Please help. I have owned a 1987, 17.5’ Bayliner Capri bow-rider with an OMC 2.3L engine for a few years. The engine has become increasing difficult to start especially when it is hot. After starting cold, it idles rough but accelerates well with what seems to me to be lots of power and gets right up on plane. After the engine warms up however, it is very hard to start, the engine acts like it is flooded after it starts (just barely running) and won’t take throttle. It idles rough, stumbles and then stalls out when throttle is advanced, even in neutral, or when shifted into gear. If you can nurse it into gear and to a higher rpm when the engine is warm, it then runs fine with good throttle response and power until you bring it back to idle again. I have checked that the accelerator pump shoots a healthy shot into each venturi and that there is still spark when the engine is hot. The carburetor idle stop and the two idle mixture were adjusted to the specified 600 to 650 rpm in gear. The engine starts much easier out of the water on ear muffs, hot or cold, and idles much better on the earmuffs.
The problem started some years before but has gotten worse over time. Compression should be 165 psi per OMC service manual. I just did a compression test and leak down test. The results are shown in the tables below.
The engine uses raw water directly into the block for cooling but has always been used in fresh water lakes.
I did change the points to a Pertronix ignition module and the ESA module that does not need the diode fix some years ago. The engine ran ok when the Pertronix and ESA were first installed.
I have seen a few small drops of water on the bottom of the intake manifold after it stalls when hot so I suspected a cracked block, intake, exhaust or riser manifold or a blown head gasket. I removed the riser, blocked off the exhaust manifold water jacket and with the manifold and block drained, applied ~ 20 psi air pressure to the raw water inlet and listened for water jacket air leaks at the output from the exhaust manifold, the oil fill and the intake manifold. I also removed the plugs and hand rotated the engine through several rotations while pressurized. I couldn’t hear any air leaking anywhere and it took about an hour for the air in the water jacket to leak down which could just be all the hose connections, the pressure regulator or the water jacket sealing block I made for the exhaust manifold outlet. The leak test was done with the block cold.
There is no sign of excessive blow-by pushing oil out the oil fill vent cap.
The riser to exhaust manifold gasket was in good condition and there was no evidence of a water jacket leak into the exhaust cavity at this gasket. I tested the riser as suggested by other posts in this forum by filling the water jacket with acetone. I did not see any of the thin acetone leaching into the exhaust passages.
Also, on removing the riser elbow, the backflow flapper valve in the exhaust tube to the gimbal housing was found in the closed position and rotated easily without binding.
The spark plugs had mostly tan insulators with maybe a slightly rich burn residue on the metal parts but no obvious black, fluffy or oily residue.
As suggested by other posts in this forum, I performed compression and leak down tests as show below. The tests were done in the order shown on a cold engine with all the spark plugs removed, the fuel tank line disconnected, and the carburetor throttle, choke & exhaust outlet wide open. A battery charger was attached to the battery. The pressure gauge used for the compression test may have read low because it was 20 psi lower than the compressor tank gauge at 145 psi when connected directly to the air line. The leak tester zero set point was verified before and after each measurement.
The battery seemed weak as the starter really slowed down on the last two compression test strokes. The battery charger jumped back up to 15 Amps after each cylinder was tested.
The only remaining thing I can think to do is to repeat the compression and leak down tests after warming up the engine. Does anyone have any idea what is wrong with this engine?
The problem started some years before but has gotten worse over time. Compression should be 165 psi per OMC service manual. I just did a compression test and leak down test. The results are shown in the tables below.
The engine uses raw water directly into the block for cooling but has always been used in fresh water lakes.
I did change the points to a Pertronix ignition module and the ESA module that does not need the diode fix some years ago. The engine ran ok when the Pertronix and ESA were first installed.
I have seen a few small drops of water on the bottom of the intake manifold after it stalls when hot so I suspected a cracked block, intake, exhaust or riser manifold or a blown head gasket. I removed the riser, blocked off the exhaust manifold water jacket and with the manifold and block drained, applied ~ 20 psi air pressure to the raw water inlet and listened for water jacket air leaks at the output from the exhaust manifold, the oil fill and the intake manifold. I also removed the plugs and hand rotated the engine through several rotations while pressurized. I couldn’t hear any air leaking anywhere and it took about an hour for the air in the water jacket to leak down which could just be all the hose connections, the pressure regulator or the water jacket sealing block I made for the exhaust manifold outlet. The leak test was done with the block cold.
There is no sign of excessive blow-by pushing oil out the oil fill vent cap.
The riser to exhaust manifold gasket was in good condition and there was no evidence of a water jacket leak into the exhaust cavity at this gasket. I tested the riser as suggested by other posts in this forum by filling the water jacket with acetone. I did not see any of the thin acetone leaching into the exhaust passages.
Also, on removing the riser elbow, the backflow flapper valve in the exhaust tube to the gimbal housing was found in the closed position and rotated easily without binding.
The spark plugs had mostly tan insulators with maybe a slightly rich burn residue on the metal parts but no obvious black, fluffy or oily residue.
As suggested by other posts in this forum, I performed compression and leak down tests as show below. The tests were done in the order shown on a cold engine with all the spark plugs removed, the fuel tank line disconnected, and the carburetor throttle, choke & exhaust outlet wide open. A battery charger was attached to the battery. The pressure gauge used for the compression test may have read low because it was 20 psi lower than the compressor tank gauge at 145 psi when connected directly to the air line. The leak tester zero set point was verified before and after each measurement.
Cylinder 1 | Cylinder 2 | Cylinder 3 | Cylinder 4 | |
| TEST 1 Dry Compression OMC Spec=165 psi Harbor Freight tool | 150 psi | 140 psi | 140 psi | 145 psi |
| Percent Low | 9.1% | 15.2% | 15.2% | 12.1% |
| TEST 2 % Leakage & Source; (Listened to Oil Fill, Water Jacket, Intake, Exhaust & Adjacent Cylinder) Test Pressure = 20 psi All tests @ TDC Harbor Freight tool | 13% Hiss only @ Oil Fill Cap | 25% Hiss only @ Oil Fill Cap | 17% Hiss only @ Oil Fill Cap | 25% Hiss only @ Oil Fill Cap |
| TEST 3 Wet Compression (4 pumps of oil can) Harbor Freight tool | 150 psi | 140 psi | 140 psi | 145 psi |
The only remaining thing I can think to do is to repeat the compression and leak down tests after warming up the engine. Does anyone have any idea what is wrong with this engine?
