Mercruiser 170 stalling problems

[Wellcraft170]

Need some suggestions and input! I Have a merc 170 in my boat and I recently got it tuned up with points, plugs, plug wires, distributor cap, etc. i have a close friend who works on my father and i's boats over the years and he ran it for 45 minutes straight at his shop out of the water with no issues. So I took it out and it ran for 5 minutes at the dock then i slowly got away from the dock and it stalled about a minute in. I waited a minute then tried again and i was running good at around 25 miles per hour and it bogged down and stalled again after a 10 minute ride and wouldnt start back up. Could this be bad gas or clogging in the fuel pump because of it? Any input is helpful

 

[CamaroMan]

check if the coil is hot - does it have a ballast ceramic resistor inline to coil +? check if the coil is mounted upright or 45 degrees max, so many times ive seen marine coils mounted horizontal, they heat up and break down, eventually the cook out - unless theyre the high vibration epoxy type (most likely not) mounting angle is key.

Check for fuel air leaks in tank fuel switch / lines? look for bubbles going thru a clear filter ..

check for fuel pressure at carb while running.

tools, yes u need more tools!

 

[Wellcraft170]

check if the coil is hot - does it have a ballast ceramic resistor inline to coil +? check if the coil is mounted upright or 45 degrees max, so many times ive seen marine coils mounted horizontal, they heat up and break down, eventually the cook out - unless theyre the high vibration epoxy type (most likely not) mounting angle is key.

Check for fuel air leaks in tank fuel switch / lines? look for bubbles going thru a clear filter ..

check for fuel pressure at carb while running.

tools, yes u need more tools!

Is there more of a chance it's the coil instead of bad gas?

 

[Benny67]

When he ran it at the shop was it the same fuel tank feeding the motor?

 

[CamaroMan]

could be - hard to tell, lower shift cables also tend to stall motors - loose wire to ignition, faulty neutral safety switch in control box -

issue is it only happens every 25 mins - thats alot of driving to replicate the issue.

on an old school points setup you want this:

batt -> ignition switch -> into ballast resistor -> out from ballast resistor (drops from 12+v to about 9-10v when running) -> coil positive (this RUNS at 9-10v, STARTS at 12.6v. Connect the wore form slave solenoid "i" terminal straight to this one - it boost ignition to a full 12.6v when cranking)

A slave solenoid has an "i" terminal that bypasses the above ballast resistor.

Make SURE you are not running without the resistor - you will fry your points very quickly. I have an old suntune kit that tests points - u can find the kits all over ebay for 25, usually with timing light, comp tester and vac too!!

now the shift interrupt switch momentarily cuts your motor while going into gear and out, u hardly notice it its so quick, if the switch pin is gummed up and staying closed this will cut the motor.

If your lower cable is hard to move the interrupt switch will "think" like you are shifting gears because the cable tension is high and cut the motor when in fact its hanging due to the cable not moving freely.

You can remove the cable by the engine bracket, clamp a clear hose over the opening, fill it with ATF and apply air pressure and force the atf thru cable, shd free it up alot. takes some time but made a world of difference to mine -

the coild should never get hot when running - if its hot its cooked, get a new one. even after running HARD for a long time it whd be warm only..


SOOO - your coil might be shot, you might be running without the ballast and/or correct wiring (full 12+v to coil is bad!), if so - your "new" points might be fried.

Your new condenser might be junk - its VERY common, in fact a condenser thats been working great shd be thrown in the spares box with an OK mark!

a failing condenser/pints will stall randomly.. same for a bad coil - as it heats up especially.

 

[Wellcraft170]

When he ran it at the shop was it the same fuel tank feeding the motor?

Yeah it was the same one, the one thats in the boat

 

[Wellcraft170]

could be - hard to tell, lower shift cables also tend to stall motors - loose wire to ignition, faulty neutral safety switch in control box -

issue is it only happens every 25 mins - thats alot of driving to replicate the issue.

on an old school points setup you want this:

batt -> ignition switch -> into ballast resistor -> out from ballast resistor (drops from 12+v to about 9-10v when running) -> coil positive (this RUNS at 9-10v, STARTS at 12.6v. Connect the wore form slave solenoid "i" terminal straight to this one - it boost ignition to a full 12.6v when cranking)

A slave solenoid has an "i" terminal that bypasses the above ballast resistor.

Make SURE you are not running without the resistor - you will fry your points very quickly. I have an old suntune kit that tests points - u can find the kits all over ebay for 25, usually with timing light, comp tester and vac too!!

now the shift interrupt switch momentarily cuts your motor while going into gear and out, u hardly notice it its so quick, if the switch pin is gummed up and staying closed this will cut the motor.

If your lower cable is hard to move the interrupt switch will "think" like you are shifting gears because the cable tension is high and cut the motor when in fact its hanging due to the cable not moving freely.

You can remove the cable by the engine bracket, clamp a clear hose over the opening, fill it with ATF and apply air pressure and force the atf thru cable, shd free it up alot. takes some time but made a world of difference to mine -

the coild should never get hot when running - if its hot its cooked, get a new one. even after running HARD for a long time it whd be warm only..


SOOO - your coil might be shot, you might be running without the ballast and/or correct wiring (full 12+v to coil is bad!), if so - your "new" points might be fried.

Your new condenser might be junk - its VERY common, in fact a condenser thats been working great shd be thrown in the spares box with an OK mark!

a failing condenser/pints will stall randomly.. same for a bad coil - as it heats up especially.

This makes sense. And i was driving for 10 minutes at about 25 MPH not minutes. Ive heard of bad coils stalling out engines so hopefully its that or the condenser, which are easy fixes. I just really need this thing ready to go haha

 

[Benny67]

Save yourself some aggravation and switch to the pertronix setup. I did both of my 470's and was pleased with the results.

Amazon has it. For around $140 you can outfit the motor with the matching coil...set it and forget it.

 

[Benny67]

camaros explination might be a bit off the mark...as far as the slave solenoid goes and ballast resistor.

My 470 wiring has a resistive wire instead of a ballast resistor that passes from the coil to the points and has another wire that's feeding the full 12Vdc to the points to combat the voltage drop created from the sudden current that the battery looses when it supply?s the starter with the needed current to turn the motor.

I'd get a wiring diagram of your boat to be sure.

If you go the pertronix setup junk the old coil and get the proper resistance matching coil that they recommend and follow their instructions. Make sure to get rid of the resistance wire if you change it as a matching set. The module will prematurely fail if you lower the needed voltage to it.

Also..the coil doesn?t care if you feed the full 12Vdc to it....it's a coil...

 

[Benny67]

In simplified terms....you need a 12Vdc feed to the points when the starter is engaged and a slightly lowered resistance when the engine is running so you don't burn the points out prematurely.

You know what? it's friggin 2017...loose the points and get with the times

 

[Wellcraft170]

In simplified terms....you need a 12Vdc feed to the points when the starter is engaged and a slightly lowered resistance when the engine is running so you don't burn the points out prematurely.

You know what? it's friggin 2017...loose the points and get with the times

Haha youre right. Im gonna buy that kit and bring it to my guy

 

[Benny67]

it's well worth the few bucks...iboats might sell it as well. I don't want to steer business away from them.

 

[Benny67]

Also...You want a 3 ohm coil for the 470 setup.

 

[Wellcraft170]

Also...You want a 3 ohm coil for the 470 setup.

Gotcha. What are the symptoms of a bad coil? The ones i was having? Basically the boat starts and idles but when i had it in the water twice it stalled the first time when i was in forward after about 2 minutes then the second time it lasted about 10 minutes then sputtered out and wouldnt re start.

 

[Benny67]

If it was me I'd just throw the pertronix setup at it. From what you have discribed it's probably a bad points/coil/maybe even a distributor issue

 

[Wellcraft170]

If it was me I'd just throw the pertronix setup at it. From what you have discribed it's probably a bad points/coil/maybe even a distributor issue

Thanks for the advice man, just ordered the kit

 

[Benny67]

Hope it's the issue..good luck

 

[nola mike]

Disagree. Could be either ignition or fuel related. You need to find out which before you throw parts at it. Btw, I think I've read one post here where the culprit wad actually the coil.

 

[Benny67]

Disagree. Could be either ignition or fuel related. You need to find out which before you throw parts at it. Btw, I think I've read one post here where the culprit wad actually the coil.

We discussed changing the coil....as a matched set for an upgrade away from points.

You COULD swap the coil and see if it solves it OR upgrade both and se if the issue goes away.

To call it THROWING parts at it is a bit silly....you have what may appear to be a ignition issue. Why not eliminate old technology and move forward in troubleshooting?

What's your solution?

 

[Benny67]

Maybe take the coil out and warm it in a toaster oven and record it's resistance warm and cold and see if its any different?

For s**ts and giggles...how old is the suspected coil?

Sometimes you need to be a bit smart and replace wear items and move on...and upgrading from technology that's over 100 years old .I would say is worth gambling on