I have a 1991 Force 150 that has low hours on it. Sat in a garage for 10-15 years with old gas in it. After much cleaning, it starts up fine and idles fine. On the water it will tach up to 5500 RPM and deliver full power at WOT with no problem, seems to be firing on fall 5 cylinders. Once I stop the engine and let cool down for a few minutes, if I restart it won't go above 4,000 RPM, runs rough and seems to be misfiring on at least one cylinder. Runs rough at lower speeds too but will stay running. Idle is fine. Lots of unburned gas coming out of exhaust under water when I stop.
I've read alot about what could be wrong, everything points to fuel to me, but I've also read it could be the power pack, a coil, or a bad spark plug wire. Cylinder #5 seems to be the culprit to me, but I'm stumped. Here's what I've done to troubleshoot so far:
1. I cleaned the gas tank, dumped the carb bowls (had tons of residue in all of them), cleaned the carbs by spraying (but not removing and dismantling), added a fuel filter, and flushed the fuel lines with new gas. I saw some improvement doing this. The factory 30 gal fuel tank is remarkably clean.
2. I have replaced all 5 spark plugs.
3. Compression test on all 5 cylinders is right at 120 psi.
4. Spark test on all cylinders at idle shows I'm getting spark to all cylinders.
5. When I remove the spark plug wire from #5 there is no change in engine pitch, but all others seem to make a drastic difference.
6. The lower carb would spill gas out when priming with bulb until I emptied the bowl and cleaned it out with carb cleaner.
7. Inspected fuel pumps (but did not rebuild, seals all looked fine).
8. To eliminate fuel tank pickup and anti-siphon valve, ran engine at WOT on a separate can single gallon of gas with a whole can of sea foam in it.
Next step seem to be to take the carbs off, dismantle and clean. My question is would a stuck float valve exhibit this behavior? Could it be that the lower carb for #5 is just flooding it with gas that doesn't get burned and that's why I have such poor performance? Why would it run better when cold and not when hot?
Thanks in advance for any ideas.
I've read alot about what could be wrong, everything points to fuel to me, but I've also read it could be the power pack, a coil, or a bad spark plug wire. Cylinder #5 seems to be the culprit to me, but I'm stumped. Here's what I've done to troubleshoot so far:
1. I cleaned the gas tank, dumped the carb bowls (had tons of residue in all of them), cleaned the carbs by spraying (but not removing and dismantling), added a fuel filter, and flushed the fuel lines with new gas. I saw some improvement doing this. The factory 30 gal fuel tank is remarkably clean.
2. I have replaced all 5 spark plugs.
3. Compression test on all 5 cylinders is right at 120 psi.
4. Spark test on all cylinders at idle shows I'm getting spark to all cylinders.
5. When I remove the spark plug wire from #5 there is no change in engine pitch, but all others seem to make a drastic difference.
6. The lower carb would spill gas out when priming with bulb until I emptied the bowl and cleaned it out with carb cleaner.
7. Inspected fuel pumps (but did not rebuild, seals all looked fine).
8. To eliminate fuel tank pickup and anti-siphon valve, ran engine at WOT on a separate can single gallon of gas with a whole can of sea foam in it.
Next step seem to be to take the carbs off, dismantle and clean. My question is would a stuck float valve exhibit this behavior? Could it be that the lower carb for #5 is just flooding it with gas that doesn't get burned and that's why I have such poor performance? Why would it run better when cold and not when hot?
Thanks in advance for any ideas.
