Boat Motor Compression

My boat seems to not be running with as much power as it should when a get on the throttle. I have never owned a boat before so am new to this. Do I have to have my motor in a tub of water to turn the motor over checking for spark and compression? Does it have to be in water to run even if you don't engage the transmission into foward or reverse, but rather to just have the motor idle?

In all reality you should never turn a bout motor over without the lower unit being in water. It can damage the impeller ( water pump ) Now with that said, do I do it like that...... No. I will only put it in a tub of water or put the ear muffs on when I am actually starting it............ My suggestion, check your fuel system. the lines from the gas tank ( including the fittings ) to the carb..... trust me, I melted a motor because I did not do this

2008-03-22 12:13:16 by Jay G

11th part of the Oldsmobile 455 marine engine build. The worked over cylinder heads are looked at in this video. Timing marks, compression and ...

4cyl compression is 30 lbs lower than the rest was told not worth fixing per price

The cost of repairing it really depends on what everything looks like when you get it torn down and how bad it is.It will also depend on if you are doing it yourself or are having someone else doing the work.As
I'm sure you know labour is not cheap.The parts are really not that expensive if you can do the work yourself,but if you cannot it would depend on how much you are willing to spend.It could cost anywhere
from $1000.00-$2000.00 depending on how bad it is.Good luck.

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An outboard? 2 or 4 stroke. Piston rings, valves if its a 4 stroke, head and head gasket. It gets worse from there, block, piston could have a hole in the top. You may be able to fix a bunch of these problems, but if it is damaged it would be best to rebuild or replace.

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I have a 1972 maybe a few yrs less or just a few older. I cant remember yr. The tag is gone of the motor. But i know its in the 70's Its an evinrude 6 hp. What is the compression suppose to be on that. I am getting 35 on top cylinder and 30 to 34 on bottom cylinder. Thanks for the info.

that'll get you there on that particular engine. i joke with customers sometimes about the 6hp not needing any compression at all if you get the spark and fuel right. nice motor...be sure and service the gearcase too.

2007-04-16 19:53:57 by Jerad

Its a 20 foot cobia cuddy cabin with an OMC 4 cylinder sterndrive inboard motor. Did a compression test and all tests on each spark plug valve were low (around 50). Do you think taking the valve cap off and cleaning them would give me better compression? What else could cause this?

thanks

You need to have a leak-down test done to determine where the compression loss is. If the loss is because of bad valves or seals, you may get away with just having the heads rebuilt. If it is leaking past the rings, it's time for a total rebuild, or a long-block replacement. Depending on the hours on the engine, this could be caused by age, if the valves are burnt, this indicates incorrect fuel/air mixture or timing.

2009-04-15 19:27:33 by STEVE-0