Tohatsu 50D2

[Bobbyjoeufb]

Having problems with my Tohatsu, It Revs all the way up to 5250 rpm and cuts back to approx 4500 rpm.

I have removed and clean carbs, removed and checked Reed Valves, removed and cleaned all Fuel Lines, Filters, Tank Pickup and carried out a compresion test. Today I disconnected the Rev Limter and still will not rev past 5250 - 5400 rpm. Took off all three coils and checked them with a mulitmeter all within tolerence.

The only thing I have noticed today was that one of the Spark Plug Caps has been broken, black plastic part, not sure if this happened today or been like that for a while as was hidden by the rubber sleave. Going to order new Spark Plug Caps and fit.

Can anyone suggest anything else I should be checking to solve this problem?

 

[pvanv]

Re: Tohatsu 50D2

This motor is rated for a WOT of 5150 to 5850. It would be preferable to be over 5400, but you are in the range. What RPM had it been running before this situation? Any other changes with the boat?

 

[Bobbyjoeufb]

Re: Tohatsu 50D2

The engine has never really run prefect since I got it 4 years ago at the time it would either run at tick over or full throttle and nothing in between.

I got hold of a service manual and performed a tune up which inproved but then lost some top end speed. Manged to sort it out with timing set up was set at the wrong mark.

Had the engine to my so called dealer earlier this year to carry out a service and see if he could improve the cold start and WOT problems. Guy claims to have advanced the timing and it should start from cold on two pulls, more like 6 pulls, and has put cut out problems down to rev limiter although cant explain why the boat had never done it before.

Only put the Tach on the engine this year so dont know what Revs it was running at, I know it is showing in the correct range however I would have expected the engine to exceed this when the Rev Limiter was disconnected.

 

[pvanv]

Re: Tohatsu 50D2

Sounds like you're headed in the right direction. Is the motor (now) generally well-behaved (except for extra pulls when cold starting)? Are you using the actual Tohatsu service manual, or one of the aftermarket "fits all years, all models" manuals?

Assuming that the motor is generally OK, and that you cannot get enough WOT RPM's... If you have verified the fuel and ignition systems, perhaps it's time to go all the way back to basics... check the actual rigging. Check a good prop guide. You may be over-propped. Can you beg/borrow/steal a lower-pitched prop for testing?

 

[Bobbyjoeufb]

Re: Tohatsu 50D2

Once the engine starts it runs perfectly upto 3/4 throttle, when WOT it runs up to 5200 - 5500 rpm then surges and drops to 4500 ish rpm back off the throttle and back on runs again for a short while.

Prop is a power tech and standard fit to Zapcat boats in the UK. Ordered new Spark Plug Caps so will refit and try again, also got a spare fuel line so will try that too.

If that does not work will be back to basics and check timing and carb sync in Tohatsu Service Manual.

 

[comanr]

Re: Tohatsu 50D2

my 2 cents. check tank ventilation or use a temporary tank near motor and go on a little.

 

[pvanv]

Re: Tohatsu 50D2

Once the engine starts it runs perfectly upto 3/4 throttle, when WOT it runs up to 5200 - 5500 rpm then surges and drops to 4500 ish rpm back off the throttle and back on runs again for a short while.

Prop is a power tech and standard fit to Zapcat boats in the UK. Ordered new Spark Plug Caps so will refit and try again, also got a spare fuel line so will try that too.

If that does not work will be back to basics and check timing and carb sync in Tohatsu Service Manual.

OK, but what are the specs on the power tech prop? The initial RPM limiting may be due to too much pitch. The "running out of RPM" may be due to fuel starvation. Yes, it's prudent to check the link and sync, and also a good idea to verify fuel line, vent, etc.

 

[Bobbyjoeufb]

Re: Tohatsu 50D2

Not too sure about the prop specs I know it is a Powertech Semi Cleaver and another website states that it may be (Power Tech 10 X 16SCB) either way the prop has been on the boat from new so dont think its causing the problem.

I have received the new spark plug caps and fitted these today and checked timing, carb synch and fuel vent all ok; fuel filter had a slight bit of crap in the bottom so cleaned out.

Hoping to get out a run later this week so will see if its any better if not will try spare fuel line.

 

[Bobbyjoeufb]

Re: Tohatsu 50D2

Had the boat out today for a short run.

Pleased to say it ran at full throttle without any cutting out or surging

Will double check settings and adjust fuel/air mixture next time out. Also Tiny Tach has stopped working again so will have to look at it again.

Thanks for everyones replys.

 

[deejaycee_2000]

Re: Tohatsu 50D2

Did you disconnect the rev limiter?

 

[Bobbyjoeufb]

Re: Tohatsu 50D2

Did you disconnect the rev limiter?

I did orginally for testing, is now reconnected as crack has not been welded.

Engine is running good, think it still has some tweaks to get full Rpms. Got a replacement Tiny Tach will install check what is running at.

 

[deejaycee_2000]

Re: Tohatsu 50D2

Get the crank welded asap, even if running standard, a Slo-hatsu loves twisting cranks .....