Unhappy Yamaha 25.

cleland72 · 04 August 2013, 20:13

So Saturday was the first outing of the new inflatable (Bombard Aerotec 420) with Yamaha 25hp 2-stroke (built around 2000). The engine's been running fine in a bin of water and started out fine on Saturday but a mile or so up the Deben, power seriously dropped so that WOT was making maybe a couple of knots and the engine sounded like it was really labouring. It kept running long enough to get us back without paddling but as soon as I got off WOT the engine would cut out.

Had a play with the engine today in the bin of water and it's still messing around - very hard to start (was fine before yesterday) and cuts out shortly after starting. Started easily enough with a sniff of ether but then died as soon as the ether was burnt. Checked the fuel filter in the engine and it was clean, gave it a clean anyhow and the filter on the dip tube in the tank was clear as well. Pulled the plugs and they seem fine - dry, light tan on the insulator, slightly oily on the body and no smell of unburnt fuel. No obvious signs of distress on the CDI coils or HT leads.

So my guess is a fuel problem, maybe blocked jets due to dirt, although I'm not sure where the dirt would have come from, everything looks clean. One thing I noticed is that I couldn't get the bulb on the priming pump on the fuel line to go hard when connected to the engine. Playing around with it off-engine it would go fairly solid if held upright (outlet up) but not if horizontal - fairly sure that's not right and probably a stuck non-return valve, but would this cause engine problems (bearing in mind the fuel filter in the engine was full)?

Failing that I'm going to have to take the carbs off and clean them, but before I do that I'd like a service manual for the engine so I can get the settings right after I put it back together again. Is this available online somewhere or can it be bought?

Cheers,

Andrew.

Barrowboy · 04 August 2013, 20:22

I'd humbly suggest that air is getting into the system. What's the condition of the fuel line upstream from the bulb? Maybe a thorough check of the integrity of the hose and the connections before setting about the carbs....

ShinyShoe · 04 August 2013, 20:28

Fuel pump diaphram?

cleland72 · 04 August 2013, 20:28

Quote:

Originally Posted by Barrowboy

I'd humbly suggest that air is getting into the system. What's the condition of the fuel line upstream from the bulb? Maybe a thorough check of the integrity of the hose and the connections before setting about the carbs....

Looks pretty decent, although I haven't particularly looked for air leaks (no fuel leaks though!) but you're right - I'll happily replace the fuel hose and bulb pump before I start mucking about with the carbs (said things being frankly hateful devices anyhow).

Cheers,

Andrew.

cleland72 · 04 August 2013, 20:29

Quote:

Originally Posted by ShinyShoe

Fuel pump diaphram?

Possibility - is it fairly obvious to find? Between the filter and carbs I imagine...

A.

ShinyShoe · 04 August 2013, 22:10

Looks like there is more than 1 c.2000 25HP 2 stroke Yammie... but here's a possibility of what you are looking for:

Part 1 is the pump. 9 is the diaphragm

ShinyShoe · 04 August 2013, 22:22

Oh and what happens when its badly running and you try and prime the fuel line? If it improves its more likely a leaky line or the pump than the carb...

Festinghouse · 05 August 2013, 06:21

some primer bulbs only work when upright - i was told its because they have a ball inside which sits in and so seals against a hole. crap idea if you ask me!

cleland72 · 05 August 2013, 08:24

Quote:

Originally Posted by ShinyShoe

Looks like there is more than 1 c.2000 25HP 2 stroke Yammie... but here's a possibility of what you are looking for:

Part 1 is the pump. 9 is the diaphragm

Thanks, that's useful. It looks like it's not quite the same engine as the fuel filter is different - mine's a vertical one with a filter bowl that can be unscrewed to get muck out of the bottom. Fuel pump's probably not dissimilar though. Looking at the id plate on the engine I think it's a 25NMHO.

re. trying the pump while the engine's running - I didn't try that, it would be tricky as it literally runs for a second or two before it dies, maybe I'll rope in my young assistant to squeeze the pump bulb (or maybe try to raise the fuel tank above the engine).

Cheers,

Andrew.

cleland72 · 05 August 2013, 08:25

Quote:

Originally Posted by Festinghouse

some primer bulbs only work when upright - i was told its because they have a ball inside which sits in and so seals against a hole. crap idea if you ask me!

Yes, I can hear a little ball inside, so it may be that. You'd have thought they might have heard of springs eh!!?

Thinking about it though, the pump was 'going solid' when I tried the engine before the problems started. I may have been holding the bulb upright by coincidence though...

A.

Fenlander · 05 August 2013, 09:00

It does sound like extreme fuel starvation.

I don't know what sort of bits you have in the garage but I'd quickly rig up a very small amount of fuel in a "header" tank (something like a car gear oil container would do) just with a short hose onto the outboard connector, no primer bulb. This will confirm if you have a tank/hose/primer issue or if it's the outboard.

One of the things I always carry on the boat is a full length spare fuel line complete with primer bulb and clips to fit.

I assume this is the 25hp bought from Peter? Did the tank and line come with the outboard? He seems a very decent guy, have you asked him for ideas?

cleland72 · 05 August 2013, 09:25

Quote:

Originally Posted by Fenlander

It does sound like extreme fuel starvation.

I don't know what sort of bits you have in the garage but I'd quickly rig up a very small amount of fuel in a "header" tank (something like a car gear oil container would do) just with a short hose onto the outboard connector, no primer bulb. This will confirm if you have a tank/hose/primer issue or if it's the outboard.

One of the things I always carry on the boat is a full length spare fuel line complete with primer bulb and clips to fit.

I assume this is the 25hp bought from Peter? Did the tank and line come with the outboard? He seems a very decent guy, have you asked him for ideas?

I should be able to jury-rig something to try a gravity feed fuel supply and see if that works out.

I've found the parts catalogue for the engine and the fuel pump assembly, which I think should be easy enough to get to if need be.

It is the engine from Peter, I may well ask him for advice but I've already made extra work for him (the delivery lorry reversed into our neighbours car and then drove off!), so I'll try to sort it out myself first - typical stubborn bloke syndrome!!

Cheers,

Andrew.

Locozodiac · 05 August 2013, 19:14

Go for a test spin, when engine starts dying, prime bulb several times, if engine catches rpm again in most cases iit's a faulty fuel pump diaphragms condition. Is carb inmaculate clean ? You could have dried 2 strokes oil residue on internal carb paths that reduces the required fuel amount for engine to run properly.

Happy Boating

cleland72 · 08 August 2013, 20:56

Developments....

I ordered a new fuel hose and primer pump and gave the engine another shot this evening. At first the priming still felt 'soft', although the fuel filter bowl was full. I removed the fuel pipe where it went into the fuel filter and tried the primer pump again and fuel was coming out happily. Reconnecting that pipe to the filter mad the priming felt much better and the bulb went hard. Maybe an airlock?

Anyhow, the engine still wouldn't start, not a sniff of a fire, choke in or out. Next I tried putting the fuel tank on the garage roof which have a good meter or so of gravity head. Now the engine started quite easily with the choke fully out, raced a bit then settled down to a fast idle. Pushing the choke in and it died within a couple of settings.

I was then able to put the fuel tank back at ground level and it still started on the choke but died after the choke was put in. You can see this behaviour on this video:

http://www.youtube.com/watch?v=4xGhmlP6xuk

It does this consistently now - choke out, starts; choke in either doesn't start or if it is running it dies.

I guess the next thing to look at is the fuel pump, if only because it's not too tricky to get into by the looks of it...

ShinyShoe · 08 August 2013, 21:07

So if you leave it on choke a bit longer and then creep the choke back in? So maybe 1/4 of the way in and wait 30 seconds then another 1/4 etc?

Clean fuel?

But my gut is still on the pump. When you moved the tank from the roof to the floor have you released any pressure - disconnected fuel line and opened filler cap on tank?

Nos4r2 · 08 August 2013, 21:13

Blocked jets. Carbs need a strip/clean.

That's not running for long enough to empty the floatbowls so it can't be the fuel pump-particularly as the gravity feed made no difference.

PeterM · 08 August 2013, 22:34

Quote:

Originally Posted by Nos4r2

Blocked jets. Carbs need a strip/clean.

That's not running for long enough to empty the floatbowls so it can't be the fuel pump-particularly as the gravity feed made no difference.

+1 had exactly the same on a 30 yam. Cleaning up the carbs fixed it.

If it's running with the choke out it seems to me the mixture is way too lean without the choke cutting out some of the air...so blocked jets would be my guess.(maybe dirt or grit or something come loose when in transit and found its way to jets?)

cleland72 · 09 August 2013, 08:55

Yeah, I had a feeling it would be the carb jets. My first bike (Suzuki GN125) had very similar problems when I got it and that was obviously because it had been left sitting with fuel in the tank for the best part of 10 years - rusted tank and gummed carb. Took about 4 strip downs and rebuilds to get the carb clean.

I've found a service manual (http://www.mdmotors.ru/netcat_files/216/180/20d_25n.pdf if anyone needs it) and will give it a go, but it's going to have to wait until September now, as it's holiday time (luckily I wasn't planning on taking the outboard!).

Cheers,

Andrew.