OMC 5.0 from nearly fixed to nearly dead!

[hijinks1951]

So I fixed my water in the oil (intake manifold gasket), set the dwell and set the timing per the manual.

First time out the boat ran as well as it ever has done. I could only get 3500 rpm but I am leaning towards too high a pitch prop (14.5 x 21+ on 200HP and 4K lbs of boat)

Second time out it seemed to have lost some power as it took longer to plane and had a problem planing with a skier or even a tube. I attributed that to 2 extra adults and 2 kids, perhaps +400lbs

Third time out barely got on a plane then just everything seemed to fall apart! won't idle under about 1000 rpm, difficult to start, seems to be missing badly, and when I pulled the plug wires from 4 and 6 it actually seemed to run smoother.

I checked the firing order and that is good, the dwell is still good, changed out the coil and still same problem. Pulled the ESA connector, checked the plugs which were a little black but not that bad. Didn't have timing light so couldn't do that but distributor was tight and I can't see how it could have moved.

Mystified!

 

[Reel Poor]

Re: OMC 5.0 from nearly fixed to nearly dead!

Did you know running with the wrong prop can cause engine damage?

Time to do a compression test.

 

[hijinks1951]

Re: OMC 5.0 from nearly fixed to nearly dead!

yep know the prop issue you raise, thought that dropping pitch was going to be the RPM/WOT solution once I got the water in the oil and general tune up stuff done. Then I go from bad to worse!

So if its not timing/dwell then I would suspect carb. But why would it run fine, nearly fine and then like crap? in three outings days apart

 

[Gary H NC]

Re: OMC 5.0 from nearly fixed to nearly dead!

compression test before anything!

 

[hijinks1951]

Re: OMC 5.0 from nearly fixed to nearly dead!

i did one a couple of weeks ago with everything being from 122 - 135, plan on doing it again tomorrow

 

[hijinks1951]

Re: OMC 5.0 from nearly fixed to nearly dead!

did compression tests with new gauge and insert today, 160 across six and one at 170 and one at 155, logic to the lousy idle said timing, popped points out of distributor and advance weights had stuck in an advanced position. Gave them lots of WD40. Set the idle screws on the rochester 2 brl to 1 1/4 out from the seats and took it out. Much better power and it did something it has never done before which was make 4100 rpm but definitely with a lot of "clattering" that again I think was caused by the advance weights not fully advancing. when I throttled back it went away

So when at idle there is a steady drip of fuel down one barrel and at full throttle seems like fuel is spraying everywhere from the low idle ports, plugs came up black but dry.

Probably will try to find a new distributor or rebuild kit and perhaps throw a 4 barrel and manifold on it. What do you think

 

[Rob454]

Re: OMC 5.0 from nearly fixed to nearly dead!

I had the same similar problem. Ran great on land but as soon as it went in water it popped farted coughed backfired and basically ran like crap. Found out the firing order was put on wrong by the guy who did the motor swap in my boat. Well I re did the firing order and it ran great. The guy said it shouldnt run but I told him it did.
Not sure if the firing order is different from a car to a boat but I think he had it as a chevy firing order and i had a ford
Rob