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Old 21 February 2014, 14:57   #1
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Tohatsu outboard

Hi

Hoping some one can help me out. I took my rib out for the first time last Sunday, and had trouble with the engine cutting out when I accelerated (its a tohatsu 50hp two stroke 2007) In the end I found running it on quarter choke solved the problem I did over forty miles like this.
I have checked the following.
Fuel pump diaphragm which I replaced as it had a raised hump by the outlet.
Stripped all three carbs and cleaned jets.
Borrowed a mates fuel line and bulb
When I ran up it worked ok for a few mins then cut, I had to push more fuel up with bulb restarted, no choke needed but cut out after a few mins.
I placed fuel tanks above engine and it runs fine with the bulb holding pressure but as soon as I drop onto floor of boat within a few mins its struggling again.
Any ideas would be very much appreciated.

Many thanks

Dean
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Old 21 February 2014, 15:10   #2
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The first thing I would check is the fuel bulb itself to make sure the one way valves are ok.

If an engine runs fine by raising the tank it will be being gravity fed. The first port of call has to be the fuel pump. Try a new fuel pump, rather than just a diaphragm.

Pulling the choke out to keep it running is a sign of a blocked jet or Venturi. As much of a pain that it is, sometimes you have to go through the carbs again.

However, if it is easy to launch, simply run the engine with the airbox cover off and run in gear at speed. You will see the fuel entering the engine. If one of the carbs seems restricted you will know which one, saving you from overhauling them all.

You can run it in gear alongside but I've seen a few cleats break off doing that.
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Old 21 February 2014, 15:18   #3
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Thanks for your help, looks like I will be busy tomorrow stripping carbs again, are there any signs to look for within the fuel pump.
The engine hadn't been run for well over six months could something deteriate over this time? I have fresh fuel and have bypassed the fuel filter just I case this had sediment in it.
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Old 21 February 2014, 15:29   #4
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Remove the fuel pump from the side of the block, and disconnect the hose to the carbs and cover the outlet with your finger. Squeeze the fuel bulb and see if any fuel comes out of the hole which the engine operates by the action of the pistons.

If you tear the gasket get a new one and lightly grease it, they don't tear after that.

Then try to suck back on the inlet side. Then try to blow back from the outlet side. you should not be able to do either. This will show if the valves are working properly, ie one way.

If you are having to put more suction on via the choke the pump may be blowing fuel back to the tank. After all, you have already identified the pump as having a problem.

Lastly, how dirty were the carbs?? If they were clean first time, they should still be clean.
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Old 21 February 2014, 15:38   #5
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Thanks will try that tomorrow, across the three carbs I got probably a tip of a tea spoon of crystallised sediment if that makes sense. Do you know the best place to buy a fuel pump from if needed.
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Old 21 February 2014, 15:49   #6
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eBay for the fuel pump.

If you want to avoid crystallised deposits, at the end of the year just run the carbs out of fuel by running on the flush muffs and disconnect the fuel line, as the engine splutters pull out the choke gradually. This will empty carbs. If it not your fuel pump, it will be the sediment.
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Old 21 February 2014, 15:52   #7
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Thanks very much for your help,

I will do that with fuel next time

Thanks again
Dean
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Old 21 February 2014, 16:12   #8
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Another couple of tips. If you know it is your last trip of the year, run the engine with a higher oil mix, it will offer protection over the winter. If you are oil injected run at 100-1 in the tank. If there is any fuel left, I put mine in the wife's car a gallon at a time. The oil mix won't harm the engine at such a low mix, and if anything will act as upper cylinder lubricant.

Once you have emptied the carbs as earlier, fogging oil or wd40 down the bores.
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Old 26 February 2014, 08:32   #9
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I knew there was a reason I like premix!

Other thing-you said "first time out" .... Did you have a smaller boat before and are you using it's fuel tank?

I had that very problem a few years ago when I swapped my tank from my old Suz 25 to my "new" Yam 55.... I couldnlt run > 4000 rpm or it died of fuel starvation. The Suz was running a 1/4" fuel line - fine for 25HP. problem was the fuel pump on the 55 couldn't overcome the friction of dragging the extra fuel through a few feet of 1/4" line.

A few quid for new 3/8" hose, primer & connectors and never had a problem since.
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