Blackmax 200 spraying fuel

dsiekman

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I was doing a compression test this weekend as I am trying to determine why I am not reaching max WOT. I recently downsized my prop with very little impact - see the post in the prop section. Anyway, I had the cowl off the engine warming it up and noticed it was spraying fuel from what I assume would be the gasket between the carbs and manifold. Right onto the starter and other electricals. Awesome. Very quickly shut down and dried everything before doing my compression test.

I did not have a wrench to access the bolt around which it seemed to be leaking around. This was the only spot it seemed to be leaking from. So, do you think I am going to need a new gasket? Just a loose bolt? Could this be causing my lack of top end? Compression tested 100-110 across all six with a warm engine. Not sure if that is good or just passable with a warm engine.

I also found my idle issue. It liked to stall after a couple of minutes of idling and ran very rough. The exhaust bypass was stuck against the inside of the cowl and not allowing the exhaust to exit as it should. With that straightened out and the cowl off it ran just fine. I'm assuming it was a combination of too much backpressure and the intakes sucking in exhaust.
 

Chris1956

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The intake leak is likely to affect performance at low speed. It could affect high speed performance as well, but this is more rare. I would replace the carb base gasket, as they are cheap and it will save time.
 

dsiekman

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The idle is a little rough. I'm debating how much effort to put into this motor as I'm supposed to have a 4 stroke rebuilt this winter - the boat isn't worth a new motor. Obviously I have to fix the fuel issue before I can use it again but I'm not sure it is worth much more effort...unless the rebuild doesn't work out
 

dsiekman

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I watched the video in slow motion on a larger screen. It appears as though the fuel is actually coming from between the block and the manifold where the reed valves are. It also seems to be coming out under pressure which doesn't make a lot of sense to me unless it is blowing out past the reed valve and/or gasket as the piston comes up. If I understand 2 stroke function, which is questionable, as the piston goes down it is drawing in fuel and creating suction. In that movement I would think it would be sucking air and creating a lean condition if anything, not spraying fuel. Then on the compression stroke the reed should close, so the fuel beyond the reed should never be pressurized, right?
 

Chris1956

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Wow, that is a lot of fuel. I presume it is not water?

The only way to get that much liquid fuel in that ares is with a bad fuel pump diagram, I would think. If that is not the issue, and the crankcase cover bolts are tight, you need to look for a crack in the block, likely near or on the crankcase cover.
 

Chris1956

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On the other hand, check the enrichener solenoid and hoses for a leak as well. I think it is likely on that side, whereas the fuel pump is on the other side.
 

dsiekman

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Wow, that is a lot of fuel. I presume it is not water?

The only way to get that much liquid fuel in that ares is with a bad fuel pump diagram, I would think. If that is not the issue, and the crankcase cover bolts are tight, you need to look for a crack in the block, likely near or on the crankcase cover.

Yes it is a lot! I already had some fuel on my hands so I didn't smell it but it felt very slippery.

It is hard to make out in the video, but it appeared to me to be coming from the joint between the block and what I would call the intake manifold. Like I said, I shut it down pretty quickly and I'm a little hesitant to start it up again. I will definitely have my extinguisher handy.
 

dsiekman

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On the other hand, check the enrichener solenoid and hoses for a leak as well. I think it is likely on that side, whereas the fuel pump is on the other side.

Top, bottom, and the other side were completely clean, so whatever it is is coming from just the one location. Is the enrichener solenoid the piece that looks like a very small fuel bowl?
 

dsiekman

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And the saga continues. Cut a hole in the cowl for the exhaust bypass. Engine is MUCH happier.

Found one loose bolt and one sheared off bolt. No more fuel leak. I also realized I have to push the throttle really far forward to get an increase in rpm. I?m starting to wonder it the cable is not adjusted right.
 

Chris1956

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Curring a hole in the cowling is not standard. You might look for an exhaust leak at the base of the powerhead, or an exhaust bypass hose, if you have one. My '93 Merc V6 has such a bypass hose. They can leak.

The sheared boat and loose bolt were on the crancase cover? Did you replace the sheared one?

What shape were the spark plugs? Was one worn or fouled?
 

dsiekman

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Curring a hole in the cowling is not standard. You might look for an exhaust leak at the base of the powerhead, or an exhaust bypass hose, if you have one. My '93 Merc V6 has such a bypass hose. They can leak.

The sheared boat and loose bolt were on the crancase cover? Did you replace the sheared one?

What shape were the spark plugs? Was one worn or fouled?

No, certainly not standard. My understanding is that the upper cowling is a slightly different vintage than the leg. There was no opening for the bypass hose so it was just pressing against the inside of the cowling and then filling the cowling with exhaust. At idle when not moving it would choke itself out. I used a small hole saw to drill a roughly 1" hole for the bypass hose. With no load it wants to idle near 1200 rpms. In gear in the water it is about 750 rpms.

That would be my assumption. The lower half of the bolt is still lodged in place. I lost the head and maybe top 1/4". To replace it will likely mean pulling the carbs. I am going to assume it has been that way for some time, so I will deal with it this winter when I pull the boat.

The plugs did not look bad to me. No obvious evidence of fouling that I saw. Insulators were brown, all were a little wet after running, but no other signs.
 

Chris1956

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Well having an idle bypass hose, with no outlet is a new on for me.......That hose would starve the motor for O2 at all speeds. Maybe the reason for RPM increase after you fixed it.

Try a left handed drill on that broken bolt. It may just screw out......
 

dsiekman

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Well having an idle bypass hose, with no outlet is a new on for me.......That hose would starve the motor for O2 at all speeds. Maybe the reason for RPM increase after you fixed it.

Try a left handed drill on that broken bolt. It may just screw out......

Yeah, it is a bit of a Frankenmotor. It was never intended to be on the boat this long. And I agree that it was certainly starving the motor. At idle out of gear I think I'm running a little fast. In gear I'm still fast but only by about 150 rpm or so, I think. It does make docking a little interesting.

I will definitely try that. The issue is getting the clearance to get in there. I have a set of screw extractors, but again I can't quite get there. I'm guessing that screw was stainless. It is awfully shiny for something of that vintage otherwise.
 

Chris1956

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The bolt is likely a good grade of steel, if original. Merc did not use much SS to assemble their blocks. I assume the bolt broke when someone tried to tighten it, not from corrosion, when someone tried to loosen it. If so, it could be pretty easy to remove. The left handed drill could replace the screw extractor. I never had any luck with screw extractors, as the bolts were too far gone. Once a screw extractor breaks off the bolt is really hard to remove,,,,,

Obviously the second choice is to pull the crankcase cover (and powerhead, cowling support, etc) and turn out the broken bolt with a vicegrip.
 

dsiekman

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It was a clean shear, so I agree that it was most likely over-tightened. It felt different. I'm not sure I can explain how. Not as light as aluminum, but different.
 

dsiekman

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Realized last night I have a trim issue as well. It is leaking down under load. That is certainly robbing me of speed and rpms.
 
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