Couple of thoughts on the matter:
You stated that it has always (since you owned it) has had trouble idling and starting.
1.) You think the PO put a 30hp carburetor on (People play around with motors by switching carburetor and other things and making modifications and the motor does not run right)*** This is not uncommon symptoms of a motor with the wrong carburetor.......who knows what year carburetor he put on that motor. My advice, if it is 30 or 35hp carburetor on that motor, then you need to get the correct carburetor(25hp) on that motor.
I agree 100% the .2hp the carburetor might be providing is not worth the trouble and fuel cost it is causing. Any ideas on where I can find one I havent been able to pin one down so far.
- That motor is running lean...you can hear the lean sneezing and erratic idling despite adjustment of the slow idle needle.
- A lean running motor will deliver a poor fuel/oil mix to the internals. That fuel/oil mix is your motors only internal lubrication. So you and the previous owner maybe causing premature internal wear of the pistons, rings, cylinders, crankshafts, rods and bearings.*****Thus leading to low compression not related to carbon build up and stuck rings. (Seafoam only helps when rings are stuck from excessive carbon build up)
2.) A motor that has low compression will display these signs:
- difficult starting
- poor and erratic idling
- some loss of power and speed at higher throttle settings.
You stated that your compression values were 90 psi top and bottom cylinders. Am I correct?? Those models had higher compression values.....usually 120 or greater psi. But would run ok at about 100psi or greater.. (1980's improved on compression values)
- after the decarbing with the seafoam....did you recheck your compression. Please recheck, when the motor is cold. So, recheck the compression before you start trying to restart it.
I already did and thought I stated it went up to about 110lbs on each cylinder top and bottom.
***Another thought, just to make sure it is not something simple...get a known good hose and bulb and tank then try run the motor.
The tank and lines are already know good I use the same one on my 9.9 with no issues. The lines on the motor are brand new and I have checked all the fitting to make sure they are tight.
- If the current fuel lines going from the tank to motor and also from motor to fuel pump and then to carburetor has small cracks or is stiff, then you can get poor fuel delivery because air might be pulling into the fuel line and displacing fuel.
*** Another thought, when you start the motor and it starts idling erratically or lean sneezing, then pump your primer bulb on your fuel line. If the motor starts to run better or idles much faster then you may have a bad or leaking fuel pump. Resolution a new fuel pump.
I no longer have the lean sneeze or erratical idle I have since opened my low speed adjustment up to compensate.
One last thing, after you did the decarbing with the seafoam, did you remove your spark plugs and clean them. When you decarb, the spark plugs will get fouled up with carbon and coke. Clean them and return them back and retorque them.
Ill clean them this afternoon.
The above assumptions are made upon your statement that you have good spark and the carburetor is clean and the settings are correct and you have the appropriate carburetor for your motor.
