compression test ??'s

[buckeye_paul]

Is there a sticky in here somewhere with guidelines for compression testing?

If not:

A. Should it be done with the motor cold or warmed up?

B. Is it safe to crank the motor with the key and the lanyard pulled off, or should I just jumper the starter?

C. How long should I wait after cranking to see if it's bleeding down?

 

[Dr Honda]

a) Cold... plugs out... full charge on the battery... open throttle.

b) You can either put a remote starter switch on the solenoid, or have someone turn the key, with the lanyard off, so there is no spark.

c) There isn't any "Bleed down" on this test. The gauge has a valve... and it's going to hold max pressure.

 

[Coastiejoe]

You should ground the wires as well to protect the MPEM,,,

 

[Dr Honda]

You should ground the wires as well to protect the MPEM,,,

On any of the Rotax powered boats... absolutely. But, on the Merc boats... we don't have an MPEM. So... they don't suffer from being fragile. And... the lanyard on these boats is an ignition ground. So... you can crank the engine, with the lanyard off... and the coils won't charge.

 

[buckeye_paul]

Thanks for the info.

The reason I think I may have a problem is:

While out on the water last weekend, on two different days, I experienced a slow reduction in RPM's after the motor warmed up a while and cruising around 35 mph. This has never happened before.

I got a bunch of seaweed stuck in the grate earlier on the first day, but I don't see how that should cause this issue. I checked out the intake and impeller / wear ring and they look very good.

I've checked the plugs. A couple of them were slightly fouled but I attribute that to the fact that I run premix. One thing I did differently last weekend was get gas at BP. I usually fill up at Shell or the Kroger Fuel.

I'll post the results of the compression test later in the week. Unfortunately, we have had a death in the family and I'm not going to be able to get to this right now.

 

[Sportster-2001-951C-Stock]

I suggest before connecting the compression gauge, crank it over a second or two to clear liquid out of the cylinders, otherwise the readings may be skewed to the high side.

 

[Coastiejoe]

On any of the Rotax powered boats... absolutely. But, on the Merc boats... we don't have an MPEM. So... they don't suffer from being fragile. And... the lanyard on these boats is an ignition ground. So... you can crank the engine, with the lanyard off... and the coils won't charge.

Learning every day,,,,

 

[Dr Honda]

Learning every day,,,,

Hey... you get an A for effort!! A lot of guys won't venture into this section. (we're just a bunch of crayz Merc owners)

Speaking of that.... I need to send you a PM. :thumbsup:

 

[Dr Honda]

Buckeye: It could be the plugs... and a partly plugged pump. I know on some of my 2-stoke dirt bikes... a good plug is a "Night and day" difference in power.


Also... IF, you sucked in some grass/weeds.... some of that could have partly blocked the feed hose. You may want to give it a good flushing too.

 

[buckeye_paul]

Buckeye: It could be the plugs... and a partly plugged pump. I know on some of my 2-stoke dirt bikes... a good plug is a "Night and day" difference in power.


Also... IF, you sucked in some grass/weeds.... some of that could have partly blocked the feed hose. You may want to give it a good flushing too.

Compression was good 125-130 on all six. I changed the plugs. Wanted to change the fuel filter too but the local Mercury dealer didn't stock it. Started it up and it ran OK on the hose. I'm taking it out tomorrow, hopefully it runs better!

 

[buckeye_paul]

Had it out today. Took my nieces and nephew tubing. It seemed to run better but it was hard to tell because it was very windy and the water was really choppy.