Logo

Tohatsu 4 stroke, 4 hp flooding

graama

New member
HELP - My 2013 Tohatsu 4 stroke, 4 hp failed to start for me the last time I was going out on the lake. On inspection, I discovered that it was seriously flooding - to the extent that fuel was dripping out of the carburetor intake. I removed the carb, checked float and needle and blew out all jets and other openings. All appeared in order. When I tried to start the motor again, it fired a few times and quit. Pulling on the cord a couple more times produced fuel dripping from the carb intake. After repeating this remove and inspect procedure twice with no improvement, I was baffled. I just tried a brand new carburetor and once again, it fired a few times and quit with fuel again dripping from carb intake. :confused:
Can anyone suggest to me what the problem might be? If it's not the carb, is it the fuel pump? I have not inspected it. Is it possible that it is producing too much pressure and defeating the float and needle metering?
Thank you for any suggestions.
 
Probably an MFS4C, right? Year is irrelecant.
Highly doubtful. The fuel pump makes at most maybe 3 psi. You can check that with a gauge.
When inverted, is the float parallel with the carb casting?
What new carb PN did you try? Did you verify float height?
PS: The carb for the MFS6A2 will give you 50% more power, and a better idle.
 
Thank you for your help Paul. Yes, its and MFS4C. I simply installed the new carb as received - its identical but appears to be from a different manufacturer. I have not checked the float height but will. Not sure what you mean by carb "PN". Also, thanks for the tip on the MFS6A2 carb.
 
A different manufacturer = a different (wrong) carb. You need the original Kehin carb.
3JD032000MCARBURETOR ASSY, MFS/NSF4C

Or, the better choice, for the 6A2,
3R4032001MCARBURETOR ASSY, MFS/NSF6A2
 
I really appreciate your input Paul. Yes, the original is Kehin. The replacement has no casting marks (although appears identical) - except choke valve is metal rather than plastic. So, if the fuel pump isn't capable of over producing, it looks like I'm back to square one. Do you know of any cause other than float, needle, and seat adjustment that would allow this kind of flooding? This problem appeared out of nowhere. Although it only gets occasional use (on a sailboat) the motor had been running fine and then one day it didn't. It has very few hours on it.
 
Paul - Again, I thank you for your input. I had other things to do for a while so just recently re-focused on my outboard motor. I decided to experiment and by-passed the fuel pump by gravity feeding fuel directly into the carburetor from an external container. The motor started fairly easily and once it had warmed up a little, settled into a nice smooth idle. This would seem to eliminate the carburetor as being the source of the problem and indicates to me that the fuel pump is more likely the problem. Can you suggest a particular part of the pump that might be a simple fix?
 
I would test fuel pressure. Still, I have never seen an over-delivering pump. The complete pump is
3H6040007MFUEL PUMP, 4/5/6/8/9.8 4-STR ONLY$66.43

002-21046-9_FIG04.jpg
 
Thanks for the info Paul. I do not have a gauge to check fuel pressure (not sure I have even seen one) but if I were to check it and it was at the 3 psi that you indicated, i would be baffled indeed. I will get to the bottom of it though.
Regards, Graham
 
The pump is not causing the issue. If gravity feed helped, the needle is not seating. Either a bad needle, or the float is set too high.
 
Probably an MFS4C, right? Year is irrelecant. Highly doubtful. The fuel pump makes at most maybe 3 psi. You can check that with a gauge. When inverted, is the float parallel with the carb casting? What new carb PN did you try? Did you verify float height? PS: The carb for the MFS6A2 will give you 50% more power, and a better idle.

Why is the 'older' 6hp carb better? I have a 4hp from 2019, just bought it, perhaps I should try "3R4032001M"
(6hp carb is 3JE032000M)
 
Probably an MFS4C, right? Year is irrelecant. Highly doubtful. The fuel pump makes at most maybe 3 psi. You can check that with a gauge. When inverted, is the float parallel with the carb casting? What new carb PN did you try? Did you verify float height? PS: The carb for the MFS6A2 will give you 50% more power, and a better idle.
Why is the older 6hp carb better? I have a 4hp from 2019, just bought it, perhaps I should try "3R4032001M" (6hp carb is 3JE032000M)
 
Back
Top