Merc. 115 Inline 6 - poorly running ?

[gman1001]

1st time out this year and many issues. I know this is all a long shot but I thought I'd throw it out to see what you all think.

1989 Merc motor. 2.5 or 3 year old gas, full tank with stabile.
Motor operated great last fall (October)

This spring, in driveway I changed the water pump. Other than that, no other changes to motor.

Now the motor will not idle when shift selector is in neutral. Engine dies.

I dipped the boat today, thought I'd run the Mercury Power Tune spray through the motor. Once in fwd gear the boat appears to run fine, however it cannot get onto plane - RPM's cannot go over 3k! The prop is a 13.25x17 on a 18' SeaCraft CC.

My thoughts are this: (without any testing)

1) Since the boat ran fine last fall - maybe this gas is really really bad?
2) Maybe not all cylinders are not firing? Even though in Nuetral I can rev the motor to 5K
3) Maybe my lower unit water pump job screwed up the gearing somehow?

Thoughts anyone?

Many thanks advance.

 

[turbinedoctor]

Re: Merc. 115 Inline 6 - poorly running ?

I would try a portable gas tank with new gas and don't rev past 1500.

 

[Bob_VT]

Re: Merc. 115 Inline 6 - poorly running ?

An inline will rev to 5000 on a single cylinder firing.

Verify your spark on all cylinder's. Is it an electronic or point/distributor motor? Might be time for a slight tune up and check your ignition system.

 

[gman1001]

Re: Merc. 115 Inline 6 - poorly running ?

Tx all, was thinking... When I did the Power Tune spray, the top and bottom carbs caused the motor to bog when the spray entered the carbs. No bogging out of the center or middle carb.

I'm guessing that this carb is the 'metering' carb right? In other words the middle carb controls idle. My motor won't idle because the middle carb is gunked up with old gas varnish oil etc.... Then my motor can't provide power to the boat for the same reason.

Thoughts? Am I correct in my guess that the middle carb meters?

 

[country boy]

Re: Merc. 115 Inline 6 - poorly running ?

When was the last the carbs were serviced ? you may want to clean them up and check your needle and seats & floats adjustments .I have seen these simple issues like dirty carbs and incorrect float adjustments ruin engines from the lack of fuel to the cyl.

 

[gman1001]

Re: Merc. 115 Inline 6 - poorly running ?

Not sure as I just bought the boat last fall. Great point about lack of fuel to cylinders. I'm very worried about that.

I'm going to try the 'tap' the bowls trick before disassembly and cleaning.

Fingers are crossed.

 

[gman1001]

Re: Merc. 115 Inline 6 - poorly running ?

I found the problem, and just this once I'm happy to say its my fault. ;-)


I had disconnected all plug wires when changing out water pump, and switched up cylinders 3&4. I changed them back and the motor runs great now.

Tx for the replies.