What makes an easy cranking engine?

[sparky]

In another thread, it was mentioned that the Robin/Subarus have a "decompression" feature that makes cranking easier.

I know of another engine, the Chung Yang GP420 / GP460 that also has an easy cranking feature. From a cold start, it very rarely takes more than 2 slow pulls. Daves motors has the pull start here, and the listing says "Spring-assisted for ultra-easy starting." This engine prolly also has the decompression feature, tho.

I'm just trying to figure out what the real features are that make for an easy cranking engine.

 

[duivendyk]

A rich micture+a potent spark,the rich micture is required because the fuel condenses in the intake passages and may not get in the combustion chamber At low temp this is a real problem.Choking (restricting the air intake) enriches the micture but may lead to flooding and oil fouling of the plug(in 2 strokes) with repeated cranking. Small engines generally have magneto ignition.Magneto output is proportional to rpm and at the low cranking speed the plug may not fire and with repeated cranking may get oil fouled (2 strokes) and the engine flooded (over-rich micture), a smaller gap in the plug will help with starting .It is worth remembering that the firing voltage in the combustion chamber is much higher than in open air.To check plug firing, increase the gap 2/3 times normal (on a test plug).since firing voltage increases with compression.Decompression feature make it easier to get adequate cranking speed.

 

[kerf]

Chung Yang has no compression release but the spring loaded pull start does help. Four to six pulls cold but just one warm.

 

[sparky]

That is amazing if this spring loaded function is all in the pull start. I wonder if one could easily adapt this pull start to other motors??

 

[HoughMade]

Easily? Don'r know about that, but it works like this- when you pull the rope, you aren't actually pulling the engine around, at least initially, you are winding a spring so that when the spring is fully wound, it kicks the engine around. That is why you can pull it slowly and steadily instead of quickly like you would with a normal rope start. I have a similar spring assist on my leaf blower.

 

[duivendyk]

Once I had a mower with a B.S. engine in which to crank the thing you first wound up a spring with a turn handle and then released it.It didn't work worth a ****, cranking was simply too slow and I had to replace that contraption with a regular pull-start.In the SubaruRobin engine the intake valve is lifted momentarily at the end of the compression stroke,reducing the cranking effort and also making it easier for the plug to fire due to the reduced pressure,JJ

 

[HoughMade]

...In the SubaruRobin engine the intake valve is lifted momentarily at the end of the compression stroke,reducing the cranking effort and also making it easier for the plug to fire due to the reduced pressure,JJ

I have a 1967 Briggs and Stratton engine that I restored that has this feature. They called it "Easy-Spin".

 

[sparky]

... when you pull the rope, you aren't actually pulling the engine around, at least initially, you are winding a spring so that when the spring is fully wound, it kicks the engine around. That is why you can pull it slowly and steadily instead of quickly like you would with a normal rope start.

Yea, I get the idea. I just wasn't sure... it seemed so difficult to me that a spring could actually spin a motor like that.

When my friend's Chung Yang is cranked up daily, it never takes more than 3 pulls. Maybe when it has sat up for a few days.... but that's about it. Then it seems as if for the rest of the day that all starts are warm, only needing 1 tug.

I dunno how somebody would prefer an engine with a manual clutch to one of these spring assisted pull starts. I dig 'em.