Logo
FULL SITE MENU

2003 30hp 4stroke tohatsu bogging down at 3000 rpm in drive only

T

Tejohns3

New member
2003 30hp 4stroke tohatsu bogging down at 3000 rpm only in drive, it revs to max perfectly in neutral by pulling choke and it even ran fine in a barrel full of water but when the whole boat is in water and having to push its self is when it boggs down terribly and itruns perfect from idle to 3 grand. I have just got the carbs cleaned and resynchronized last year. could it be the computer??
 
Could be a lot of things. You need to do a thorough diagnosis, with the assistance of the Factory service manual, Part # 003N210530 $26.52, available from any dealer, including me. You did not mention specific model, but the MFS30A is the carbed 30 hp 4-stroke motor. The ECU on the A model 30's is basically a glorified CD module. It can limit RPM due to error/problem conditions, such as temperature and oil pressure, but it is not in charge of fuel management -- the carbs do that mechanically. The ECU does control the advance curve, so a check with a timing light would tell you a lot. Do you run the carbs dry at the end of each day? Do you drain the carbs for the off season? If not, a likely culprit is varnishing in one or more of the carbs. Do you have an overheat buzzer sounding (if EP type)? The ECU will limit RPM to about 2800 if overheat is detected. Will the motor go over 3,000 RPM without choke? If not, you are probably starving for fuel. Are you running fresh fuel, and do you have a water-separating filter (with fresh cartridge) installed? A slight water contamination in the fuel might contribute to your symptom. If the motor oil is overfilled, that can also produce a symptom such as yours, as a result of high crankcase pressures and sloshing of oil in the crankcase.
 
Tejohns3 said:
2003 30hp 4stroke tohatsu bogging down at 3000 rpm only in drive, it revs to max perfectly in neutral by pulling choke and it even ran fine in a barrel full of water but when the whole boat is in water and having to push its self is when it boggs down terribly and itruns perfect from idle to 3 grand. I have just got the carbs cleaned and resynchronized last year. could it be the computer??
Click to expand...

Yes, it could be the ECM...But you have a 95% chance the carb has varnished out. It's not unusual to clean carbs once a year if you are leaving fuel in the carbs or using fuel over 30 days old(old fuel attracts contaminants)
 
Most / all motors will rev up in nuetral and sound perfect because THERE IS NO WORK TO BE DONE ( LOAD ) and it realy proves nothing.-----------So put a timing light on it and see if you have good ignition on the plugs.----------Do a compression test.--------------Valve clearance has been checked ??
 
Tejohns3 said:
is there any chance I could put the ecu on myself
Click to expand...

Yes, it's a straightforward procedure. But diagnose the thing first, before buying an expensive ECU that may not be needed. And get a Factory service manual to help you along.
 
Back
Top