Help me get my Yam 2B running again

[chris-s]

We’ve had this wonderful engine for five years, it’s never failed to start on the first or second pull, I’ve dug it out of hibernation and it’s no longer happy.

The first dozen or so attempts to start it felt ‘tighter’ than I recall. Never noticed this before, but now feels like it did last season after many starts/attempted starts.

It will run for a few seconds, how long exactly depends on how long I left it before retrying but never for more than four seconds. It will not fire with the choke on, this is different than before.

Almost certainly a fuel issue.

Fresh fuel, plenty of flow out of the pipe to the carb, fuel in the bowl, clean bowl, stripped the carb, not that there is much to it, nothing looked dirty or blocked but blasted it thru with carb cleaner anyhow. Checked the little o-ring that would be the inlet manifold gasket if it had one and made sure to give it a good push-home when refitting. Also fitted a new plug.

No difference to before. The only thing I haven’t yet tried is to squirt some fuel in the air intake as it starts to run.

Anything obvious I have missed?

 

[hurley]

Blocked fuel filler cap vent ?

 

[chris-s]

Blocked fuel filler cap vent ?

Nope, cap off.

 

[elenya]

Have you physically proved the jet by using fuse wire or similar to push through the hole? Doesn't take much to block or partially block.
I'll be interested to hear what finally solves the issue.
Best of luck

 

[jamie N]

Somebody will be along soon to suggest that the float and its needle aren't right, and that the float height might need checking. Good luck, it'll not take you too long.

 

[chris-s]

Have you physically proved the jet by using fuse wire or similar to push through the hole? Doesn't take much to block or partially block.
I'll be interested to hear what finally solves the issue.
Best of luck

I removed the jet and could clearly see thru all the holes before using any carb cleaner.

 

[chris-s]

Somebody will be along soon to suggest that the float and its needle aren't right, and that the float height might need checking. Good luck, it'll not take you too long.

That was my first port of call. It’s not adjustable on this carb and all looks clean after removing it, didn’t appear to be sticking and blasted thru with carb cleaner anyhow.

 

[Poignard]

I was going to suggest checking the fuel filter attached to the fuel tap , because I had the same symptoms with my engine when the fuel filter was blocked, but you've said there's plenty of fuel flow so that knocks that idea on the head. Sorry.

 

[Boathook]

I'm wondering why it felt tighter when trying to start it than last year. Doesn't take much extra resistance to stop a 2 stroke from running as I found out with my malta a few years back.

 

[chris-s]

I'm wondering why it felt tighter when trying to start it than last year. Doesn't take much extra resistance to stop a 2 stroke from running as I found out with my malta a few years back.

That’s in the back of my mind too, but I can’t work out how that explains the behaviour I’m now seeing, where if I try to start it immediately after it stops it barely fires, leave it a couple of minutes and it will start right up and run for three or four seconds, leave of for less and it will start but run for less time. That’s a fuel issue.

Thanks for all the replies, doesn’t look like I have missed anything obvious or a hidden trick with this old engine. I’ll strip the carb again and take another look.