Mercury speed question

[J FISH]

I have a 1997 125 outboard. Out on the lake yesterday I ran it for about 2 hours. First run was about 6 miles into and downwind at 47 mph according to my GPS.

During the run home the wind laid and the water was slick and it bearly ran 33-37 mph.

Anyone have any ideas?

I will add that my tach is out. I beleave that it is the voltage regulator that the gray tach wire originates from. I tried another used tach to verify that mine was not working and bypassed all the wires in the boat incase one of them was the problem.

anyone have any ideas?

 

[tashasdaddy]

Re: Mercury speed question

is your boat taking on water? was the engine trimed differently? firing on all cylinders, check compression.

 

[J FISH]

Re: Mercury speed question

I will pull the plugs today and check compression and for fouling.

I am wondering if the gray wire could be linked to a larger electrical problem with the stator and the association of heat from running for most of 2 hours.

No water or timing change.

Thanks for the thoughts!

 

[tashasdaddy]

Re: Mercury speed question

gray is usually primer or choke. not timing, was the engine trim in or out or was it the same. running 5 minutes or 5 hours should not make a difference, as long as the cooling system is working,

 

[Rex]

Re: Mercury speed question

Sounds like the battery was starting to get low!!!
Rex

 

[J FISH]

Re: Mercury speed question

I will double check that gray is the tach wire coming off the rectifier. Can anyone double check me on this?

13.1 volts on battery and have not had a draining battery issue as of yet.

I was triming the motor above and below the usual trimed aera.

 

[Rex]

Re: Mercury speed question

I will double check that gray is the tach wire coming off the rectifier. Can anyone double check me on this?

13.1 volts on battery and have not had a draining battery issue as of yet.

I was triming the motor above and below the usual trimed aera.

 

[Rex]

Re: Mercury speed question

I will get the book out and see if I can find it, but why
4 plug started to foil? R U sure the battery was not low
because if it was then U start to loose our voltage to every thing. Why do U see nascar change battery in the middle of a race. Give me a little time to check on that for U.
Rex

 

[Texasmark]

Re: Mercury speed question

Merc runs the tach off the grey wire which comes from the voltage regulator. The voltage regulator reveives ac energy from the stator on 2 yellow wires.

The tach counts the peaks of the rectified alternator output. You can either have a bad tach or bad regulator/rectifier assy.

If you battery is being charged properly the regulator is probably ok and the tach is what needs changing. Numerous people on here have indicated that the tach sometimes is an early indication of a bad regulator/rectifier......that is when it's the regulator at fault and not the tach.

Also had others indicate that replacing tach's every several years is to be expected.

Was just working on the son's boat the last few days. It has 2 of those (V6) so it was a piece of cake to substitute them out looking for the root cause. Right now it looks like the tach is the culprit.

His wanders, reads correct sometimes, jumps erratically, and sometimes just reads zero when it's not supposed to.

Ordered an OEM Quicksilver from the Merc dealer for about $88 (surprised was so cheap). Will be here Tuesday then I'll know for sure.

Mark

 

[Texasmark]

Re: Mercury speed question

Lafitte, did you catch this?

Are you from Lafitte, LA? If so, been down there chasing some of your bull reds. Caught a 12 pounder; not out in the flats, but back in the brackish water above the seafood plant.

Did however enjoy the Porposes playing out there (the flats). Specks were cooperating nicely, but averaged about 3/4 to 1 lb; which as you well know is a great size to eat.

Will probably go again after things settle down from the hurricanes.

Ever hear of the C&M Bayou Fuel Docks? Got some great cabins.

Mark

 

[J FISH]

Re: Mercury speed question

Mark,

I am from some where in LA back about 100+ years ago when the folks came over with the saw mills in East Texas. I couldn't tell you the last time I was even over that way.

I have been thinking about what you wrote about the tach and regulator. I would agree that the regulator is probably failing. I installed a new tach and it did not work. Then I went back and uninstalled it and connected it directly to the motor to bypass any bad connections in the boat. Same thing, nothing at all.

I am going to purchase a non factory manual and do some testing. I have the factory service manual and find it so hard to read. Every paragraph has a new descriptive word for the same part it was just describing. It is absolutely awful!

I will post back some time on Monday after I get to spend some time with her.

 

[Texasmark]

Re: Mercury speed question

See you then.

 

[steelespike]

Re: Mercury speed question

If I read your post right you said the water was slick
(flat). While your speed drop seems excessive sometimes a boat will run slower on flat water because the waves don't break up the contact with the boat.
Especially if your boat runs a little flat on the water.

 

[J FISH]

Re: Mercury speed question

Ok, some good news. I found a problem with my carb linkage. The top carb was not fully in the "ball socket" so at times the top carb would disengage and remain in the idle state even though the other 3 carps would be at WOT.

It is a fluke that I found the problem because at rest the socket would line up with the carb lever just perfect. Most of the time it had enough friction that it would operate the lever like it was suppose to.

Thank you all for your help and knowledge. I just need to fix an tach problem now. I will start a new thread.

 

[joblo33]

Re: Mercury speed question

Just to be on the safe side you might want to check your compression in the top holes now. I've seen a similar problem on the 50-75hp 3cyl Mercs where someone loses the little metal piece in the linkage after a carb job and it eats the top piston from fuel starvation at WOT.
Eric

 

[J FISH]

Re: Mercury speed question

I did that yesterday while poking around on the motor. All were between 140-145 psi.

Pretty lucky. The boat ran good until the end of my trip. I put a new Lowrance GPS in the boat a couple of months back so I can watch and trust the speed differences until I can replace my regulator and fix my tach.