JoLin
Vice Admiral
- Joined
- Aug 18, 2007
- Messages
- 5,146
This motor hasn't been in the water in over a year (ran okay then), though it has been run periodically on muffs since then. I've rebuilt the carbs and replaced all the fuel hoses and fuel pump. Gave it a full tune-up, set idle timing (2-3 deg BTDC) and did a link and sync. All good, and it idles fine at 850-900 rpm on the muffs. Couple of weeks ago I took the boat to the ramp and splashed it.
1. As soon as the leg was in the water and exhaust back pressure came into play, the idle speed dropped by a good 300 rpm. I raised the idle speed and reset the timing accordingly until it once again idled at 900 rpm in the water.
2. When put it in gear, idle speed dropped way down again. It would chug along for 5-10 seconds before it stalled. If I advanced the throttle, it died immediately.
After stalling, the motor restarts immediately (first revolution of the starter) and runs okay in neutral.
I think the key to whatever is going on here is that the motor doesn't want to accept any load, even exhaust back pressure, without losing power.
I know the fuel and carburetion systems are good. This morning I verified the following:
a. Compression is good on all cylinders (95-100 lbs).
b. Using a DVM, I verified resistance (per the factory manual) of the spark plug cables, ignition coils, pulser coil, charge coil and lighting coil. All are very close or right on spec.(outside temp was mid-30's today, and the manual calls for testing at 68 deg.). I put a spark tester on each plug and got a consistent blue spark across a 7/16" air gap. That's the 20K volt marking on the tester.
I'm out of ideas. Anyone?
1. As soon as the leg was in the water and exhaust back pressure came into play, the idle speed dropped by a good 300 rpm. I raised the idle speed and reset the timing accordingly until it once again idled at 900 rpm in the water.
2. When put it in gear, idle speed dropped way down again. It would chug along for 5-10 seconds before it stalled. If I advanced the throttle, it died immediately.
After stalling, the motor restarts immediately (first revolution of the starter) and runs okay in neutral.
I think the key to whatever is going on here is that the motor doesn't want to accept any load, even exhaust back pressure, without losing power.
I know the fuel and carburetion systems are good. This morning I verified the following:
a. Compression is good on all cylinders (95-100 lbs).
b. Using a DVM, I verified resistance (per the factory manual) of the spark plug cables, ignition coils, pulser coil, charge coil and lighting coil. All are very close or right on spec.(outside temp was mid-30's today, and the manual calls for testing at 68 deg.). I put a spark tester on each plug and got a consistent blue spark across a 7/16" air gap. That's the 20K volt marking on the tester.
I'm out of ideas. Anyone?