Engine broke down at sea today :( Need some help

[mctaggart]

Hi

(just to bring you up to speed on my engine specs)

Mercury 2001 75hp 2 stroke, 3 cylinder.

Been out of the ribbing scene for a few years but have got back into it this week by purchasing a new one Was very happy with it for the price and shes been looked after, or at least so i thought!

I had been looking for a while for somthing that was supposed to be reliable and thought i found it when i purchased below from Newcastle.

eBay - The UK's Online Marketplace

Checked it all over and it all seemed great, purchased it for £4450 and couldnt wait to take it out today for its maiden voyage around Swansea coast, I had noticed on idle with the muffs on that that every now and then the engine would misfire, but just put it down to it being 2 stroke as the idle can be more erratic than a 4 stroke. I had also compression tested the engine on purchase and it had about 138psi across all 3 cyclinders all within 1psi of each other so thought that was spot on.

So we had been out for about 2 hours and on the way back about 1km from the slip the engine started to develop a intermittent misfire, which then turned into a serious one. I heard a loud pop sound from inside the engine cowl and then there was a distinct patter sound followed by very rough running (sounded like an exhaust inside the casing). We took the engine cowl off and noticed that a pipe had literally exploded and the air pressure was being blown from the pulse pipe on the fuel pump. When it was misfiring it was backfiring through this small pipe. I have included a video and photos below.

We managed to limp back with the engine running terrible, we were glad we were not any further out.

Can anyone explain to me what has happened! I am well miffed on my first day back out!!

You can see where the backfiring gasses have actually melted the sound proofing inside my cowling!!



This is the fuel pump, fuel in the bottom with the oil and it goes out the top, the other pipe which is the one which were all this pressure is coming from is the "pulse pipe" acording to the manual. When the engine is running there is a significant amount of air pressure coming out of this hole on the block. Is this normal, also when it was back firing, it must have been igniting the fuel mixture that was in this pipe! (you can see it melted the pipe inside and split it open)



Here is a video also

VIDEO0016 - YouTube

Can anyone shed any light on whats happened, i need to replace the pulse pipe as its shattered the fittings so i cant repair it, but i dont think this is the sole problem. Your thoughts would be appreciated

Thanks
Craig

[Peter_C]

Got a picture of the plugs? Keep them in order! They have a story to tell, and should show which cylinder is the problem child.

Compression test after the damage was done?

[9D280]

I can't see the pics, but form your sdesctription it sounds like the pipe that connects the fuel pump to the crankcase ruptured, taking part of the palstic fuel pump with it?

If so, sounds like a replacement pipe / new might be in order. In whiohc case replacing all might not be a bad idea, as if one has ruptured, chances are the rest might not be too far behind....


Apologies if I've misunderstood the failure.

[mitchc]

A very quick diagnosis....
It looks as as if the vacuum feed hose from crankcase to fuel pump has failed.
Simply put, the crankcase depression pulse operates a diaphragm to pump the fuel to the carbs.
It looks as if this vac pipe had split. You will then get a fuel/air mixture being pumped out of the block. Replace the split hose and spigot on the fuel pump and all should be well. The hose has probably just perished with time.

Good luck.

[uncle al]

this is a common problem when you are running to weak a mixture, set all three mixture screws to one and a half turns out from lightly seated, ignore the service manual on these settings , and you will find that when you tilot in so that it is tucked under it will have a not very good tickover that is normal.Also check the union in the cyl block as they get a hole blown in them as well, check your timming and if it was mine I would replace the fuel pump repare kit

[mctaggart]

thanks for the replies, compression tested after and it was the same as before, all 3 plugs were black and oiley the same as when i first looked before this happened, shouldnt they be a tan brown colour?

The pipe has melted and not perished which is why its split, high pressure gasses were being ignited inside this pipe, when the pipe is off there is hell of a lot of air being pushed out that hole, i.e you can feel it a foot away with your hand easily, is this normaL?

i have inspected the fuel pump and the diaghrAM is all ok inside, although just replacing the pipe i dont think is going to fix it. i need to solve this backfire problem which is coming backup that pulse pipe.

[uncle al]

No the pump diapghrams now have a question mark over their integraty because of the heat, I stand by my comment to fit a fuel pump repair kit, I would also make sure that the spark plugs are the correct ones (ngk something -2)and make sure your carbs are syncronized at tickover

[dougcrock]

go with Uncle Al
he is the man with the know how

[mitchc]

Originally Posted by mctaggart

when the pipe is off there is hell of a lot of air being pushed out that hole, i.e you can feel it a foot away with your hand easily, is this normaL?

i have inspected the fuel pump and the diaghrAM is all ok inside, although just replacing the pipe i dont think is going to fix it. i need to solve this backfire problem which is coming backup that pulse pipe.

What you are feeling is the crankcase pressures created in conventional two stroke engine. When the piston is on the down stroke it forces the fuel/ air mixture from the crank case through the transfer ports into the cylinder.
I doubt if you have a timing issue.
If it was mine I'd replace the split hose and run up the engine. Once you fix the split hose, fit new plugs so you have a clean sheet as to how the engine is running.

Re the black and oily plugs, is it shiny and smooth or crusty and lumpy. Could be over oiled or ignition issues depending on the answer. Google NGK two stroke spark plug colours for more info.

Replace the pipe, run up the engine and work from there.

[BumbleAbout]

a) Listen to Uncle Al - he knows what he is talking about!
b) Phone up TuboDiesel (highly recommended member on here who offers a RibNet discount and mail order service - contact details here http://www.rib.net/forum/members/turbodiesel-1371.html) to order the replacement hose and fuel pump diapghram kit (and possibly spark plugs)
c) Listen to Uncle Al ...

[uncle al]

thanks boys

[EnglishLes]

See UK Karting - Notice Board (2-Stroke Karting) : TKM pulse pipe. these boys also have problems with pulse pipes.

[mctaggart]

Thanks again for all the helpful replies, i didnt expect such a welcoming response, I am glad you have mentioned a parts supplier, i have been finding it difficult online to find one, so i will ring him today

I have got quite an in depth knowledge on engine building (I do race cars) buts its been years since i turned my hand to 2 strokes, last time i did it was motorbikes in my youth! These outboards look a bit more complicated, but i guess in practice 2 strokes are all the same.

I'll get the parts ordered then with a new pulse pipe and diapghram kit for the fuel pump, plugs etc and go from there.

I'll report back with my results.

[mctaggart]

Just spoke to him at blackdog marine and hes confirmed what Uncle Al's said, the engine was doing what he called "sneezing" which it had been doing intermittently and its blown that pipe off.

So need to reset the carbs and then the check timing

Thanks all!

[Kernow Buoy]

Welcome to Ribnet, you'll be pleased to know we spoke about your boat when it was on ebay!
here's the thread
http://www.rib.net/forum/f8/new-to-this-game-47626.html

[mctaggart]

Its a very clean rib, having it retubed in 2009 has definetly made a huge difference. Upon purchase and inspection I was really happy with it and paid a great price for it at only £4450, knocked him down from his original £4800 figure.

However upon getting home I have noticed a few things wrong with it which i didnt pick up on on viewing which was slightly anoying, in particular.

1. The onboard VHF radio for some reason can only receive incomming transmissions, it doesnt work when it transmits. Tested the mic and everything and its just dead completly with no output. So no biggy on that really but it would have been nice to been told!!

2. The bilge pump was knackered so i have ordered a new one

3. The rev counter doesnt work

4. Dropping the gearbox oil, it was milky as hell so its been contaminated with water. I noticed there were no gaskets on the screw holes for emptying/topping up, so potentially leaking there.

5. The engine blew off a pipe the other day and is sneezing badly at the moment so needs the carbs setup.

Aside from the above points lol its a lovely rib, I just need to spend maybe £200 on it to get it back to its former glory so all in all I think I am going to have a great summer!

[chewy]

The VHF may have never been used in anger so he might not have known it was fooked?
Looking at the RIB I'd say you did alright.

[TomKat]

As I have the same engine please update when you have it fixed, one more thing to worry about! On mine the stator went with less than 20 hours use. I am sure yours has the new red one but if not carry a spare engine as its apparently not a question of if but when...

[mctaggart]

A big thank you to www.blackdogmarine.com for getting me the parts in less than 24hrs, i ordered them 1 oclock yesterday and they turned up at 9am this morning, how is that for service!

Parts cost about £8 so hoping this is going to be a cheap repair once i have set the carbs up and checked the timing.

[TheMadMariner]

Yep, I recognise this. Always wondered where that burned spot came from;
One of the the previous owners of my 40 Merc also suffered the very same. Pipe from the same type of fuel pump blew out and burned + also made a small crack in the hood, glad you were more vigilant than he was...

I guess it was the retarted timing on mine..
Mercury was testing new TPM modules early 90ties to replace need of a rotating trigger, and somehow improving the ignition. The TPM went to crap, and not just mine I guess, as they dropped the TPM ignition just 2 years later