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97 150 Intruder Rough Idle/No Power

6

62ChevyII

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1997 Intruder 150 (E150GLEUC). Over the course of six months the engine would run great until the heat of the day, then stumble above 4000 rpms. It got progressively worse (lower peak rpms) until it didn't have the power to get on plane. Pumping the primer bulb would help some. I found a tear in the fuel pump diaphram and rebuilt it but it helped only a little, still seemed to starve for fuel. What has been done: new fuel pump installed/switched out with rebuilt unit to no difference, all carbs cleaned/rebuilt, all fuel lines/worm gear clamps replaced, fuel filter/gasket replaced (no debris), VST/choke bypassed with fuel directly to pump then fuel rails (no difference), no visible overheating/melting of stator coils/rectifier/powerpack/ignition coils, tach has always functioned perfectly, spark is good and even to all cylinders (based on observing several times with a timing light and observing individual plugs), two different sets of plugs tried. I have run the engine on a portable tank (no difference) and without check valves and with/without several different primer bulbs. I have only had this engine for about two years and it has >120 psi on all cylinders. I don't have a manual (yet) for this one so I haven't tested voltages/resistances yet. The engine will start and idle decently for 5 -10 seconds then idle like it is missing or starving for fuel but the spark seems even and consistent and fuel flow appears good by all measures. Pumping the primer bulb or holding the choke after all the above work now does not affect the engine. It barely can push the boat at idle and dies if you give any throttle. The only odd observation is the external temp of the heads. I noticed that with running the engine in the water, on muffs or even dry (for about 15 seconds) the surface of the starboard head is uniformly 40 degrees cooler than the port (IR measurement.) That is a might much and usually the opposite. I kind of lean towards a powerpack issue but any input would be appreciated.
 
I failed to mention leaning towards the powerpack or optical sensor. I've worked on several OMC outboards over the years but this is the first one I've had with the optical ignition. Some say it's difficult to set up, others say it's easy. I have a manual on the way.
 
Checked the shift switch on the motor linkages ?-----Might be running on 3 cylinders.--------Does spark jump a gap of 3/8" on all leads ?
 
racerone said:
Checked the shift switch on the motor linkages ?-----Might be running on 3 cylinders.--------Does spark jump a gap of 3/8" on all leads ?
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Good suggestion, it would explain the cooler starboard side but those cylinders are firing. I ungrounded the switch just to check, no change. I will measure the spark jump more closely this evening.
 
Just checked the idle timing (6 degrees ATDC) and noticed something else. When I gave a very quick shot of ether into the bores, the port carbs either gave no change or choked the engine. The shot into the starboard bores really picked up the engine. So it does appear to be starving on the starboard side which makes the cylinder heat temps make sense. However, given what I've done, what am I missing?
 
Does spark jump a gap of 3/8" , yes or no ?----Are compression vales new or from a year ago.-----If you ran the motor dry for 15 seconds you need a new water pump impeller !!!----Motor might be in S.L.O.W. mode.
 
I hope the 97 150 hp Ocean Runner works well when I finally put it on a boat.----Has been sitting for 3 years waiting for me to finish a project boat,.----These motors can't be that hard to trouble shoot I think / hope.
 
racerone said:
Does spark jump a gap of 3/8" , yes or no ?----Are compression vales new or from a year ago.-----If you ran the motor dry for 15 seconds you need a new water pump impeller !!!----Motor might be in S.L.O.W. mode.
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Compression values from today (cold) = 114 - 117 psi. I've had another engine go into SLOW and this is different. This engine will barely idle and stalls after a few seconds in gear or when throttling up. The different engine reactions to ether from port to starboard carb bores can't be explained by ignition. As far as the impeller, I'll agree to disagree. Perhaps for newer engines but on a good dozen different OMC outboards over the years in my family I've not seen any degradation in water pumping or pressure from the infrequent practice (all pre-2003 engines.) Not saying its best practice. (Sold an '89 GT after 17 years of many, many lake hours without ever changing the impeller. It had 6 psi idle/ 27 psi WOT.)
 
racerone said:
Perhaps float bowls are warped.
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I've learned all OMC plastic/nylon carb bowls warp and usually lead to hesistation when throttling up along with idling issues. You can sand them flat but I found a good deal on new ones for these little one barrels so all were replace when I rebuilt them. I've pulled them and checked everything again. Yes, the originals were warped a little and one was slightly cracked but apparently not the culprit. Thanks for the ideas.
 
Update: I finally had time to remove and clean out the throttle bodies. I did see one or two specks of debris while cleaning. Reassembled and it ran nicely, for about 5 min. It then would barely idle. A check of spark showed a strong but intermittent spark on all cylinders - hadn't seen this up until now. Idle timing dropped to 3 degrees ATDC but after a minute on the muffs the engine began to cycle between two modes every minute or so. One mode = intermittent strong spark on all cylinders, stable timing at 3 degrees ATDC. The other mode = regular quick (less than a second) switching between timing of 3 degrees ATDC and 6 degrees BTDC with a strong, consistent spark on all cylinders. The timing had been at 6 degrees ATDC (several checks over the last few weeks) which I have never adjusted on this engine (literature values suggest 5 - 7 ATDC for these engines.) A few love taps on the powerpack had no affect. I fried my DVA multimeter a while back so I can't check the stator output but I'm leaning towards the stator and the fact that this engine had multiple issues making this a pain to diagnose. The optical sensor was clean with no cracks or missing plastic up top.
 
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