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Old 02-05-2018, 05:17   #1
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Tohatsu 18hp 2-stroke - FRUSTRATED - Please help!!

I purchased a used Tohatsu 18 hp 2-stroke 3 years ago. Since I got it I have had continuous trouble starting it when not used for a day or so. When I start it after an hour or two of starting it starts like a dream! And it runs like a dream! The fuel always seems to drain out so that it needs two or three pumps of the bulb to bring fuel to the engine, then about half the time it floods and won't start!

Over the last two years I have tried everything I can think of. I had it tuned up twice by small engine repair shops - once they overhauled the carb. I replaced the fuel tank, fuel line and bulb. This year I installed a spin-on type external fuel filter and bypassed the original fuel filter. I removed the quick disconnect and piped the fuel line directly to the fuel pump and installed new spark plugs (again). And still, every morning the fuel has drained out and I need to pump 3 or 4 times, and then about 1/2 the time the engine floods and won't start. I have seen fuel come out of the engine into the water!

All suggestions are much appreciated!!
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Old 02-05-2018, 06:40   #2
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Re: Tohatsu 18hp 2-stroke - FRUSTRATED - Please help!!

Sounds to me like the float and float pin ( itís what regulates the amount of fuel getting from the carb bowl through the jets) need replaced in the carb. Easy enough job. While you have the carb off give it a good clean with carb cleaner and compressed air. Take off all the jets and such.

For the meantime. Try opening up to full throttle just till you hear it fire. Then bring it down quickly. When an engine is flooded opening up the carb will bring all the access fuel through.
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Old 02-05-2018, 06:49   #3
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Re: Tohatsu 18hp 2-stroke - FRUSTRATED - Please help!!

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Originally Posted by hobopacket View Post
Sounds to me like the float and float pin ( itís what regulates the amount of fuel getting from the carb bowl through the jets) need replaced in the carb. Easy enough job. While you have the carb off give it a good clean with carb cleaner and compressed air. Take off all the jets and such.

For the meantime. Try opening up to full throttle just till you hear it fire. Then bring it down quickly. When an engine is flooded opening up the carb will bring all the access fuel through.
Thank you! I was thinking that perhaps the carb rebuild was perhaps less than a good job! I shall give that a shot. Thanks
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Old 02-05-2018, 06:56   #4
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Tohatsu 18hp 2-stroke - FRUSTRATED - Please help!!

Itís actually called a needle.
I bring that up so if you order parts.
99% of the time the only thing that can happen to a float is it fills with fuel. Some floats are hollow metal, some hollow plastic, those you can shake to tell if there is fuel in them, some floats are solid plastic, sort of like foam filled, and those you can only weigh, if you know what their weight is supposed to be. Usually those I go by feel and just guess.

However I suspicion your problem is a fuel pump check valve that is slowly leaking and allowing fuel to drain back to the tank, then when you manually pump the squeeze bulb, you put enough pressure on the float and needle valve that it allows fuel into the carb and flood the engine. That part is normal, you can do that on most if not all motors if you pump too hard and or too long. Of course an old needle can aggravate this as most have a neoprene tip that helps seal, it gets old, turns hard and often does leak a little.
Read up on adjusting float height too, itís easy to do and easy to accidentally bend the little tab and get it off and not realize it too.
Iíd rebuild the fuel pump, being sure to replace the check valves and maybe put the diaphragm in spare parts, cause it will eventually give up the ghost, of course right when you need it the most.
Maybe check the float if itís a hollow one by shaking. Metal ones are old school, and those can be repaired by desoldering the weep hole that is soldered shut, draining the fuel and resoldering the float.
I had to do that on the carb on my 1946 Cessna, cause those havenít been made in a long time.
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Old 02-05-2018, 07:17   #5
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Re: Tohatsu 18hp 2-stroke - FRUSTRATED - Please help!!

Good advice there. If it were me I would do the carb and fuel pump. Might as well. You can usually by rebuild kits for both that come with everything you need. Then YouTube away for people that have done it. Learn from their mistakes.
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Old 02-05-2018, 07:23   #6
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Re: Tohatsu 18hp 2-stroke - FRUSTRATED - Please help!!

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Itís actually called a needle.
I bring that up so if you order parts.
99% of the time the only thing that can happen to a float is it fills with fuel. Some floats are hollow metal, some hollow plastic, those you can shake to tell if the.....
Great advice - I will rebuild both the carb and fuel pump. It's about time I do it myself anyway!!

Thank you!!!
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Old 02-05-2018, 07:43   #7
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Re: Tohatsu 18hp 2-stroke - FRUSTRATED - Please help!!

I would lean toward the fuel pump. It's a diaphram which is pulsed by the crankcase pressure. If you are getting unburnt fuel sheen in the water there is fuel going into the crank case and then draining out of the engine.

Also check the reeds when you have the carb off. You may need a small mirror to see them all. If any of the little blades are missing that can cause an issue.
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Old 02-05-2018, 08:10   #8
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Re: Tohatsu 18hp 2-stroke - FRUSTRATED - Please help!!

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Originally Posted by CookiesnTequila View Post
I purchased a used Tohatsu 18 hp 2-stroke 3 years ago. Since I got it I have had continuous trouble starting it when not used for a day or so. When I start it after an hour or two of starting it starts like a dream! And it runs like a dream! The fuel always seems to drain out so that it needs two or three pumps of the bulb to bring fuel to the engine, then about half the time it floods and won't start!

Over the last two years I have tried everything I can think of. I had it tuned up twice by small engine repair shops - once they overhauled the carb. I replaced the fuel tank, fuel line and bulb. This year I installed a spin-on type external fuel filter and bypassed the original fuel filter. I removed the quick disconnect and piped the fuel line directly to the fuel pump and installed new spark plugs (again). And still, every morning the fuel has drained out and I need to pump 3 or 4 times, and then about 1/2 the time the engine floods and won't start. I have seen fuel come out of the engine into the water!

All suggestions are much appreciated!!
Check your fuel pump. The diaphragm may have a tear in it. Or the one-way check valves may not be working correctly. If you squeeze the bulb too hard you can tear the diaphragm. The tear may be small and along an edge of it. That happened to me with my 1960 Merc 400 45 hp 2-stroke. It would be good to just replace the diaphragm and blow into the check valves to see if they're working correctly.
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Old 02-05-2018, 12:50   #9
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Re: Tohatsu 18hp 2-stroke - FRUSTRATED - Please help!!

Here are four unobvious (to me) problems I've solved.


1) The newer CARB (Calif. anti-pollution folks) requirements require a fuel cap that won't freely vent. (They apparently think consumers are too dumb to close the twisty-cap during storage.) Instead, a partial vacuum has to exist in the tank before a valve in the cap will open to admit air. You can recognize this problem either by: a) when the engine quits, the primer bulb collapses and won't pump fuel or, b) when you remove the cap trying to troubleshoot a dead engine, you hear air rushing into the tank. Solution: get a new cap that doesn't have the problem (short term on the water: don't fully thread the cap).
2) Fuel drains out of the carburetor reservoir and fuel line when the engine is off. Solution: a) place the fuel tank higher than the carburetor, b) gently reprime the engine every time before starting.
3) The engine runs ruff or stalls at random times. Cause: loss of seal at the fuel line to fuel tank connection. Solution: disconnect the fuel line after each use and clean the tank junction to the fuel line with a wire brush every time before use.
4) The carburetor reservoir (bowl) gets gunked up. Solution: Run the engine dry whenever the engine will not be run for a prolonged time. Leaving fuel in the carb will eventually cause unevaporated gunk to accumulate.
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Old 02-05-2018, 13:45   #10
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Re: Tohatsu 18hp 2-stroke - FRUSTRATED - Please help!!

All good advice. I also found with my Tohatsu 18 that you need to get the choke off quickly, almost instantly, once it fires or it will flood.
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Old 02-05-2018, 16:24   #11
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Re: Tohatsu 18hp 2-stroke - FRUSTRATED - Please help!!

Do a compression test cold and then after it's warmed up. It's possible the previous owner ran it without 2-stroke oil and you have a scored cylinder which affects vacuum and compression.
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