Tohatsu M70B high RPM fuel problem

[Flukinicehole]

I have a Tohatsu M70 B 70hp outboard with a high RPM bog. I know it is running out of fuel and I know the steps to test where the problem is. I was just wondering how much fuel is needed. I'm going to hook up an electric pump to the fuel line and see how it flows from the tank. I have a feeling there could be varnish and blockage on the pick up screen. The tank was not used for a few years and I just finished rebuilding the boat. I rinsed the tank a few times with gasoline but I'm sure there was still some undesirables left behind. I installed a water separator/filter inline just before the primer bulb as an added precaution. The boat will run all day at 3000 but when I get anything over it will start to starve for fuel. So how much fuel do I need? A gallon a minute free flow through the line? I would figure that would be plenty.

 

[pvanv]

http://tohatsu.com/tech_info/fuel_consumpt.html

 

[Flukinicehole]

Thank you Paul. This is exactly what I needed.

 

[Sea Rider]

How old is that engine ? Must remove fuel pickup from tank and clean it to immaculate condition, check also internal mesh fuel filter inside engine, could have an internal fuel line restriction, probably sucking air through fuel connectors o'rings, try a new fuel line, or have a cyl head gasket on it's way to become kaputt. Retorque head gasket back to specs.

Happy Boating

 

[Flukinicehole]

I believe it is a 96. The pickup was cleaned along with the screen. It is new fuel line from tank (under floor) to engine. The internal filter was clean as well but I will pull it apart and recheck. I will hook up an electric pump to see how the flow is from tank to the engine. If that is good then I will move forward. I just need to make sure I have enough fuel being delivered to the pump before I get to deep. I will also check the head bolts. Thank you for the help.

 

[Flukinicehole]

Checked the filter at the engine and it is clean. Also checked head bolts and they are good. If I could find me electric fuel pump I would check the flow. I had to order another one because I have a feeling I left it in my old boat.

 

[Sea Rider]

What you can do is disconnect fuel connector from engine, with a pointy object push open the interior white valve while priming hose bulb several times with bulb arrow pointing upwards, check if fuel flow is good or hose has some form of fuel delivery restriction, use a container to collect flowing fuel from connector.

Happy Boating

 

[Flukinicehole]

I will try that after work today, Thanks for the tip!

 

[Flukinicehole]

OK so I have a fuel pump and went out to check the flow. It seems good before and after the filter/separator. I then checked the fuel pump (removed and took it apart). There was nothing obvious but I have never had one apart before. Everything looked clean and nothing seems worn or out of place. I know it is a delivery issue as when it starts bogging I go back and pump the bulb a few times and she takes off. Could my pump be to weak to run the extra filter I installed?

 

[Sea Rider]

That model uses plastic like diaphragms inside fuel pump, right ? are all plastic diapragms in mint cond that's not cracked, dried, worn out ? How about check valves, are they flat and well aligned against middle holes of housing ? Did you tried other fuel hose that was working ok as to discard fuel hose issue. Try connecting tank to engine directly bypassing filter, will know if filter is the issue or not.

Happy Boating

 

[Flukinicehole]

Yes the diaphragm is plastic. There is only one and the check valves are aligned. I did notice on the outlet side the check valve does not seem to sit exactly on the housing. On the inlet side it does. When I blow on the inlet side it make a reed sound. Next time I take it out I will bypass the filter and see if that helps. Honestly though I hope not as I really want to keep a water separator. I use non ethanol gas but still like to have them. I have always run them on all my boats. As for the fuel hose it is new from the tank to the engine. I will say the small hoses inside the engine could be suspect. I think I will unhook them and pump the primer bulb to make sure there are no restrictions. Thanks again for the help.

 

[Sea Rider]

If both check valves does not sit flat against housing could have unwanted fuel delivery issues, must center the outlet one, unlock upper screw a bit till loose, align at middle center and tight again screw.

Happy Boating

 

[Flukinicehole]

The check valve on the outlet side was centered but not sitting against the housing. The inlet side was centered and sitting against the housing. I took the outlet side off and flipped it over. It is now sitting flush against the housing. When I blow through the inlet side I get a reed sound. When I blow against the outlet I get a blocked port but when i suck I get the reed sound. I have a feeling the outlet was not seated right and it was sucking back. I got it back together and decided to prime it to make sure nothing was leaking and I had to pump the bulb like 200 times. It is like all the gas siphoned back to the tank. Could I have a bad primer bulb? Thanks again for all your help. I just finished restoring this thing and the kids love going out on it. Honestly other then the high RPM problem it runs great. Starts right up and idles smooth.

 

[Sea Rider]

Open fully the air intake valve on tank, with casted arrow on bulb facing upwards prime till bulb is firm, go for a wot spin and check performance, lets hope the issue was a slight valve misaligment, fingers crossed.

Happy Boating

 

[Flukinicehole]

Have not had a chance to get back out but changed the "new" filter today too. The tank was empty when I got the boat and he ran it off of an auxiliary tank. When I restored the boat I replaced all the guts in the tank and washed it the best I could. Well the "new" filter is packed with stuff. I presume it is the varnish coming off the spots I could not reach. I was going to go out today but after I fueled it up and came home my motivation has left the building. This is my first day off in 2 weeks so I'm a little beat. We will head out next weekend and I will report back. I have a feeling we will have good results.

 

[Sea Rider]

Internal fuel tank are very complicated to clean while sitting under deck, sometimes must be removed and properly cleaned outside. Anyway test with aux portable tank as you don't want fuel filter contamination while testing engine with internal fuel tank.

Happy Boating

 

[Flukinicehole]

I had the internal tank out when I rebuilt the boat, I even pressure washed it... all that I could get to. I figured there would be some shellac left in the tank after not being used for a few years. I ran off a few gallons and the flow to the engine is good. I also found that the gas fitting on the side of the engine was gummed up. I disconnected the fuel hose and could barely blow through it. I took it off and cleaned it up. Now the flow is much better. I found that problem because the primer ball would not prime. I just kept squeezing and the ball would not move any fuel. When I took the line off it would pump fuel fine. Put that back together and a few pumps later it was hard. I will bring the auxiliary tank with me and if it starts acting up I will switch over and see what happens. Thanks again.

 

[Flukinicehole]

Been a while and life gets in the way but my daughter and I made it out yesterday. Motor ran like a top with no more issues. Thanks again Sea Rider!