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Mercury 1150 inline 6cyl blueband problems need help asap

C

Cory247

New member
Hey guys I have a 1977 mercury 1150 and it's starting to get the better of me, it will not start I have no idea why! I have done a compression check and all 6 cylinders came back with good compression being around 135-140P.S.I, I have tested for spark and there is plenty I have replaced the spark plugs just incase, I have rebuilt the fuel pump and carburetors, so I know for sure I have compression, spark and fuel so theoretically it should start, however it doesnt even try and fire anymore and when it did it would backfire like crazy, when I last had it running it was also running rough as guts but as soon as you even touch the throttle it dies, has anyone got any suggestions as to what could cause this much drama? Any help is greatly appreciated cheers
 
I don't work on these older "tower of power" motors, but the symptoms you describe could be 1) a bad power head base gasket (one cause of back fires and "no run" condition) or 2) toasted reeds - on this motor they are located in (donuts) on the crank - crappy design, you have to split the block to get at them.

Could be other causes, but that's the two that come to my mind...
 
Ok I will try and check them out tonight I have heard a bit about the reeds, but what exactly are they and what do they do?
 
Reeds are little "petals" (valves) that allow the air/oil/gas from the carbs to enter the crankcase and prevent them from escaping back through the carbs - so a one way valve.

When the piston of any given cylinder it traveling toward the top of the head, a vacuum is created in the lower crankcase for that cylinder. Since the simple air pressure in the throat of the carb is greater, the "reed" opens (inward) and the air/gas/oil is (sucked) through. As the piston starts moving downward it compresses the mixture in the crankcase, forcing the reed petal "closed" - when the piston crown gets below the intake transfer port the compressed mixture is forced into the cylinder.

Each cylinder has its own set of reeds. They are metal but they are pretty thin (think of the reed on a musical wind instrument)

On your model they are in a donut shaped cage. There are 3 cages (located between each pair of cylinders), and each cage has (I believe) 5 petals per cylinder (so each cage has two sets of 5 reeds - the 5 reeds are considered one unit).

They can get chipped or broken if debris is sucked through a carb, gets stuck between the reed and the cage and then when crankcase pressure tries to close the reed something has to "give", and it's almost always the reed that loses the battle if the debris is "hard".

If one or more of the petals gets chipped/broken/cracked, when the crankcase "pressurizes" it blows all your gas/oil/air back through the throat of the carb - also, because now the crankcase ISN'T "sealed" the exhaust, which takes "the easy way out" also pukes back through the intake (as well as out through the exhaust port) into the crankcase and out the carb throat (backfire).
 
On these older motors there is a problem with cold starting.-----It only has choke flappers on the upper 2 carburetors , they are plastic and may be warped.------Internal wear on reed block labarynth seals may have occurred.-----Bleed valve inserts may be missing as well.---------Pistons and rings may be worn as well.-----Starter motor / battery in poor condition.----This all adds up to poor starting.----------Try to squirt fuel into each carburetor as a test.---If it starts OK then there is a fix.-------------I would install a Johnson / Evinrude primer system as it will spray fuel into the intake system on command.
 
if you crossed plug wires when working on it you could have sheared the flywheel key and that will cause backfire as the timing has changed...
 
Do they have a flywheel key ??
Click to expand...
No.....
Check to see if timing belt has jumped a notch and check carbon tip in distributor cap as if worn out or shattered it will cause this , and yes they are replaceable. It is not the reeds and check to see if cap is wired correctly if someone had it off.
 
No keys, but has timing belts, rotor/distributor :( - almost sounds like a 4 stroke....

That's why I avoid these...
 
The chokes on those have a nasty habit of not closing tight enough to get them going when cold.

Try this little test: Buy a can of carb cleaner with the long red tube that attaches to the sprayer. With the throttle wide open (to open the butterflies) shoot some carb cleaner in each carb. Go back to normal starting mode and hit the starter. If it lights off, that's your problem.

On Mercs with similar choke set ps I've had to go with an enrichener system to get 'em going. Not hard to hook up.

Jeff
 
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