Hey everyone, looking for some help diagnosing a 1996 Evinrude Intruder 150 2-stroke with the Optical Ignition System (OIS). I've been restoring the boat/motor and have gotten pretty deep into troubleshooting this issue.
The main problem is that the motor runs great on muffs but will not stay running when the boat is actually in the water.
On muffs at home, it starts almost immediately, idles well, has a strong telltale, and will run for 10+ minutes without an issue. We measured around 135°F after letting it run, and nothing seemed abnormal.
At the ramp, it is completely different. It will usually start and run for roughly 30 seconds, then gradually lose RPM and die. After that, it will restart but generally only run for a few seconds before dying again.
Here's what we've done so far:
We decided to go pretty far with that theory. We removed the powerhead from the midsection and removed the lower unit so we could inspect the exhaust housing. The main exhaust path appears completely clear aside from normal carbon/use. We didn't find a nest, major carbon blockage, collapsed component, or anything else that looked capable of restricting the main exhaust.
There is one other area we're investigating: OIS timing/link-and-sync.
After having the OIS/timing linkage apart, we initially had a no-spark condition when putting it back together. We discovered the OIS sensor support/timing linkage wasn't properly engaged. Moving the spark lever/timing mechanism brought spark back. We obviously aren't going to leave it manually advanced, so our next step is to properly go through the link-and-sync procedure and check actual timing with a timing light.
At this point we seem to have:
Good/even compression → rebuilt carbs → functioning primer → fuel supply checked → strong 11 mm spark on all six → main exhaust housing clear.
The thing that still has me puzzled is how dramatically the engine behaves differently on muffs versus sitting normally in the lake. If anyone has experience with these 1990s 60° V6 Evinrude/Johnson OIS motors, especially one that runs perfectly on muffs but falls on its face once exhaust backpressure is introduced, I'd really appreciate any ideas on what you would check next.
The main problem is that the motor runs great on muffs but will not stay running when the boat is actually in the water.
On muffs at home, it starts almost immediately, idles well, has a strong telltale, and will run for 10+ minutes without an issue. We measured around 135°F after letting it run, and nothing seemed abnormal.
At the ramp, it is completely different. It will usually start and run for roughly 30 seconds, then gradually lose RPM and die. After that, it will restart but generally only run for a few seconds before dying again.
Here's what we've done so far:
- Compression tested all six cylinders three times. Lowest reading was 106 PSI and highest was 115 PSI, so compression is very even.
- Completely removed, cleaned, and rebuilt all three carburetors with full rebuild kits.
- Slow-speed mixture needles are set to the factory starting point of 5 turns out from lightly seated.
- Rebuilt/repaired the primer solenoid. It now actuates properly when the key is pushed in.
- Went through the fuel system, including the tank, primer bulb, lines, filter, fittings, etc. We previously found a leak around the fuel-filter fittings and corrected it.
- Installed six new spark-plug wires.
- Tested spark with an adjustable tester. All six cylinders now consistently jump an 11 mm gap.
- We also previously bypassed portions of the boat's fuel system during testing and got the engine running well, but after correcting the fuel system and reconnecting everything, the in-water problem remained.
We decided to go pretty far with that theory. We removed the powerhead from the midsection and removed the lower unit so we could inspect the exhaust housing. The main exhaust path appears completely clear aside from normal carbon/use. We didn't find a nest, major carbon blockage, collapsed component, or anything else that looked capable of restricting the main exhaust.
There is one other area we're investigating: OIS timing/link-and-sync.
After having the OIS/timing linkage apart, we initially had a no-spark condition when putting it back together. We discovered the OIS sensor support/timing linkage wasn't properly engaged. Moving the spark lever/timing mechanism brought spark back. We obviously aren't going to leave it manually advanced, so our next step is to properly go through the link-and-sync procedure and check actual timing with a timing light.
At this point we seem to have:
Good/even compression → rebuilt carbs → functioning primer → fuel supply checked → strong 11 mm spark on all six → main exhaust housing clear.
The thing that still has me puzzled is how dramatically the engine behaves differently on muffs versus sitting normally in the lake. If anyone has experience with these 1990s 60° V6 Evinrude/Johnson OIS motors, especially one that runs perfectly on muffs but falls on its face once exhaust backpressure is introduced, I'd really appreciate any ideas on what you would check next.