OMC 115 hp won't run

[wblTurbojet]

1995 OMC 115 hp in Jet Drive Zodiac.
Has fuel, spark on all cylinders and compression is 110 psi on all four cylinders, new plugs.
Engine is usually but not always hard to start, sounds rough, usually will shut off after a minute or so, will stall if i try to open the throttle.
Anyone know what else to try? before this happened boat would only do 20 mph not the 40 mph she should but worked really good!!

 

[boobie]

How are you checking your spark ??

 

[wblTurbojet]

with a spark tester set at 7/16 in, seems to be continuous blue spark to all four plugs!!!

 

[interalian]

Check the flywheel is pointing at 0 when cylinder 1 is at top. Use a pencil through the spark plug hole. Might have a sheared key.

 

[wblTurbojet]

Checked, flywheel at 0 when #1 at top, any other ideas please?

 

[interalian]

Compression, fuel, spark. If these are all OK, look for a couple of other things:

Check it isn't overheating. You should be able to hold your hand on the cylinder heads at any time.

Confirm the timer base is moving with the throttle and hits the stopper when the throttle is wide open. Make sure also the carb butterflies are fully open at WOT too. Do a throttle link/sync to be sure.

Model number?

 

[wblTurbojet]

Model #115TJEDB

 

[boobie]

Been through the carbs yet ??

 

[wblTurbojet]

been through the carbs twice,

 

[wblTurbojet]

"Confirm the timer base is moving with the throttle and hits the stopper when the throttle is wide open. Make sure also the carb butterflies are fully open at WOT too. Do a throttle link/sync to be sure."

DONE, no change,

also installed new powerpack!!!!

 

[Johnrudemech]

Good compression. Good spark and on time. Carbs have been gone through.... What is your fuel pressure from the VRO and what is your fuel vacuum reading?

 

[wblTurbojet]

seems to have lots of fuel pressure, how do you get a fuel vacuum reading? sorry I missed your post Johnrudemech, been trying everything.
Have swapped out almost all parts with another motor. Wiring harness next. No problem with the boat harness or key switch and emergency stop.
someone suggested crank seals. how would you check those?

 

[boobie]

Try some different fuel......or squirt some in the carb throats.

 

[oldboat1]

try a fresh tank, fresh gas. Water in fuel?

 

[racerone]

That would be a crossflow engine.----Post compression values.----Are wires to top coils both orange / blue stripe ?

 

[spybot]

Are you running premix fuel ?
If so try a 25/1 mix rather than the normal 50/1
I had the exact same issues with my 1980 johnson 85. I tried the 25/1 and she runs great

 

[batman99]

Sounds like "hard to start. no upper RPMs, runs when it wants to - like an ex-wife. LOL!) like my previous 120 HP engine - that had 3 cracked reed leafs. Only way to confirm was a visual inspection - by removing its carbs and their reed cages.

With its carbs off, did you check its reeds? If you remove spark plugs (ground the wires), hold flat palm tightly over the carb's intake and have someone crank the starter button, do you get "incoming" suction into the engine?

If new reeds are needed, recommend replacing all reed leafs and go with carbon fibre reeds from CCMs. I used their reeds in my previous engine and no re-jetting was required (unlike the Boyseen company reeds). re: http://www.chriscarsonmarine.com/contact.htm

Hope this helps....