MyHoleInTheWater
Recruit
- Joined
- Jun 19, 2017
- Messages
- 3
I have a 22 foot pontoon with the above mentioned Merc for power. It spent most of last summer in the shop because the clowns at the shop couldn't figure out the carb vents being plugged would continue to flood the motor out. That was solved after the carbs were rebuilt, compression checked, etc. I took it out for one run last year and there was no top end. I took it to a different repair shop who replaced most of the fuel system and said it was good. It wasn't so I brought it back and they replaced the plugs. I took it out the night I got it back and it ran better than I have ever heard it for the 20 min idle in the no wake area and about 3 minutes WOT. I took it out with the family the next day and it ran great again for 5 minutes and then suddenly during a turn it went right back to having no top end. The motor runs and sounds awesome. It just tops out at about 4000 rpm and about 2/3 of the throttle travel. It doesn't surge, miss, or mis-behave at all. It sounds unlabored, doesn't vibrate, or do anything that would make you think there is anything going on, it just seems like the throttle isn't going past a certain point. I have checked the linkage and it still advances the individual carb bell cranks through the entire range so that does not appear to be the issue. I am $1400 into repairs and guessing so far so I am looking to see if I can narrow this down at this point on my own.
Normally this sounds like a fuel supply problem and maybe an ignition problem but it seems like it runs too perfectly for that. I didn't check the fuel pressure but cracking a line even 10 minutes after it has been run sprays gasoline pretty forcefully so I am going to think it is alright. I have also pumped the primer bulb while it is running with no change.
Is there anything in this vintage motor that would limit the RMPs for safety or any other reason?
Looking at the motor through my non-marine motor eyes I am wondering if the throttle position sensor is bad. I am assuming it is used to adjust ignition timing. Is it possible the spark is being retarded so greatly due to wrong info from the TPS that it has no top end? I have to go to storage to get the model and serial number but does anybody have general guide for a pinout and values I could use to check that sensor?
Note: It is a Faria tack that occasionally reads really high and is clearly not reading accurately at times. I am not sure if that is relevant.
Thank you in advance.
Normally this sounds like a fuel supply problem and maybe an ignition problem but it seems like it runs too perfectly for that. I didn't check the fuel pressure but cracking a line even 10 minutes after it has been run sprays gasoline pretty forcefully so I am going to think it is alright. I have also pumped the primer bulb while it is running with no change.
Is there anything in this vintage motor that would limit the RMPs for safety or any other reason?
Looking at the motor through my non-marine motor eyes I am wondering if the throttle position sensor is bad. I am assuming it is used to adjust ignition timing. Is it possible the spark is being retarded so greatly due to wrong info from the TPS that it has no top end? I have to go to storage to get the model and serial number but does anybody have general guide for a pinout and values I could use to check that sensor?
Note: It is a Faria tack that occasionally reads really high and is clearly not reading accurately at times. I am not sure if that is relevant.
Thank you in advance.