Help with a 50hp blueband

[Procat78]

G'day guys longtime reader first time poster, any help would be appreciated I have a 50 hp blueband have a problem with wont rev/or pull the boat past 8 knots ,have had work done to it about 12 months ago, Carbis rebuilt and fuel lines replaced for a similar prob, I have replaced the throttle/gear cables and rebuilt the throttle control got all the free play out of it (thought it was that ). I just need the motor to go until the end of the year until I but a much newer one (had the money buy had a child going to high school and didn't think it would cost so much)

What I have checked
:I have spark at all cly
:All plugs are firing
:Comps are 120psi on all cly(with throttle closed)
:Checked Carbis when revving it they are giving out plenty of fuel
:No 1,2 and three plus have signs of fuel mixture on it
:No 4 spark plug has nothing on it at all
:Under load or idling pull no 1,2and 3 motor misses
:Remove no 4 lead makes no difference
From what I can figure out no4 is getting no fuel at all

Thanks guys if you can shed any light on it

Chris

 

[Arkyhunter46]

Re: Help with a 50hp blueband

This one is kinda weird if I understand you right. You have spark confirmed, compression, fuel from bottom carb and the plug is clean with no gas on it? That engine has two carbs that split between four cly.. The only thing fuel related that separates the cyl is the reed block on the crank. I have seen a few fail over the years but it is rare. I think I would first see if the reeds were leaking then take a look at the exhaust gasket to see if it is blown. Another possibility is the lower crank seal is out but that is rare as well.

 

[racerone]

Re: Help with a 50hp blueband

Check for crankcase compression. ----Could be bad reeds or something stuck in the reeds.-------Pull the powerhead off and inspect the bottom crank seals if reeds prove to be OK..

 

[Chris1956]

Re: Help with a 50hp blueband

Is the bottom spark plug real clean like it was steam-cleaned? If so, it is likely water infiltration into the cylinder. This can occur via bad crank seal, a hole in the exhaust baffle, a hole in the inner exhaust cover or bad gaskets on the exhaust cover or plate.

 

[Procat78]

Re: Help with a 50hp blueband

It looks to be like it's steamed cleaned as I can't find a serial number on my motor I can't get the workshop manual for it (can only buy from US and at $70 del per book wanted to make sure first)I can't find any info on how the motor flows internally , I am a mechanic buy trade but not much on outboards got a simple idea but can figure out cause in relation to the the problem
But when it runs have a lot of exhaust gasses coming from somewhere when I have the motor in a drum of water running not sure if it is right as this is my first outboard
Thanks Chris

 

[Chris1956]

Re: Help with a 50hp blueband

Procat, Flat plate on port side of motor is exhaust cover, under that is exhaust baffle and under that is inner exhaust cover. You can look up part diaghrams on the crowleymarine web site. Merc inline engines are all designed the same, so pick a year close to yours (early 70s) and take a look. I would not order parts, until you get real serial number, as there are some differences.

Crank seals are located in end cap on bottom of motor. Powerhead needs to be put on bench to fix either of these issues. Also, water jacket and inner water jacket cover bolts break all the time. if you plan to remove them, plan to use heat, penetrating oil and prayer to remove them intact. Curses are allowed after you break some.