Tohatsu outboard problems

1

10oxometer

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6 Dec 2007
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Hi All, just bought a tohatsu 4hp 2stroke in lovely condition, runs and ticks over beautiful all day, starts easy answers to the throttle all in neutral. once i engage forward gear an open the throttle it will die and cut out. back into neutral and it will start imediately.back into gear try to accelerate and it wants to die again. I can sometimes get it to accelerate very gingerly on the twist grip. both idle and main jets seem to be clear no sign of dirt in the float chamber. im now scratching my head. can anyone point me in the right direction.
Many Thanks.
 
That was the same symptoms as I had on my strimmer. Old fuel, so a new mixture and it ran fine. I assume the petrol had 'gone off' and it was oiling up the system.

Could be that.
 
First thing is to change the spark plug.

If that makes no difference then get it idling and open the throttle whilst squirting a few mls of two stroke mixture into the air intake. If it revs up and then dies back you have a carb blockage/fuel supply problem.

If the squirt of fuel does nothing, you have an electrical problem but not the plug. Probably a failing HT side.

No harm in using fresh mixture.

Richard
 
If its not the spark plug, quick to change and check, then it's most likely to be a blocked main jet in the carburetor. Its not usually hard to remove the carb on these small engines, remove disassemble and you bound to find the jet that's blocked.
 
By far the most likely cause is a partially blocked main jet in the carb. Remove the float bowl clean out the gunk and blow through the main jet. You may have to repeat this if there is gunk in the fuel system which will find its way into the carb as you run the engine.

While you have it off check that fuel is flowing freely into the carb.

This is caused by the OB being stored with fuel in the carb which leaves behind gunk as it evaporates off. It is made worse if there is ethanol in the fuel.
 
I agree with Richard... always worth trying a new plug (NGK BPR7HS-10)... even when the symptoms scream out "fuel problem"

Check the spark ... it should be possible to get a 7/16 " long spark from the lead

If you have or can borrow or steal a compression tester check the compression

use fresh fuel mix ( 50:1)

Check fuel flow to the carb. Integral tank models may have a filter combined with the fuel tap but if so it is not shown in parts diagrams.

Remote tank models should have a fuel filter in the pipework between the inlet fitting and the carb/fuel pump.

Try pumping the fuel line bulb of a remote tank model as that will help diagnose a faulty fuel pump or fuel line air in-leakage.

check carb float valve ... soft tipped needles have a minute clip between the needle and the float arm ... check that it is in position.

Clean the main jet and the fuel nozzle, as suggested, and all carb passages. Poke a soft copper wire, eg fuse wire, through the jet
 
Fuel and electrics are the obvious things. Is there any tightness in the gearbox/prop that is simply stalling the engine?
 
I had a similar issue on my 3.5 that turned out to be caused by corrosion where the coil was earthed to the block. It's plenty enough to cause a weak spark, the same as a tired plug, but a quick clean and a bit of ACF50 sorted it.
 
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