Mercury 135 Blackmax

pgoodger04

Cadet
Joined
Aug 15, 2020
Messages
6
I have a a 135 Blackmax serial #0B104422 that I am at wits end. I have checked everything imaginable. I am going to apologigize in advance because this is long normally I only resort to posting on forums if I have exhausted all of my options.
I bought the boat and motor about a year ago and I have been wrenching and testing when and weather. I have a sealoc manual for this engine so here is everything that I have tested and fixed to this point. The motor starts great on muffs or out in the water. Hold the choke button in for a couple seconds and she pops right off no issues at all currently.
Here is the list of what I have checked and changed in the last couple of months
Changed water pump and gear lube, t-stats and poppet valve.
Compression in all 6 cylinders is 130.
New plugs, fuel lines, transfer port lines, filters squeeze ball. I currently have a water separator on order but it has not arrived yet
carbs have all been gone through as well as when the carbs were off I pulled the reed plate and checked the reeds over since this boat and motor were new to me and I didn't know anything about the maintenance. The only thing that I found on the Carbs were the float height was low. Manual says 1/16" below the bottom of the bowl while inverted. Don't know if this is right, but that is what I set them to.
The engine wouldn't rev over 3000 rpm out on the water. The stator ended up failing on the resistance values and DVA outputs. The trigger all tested out fine. I replaced the stator assembly with one from Sierra. After changing the stator did a complete link and sync and spark gap check and found out that cylinder #3 was dead. I performed a complete DVA and resistance check on switchboxes. Soooo..... replaced the pair of switch boxes. I now had a good fat spark on all six cylinders. When it is spark gap checked will jump 7/16 to .5 of an inch.
I took the boat out on the lake and she ran great up to 5000 rpm and then i shut it down to try and check the holeshot and it would not rev over 2000rpm and would not get the boat on plane.
I first thought I had an ignition problem again so I broke out the timing light in the middle of the lake. I still had fire on al 6 cylinders. I got my wife to drive the boat while I had the cowls off and the air box cover off. Cylinders 1,2,5,6 you could see fuel atomizing as it came out of the main into the reed block opening. Cylinders 3 and 4 were dry. We got a tow back to the boat ramp and loaded the boat, I pulled the plugs out of 3 and 4 and they were dry.
When we made it back home I pulled all the carbs off again a checked to see if I had a stuck float or a blockage in the carbs of some sort but they were squeaky clean.
Does anyone have any ideas on what would be causing this problem these WH carbs are in series so I find it odd that the top and bottom carb are working like they are supposed to? Is there something rudimentary that I am missing on all of my checks and wrenching on this motor. Any help would be greatly appriciated.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
37,824
Remove one of the drain plugs on the middle carburetor.----Operate manual fuel pump.----Gas should pour out.----Running with a blocked carburetor will starve 2 cylinders of gas and OIL.----So do the compression test again.
 

pgoodger04

Cadet
Joined
Aug 15, 2020
Messages
6
Remove one of the drain plugs on the middle carburetor.----Operate manual fuel pump.----Gas should pour out.----Running with a blocked carburetor will starve 2 cylinders of gas and OIL.----So do the compression test again.
I pulled the spark plugs and did a compression test. All cylinders are still 130 psi. I will pull one of the drain plugs on the carb and report back.
I did some reading on iboats last night but could not find a definite answer. I know on some of the older mercs where they used a reed cage bearing where you would loose transfer pressure.
How does this engine seal between the cylinders?
Is there a way to check transfer pressure on the engine?

While I am at it I have a fuel pump gasket set in the spare parts, I will change it just to eliminate all possibilities
What is the minimum pressure on the old style mechanical fuel pump supposed to be. I know this will change as rpm increases.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
37,824
The crankshaft has sealing rings on it.-----Look like a big piston ring.----Separates the 6 crankcases.-----Johnson / Evinrude used those from 1958 to last year when production stopped.
 

Dukedog

Captain
Joined
Oct 6, 2009
Messages
3,420
something is wrong with middle carb.. tha feed for carbs go through each carb from top to bottom.. if its before carbs it would effect all three..
 
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