Compression question:

[1Gunner]

My 16yr old 30hp Johnson feels like it's getting slower and acceleration on take-off seems less as well.
The compression is ~120psi per cylinder + - 2 ea.
What reasons would cause this lowering of performance??

Thanks!!

 

[rickdb1boat]

Re: Compression question:

Hi Gunner

Is the prop still in good shape? No nicks, bends, Etc? Might take a look at the throttle linkage and make sure it's advancing fully. The throttle plates should be horizontal when the throttle is wide open. Is the timing advancing fully? Just some things to check since the engine sounds healthy at least from a compression standpoint....Don't discount that it could be the boat causing problems, too...What kind is it?

 

[Solittle]

Re: Compression question:

Might check both the plugs and spark. Spark should jump a 3/8" gap with a bright blue snap.

 

[Kevin W]

Re: Compression question:

Ethanol based gas produces less HP than non-ethanol gas.

 

[Texasmark]

Re: Compression question:

And if you are carboned up the engine gets sluggish. Do a decarb and keep some in the gas....always. Will be glad you did even if it doesn't solve your problem; but I guarantee you (and they do too) I'll surely help.

Mark

 

[1Gunner]

Re: Compression question:

Thanks for all the replies!!
Rick Throttle plate is horizontal at WOT. Prop is in excellent shape. Boat is a Princecraft Resorter 15. I'll look at the spark advance although is the throttle plate is fully horizontal I'm unsure how the advance will be affected.
Solittle Plugs are brand new and gapped per OMC spec. If I remember correctly.... 0.30"
Kevin W I'm using premium 91 octane gas with a 50:1 mix.
Mark What exactly is a "decarb" ?

Thanks for all your input guys!!!!

 

[guywithboat]

Re: Compression question:

To decarb is to remove the carbon build up in the carb and engine. Use Seafoam. Mix a can with about 3/4 fuel and run the motor for 15 min. Let set for 15 and run it again. It will smoke like crazy, but this does work.

You can also use Deep Creep. It works good as well. Remove the spark plugs and spray a liberal amount into the cylinders.

You may need to replace or atleast clean your plugs after this.

Good Luck.

 

[Kevin W]

Re: Compression question:

I would give the Seafoam a try.
Check in the FAQ section.
it has a detailed decarb proceedure that can't hurt.
Decarbing is a must for outboards.