A couple basic testing questions

[guy48065]

SPARK
I frequently read here the importance of the spark jumping 3/8" but is that with an inline tester or one that takes the place of the spark plug?

COMPRESSION
On my low compression Johnson 9.5 I get vastly different compression results depending on how I do it.
If I pull the starter rope one time I get 50psi
If I pull it like a madman I get 60psi
If I spin the flywheel with my drill on low range I get 70psi.
I see all examples on YouTube. Which is correct?

For testing to be meaningful we need to do it the same way.

 

[tpenfield]

what do you get if you spin the flywheel with the drill on high range?

You do need a few compression cycles to fully pressurize the test gauge & hose. So, you could go with the 70# number. It is just a matter of consistency.

 

[flyingscott]

Pull 5 BRISK times and read the compression. 2 strks build compression with Rpm.

 

[guy48065]

... It is just a matter of consistency.

Consistency is the reason I ask. Can't have everyone doing it different and trying to compare results.

what do you get if you spin the flywheel with the drill on high range?

Low gives me the torque needed to spin it.
High won't do it.

 

[Grub54891]

I have all plugs removed, pull it 5-6 times and take the reading.

 

[tpenfield]

It is hard to compare with the compression tests of others, because the methods of others and their 'pulling strength' varies, as well as the accuracy of the gauges.

Therefore, if you are using reasonable methods of static compression testing take the highest value and call it good.

 

[flyingscott]

How hard is it to pull as fast as you can until the gauge stop. If you have a manual start motor that you can start by hand. You can pull it 5 times with the plugs out and get an accurate reading. 5 times should be plenty to go until the gauge stops. Let's not overthink the simplest test you can do.

 

[guy48065]

How hard is it to pull as fast as you can until the gauge stop. If you have a manual start motor that you can start by hand. You can pull it 5 times with the plugs out and get an accurate reading. 5 times should be plenty to go until the gauge stops. Let's not overthink the simplest test you can do.

I'm not overthinking it. I'm asking what method we're all supposed to use.
My day job involves testing, standards and procedures so getting everyone on the same page is just how I approach things.
The answer given is
FIVE BRISK FULL PULLS
If that's not standard procedure I'm sure someone will chime in. My service manual is vague on this.

Now about that spark test...

 

[stresspoint]

put you finger on the electrode of the spark plug >>> pull the cord or crank the motor with a drill , you will soon feel / see if sparks are good enough to start a motor.

compression that blows you finger off the plug hole .
spark in the correct time and enough to make you let go of the electrode .
fuel that passes the sniff test .
a motor should go if all these test pass.

 

[guy48065]

put you finger on the electrode of the spark plug >>> pull the cord or crank the motor with a drill , you will soon feel / see if sparks are good enough to start a motor.

compression that blows you finger off the plug hole .
spark in the correct time and enough to make you let go of the electrode .
fuel that passes the sniff test .
a motor should go if all these test pass.

You want to stake your reputation on those procedures?

 

[stresspoint]

You want to stake your reputation on those procedures .

i have helped people out at the ramp when their boat wont start using the procedures above , so yea , why not .
for that matter , you could throw some fuel on the ground and try to set it alight , if you get fire , then that fuel should at least get a pop from a 2 stroke when you have enough spark to make you let go of the plug in a hurry when you pull the starter cord briskly enough.

you asked for basic testing , they are about as basic as it gets , there is not much more to it.
now the question is then ,how well it is going to run , that is where the fun begins.

there is no rocket science to a 2 stroke starting up, i have made some pretty clapped out motors run over the years on both boat and dirt bikes with just basic test procedures , once you figure if they are going to fire up then you can start testing for performance.

 

[dingbat]

SPARK
I frequently read here the importance of the spark jumping 3/8" but is that with an inline tester or one that takes the place of the spark plug?

I use one of these

COMPRESSION
On my low compression Johnson 9.5 I get vastly different compression results depending on how I do it.
If I pull the starter rope one time I get 50psi
If I pull it like a madman I get 60psi
If I spin the flywheel with my drill on low range I get 70psi.
I see all examples on YouTube. Which is correct?

For testing to be meaningful we need to do it the same way.

On single cylinder motor I don't care about the actual number. Just comparing it to an earlier base line I took.

Having said that, I either crank or pull until I get to peak compression. It's either going to be in the ball park of the OE specification or it's not.

If the compression gets too low they either start blowing fuel or won't start.