning, gap and ohm check of the plugs.

I had 8 of 12 Champion plugs with out of spec high resistance in less than 300 hours (back when Champion had this problem). A new set of Tempest plugs made a huge difference.

Carl
 
If it is true that the mags have not been touched in 400 hours, you'll want to check timing, which is recommended every 100/CI/annual by Slick. They recommend your IRAN them every 500.
 
If it is true that the mags have not been touched in 400 hours, you'll want to check timing, which is recommended every 100/CI/annual by Slick. They recommend your IRAN them every 500.

yes, I've check timing but never needed any adjustment. I also know about the 500 thing as well, I'm hoping mine didn't give up 100 hours early!!! I'll pull the plugs again and see if that tells me anything.
 
Timing and egap (this affects the strength of the spark) will drift on a mag after a 25-50 hours on most new mags as the points and cam wear in. Recommend checking e gap and timing after the first 50 or so hours and then should be relatively stable stable until the 500 hours, though some wear and commensurate drift should be expected.

Larry
 
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Starting

I had same problem and it was my impulse mag needing new points.Something to check.
Bob
 
I agree.

Check your points, condencer, and plugs on an Ohm meter. Slick also had a S.B. for the breaker cams and carbon rotor contact to be replaced. You may want to try an old trick we use from time to time with this being an IO-360.
Sometimes if it is really hot and we shut-down for just fuel and a nature break that is only a few minutes before we want to fire back up, we try this.
Mixture rich,- Throttle just open a little so it will idle after it catches,- start turning and bring the bust-pump on just after we start turning. If it or when it catches, turn the bust pump off as soon as it catches, and then chase the throttle to keep it running till the vapor clears from the spider lines and the engine settles down smooth again. This one is not in the books, but we have fount that on an "IO" that does not like you, sometimes it gets us going. The fuel lines will be hot and once you get running, you will have to set there and wait till it has settle and those hot lines have solid fuel flowing smooth threw them again. Just something to try if you wish. Yours, R.E.A. III # 80888
 
Other age related issues

Mag shops tell me in addition to Egap, magnet ?remagnetizing ? is a key to spark strength. I experienced it first hand on an antique engine, night vss day on hand prop hot starts .
 
Boy I feel your pain. I try not to use the hot start technique unless absolutely neccesary because I fear a back fire and a fire from it. I usually start it with the throttle cracked and mixture at cutoff. If that does not work I try starting with mixture in and then back out. Most of the time it starts but it shakes for 30 seconds or so before it clears up. I don't like the shake.
 
Check the cams in the mags. On a Slick the cam is a little plastic paddle, there was a batch of them a few years back that wore very quickly.

If the points are not opening enough because of a worn cam starting will be tough.
 
Thanks for all the suggestions, looks like I'm on the right track looking at the ignition. I'll check the plugs again this weekend and if they're OK I'll likely seek some experienced help as I don't have any experience with the inner workings of a mag.
 
I built a 7A with a new IO-360 M1B. I had hot start problems from day one. I tried all the hot start procedures and nothing worked consistently. I even tried the IStart system that meters the fuel during start. I called Lycoming and got an answer that the engines in the new Cessna?s have the same problem with hot starts. Even the factory recommended procedure won?t work.

I finally stumbled onto the Slick Start system. I installed Slick Start and now my engine starts hot! Every time! I spent three years trying to figure out what the problem was. The brand new Slick magnetos on my engine would not start the engine hot. Slick Start gives the boost needed to fire the engine when hot. The difference was night and day.

Best regards,

Bill
Osprey 2 amphibian
RV-7A
 
Starting technique

If your engine starts cold, there is no reason for it not to start when hot or warm. Maybe you have always been on the edge of starting with your lever dance, and now that your magnets are older, it doesn?t work anymore.

I believe that it is never correct to start an engine with full throttle, except if it is flooded. You need the perfect fuel/air ratio to fire the fuel in the cylinder. A hot or warm engine needs just a tad of fuel to fire. If you open the mixture and touch the fuel pump, it is flooded. So you try to start with the small amount of fuel, that is left after you shut down the engine.
if you start with full throttle the left over fuel maybe is barely enough to fire one cylinder. On the next Stroke that cylinder sucks so much air, that the remaining fuel is not sufficient to keep the engine alive, until you pushed in the mixture.
Try it with less air. Set the throttle position to where it would run just under 1000 rpm, mixture closed, and push the mixture in, when it starts to fire. If you still have difficulties with the restart, open the mixture and close it again. The pressure in the fuel system will give you a small drop of fuel. If your engine cooled down for a while, maybe twenty minutes, and the pressure in the fuel system is down, run the fuel pump with closed mixture to build up fuel pressure, open and close the mixture and crank the engine.

Good luck!
 
I had what sounds like a similar problem many years ago on my trusty C150. It turned out to be the Slick mags that were of unknown age. New mags fixed the problem. I would suggest Pmags. I made the switch a few years back and am very satisfied that I did.
 
Hard to start

I agree with Ingo. The only reason to use wide open throttle is if the engine is flooded. At shutdown the engine is lean because you pulled the mixture to cutoff. But as you walk away, the fuel in the spider lines starts to boil from the heat of the cylinders. (Stick you ear near the cowl inlets and you can hear it.) There is no place for that fuel to go except through the injectors and into the cylinders. That means the engine just primed itself! Now the mixture is rich! All you should do when you return is to turn the master and ignition on, crack the throttle, and hit the starter. NO BOOST PUMP. NO MOVING THE MIXTURE LEVER FORWARD. Crack the throttle and crank the engine. When the mixture reaches a combustable mixture the engine will fire. Slowly advance the mixture lever to rich. That is how you start a hot fuel injected Lycoming.

The mixture range between rich and lean that a magneto can fire is fairly narrow. If you add the spark booster as already mentioned, the ignition range will become wider making the engine easier to start.

I believe the best ignition solution is Emags. The Doll started life with Slick Mags. Then I went to LASAR igintion. LASAR was a big improvement over the mags. When the LASAR wore out, I went to dual Pmags. That was back in 2011. The Pmags will start my I0360A1B6 under any condition. The ignition range is very wide between rich and lean for the Pmags. Slick magnetos require a spark plug gap of just .017 because that's all they can handle. Pmags spark plug gap is .035. That's more than twice as wide, and they will shoot a hot, blue spark across the wide gap! Like the Slicks mags, the Pmags are independent and self energizing after start, sit on the same accessory case pad, and do not require any other boxes.

The auto spark plugs I use are less that $3 dollars each. I don't clean them. I just put in a new set at every conditional for less than $20 bucks.

I hope that helps.
 
I believe the best ignition solution is Emags.

I was planning on at least one pmag when I got to 500 hrs, if this ends up being something that requires substantial work on the mag that's likely the direction I'll go.

With regards to the starting technique, I know there are others that work; but the one I use has always worked consistently for me until this year...that's what makes me think its something else going wrong.
 
Do you have Shower of Sparks? If not, do you have an impulse coupler. If you do not have them, the engine will start fine without them while everything is new. After a while, hot starts become impossible.
 
Hand prep the engine

One sure way to get a start is to prepare the cinlynder fuel mixture to fire. Best done with someone in the aircraft as safety person.

First, flood the engine with priming, them mixture off, throttle wide open, mags off, pull the prop thru backwards for 8 to 10 blades throttle still wide open.

Treat the prop as if it live and someone ready to close the throttle if needed.

What you?ve done it place a perfect fuel air mixture in the cylinders and it will start first blade.

I borrowed this from my days hand propping old continentals that had no starter.

It?s worked great and sure beats running your battery flat trying to make a hot start happen.
 
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