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View Full Version : Compression test results and day at the lake



Thunderkat13
08-25-09, 11:35 PM
Ok, so I did a complete tune up on the boat this weekend.

Heres my compression results,
#1 - 125
#2 - 118
#3 - 125
#4 - 130
#5 - 130
#6 - 130

Im a little concerned with the #2 cylinder (should i be?).

After changing all the lubes in the boat and checking all the fuses and just checked everything I head to the gas station.
The boat took 22 gallons of gas and topped my oil tank off.
Picked up my 3 buddies and we head out to wakeboard the boat is kicking butt, 2 hrs later only on take off with a wakeboard intow the boat studders. If I take the boat over 5500 rpms the studdering continues till plane and then settles back out..
So I guess what I am asking is could my missing/studdering be from low gas (1/2 tank or less),slooshing around, fuel not being picked up to support the demand? Where is the inline fuel filter (could this cause and issue).
Could this be an exhaust hose issue? What else could I check out? Any ideas or opinions appreciate...

The boat still hauls butt, 55mph+ and only studdered after 2hrs

I am running out of ideas on why shes studdering

Thunderkat13
08-26-09, 12:41 PM
ok did a little more reading came across this in the manual...

Checking for restricted fuel flow caused by anti-siphon valves
while anti-siphon valves may be helpful from a saftey point they clog with debris they may be too small or they may have too heavy of a spring. the pressure drops across these valves can create operational problems and or powerhead damage by restricting fuel flow to the fuel pump and carburetor(s). Some symptoms of restricted (lean) fuel flow which could be cause by use of an anti-siphon valve are:
loss of fuel pump pressure
loss of power
high speed surging
pre-ignition/detonation
engine cuts out or hesitates upon acceleration
engine runs rough
engine quits and cannot be restarted (some other 240 owners having this issue)
engine will not start (some other 240 owners having this issue)
vapor lock


Ok so my next question is where are these anti-siphon valves located ?

Thunderkat13
08-27-09, 09:13 AM
no one has any suggestions ? or comments ?

rookie101
08-27-09, 11:02 PM
You shouldn't have anti-siphon valves, so don't worry about them. As for compression the #2 cylinder is a bit weak, but it just squeaks in under the 15psi allowable difference that Mercury mentions in the manual. I don't think it would be enough of a difference to cause a problem yet, but it may be a sign of things to come down the road.

What does the plug look like from that cylinder? If you can try to run the boat like normal the next time out, and near the end of the day when it is acting up, just as you go to load the boat on the trailer run it at the rpm it is misfiring at, then immediately kill the engine and paddle the boat back to the trailer. I know that may be tough to do, but it will help narrow things down. Once you get home and the engine has cooled off pull all the plugs and see if one looks like it is running differently than the other cylinders. This will at least give you some sort of a starting point.



Aaron:cheers: