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Old 16 May 2012, 17:57   #1
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Engine problems today :( Need some help

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
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Old 17 May 2012, 02:12   #2
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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?
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Old 17 May 2012, 04:12   #3
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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.
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Old 17 May 2012, 04:14   #4
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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.
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Old 17 May 2012, 04:16   #5
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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
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Old 17 May 2012, 04:36   #6
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engine

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.
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Old 17 May 2012, 04:40   #7
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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
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Old 17 May 2012, 04:53   #8
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go with Uncle Al
he is the man with the know how
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Old 17 May 2012, 04:55   #9
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Quote:
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.
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Old 17 May 2012, 05:35   #10
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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 ...
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