Yamaha 8hp Running problem

[ontheplane]

Hi there,

Have an older (90's) Yam 8hp outboard 2cylinder, 2 stroke outboard.

She will start very easily - pull choke out, prime bulb, throttle open to the "start" setting (about 50% throttle), couple of pulls and she starts.

However no matter what I do she will not run below around this 50% throttle setting. This means I can't really put her into gear, as it could damage the gearbox. If I turn the throttle gently down, she'll reach a certain point (just below the "start" position) where suddenly it will just die.

If I "Blip" the throttle it will catch (sometimes) but fundamentally it won't run under 50% throttle.

On the throttle, I can feel a slight resistance just below the 50% throttle position, and I wonder if this opens a second jet or something, and if the low speed jet it blocked or something??

Any ideas guys?

Thanks

 

[VicS]

[ QUOTE ]
Have an older (90's) Yam 8hp outboard

[/ QUOTE ] Older? what 1890s?

Without much doubt it is the slow running jet in need of a clean. Not familiar with Yammies so cannot offer any guidance. May need poking through with something that wont damage it.

Pumping the bulb does not help? will it run if choked?

Parts diagrams here http://yamaha.part-motor.com/?ls=outboard

(I know its a US site but don't know of a UK one)

Cant offer workshiop manual but need a link to the owners manual?

 

[Kawasaki]

yam prob

The pilot air jet is blocked.
If you are capable of sorting it out do so.
If not take the carb off and seek out someone who can.

I have mentioned this before for peeps.
Your local motorbike mender will cope.
The bike lads who fettle mopeds and the like, come across this snag all the time.
Will have the tools and knowhow to strip and clean said carb.

You could drain the fuel bowl, check the float level, etc etc etc .
But she starts easily as you mention.

OR!

If it is a really worn out unit.
It does sound like this a she starts so well!

 

[ontheplane]

Re: yam prob

So if I whip off the carb, and just clean everything out with some wire, carb cleaner etc, then all should be well??? Hurrah.

Only ever stripped Car carb's down before - and they are a lot bigger - is there much difference??

Will I need a new carb gasket set or will I only need it if one of the gaskets breaks?

Thanks guys - good advice as ever...

 

[ontheplane]

Re: yam prob

Thank you thank you thank you all

Carb came off, stripped apart, blasted through with carb cleaner in every orafice - full can used!

Re-assembled, petrol plugged in, primed bulb, pulled three times gently to pump fuel through to the carb, gave it two pulls and it fired beautifully....

Now runs perfectly across the rev range, will drop in and out of gear at tickover without stalling, and accelerates smoothly.

Total cost £4.00 for a can of carb cleaner.

Also bought two new spark plugs, but I'm not sure she needs them as runs as sweet as a nut - might fit them anyhow and keep the old ones as spares.

Now Question:- In reassembling the carb, I accidentally turned a screw that had a spring on it, but wasn't connected to anything and looking at the side, it just seemed to go into the body of the carb, however there was a hole that it may cover if you turn it in completely. I think I turned it back to exactly where it was, but in case I didn't, anyone any ideas what that might be - my guess is a mixture screw, and if so, is it best to adjust that at full throttle until the engine seems to reach max speed? If that isn't the best way, how do I set the mixture to optimum.

Thanks all

 

[Kawasaki]

Re: yam prob

The screw with the spring on is the 'tickover' screw.
There should be another screw with no spring.
The 'no spring' screw should be screwed in gently till it stops.
Then unscrewed one and a half turns as a datum as it were.

Start the engine and adjust the 'spring screw' in and out to get a nice idle.

When you are confident that the engine is idling consistantly.
Adjust the pilot jet airscrew.
Turn 'in' to richen and out to 'weaken'

As you turn in the eng will choke and die if too far in.
As you turn out the eng will quicken a bit and finally race and stall if too far out.
Combine the two adjustsements to find a nice idle speed and reliable tickover.

Tiss hard to explain in words.
Best I can do!!!
.

 

[ontheplane]

Re: yam prob

Ah ok thanks.

I adjusted the idle using the screw which seems to be a throttle "stop" - I didn't see a screw without a spring.

Will have another look tomorrow or at the weekend, but as it seems to be running nice, i may not fiddle too much!