05 50 Fourstroke

[Houser04lly]

What should compression be ?

[Elliot Griffin]

Here is excerpt of service manual.
Cylinder compression :
Standard : 1300 – 1600 kPa (13 - 16 kg / cm2,
185 – 228 psi.)
Max. difference between any two cylinders :
100kPa (1.0 kg / cm2, 14 psi.)
NOTE:
Figures shown are guidelines only, not absolute service limits.
Low compression pressure can indicate one or more of the following::
• Excessively worn cylinder wall
• Worn piston or piston rings
• Stuck piston rings
• Poor seating of valves
• Ruptured or otherwise damaged cylinder head gasket
TEST PROCEDURE
(1) Start engine and allow to warm up, then shut engine off.
(2) Remove the STBD / PORT engine side lower cover.
(3) Remove all spark plugs.
(4) Install the compression gauge into the plug hole.
09915-64510 : Compression gauge
09915-63210 : Compression gauge adaptor
(5) Disconnect the safety lanyard from the emergency stop
switch.
(6) Disconnect the remote control throttle cable from the throttle
lever.
(7) Move and hold the throttle lever in the full-open position.
(8) While cranking the engine with the starter motor, note the
maximum compression pressure reading on the gauge for
each cylinder.
(9) Reinstall parts removed earlier. ( spark plug, side lower
cover, etc.)

[Houser04lly]

Great thank you

[LG-Pontoon]

Darn.....never got to the cause of the problem....my DF40 is having similar issues. Would have liked to hear the final outcome on this one.... but i did pick up some good ideas.

[tommybe1]

Had a similar problem with my df50, took out the fitting at the gas tank(clogged), replaced it with a straight thru fitting, hooked up a one gal gas can with 50/50 mix of sea foam, solved problem

[Moonlighter]

Darn.....never got to the cause of the problem....my DF40 is having similar issues. Would have liked to hear the final outcome on this one.... but i did pick up some good ideas.

Maybe explain details of what is happening with yours.

The more info on the symptoms you provide, the better. As well as details on what has been done already to try to fix it. Someone may be able to help.

[LG-Pontoon]

To summarize...this is a 2005 DF40 motor with lots of hours. Former rental boat. I had it serviced shortly after purchase about 2 years ago....plugs, coil, and a plate replaced (had a hole) somewhere around the VST. Shortly after that had a rough running motor due to bad fuel and debris in the system. Got that cleaned out and ran good for a few months and then back to bogging down after running 15 - 20 minutes. Replaced the plugs 2 days ago (they looked fine), and the motor ran great for a 45 minute ride that day, then the next day after about 20 minutes...back to square one. I'm no expert, but am leaning toward a fuel problem (again). I'm kind of limited on what I can do (other than the simple stuff), so I may take to shop again. One question however.....I'm running with one of those EPA-correct 6 gallon fuel tanks with no vent cap.....do I need to have this cap loose when running? I tried that after it started bogging the other day with no change, but did have it loose when it ran for 45 minutes + before that. Thx...