Tohatsu 6Hp auxiliary just won't idle!

[Dtwo1946]

I use a Tohatsu MFS 6B 6Hp 4 stroke as an auxiliary. It just won’t idle!
The engine runs perfectly well at medium to high revs but if I turn the idle screw on the carb down to below a fast idle (too fast to change gear without risking damaging cogs) one of two things will happen.
Either it will simply run down and stop or it will lose revs, then gain revs, and repeat this a couple of times until it finally runs down and stops.
I’d really welcome any guidance.

 

[wombat88]

Maybe there is an air leak in the fuel line. This is easy to check by running it with the fuel tank higher than the engine. If all is then OK suspect a cracked plastic fuel filter, perished squeezy bulb, poor tank connector etc etc. I just replaced the whole lot and all was fine. Obviously the little fuel pump couldn't cope with air.

This is what I found with the same engine.

 

[coopec]

2012 Tohatsu 6hp won't idle - Marine Engine

www.marineengine.com › ... › Nissan Tohatsu Outboard Forum
Apr 14, 2017 - Re: 2012 Tohatsu 6hp won't idle Odds are the excess fuel in the oil was from flooding, possibly due to not disconnecting the fuel primer hose overnights; that can also damage the fuel pump, causing fuel to pump into the crankcase.
Tohatsu 6hp runs OK but will not idle
11 Jun 2014
Tohatsu 4hp 4stroke won't idle
12 Jul 2011
More results from www.marineengine.com

2012 Tohatsu 6hp won't idle Page: 1 - iboats Boating Forums | 10374091

https://forums.iboats.com › forum › honda-tohatsu-nissan-outboards › 103...
Apr 13, 2017 - Hi - I bought a 2012 6hp Tohatsu 6 hp(maybe 50 hrs on it) from a buddy that changed the oil but way overfilled it (2x the correct amount of oil).
Missing: auxiliary ‎| Must include: auxiliary

Tohatsu 6Hp auxiliary just won't idle! - Google Search

 

[VicS]

I use a Tohatsu MFS 6B 6Hp 4 stroke as an auxiliary. It just won’t idle!
The engine runs perfectly well at medium to high revs but if I turn the idle screw on the carb down to below a fast idle (too fast to change gear without risking damaging cogs) one of two things will happen.
Either it will simply run down and stop or it will lose revs, then gain revs, and repeat this a couple of times until it finally runs down and stops.
I’d really welcome any guidance.

You don't say if you are running off the integral fuel tank or a remote tank.
If using a remote tank defects such as fuel line air leaks and fuel pump problems will be overcome by continually pumping the fuel line bulb.
Also what happens if you switch to the integral tank?

If using a the integral tank check that you are getting a good fuel flow to the fuel pump

Check the fuel pump by disconnecting the delivery hose from the carb and cranking the engine. You should get spurts of fuel from the hose.

Even with fuel supply defects the engine should idle for sometime on just the fuel in the carb bowl before dying

If the above checks do not reveal a problem and the engine will not idle for a minute or so on the fuel in the carb suspect a carb problem.

Have you checked for a good spark? ... It should jump a gap in free air of about 1 cm

Have you tried a new spark plug ?

 

[Stemar]

I had an obscure fuel fault once that caused me to strip the carb a couple of times. Except it wasn't fuel, it was the earthing of the coil. A clean of the connection and bolt solved the problem, but it took me a while to find it.

The other thing I'd be looking at is the idle jet, if there is one. It doesn't take much crud to block it.

 

[Dtwo1946]

Maybe there is an air leak in the fuel line. This is easy to check by running it with the fuel tank higher than the engine. If all is then OK suspect a cracked plastic fuel filter, perished squeezy bulb, poor tank connector etc etc. I just replaced the whole lot and all was fine. Obviously the little fuel pump couldn't cope with air.

This is what I found with the same engine.

Thanks. It's doing the same thing on both the internal tank and the remote tank I use for the main engine. I think I'll have to take the same approach as you and service/replace the whole lot.

 

[Dtwo1946]

I had an obscure fuel fault once that caused me to strip the carb a couple of times. Except it wasn't fuel, it was the earthing of the coil. A clean of the connection and bolt solved the problem, but it took me a while to find it.

The other thing I'd be looking at is the idle jet, if there is one. It doesn't take much crud to block it.

Thanks

 

[Dtwo1946]

2012 Tohatsu 6hp won't idle - Marine Engine
www.marineengine.com › ... › Nissan Tohatsu Outboard Forum
Apr 14, 2017 - Re: 2012 Tohatsu 6hp won't idle Odds are the excess fuel in the oil was from flooding, possibly due to not disconnecting the fuel primer hose overnights; that can also damage the fuel pump, causing fuel to pump into the crankcase.
Tohatsu 6hp runs OK but will not idle
11 Jun 2014
Tohatsu 4hp 4stroke won't idle
12 Jul 2011
More results from www.marineengine.com

2012 Tohatsu 6hp won't idle Page: 1 - iboats Boating Forums | 10374091
https://forums.iboats.com › forum › honda-tohatsu-nissan-outboards › 103...
Apr 13, 2017 - Hi - I bought a 2012 6hp Tohatsu 6 hp(maybe 50 hrs on it) from a buddy that changed the oil but way overfilled it (2x the correct amount of oil).
Missing: auxiliary ‎| Must include: auxiliary

Tohatsu 6Hp auxiliary just won't idle! - Google Search

Thanks

 

[Dtwo1946]

You don't say if you are running off the integral fuel tank or a remote tank.
If using a remote tank defects such as fuel line air leaks and fuel pump problems will be overcome by continually pumping the fuel line bulb.
Also what happens if you switch to the integral tank?

If using a the integral tank check that you are getting a good fuel flow to the fuel pump

Check the fuel pump by disconnecting the delivery hose from the carb and cranking the engine. You should get spurts of fuel from the hose.

Even with fuel supply defects the engine should idle for sometime on just the fuel in the carb bowl before dying

If the above checks do not reveal a problem and the engine will not idle for a minute or so on the fuel in the carb suspect a carb problem.

Have you checked for a good spark? ... It should jump a gap in free air of about 1 cm

Have you tried a new spark plug ?

Thanks. It's been tested on remote and internal tanks and it's the same on both. It's got a brand new plug and a healthy spark. It won't idle on the float bowl contents for any time at all which was a concern. I think you're right. I need to strip the carb.

 

[CAPTAIN FANTASTIC]

I have the same outboard and had same problem because I only use it no more than once or twice in the summer and then it sits doing nothing. I even drain the carb, but still I had the problem with idling, erratic running etc. I stripped down the carb and now is fine. Much easier and quicker than I thought. Good luck

 

[sparkie]

This is a problem that seems to plague 4/5/6 HP Tohatsus of a certain age. I know of at least four that suffer from it. IMHO it's all down to the fact that the carbs are screwed down to the limit to meet emission standards, and then have no margin of safety to cope with little things like gumming, pipe breakdown etc etc. that the old ones used to take in their stride. The only remedy I've found is to renew all the components in the fuel lines, inc filters, pipes etc, and then strip the carb completely and clean it in an ultrasonic cleaner. This sometimes has to be repeated 2/3 times. If still no success, the most satisfactory solution is to bite the bullet and do either one of two things.
1. Buy a new carb. 2. Buy a s/hand one from a much older (pre-emission control) engine.

 

[ghostlymoron]

Get steve66 to clean and adjust the carb for you.

 

[stevebrassett]

I had this with mine. It was simply the idle jet that was gummed up. Took it out, cleaned it up and it has been fine since. Didn't need to strip the carb.

 

[Chris_Burns]

I had a similar problem with my Tohatusu MFS6A but additionally it would only start with no choke and minimal throttle. I did all the carb cleaning checks etc but no difference. In the end I got around to checking the HT spark with an adjustable gap tester and found it to be very weak. The cause was the magneto coil which when replaced resulted in the engine performing and starting like new.

I know the OP has an MFS6B and the ignition system differ from the 6A but point is that it is worth checking the spark strength as I was also originally convinced I had a carb problem.

 

[RobF]

I had this with mine. It was simply the idle jet that was gummed up. Took it out, cleaned it up and it has been fine since. Didn't need to strip the carb.

A few years ago, this was also the solution to my issue. The local engineer who sorted it also enlarged the idle nozzle a tiny bit and the issue never reoccurred. Apparently the idle jets are very small to meet emission standards.

I've also converted to Aspen petrol which has resolved recurring issues with the carb clogging on my Honda.

 

[Dtwo1946]

Thanks

A few years ago, this was also the solution to my issue. The local engineer who sorted it also enlarged the idle nozzle a tiny bit and the issue never reoccurred. Apparently the idle jets are very small to meet emission standards.

I've also converted to Aspen petrol which has resolved recurring issues with the carb clogging on my Honda.

ksk

 

[Refueler]

If it runs well at medium to high revs ... but bad at low or not at all ... sounds like Idle Jet or Idle screw gummed up....... especially that said - speed does not reduce until winding idle screw all way in then it stops.

If its running good at medium and higher revs - why would fuel lines be at fault ? surely that would make higher revs difficult to maintain ?

Just thoughts ..