Tohatsu 3.5 2 stroke outboard stalls

ShaunG

ShaunG

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Hi Allm

My Tohatsu 3.5 two stroke about 1998 vintage will not run without choke. I have just cleaned the carb out, changed the plug and have fresh fuel. It was a problem last season and thought i would try to sort it this year so here goes......

throttle to start position and full choke and she starts no problems

10 mins to warm up whilst gradually reducing to 1/3 choke, engine ticks over fine.

rev the engine with 1/3 choke and she struggles for power, redue choke and she stalls so she is not flooding, increase choke to 2/3 and all is well.

so i guess that this has to be mixture related, or she is just not getting hot enough to run without choke.

i guess that screwing the mixture screw in richens the mixture and should allow running without choke eventually, i have tried this but not sure how far to go.

any on have any ideas

thanks

shaun
 
You are describing fuel starvation, I think - but the cause is another matter. You have freshened the fuel and checked the needle-valve. It should run without choke after mere seconds of warming-up. Try washing out the carb one more time?
 
Not familiar with the Tohatsu but note the position of the idle mixture screw and try adjusting it. I'd expect to screw it out to enrich the mixture!

However the symptoms you describe are those of a dirty slow running jet.

How thoroughly did you clean the carb?
Completely stripped and jets cleared by poking a soft copper wire through them?
Do it again!

Worth checking the fuel level I suppose. Generally the needle valve closes when the float is horizontal.
 
I have cleaned the card thoroughly, remvoed gaskets and float, fully stripped and soaked in paraffin. blow through with compressed air. The carb is sparkling, any ideas if these have a fuel filter, i have looked through the system and the only thing i have not checked is the stop tap, could this have a filter within it?

Ablocked filter would explain the starvation above
 
Hi NFP,

thanks for that tip, i had an old evenrude around with the same card, also has the paint on the end, replaced the needle on the tohatsu card with the one from the evinrude and all seems well. the paint on the tip of the evinrude is more complete than on the tohatsu. It seems the paint helps form some sort of seal. New jet ordered for tohatsu

thanks

shaun
 
It does have a filter above the tap and it is very easy to miss as it is only vaguely mentioned in the handbook. It caused me running problems last season...
 
[ QUOTE ]

However the symptoms you describe are those of a dirty slow running jet.


Completely stripped and jets cleared by poking a soft copper wire through them?


[/ QUOTE ]
1. Agree - probably blockd jet.
2. NEVER, EVER poke anything through jets. Use high pressure air blast ONLY.
 
[ QUOTE ]
NEVER, EVER poke anything through jets. Use high pressure air blast ONLY.

[/ QUOTE ] Generally people dont have a high pressure compressed air supply in their homes. The only way then is to clear the jets with something that wont damage them. Therefore use a soft copper wire.
 
Sorry you are wrong, all the old thumble thumb mags used to go on about not poking owt thru jets. After 50 years of fixing things, both professionally and as a hobby, I know that judicious use of a wire brush wire will clean varnish and gum out of jets that have failed to respond to compressed air. Note the word judicious!
To the poster, take the carb apart again, pull a wire out of a wire brush and use it on the main jet CAREFULLY, plus look for the inlet of the pilot jet/s and the passage ways for it. Sometimes they get blocked as well and can cause the symptoms you describe
Stu
 
Good engineers are capable of using any tool to fettle machinery. I mean to say a file in the wrong hands can wreak havoc, but in a skilled pair of hands can create a square from a chunk of mild steel that is within 1 thou tolerance. So sweeping statements such as yours dont mean much!
Now quit while Im ahead!
/forums/images/graemlins/laugh.gif
Stu
 
Are you sure its a mixture screw you're turning? The Mercury/Mariner engines don't have one - the only screw is for idle speed and the mixture is set by the position of the needle on the throttle slide. Everyone say the Tohatsu is the same engine, but I've not looked at one myself.

Have you checked float height?

Edit - quick check for fuel starvation, undo the drain screw in the bottom of the carb, then turn on the fuel tap and make sure you get a continuous flow of fuel. I've seen blockages on bike where the fuel seems to flow OK, then drops to a dribble after a few secs.
 
Sounds like a blocked main jet to me. If you're sure it's clear, then check that the circlip hasn't come off the main needle (highly unusual), and that the float needle is correctly located on the float arm - not sure about this motor specifically, but some have a plain tab on the float arm that bears on the float needle, but some have a little fork on the float arm that needs to slot around the end of the float needle - if you're not careful on reassembly of this type, the needle rides on top of the fork, so giving too low a float level).

At the risk of causing annoyance, I would also recommend against poking anything through a jet to clean it. I know that VIc and I have agreed to differ about this in the past /forums/images/graemlins/smile.gif Hasn't everyone got a bike pump?

Andy
 
[ QUOTE ]
VIc and I have agreed to differ

[/ QUOTE ] I must admit I have only ever had to do it once. the idle jet of a Bing carb on an old Volvo Penta outboard. Came back after being loaned out for a year with the jet partly blocked due, I think, to having got water in somehow. Same symptoms that started this thread; would run at high speed but only idle if choked. After several attempts to clean it I resorted to a wire. That sorted it but but but I would only ever use a soft wire ( fuse wire in this instance) not a steel wire from a wire brush. Seems to me to be the sensible compromise between the "never poke anything through" camp and the "use a wire from a wire brush" camp.
A bristle from a nylon brush might be another sensible compromise but in the case of my Bing it would not have been long enough.

Anyway the OP has apparently sorted the problem by changing the needle valve. I cant explain!. It would either have shut properly, and given no problem, or let by resulting in flooding, in which case the choke would have made matters worse. Perhaps it was sticking shut, but then would it have run properly at high speed?
 
It is certainly a problem with the pilot jet passage.
Not the main jet from the symptoms described.

Ref the use of soft wire or the hair of a wire brush to clear jets and passages.
I have used this method for 40 years or more.
The same as I did last week to cure a tickover prob with a Yamaha 'Malta' outboard.

If anyone has this prob and has no access to a compressed air set up with a fine 'jet' of air the solution is as follows.
Take the offending object to your nearest motorbike mender guy.
He will have the kit.
Mopeds/scooters suffer the same probs and these guys know how to deal with it!

The fact that shaung has to mess with the choke proves the prob.
If it was a main jet prob the motor would tick over ok.
Main jet is redundant until the throttle is tweaked!

Rule of thumb with mixture screws.
Well not actually mixture screws with these little engines.
What yer have is a pilot air screw.
Turn the sucker in till it stops, gently like, then out one and a half turns.
This will do for starters.
a tweek a quarter of a turn either way will fine tune.
Choke should only be needed for 2 mins max normally.

Basically scewing the pilot air screw out lets more air in and vice versa.
Screw in and the motor will eventually 'choke up' , screw out and she will'race' then falter, get 'wooley' and more throttle will have to be applied to keep her running.

If the motor will eventually tick over normally but will not 'rev up' ie go onto main jet then the prob is different.

Then we are looking at a fuel delivery prob.
Main jet or indeed a blocked fuel filt as mentioned.
 
[ QUOTE ]
It is certainly a problem with the pilot jet passage.
Not the main jet from the symptoms described.


[/ QUOTE ]

I read the problem as the engine not 'revving' rather than not ticking over....

[ QUOTE ]
10 mins to warm up whilst gradually reducing to 1/3 choke, engine ticks over fine.

rev the engine with 1/3 choke and she struggles for power, redue choke and she stalls so she is not flooding, increase choke to 2/3 and all is well.

[/ QUOTE ]

But hey-ho, let's hope he's solved it as VicS says. (Which 'needle valve' was it? If the float needle, then maybe it wasn't engaged properly on float arm, so giving low fuel level in the float bowl?)

Andy
 
Mistreg has got it right, essentially the engine would not rev unless the choke was increased. The tohatsu engine only has 1 needle. replaced the needle and had it running for an hour last night without any choke and revved really well.

I do not know what is wrong with the needle that was in there as when placed in the other carb that one ran well also

as for compressed air, i don't have a compressor but working in IT i have a coupld of cans of compressed air used for cleaning. these can be bought in any staitoners

thanks for all your help
 
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