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Old 17 June 2016, 04:01   #1
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Tohatsu 50D2 Idling issue

Hi All,
I would really appreciate help in fault finding an issue with a Tohatsu 50. I bought the engine last season and had a good season with it, but it was never brilliant at idling well. This season it does not want to idle well and struggles to stay at low revs (splutters to a stop). I have to rev and dump into fwd gear to get going. It runs perfect at mid and top range. Serviced the outboard at the start of the season with all filters cleaned out, new plugs, fresh fuel. Removed carbs and took top carb apart to see condition (was very good). Checked reed valves. Any help please??
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Old 17 June 2016, 06:24   #2
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I had a similar issue with my Tohatsu M60C. After checking all possible fuel-related issues (renewed fuel pump, primer bulb, fuel filter and stripped the carbs three times) I put the engine to a marine engineer. They effectively reset the adjusting rods for the carbs to sync them and started from scratch to set up the timing. If you've ruled out everything else - then that would be the way to go.

One thing to check is the butterfly choke valve on the top carb. It's prone to siezing and can be checked easily enough with the air-box off.
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Old 17 June 2016, 07:40   #3
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check the fuel pump too, the standard tohatsu 50hp pump is notoriously unreliable. Could be at low revs it's pulling air in, then at higher revs the increase in pressure pulls the gasket shut. It's possible to run an aftermarket or yamaha fuel pump. I had nothing but problems with the tohatsu unit
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Old 17 June 2016, 11:12   #4
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Thank you. Any ideas on models of fuel pump that work as replacements?
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Old 17 June 2016, 11:13   #5
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Thanks. Will check the butterfly choke also
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Old 18 June 2016, 05:48   #6
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Unfortunately i don't think there are bolt on replacements for the fuel pump. Rebuilding it every season may help with reliability. I ran a mikuni triple outlet, used on 3 cyl jetskis. You could run a single or dual outlet as well, 35 l/h if I remember correctly. You need to drill and tap the intake (tohatsu already has castings in the correct place) in order to get your pulse feed. You want to keep the pulse hose as short as possible


I've got 70hp Yamaha carbs, with the standard carbs you probably want the single outlet and just connect it to the standard t-piece on the fuel lines
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Old 18 June 2016, 16:37   #7
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Thanks for all the advice. Today I stripped and rebuilt all three carbs and fuel pump carefully. Got some improvement but still struggling to idle without cutting out. Appears to miss somewhat at low revs. Pulled the three ignition coils. Primary resistance was 0.6 Ohm on all three, secondary was 8300 on bottom 2, but 8040 on top for secondary resistance. Not matching what I expected to see from the table of values in the service manual? mmmmm. More questions than answers.
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