Engine ran fine till 2 trips ago. Started with a little flutter about 3200 RPM. Never fully lost a cylinder, just a slight reduction in power and you could hear it in the motor. Still able to run at 5300 RPM full throttle.
Checked the compression and all 6 readings were between 80 and 83 PSI, which is what they have been since I bought the motor in 1998. Put new plugs in. Went out again and this time there was a notable miss at idle and low speed and some loss of power but still not fully loosing a whole cylinder and able to run 5300 RPM. Engine starts easy.
Back home checked compression to be same as before, 80 to 83. The new spark plugs look normal except the bottom two on the left side were a little darker than the other 4. These two appeared to be running a little richer. At idle on the water hose, notable miss. Pulled spark plug wires one at a time and found the bottom two cylinders on the left side to have little change in engine sound or RPM when plug wire pulled. Spark was good from pulled wire to engine block. But just to make sure, swapped two coils, plug wires and plugs from the right side to the two in question on the left and ran engine with the same results of miss and engine not changing when spark plug wires pulled on bottom two cylinders on the left.
All Carbs were rebuilt and 2 new fuel pumps installed in March 2006. Filters and fuel are clean and fresh. Engine has been running perfect since March.
My thoughts are either reed plate problems, which I think are unlikely, or head gasket/cylinder problems, which are also unlikely because of the consistency of the compression readings.
Im at a loss. Does anyone know what else may be the problem before I tear into the engine to have a look? All thoughts appreciated.
Checked the compression and all 6 readings were between 80 and 83 PSI, which is what they have been since I bought the motor in 1998. Put new plugs in. Went out again and this time there was a notable miss at idle and low speed and some loss of power but still not fully loosing a whole cylinder and able to run 5300 RPM. Engine starts easy.
Back home checked compression to be same as before, 80 to 83. The new spark plugs look normal except the bottom two on the left side were a little darker than the other 4. These two appeared to be running a little richer. At idle on the water hose, notable miss. Pulled spark plug wires one at a time and found the bottom two cylinders on the left side to have little change in engine sound or RPM when plug wire pulled. Spark was good from pulled wire to engine block. But just to make sure, swapped two coils, plug wires and plugs from the right side to the two in question on the left and ran engine with the same results of miss and engine not changing when spark plug wires pulled on bottom two cylinders on the left.
All Carbs were rebuilt and 2 new fuel pumps installed in March 2006. Filters and fuel are clean and fresh. Engine has been running perfect since March.
My thoughts are either reed plate problems, which I think are unlikely, or head gasket/cylinder problems, which are also unlikely because of the consistency of the compression readings.
Im at a loss. Does anyone know what else may be the problem before I tear into the engine to have a look? All thoughts appreciated.