18HP Toyhatsu issues. Please help!

Hey fellas,

 

A few years ago me and my mate bought a 18HP Toyhatsu for out 5m tinny, but here’s the clincher, it’s from 1989. Don't get me wrong though, up until now she has never let us down, still starting on the first few pulls and no real dramas. 

 

Recently though we have been experiencing some issues with the revs, for instance last week we went out in Cockburn sound and fished all the way down to south beach with no problems (going flat stick etc), however on the way back, the engine could not go over 1/4 throttle without over revving with no change in power and have a unusual ‘whiney’ sound, which saw us limping back to the boat ramp - but engine didn't have any issues in low revs. 

 

This is our first boat and obviously have a lot to learn, and admittedly threw ourselves in the deep end in purchasing such an old model motor - which has proven significantly hard to gather information on after hours of research, but I think I have whittled it down to a few factors. Any advice or experience you guys could provide and would be extremely appreciated, which such an older engine it could be anything, but here’s what I’ve got so far.

 

1. May be the prop is on a rubber bush, and at higher revs the bush slips 

2. Shear pin in the drive shaft has sheared 

^ We took off the prop and inspected the parts, which looked okay (to our eyes). The guy  who wrote this said if this was the issue that it would be a consistent issue, a.k.a not happening every now and then. However he also said if this was the issue you would be able to spin the prop by hand, which we can easily do?? Researched it and heard conflicting opinions on how free the prop should spin without being turn on

 

 

3. Engine vibration: The engine does vibrate more than it should, which first inclined that the prop was the problem and possibly causing parts to become loose? Apparently 18HP Toyhatsu are known for experiencing internal breakage in the ignition coil due to excessive vibration 

 

4. One of the cylinders failing?

 

5. Fuel starvation due to faulty primer bulb

 

6. Overheating:  The motor is getting too hot and  ‘pre igniting’ so the high temp of the engine ignites the fuel not the spark plug so you get the engine firing in the wrong sequence

 

When I was working up North my mate had his friend come and clean the carb, I honestly don't think this guy knew what he was doing so it could need a thorough clean again?

 

Sorry for the long post, again any advice would be tremendously appreciated. 

 

Thanks in advance!!

 

Matt


quadfisher's picture

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My guess.

Tue, 2015-05-19 19:14

http://www.ozpropellers.com.au/outboard-propellers/tohatsu-nissan-replacement-propeller-120.html

 

Although , have you dropped the leg oil lately , look for water ( milky oil) or metallic bits.

http://www.tohatsu.com/tech_info/oil_change.html

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quadfisher

bronzey92's picture

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Date Joined: 26/10/12

quad

Tue, 2015-05-19 20:23

 Hmm it could well be the oil, like I said I was away all summer when my mate was using it. I don't know if the correct procedures were taken but definitely worth repeating.

Thanks mate

bronzey92's picture

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Date Joined: 26/10/12

quad

Tue, 2015-05-19 20:23

 Hmm it could well be the oil, like I said I was away all summer when my mate was using it. I don't know if the correct procedures were taken but definitely worth repeating.

Thanks mate

poida's picture

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Is it cavitating. ie sucking

Tue, 2015-05-19 19:17

Is it cavitating. ie sucking in air and loosing thrust.  Try it on a flat lake and see how it goes, how deep is the leg below the hull? Is it a short shaft on a mid shaft transom?

bronzey92's picture

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Date Joined: 26/10/12

poida

Tue, 2015-05-19 20:20

 Hmm, we bought the boat/engine when we were working up in shark bay, so would generally be in pretty calm water. The back of the boat, where hte engine sits (sorry don't know my boat lingo), has been cut down about 20-30cm in a wide 'V' shape, don't know if that could have an effect, but from observation it is always well below water

Posts: 315

Date Joined: 07/05/11

Fuel line

Tue, 2015-05-19 19:41

 check your fuel line from connector to fuel bulb. Could be air getting in somewhere so eliminate that but that's what my money's on

air getting in will do exactly that. Had a 50 tohi once. Never missed

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 Baron Sportsman

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bronzey92's picture

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Thanks mate

Tue, 2015-05-19 20:16

 Will do some research and try test it out

 

Cheers

sstevee's picture

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After having a similar issue

Tue, 2015-05-19 19:52

After having a similar issue and researching ALOT, I'd say you have a spun prop bush. If the revs are rapidly increasing and you arent moving then that what it may be, especially if you are only getting to quarter throttle.

 

 

bronzey92's picture

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Date Joined: 26/10/12

sstevee

Tue, 2015-05-19 20:15

 It runs fine for a while though and then happens, then the next time we go out we might have no problems? Did that happen with yours?

Cheers

sstevee's picture

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Date Joined: 15/11/11

If you search for a thread

Tue, 2015-05-19 20:39

If you search for a thread called 'abnormal poor performance' you should find the thread which i described a similar problem.

Mine would still open up to full throttle but i just wouldnt get any power. Turned out to be a dodgy spark plug lead. But it sounds like you are only applying 1/4 throttle when the revs start to sky rocket. In which case if it is not doing it all the time then you could almost rule out a spun prop bush. However this is very easy to check as you just mark the prop and the bush, take it for a spin and if it does it again check to see if the marks still line up. If they dont line up you know it is spinning. If they do you can rule it out.

 

carnarvonite's picture

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Rubber bush

Tue, 2015-05-19 20:30

You have spun the rubber bush in your prop. Once you increase the revs it puts more load on the bush and it slips, back the revs off and its ok.
Take it in to Max OGrady's prop shop and he will stick a new bushing in for you at the right price.

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Date Joined: 05/05/06

Another one for prop bush.

Wed, 2015-05-20 01:51

Another one for prop bush. Take your prop off and look at the back of it and check for bits of rubber etc

Did you hit the bottom or something in the water? thats what caused mine. Stops your gear box getting ruined

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bronzey92's picture

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Thanks

Wed, 2015-05-20 09:37

 Thanks heaps for the comments everyone. Going to do trying a few different things today to see if it solves the problem. Will keep you updated. Cheers