Hard Starting

Ice Cold/Cold Start

The colder it is, the more prime fuel is required.  When an engine is really cold there is always the possibility that too much fuel can “frost” the plugs, essentially making it very difficult to start, as the moisture in the fuel frosts onto the plugs so they don’t fire reliably.  The only fix is heat.  This is something you might experience at -10 C. (You should really never start an engine colder than that as the oil is too thick and only bad things can happen).

Cold Start

(meaning—“first start of the day”– with Tanis engine heater plugged in or in warm weather—no matter—it is the first start.)   Always good to prime as follows: Full throttle and Full Mixture – press fuel button for 4 seconds—look for fuel flow indication. The time can be adjusted depending on how it starts. – If it starts quickly – only 2 or 3 blades of prop but seems to run rough and belch black smoke – you can go down to 3 seconds. If it starts but then quits then extend 1 second.

Once you prime – then turn over engine (making sure that starter adapter engages) release and “bump”  prop with starter switch to alternate location and try again. For start—I recommend that you retard throttle to just above idle and leave mixture full. When engine catches – advance throttle forward a little— this allows more air to mix with fuel and should keep engine running. If it is rough it is likely because the plugs are a little wet or a little oil has collected in the plugs overnight. Any engine burning a litre in 4 or 5 hours will likely be leaving a little oil on the cylinder walls at shut down. It can foul a plug now and then. If it was just a little too much prime it will clear easier if you retard the mixture to full lean for a split second and then advance steadily to full rich—not too quickly but don’t go so slow that the engine starves of fuel.

Hot Start

If the engine is hot the fuel in the lines in the engine compartment can boil from the excess heat and no airflow. This is called vapour lock. A good way to solve this problem is to give just a quick shot of fuel with full mixture and throttle before start. This clears any bubbles in the fuel lines. It will also spill a little gas into the cylinder. The cylinder likely doesn’t need any extra fuel so there is always a possibility that you end up with a flooding scenario. It is better to have a little flooded as it is easy to clear — therefore before start you put throttle to full throttle and retard mixture to lean. You crank the engine over and when it starts you must be quick to retard the throttle to just above idle (higher than a cold start but not half throttle– so it doesn’t run up high power immediately AND push mixture to full rich quickly after it starts to add rpms. If you do either one too quick you may have it quit—simple repeat. The point is that the engine does not need fuel to start because it is hot and just a little bit of fuel will vaporize immediately and efficiently due to the heat – vs a cold engine – fuel is cold and only the fuel in gas state is flammable.  So 3 seconds of cold fuel is like a brief shot of fuel when it is hot.

Once you get skilled at the above and learn your engine it will happen without even thinking.

2 more points:

1. Unless really cold (like in first above) – you can always solve a start problem if you are confused as to whether the engine has too much fuel or not enough….. simply flood it and then do a hot start— it  will clear all fuel and start. Sometimes a hot start seems like  a “long” start—it may take 10 revolutions or 20 revolutions before it clears all the fuel and then catches.
2. After landing,  I like to lean the mixture of the engines slightly – this makes the engine run a little hotter (due to leaning) and thereby burn off any excess oil just before shut down. Then the next morning you should have less likely possibility of oil in the lower plug.

The above is science.  Based on what is happening in a hot and cold engine and one that is new vs one that is older is what adjusts the specific timing of your actions.

These are techniques, so practice to adjust to your engines is necessary.  If however, your engine is just difficult to start—this could point to a timing issue in mags.  You also have a system installed called “shower of sparks” –quality of the shower of sparks box can be a problem (used only for start).  Usually a bad shower of sparks means it is always too hard to start no matter whether cold or hot.