Noisy at low speed

[Smagu]

Hello my 1994 Yamaha 2 stroke was running perfect then became very noisy and clanky at slow speeds.

I changed the oil seals on the prop which needed done and noticed when in forward gear I can spin the prop relatively easily as if the dog clutch isn’t engaging.

The boat still goes normal full speed and runs well at this. It’s only when just off neutral and going slowly.

I’ve posted some links below of what it’s like. Not sure where to start on this one. Any advice?

Boat running

[Smagu]

Turning by hand when in forward

https://m.youtube.com/watch?v=lduqva7ul_U

[Smagu]

Another running video

https://m.youtube.com/watch?v=7i7Ap76hjn0

[A1an]

Almost impossible to diagnose from a video but it definitely sounds like it’s missing badly off power. Middle video is perfectly normal.

[Smagu]

Originally Posted by A1an

Almost impossible to diagnose from a video but it definitely sounds like it’s missing badly off power. Middle video is perfectly normal.

That’s great news middles normal. Am I right in thinking I’m looking at a misfiring/ carb issue rather than a slipping dog clutch/ lower leg issue (which I though). Sorry if I’m way off just trying to work out where to start trouble shooting

[A1an]

The miss can be several things from lack of fuel, too much fuel, electrical issue.

Where in Scotland are you?

[Iankristy]

David Anderson marine(Newport on Tay) is the man for all things yam [emoji106]

[Smagu]

I’m currently living in portstewart. Can’t find anyone to work on it. They either won’t take it as it’s too old or they didn’t sell it. Or they are too busy for new customers. I’ve taken it to two other people (for separate issues). Both have been cowboys and I’ve ended up redoing the job myself.

I’m enjoying working at it. Great way to learn things about the engine and could help get me out of trouble. It’s the learning where to start that’s the biggest issue! But without this forum and the help from some folk at the marina I’d have done no boating this year

[TmMorris]

How do all the spark plugs look?

If it runs rough at low rpm but on fuller throttle is running OK then the state of the plugs might give you a clue as to what sort of issue you have.

If it were me, my first checks would be to look at the plugs and to also confirm that the throttle is opening all the carbs simultaneously.

If you have one plug that is clearly different from the others then it may be getting a weaker spark or it could be that the carb linkages are out of whack and one carb is getting opened differently to the other.

If both carbs are moving identically then it may be that one has the wrong idle mixture. If it is that then you'd expect the engine to be fine on throttle. If it's still a bit rough on throttle and you can check the fuel flow is ok then it might push you to consider the spark.

[A1an]

Check rear diaphragm on fuel pump. Whip the pump off but keep all pipes attached, squeeze primer bulb and if fuel comes out the small hole on back of pump then this could be your issue.

[TmMorris]

Originally Posted by A1an

Check rear diaphragm on fuel pump. Whip the pump off but keep all pipes attached, squeeze primer bulb and if fuel comes out the small hole on back of pump then this could be your issue.

Yup. Of all the plugs look to be in the same condition the.n general curling followed by general electrical would be my simple starting point.

[Smagu]

Just back from the boat today. Put new spark plugs in and went for a quick 10 minute spin (same symptoms)

I’ve attached some photos of plugs. Top plug looks darker than the rest. Bottom plug appears the cleanest. Not sure if much can be learned from them after such a short period. Going to rebuild the carbs (last done 5 weeks ago. Although there is some residual dirt in the system which the double filters may have missed)

Top photo top cylinder working left to right