motor trouble

[Rareone]

Howdy fellow Ausfishers. I would like to get some information from you guys. I have a Tohatsu 2 stroke 50 HP oil injected. This motor has been great, never a problem until now. Problem is as follows :- Starts and runs great for about 10 mins out at just under full revs. About 4700rpm, full rpm is around 5100. Goes great but after about 10 mins slowly goes down to about half throttle. First time it happened I thought the vent on the fuel tank was closed. The motor is not hot, pumps plenty of water and the plugs are new and do not seem to be fouling up. When I stop for about 5mins and go again it does the same thing. The sensor for temperature overheating works fine and so to the alarm. No alarm is sounding when the problem is evident. Do you think it could be the "electronic BLACK BOX" or bad injection oil? Thanks guys, any advice will be appreciated Graham http://www.ausfish.com.au/vforum/../yabbfiles/Templates/Forum/default/grin.gif Thanks again

[Noelm]

hhhhmmm this is going to take some fault finding, so, first off lets do the very easiest, no cost (almost) things first, find and use a complete new tank and hose setup, next , when the Motor gives trouble, pull the plugs and see what they look like, as in wet and oily, dry and hot, change the oil to the Manufacturers recomended, just to be sure, we need some very basic info first, then we can advise further.

[Roughasguts]

Maybe fuel pump, does it go okay just putting around or with 2 or 3 k rev's up.

Next time your out and she plays up squeeze the primer while the motor is cutting out, if she picks up rev's you know what to do.

Of course it could be just a fuel or air leak in the fuel system, replace all hoses and clamps, filters and seals and pressure test.

[Chimo]

I had a similar problem in two motors within 10 hrs of each other and it turned out to be the fuel pump, in both cases.

The spring on one side of the diaphram had come lose so at low revs it was fine but after a while at high revs I had much the same as you indicate.

Was a bugger to find on the first motor, very quick on the second!

I think I'd check your fuel pump as one of the early fault finding steps.

Cheers
Chimo

[Noelm]

by all means check the fuel pump, BUT do the easy stuff first before you start pulling anything to bits, the new tank and hose is the very first step!

[reelchippy]

Good advise guys just whant this site is all about.cheers

[cormorant]

When you have the situation occur again use the old hand thermometer- if you can touch and hold back of hand on heads it is OK. If hotter you have an issue- not that I don't trust alarms and sensors.

If it is hot pull the plugs and see if the flywheel spins freely- sometime when they get very hot pistons get tight in bores. This would be very rare.

This problem should be able to be recreated in the workshop with a test prop on and in the test tank.



My last guess is check your lower unit. Have had a couple that absorb power as they collapse with water in them and yet when cooled go back into tolerance but they are stuffed.

Very last guess - make sure choke is not closing slightly - creeping under rers and check linkages as it only needs to happen on one pot. On the same thougths check your Throttle cable is actually giving you full throttle and forcing buterflys open and holding them there.

[tigermullet]

It could also be those mongrel resistor type plugs. Our 40hp 3cyl Tohatsu started to do much the same thing. On stopping and feeling each plug it was evident which one was not working. They were close to new, as well.

We are now back on NGK B7HS10 NOT the BR type and all is well.

[Rareone]

Thanks fellers, I really appreciate all of the responses. The motor pumps plenty of water and does not feel hot when the problem occurs, also I took the plugs out on the water when it happened last (on saturday when I replaced the plugs) and they looked ok with no oil, water or gunk evident. I will try again with another tank and hoses. I will also look further to the choke and carbies as suggested. I might hunt around and find a replacement black box that I might be able to borrow and try and if it fixes the problem purchase it. We shall keep looking so thanks again for the advice, guys. Graham.

[Moonlighter]

Graham

Jon Eadie who is an Ausfish member (jon80) is a mobile marine mech (based Brisvegas Sthside) who is an expert on Tohatsu and a very helpful fellow - would be worth giving him a call - his mobile no is 0407 738 731. Might save a lot of grief and dry gullies.

Grant

[Tazmaniac]

I've had a similar problem, not with an outboard but with a car. Turned out to be a dirty fuel filter.