Tohatsu 5 HP 2 stroke problem

[Bcharles]

I bought a used 5 HP Tohatsu. In the tank, it starts on first pull and sounds pretty good. When I took it out for a trial run today it started first pull, and ran well in the no-wake zone. When I accelerated to half throttle it ran well for about 5 minutes, but then quit on me. It restarted easily, but would only run at idle speed. Every time I tried to accelerate, it quit. I emptied the gas tank and replaced with fresh gas. Again, it ran well for a few minutes but then quit, and would run only at idle speed. Any suggestions on what I should be looking for?? By the way, the cooling water seems to pump well, but does not get hot. Thanks.

 

[Sea Rider]

Welcome to Iboats,

Start with a ggod carb soak in real carb clean for at least 3 hours, clean all internal filters, including the one found at the lower fuel pick up tube on main tank. When OB was missing, were your using the internal or external fuel tank. Install a new NGK BP THS 10 or BPR THS 10 spark plug gaped tight to 1.0 mm after completion of previous suggested service.

When cleaning carb, check fuel pump internal condition, could have dried, cracked, ballooned diaphragm not doing their homework right. If found kaputt change all internal rubber parts and gaskets.

Happy Boating

 

[pvanv]

Correct plug is NGK BP7HS-10 or BPR7HS-10

 

[Bcharles]

Thank you for your responses. Motor has correct plug. In looking at external condition of power head, it looks like previous owner had cleaned up the carb and put on new fuel line (fed only by the internal tank) and fuel pump. I don't see any fuel filters. There is a shut-off valve just below internal plastic tank (unable to attach a photo). I disassembled the shut-off valve and don't see any sort of screening material in it. If there were problems with the fuel pump or carb, I'm puzzled as to why the motor would run well for several minutes and then suddenly lose power. Seems like it would run well at all.

 

[Sea Rider]

Those 5 HP babies needs to have fuel tanks, lines immaculate clean and obstruction free. OB will inevitably miss if with fuel issues, worse when more throttle is in demand and that is from personal experience.

There should be a fuel filter located next to fuel pumpl and fuel ****, if with any, fuel particles may already have entered carb and obstruct tiny fuel passages.

What you can do is disassemble both fuel **** line sides and with opened valve blow hard with mouth on left side, check if air passes through with no restriction. If OK check fuel pump internal cond, if OK, carb needs to be cleaned to perfect working order.

If all electrical related parts are OK which you do not know, it is a fuel starvation isue...

Happy Boating

 

[Sea Rider]

This fuel hose config is what comes standard when OB was factory delivered. Which parts are missing if so ?



Happy Boating

 

[pvanv]

No. That setup is for when the 5 hp motor is the dual-tank version. For the internal-only tank, the fuel screen is inside the tank, attached to the fuel ****.

 

[Sea Rider]

Oops, didn't know there was a single tank version, the OP did not specified the 5 HP model. Anyway need to remove the fuel **** from tank's neck and clean the internal tubular mesh filter to immaculate clean cond, if bit dirty are prone to give small or huge fuel starvation issues depending on how clogged the mesh is found.

Happy Boating

 

[raczekp1]

at the fuel tank outlet is located small fuel filter. its hiden inside.
take out fuel cook and pull out this fuel filter.
remove it and insted of this install regular motocycle fuel filter in fuel line

 

[Sea Rider]

The small mesh round filter located inside fuel **** works very well provided it's kept in a immacuate clean cond for fuel pump to work as it should.

Happy Boating

 

[Bcharles]

Thank you all for your suggestions. I see that the fuel filter is no longer attached to the fuel ****--I guess it got lost when the previous owner did some work on it. This may have allowed some contaminants into the carb,which otherwise looks like it has been recently rebuilt and a new fuel line installed. Unfortunately, whoever did the work neglected to install a fuel filter. But if there is a blockage in the carb, why would the engine run smoothly at medium-high rpm for 5-10 minutes before all of a sudden cutting out? After cutting out, it runs at a very low, rough rpm. I will install a new, in-line filter, but I still need to figure out where the blockage might be. Bernard

 

[Sea Rider]

Carb probabably needs a good soak in real dip cleaner for some hours. Install a inline fuel filter bweteeen fuel **** and fuel pump. Run a wot test and check if problem was solved, if still persists could be an electric component heating up, shorting and OB missing. Clean carb and install fuel filter to rule out if it's a fuel related issue. Open air vent on tank when testing.

Happy Boating

 

[Bcharles]

Well..., I'm still working on it. I took the carb apart, sprayed cleaner into every hole I could find, replaced all gaskets, put it back together and installed an in-line filter. The filter is clear and is helpful in that I can see if and when fuel flows through it. If I disconnect the fuel hose as it enters the carb, fuel flows out of the hose, proving that there is no obstruction in the tank, the fuel line, or the filter. However, when I connect the hose to the carb and try to start the motor, no fuel enters the filter and the motor will not start--apparently because it is starved for fuel. If I spray a little starting ether into the carb, it starts up briefly but then conks out. So, it seems like there is something about the carb that is preventing fuel from flowing in. Is some sort of priming necessary? Bernard

 

[pvanv]

Clean the carb. Properly this time. In real carb dip. Then spray out all passages. Then verify float height and needle seating.

 

[Sea Rider]

If fuel flows freely from tank to outter in line filter, probablt fuel pump if happens to have one is with issues, could have dried, cracked diaphragm or badly assembled back if it was totally dissasembled, once inverted a diaphragm while reassembling a cleaned fuel pump, gues what, OB never started besides driving me crazy. You always learn the hard way.

Happy Boating

 

[Bcharles]

I think I finally got things working okay. Tinkered with the fuel hose connections and routing, make sure no kinks in hose. (Hose routing is not original, due to missing OEM molded hose.) Anyhow, I can now see that the clear replacement fuel filter is filling with fuel properly, and fuel starvation is not an issue. Nice warm day today, so I took it out for a 20-minute run. No problems (knock on wood).

 

[pvanv]

If you did a Proper Cleaning of the carb and have good flow, you should be OK.