1979 140hp Tach issues

[James_Ketcham]

So i'm wiring up the engine to the boat which is a 1979 Mark Twain Vsonic and I notice a few issues. first being on the back of the tach has a selector 1 2 3 4, which i'm assuming is for the number of cyl of the engine. My 140 is a 6 cyl. So i'm looking at the factory service manual for the engine and it is showing the tach wire as being connected to one of the pulse wires on the rectifier. Now on the 1978 diagram ( engine wiring ) it shows the tach hooked up to the Brown connector on the switchbox. So i'm wondering do I set the tach for 1 cyl and hook it to the rectifier as the 1979 service manual says or leave the wire connected to the switchbox brown lead and set the switch on the tach for? Sorry if that sounds a confusing, but I don't want to burn up something. My engine has the trigger plate in the distributor if that helps. Under the flywheel it's just the charging stator with the 2 wires that run to the voltage regulator/rectifier. Any thoughts?

 

[James_Ketcham]

[No message]

 

[James_Ketcham]

this is the tach on the boat from 79.. not much info on it.

 

[Scott Danforth]

most of the time corrosion in the selector switches is the cause of tach problems. switch it back and forth a few times, then set it back.

verify with a laser tach on the flywheel

keep in mind that the 41 year old tach may simply have died.

 

[James_Ketcham]

I'm fine with it , if it died. I recently purchased this, the boat is a 1979, trailer is a 1979, and this 140 HP is also a 79. coincidence? i do not know. could be all original but 40 years later who knows. the tach was not connected to anything from what i saw. even the tach plug on the control box had a cap over the tach plug. So I'm trying to see if I can make it work or if i just need to pitch it and find something compatible with a 85mm hole size, 2 stroke and 6 cyl.

 

[jimmbo]

How is you engine wired? Brown wire going to a Switchbox, or to the Rectifier?

 

[James_Ketcham]

How is you engine wired? Brown wire going to a Switchbox, or to the Rectifier?

it was to the brown wire on the switchbox, however the tach was not hooked up at all. So I am unsure if it was ever connected to this engine.

 

[jimmbo]

What's your Engines serial #? I'm starting to think it is a 1972 140

 

[Chris1956]

Jimmbo, I agree. Merc switched the brown tach signal wire from the brown terminal on the switchbox, long before 1979. However, his tach looks like something from 1972.

James, if you cannot get that tach to work, you will need to buy a new one, and move the brown wire from the switchbox to one of the yellow wires on the rectifier. Modern tachometers are driven off the stator. You will use either the 6C or 12P setting, whatever the tachometer has.

 

[James_Ketcham]

What's your Engines serial #? I'm starting to think it is a 1972 140

5190360

 

[James_Ketcham]

Jimmbo, I agree. Merc switched the brown tach signal wire from the brown terminal on the switchbox, long before 1979. However, his tach looks like something from 1972.

James, if you cannot get that tach to work, you will need to buy a new one, and move the brown wire from the switchbox to one of the yellow wires on the rectifier. Modern tachometers are driven off the stator. You will use either the 6C or 12P setting, whatever the tachometer has.

Yeah I'm unsure of the tach age.. I Believe it is factory with the boat however since all of the gauges are of the same maker. but that doesnt mean they couldnt have used 72 parts in my 79 boat.. I'll get to testing it out this weekend coming. I did get on there web page for the tach and as I suspected there is NO information available for it.

 

[jimmbo]

Is there a silver disk/plug on the engine block, with the the same Serial #?

A new tach should should work on either the switchbox or the Rectifier, all it is counting is the number of pulses per rev. I find it easier and less confusing to use the number of cylinders, rather than figuring out that a 12 pole alt often uses #5 on the tach. More confusing than how Cadbury got the Caramel into the Caramilk Bar

 

[James_Ketcham]

Is there a silver disk/plug on the engine block, with the the same Serial #?

A new tach should should work on either the switchbox or the Rectifier, all it is counting is the number of pulses per rev. I find it easier and less confusing to use the number of cylinders, rather than figuring out that a 12 pole alt often uses #5 on the tach. More confusing than how Cadbury got the Caramel into the Caramilk Bar

Ya Know, that welch/welsh plug thing helped me get my 9.8 Mercury back from the police because the tag on the engine wasdefinitely not from a Mercury engine. I did not know that even existed until the police said they ran the number and it was clean. So when I got this boat i looked all over for it and could not find it anywhere. serial number shows it as a 79, and that timing decal shows it as a 79, and i've looked at early 79 exploded views for engine parts and they look correct as well. I believe the mid 79 models had multiple coil packs and such. mine just has 1 coil and 1 distributor with the triggers inside the the distrib. I beg forgiveness as i'm getting a crash course in boating terminology and the working of boat engines. car/atv/motorcycles/tractors/dozers ect I am very good with.. this being my first time with a boat i'm learning fast as I can. Mercury factory service manuals are kinda odd with the black and white photos showing pictures of a black engine and expect you to see what they are showing. I read the manual every night looking at different things trying to understand how it works and such. However I cannot ask the book anything when i get stuck on a question so I come here and throw my self upon the forum 's Mercy.

 

[Chris1956]

OK, A high tech question... is the coil brown or orange or an aluminum case over black?

Is the rectifier the size of a 1/2 pack of cigarettes and black with three colors or all black and about 2" X 2" X 1/2"?

What color is the distributor cap? Is the coil mounted on the block or cowling support?

 

[James_Ketcham]

OK, A high tech question... is the coil brown or orange or an aluminum case over black?

Is the rectifier the size of a 1/2 pack of cigarettes and black with three colors or all black and about 2" X 2" X 1/2"?

What color is the distributor cap? Is the coil mounted on the block or cowling support?

lots of questions. lol, here are some photos that should help. coil looks black to me, rectifier looks to be 1 1/2 inches by maybe 2. cap looks grey.

 

[Texasmark]

Mercs run 12P alternators (for the sake of setting up the tach) for the most part and a tach "rated for outboard motors" is pos 4 if only 4 slots, or with Farnia with 5 slots use position 5, sticker on rear of unit. Farnia has a www and their posted chart shows you the outboard engines and tach settings for most all engines listed by hp and year model. Figuring how Merc gets 12P out of 9 alternator coils is still a mystery to me! My '02 115, red stator, service manual says 9 coils and tach setting is 12P according to Farnia...the tach in my boat! Go figure.

 

[Chris1956]

OK, rectifier and coil are appropriate for a 1979 motor, as is cowling. Fuel pump looks like 1979 as well.

Your tachis much older, as it does not have 3 connections.

 

[jimmbo]

Looking at the pics, it appears some rewiring(because of the short life insulation merc harnesses had) has occurred, and I will assume that the rewirer used a wiring diagram for an earlier 70s engine, and hooked the tach wire to the switch box

 

[James_Ketcham]

Looking at the pics, it appears some rewiring(because of the short life insulation merc harnesses had) has occurred, and I will assume that the rewirer used a wiring diagram for an earlier 70s engine, and hooked the tach wire to the switch box

the entire engine inside had to be rewired. every single wire the insulation crumbled off. it was rewired using a 1978 1400 diagram as it looked to be identical.

 

[jimmbo]

Yet Merc moved the tach wire to the Rectifier prior to that. Where did you find that wiring diagram?