Mercury 70s model 1150 idle issues

[bkd13]

Having trouble getting my moto to idle took compression reading and cylinders 2-6 aare between 119 and 125 while number one is at 112 is ththis normal ? Mercury 70s model 1150

[CharlieB]

Unfortunately when a motor begins to have a cooling problem the upper cyl is the first to start to overheat.

This COULD be the reason for the low compression but before you start tearing the motor apart try a de-carb. If it is just carbon accumulation causing the rings to stick a bit you may get lucky.

Search the 'sticky' post at the top of the forum for the 'De-carb Proceedure'

Once completed repeat the compression tests and repost your results.

I'd high recommend you rebuild the water pump to be certain your cooling flow is good.

[bktheking]

An inline should get a new impeller every season, no questions asked.

There is also a plug for a fitting at the top of the block for a pressure gauge, install one that goes up to 10 psi, they are worth every cent.

[gwukena]

There is also a plug for a fitting at the top of the block for a pressure gauge, install one that goes up to 10 psi, they are worth every cent.

Water pressure gauge should be installed off of middle of water jacket cover and tell tale relocated off of top of block. Mercury had a service bulletin out for relocating tell tale to top of blocks, steam pocket could possibly form and cook #1 cylinder. Older blocks did not have provisions for fitting and actually had to be drilled and tapped for it.

[bkd13]

So with a new water pump is this motor still in usable condition with those compression readings?

[CharlieB]

#1 isn't dead yet, there is still hope that a de-carb will improve the compression.

Even if the #'s remain the same she should still run a long time with only a small percentage of power loss from the one cyl, you may not even notice it.

However, if it was an overheat of #1 there is a possibility of alum transfer from the piston skirt to the cyl wall which 'could' scrape off into the ring land and entrap the ring, causing further compression loss.

You could remove the exhaust side cover, turn the motor over until #1 piston is down and inspect the cyl wall. If you find alum transfer use muratic acid with Q-tips to remove the alum. Carefully dry all the acid out, rinse/wipe with alcohol, then coat with 2 stroke oil. Reassemble and run it, rechecking compression occasionally to watch for any change.

[Chris1956]

bkd, Remove the top transfer cover (starboard side of motor) if you want to look at the piston, rings and cylinder walls. If it were me, I would take a quick look and then run it. The compression is just fine. You will want to assure the carbs are clean as well as install a new impeller. A lean running cylinder will score and overheat.

Removal of the exhaust cover is much more difficult and unnecessary, just to inspect the cylinder.