mercury 115 won't go faster than 7mph at full throttle.

[bassfisherman14]

HELP!!!!!!!!!!!!!!!!!! I have a 1977 mercury 115 with a distributor that will not go faster than 7 mph or 2000 rpm's. When it is in neutral it will rev over 4000 rpm's which is when using the cold start lever on the control and this was exactiy the same rpm's as before when it was running perfect. I myself am sort of a mechanic so i did the usual (check sparkplugs, took prop off to check for entangled string/fishing line, checked compresion 125psi each cylinder, cleaned carbs). The problem started after it sat for 2-3 weeks while i was looking for a new starter and after putting in the used starter i got for free. I was wondering if it could be the ditributor because the gas is not even a week old. PLEASE HELP!!!!!!!

 

[Yepblaze]

Re: mercury 115 won't go faster than 7mph at full throttle.

Does it still have the original type ignition, or perhaps some aftermarket equivalent?

Is the engine throttle advancing when applied at the controls?

 

[Laddies]

Re: mercury 115 won't go faster than 7mph at full throttle.

First don't free rev a outboard or you will trash it. If the carbs have been cleaned and you have 120+ # of compression then the problem is probably in the dist. could be a dirty cap, it can be washed with hot soapy weater and a brush.

 

[bassfisherman14]

Re: mercury 115 won't go faster than 7mph at full throttle.

When i took off the distributor cap there where little fragments of metal sitting in the bottom of the cap i thought maybe i need a new distributor cap?

 

[bassfisherman14]

Re: mercury 115 won't go faster than 7mph at full throttle.

I am not sure if the ignition components are stock because i bought it used last year from the owner of a boat shop. it's a 1977 venture bass boat so there i don't doubt if there are. it ran perfect before the starter went out and yes the butterfly is wide open when the throttle is all the way down at the controls.

 

[Chris1956]

Re: mercury 115 won't go faster than 7mph at full throttle.

Clean up the cap and put an ohmmeter on each plug wire, from the cap electrode to the plug end. Those wires are stranded stainless steel, so the resistance should be zero. The rotor is not removeable, and fragile. If you break it, you will need to replace the dissy shaft ($200).

If the resistance on the wires is zero, reassemble and check for arcing from the plug wires to ground, especially on #5 and #6. If no arcing check spark plugs for water intrusion. If the plugs are really clean, it is likely you have water in the cylinders.

 

[Yepblaze]

Re: mercury 115 won't go faster than 7mph at full throttle.

Fragments of metal in dist cap might indicate possible imminent dist bearing (or worse) failure. It might require you to slide belt off the pulley, and rotate the shaft by hand to check for play and smoothness. But that would require your ability to time the dist to flywheel upon reassembly.

The reason I ask about the originality of components is that I had found that the unregulated high voltages these motors produce can harm some aftermarket (CDI/Rapair) ignition components causing the failure to be represented as limiting RPMs somewhere around 2K. And until a voltage regulator is added to circuit they will, if lucky, maybe make warranty period of a year.

 

[Chris1956]

Re: mercury 115 won't go faster than 7mph at full throttle.

Yepblaze, So the higher voltages cause CDI swtchboxes to fail? It sounds like CDI has an inferior design, rather than their usual robust design.

In that ignition system, nothing else would be likely to fail, unless the switchbox were to let overvoltage onto the distributor trigger.

 

[bassfisherman14]

Re: mercury 115 won't go faster than 7mph at full throttle.

when i am driving it it seems like maybe something is regulating the rpm's because it stops at exactly 2000rpm's no more and no less it is right on the 2k line on my tach. i realy appreciate the help it saves me alot of time and i am going to try what you have said too do .

 

[Chris1956]

Re: mercury 115 won't go faster than 7mph at full throttle.

Bass, You might do a quick check of the idle pickup timing and max timing. To do this, remove spark plugs 2-6, install them into their plug wires and tape the plugs together so you can ground them. Put a timing light on #1 plug, set the cold start lever up until the carbs are about to open, crank the motor and see what the timing advance is. It should be 4-6 degrees BTDC.

Now set the throttle to full speed in forward (prop should be removed). You will need to jumper the starter solenoid to make the motor crank, ignition key on. the timing should be 21 degrees BTDC. if either of these timing specs are off, look on this forum for the Clams Canino "Link and Synch of Inlines" topic.