Stator ohms reading and cdm ohms readings

[Levie17]

Mercury 125 - 2002.

Stator was within CDI’s ohms range of 500-700. I let the engine run for 5 minutes and the ohms reading came back at 803. What is this supposed to tell me about the stator?

Original cdm modules all read 1230ohms(3 of them), pins A to C. CDI CDM I ordered was within spec (4th one). According to CDI they should be 2200-2400. Does this mean the three originals are all faulty?

Thanks in advance as I try to learn.

 

[Faztbullet]

I let the engine run for 5 minutes and the ohms reading came back at 803. What is this supposed to tell me about the stator?​

That the resistance increased with the engine heat..which is normal. What problem are you trying to solve???

 

[Levie17]

I’ve received a DVA tester so I’ll be headed that route. Boat stutters (misses) at WOT and won’t increase RPM’s or speed. Has a miss at idle. Cylinder 4 plug is wet. Cylinder 3 was black, but replaced coil, which improved it.

 

[Texasmark]

I have that engine. WOT stuttering can be caused by your fouled #3 or 4 or both from too much low speed operation. Before you do anything else, change the plugs, make a run and report.

Something that helps to keep the plugs clean for low speed running is to tilt the rear of the engine up 10-15 degrees anytime you are running OFF plane. Only takes a minute to prove my point......have the engine in gear, idling around or running at low speed tilted down where most folks have it set to do their hole shot and get on plane. Expect the engine to be vibrating. With your new plugs installed, just tilt the rear up as stated and give it a minute and notice how smooth it idles/runs slowly. Additionally, when you punch out of the hole it will come out clean and accelerate to WOT throttle without misfiring and having to clean up #3 and 4 plug to get them to fire properly.

If you do mostly slow speeds and cruising, limiting time at WOT, I have an Iridium plug that works really great as an aid in keeping the plugs clean.

 

[Levie17]

Did my first DVA test. Stator tested 298 at idle. Triggers to cdm’s all tested 3v+. I’ll be doing a high speed water test to see if the stator changes when my WOT miss starts up.

 

[Levie17]

High speed test with the DVA connected to the white/green and green/white 300 volts. No fluctuation in the number at all. Range according to CDI is 150-400

 

[flyingscott]

You need to buy a manual for your motor a good FACTORY one. Then you need to look at your fuel system. The only way that 3 and 4 can foul out at an idle is if the accelerator pumps are leaking. Because on you 2+2 motor the bottom carbs have no idle circuits just a small hole to provide enough lube for the cylinder.. It is not uncommon for the accelerator pumps to fail on those. BS on the low speed operation I trolled my 125 Merc all day one day and skiid the next and never had a problem. I changed my plugs pnce in 10 yrs. I also never had to tilt my MERC 125 to get it to run right either. Do a compression test before anything and buy a manual. You should not have to do anything special to get your motor to come out of the hole correctly.

 

[flyingscott]

You can also look at the floats and or needle and seats in the carbs.

 

[Levie17]

Compression is good on all 4. It gets out of the hole just fine, it’s when I get to just before WOT that it starts to shutter and sounds like it has a miss.

 

[Levie17]

https://youtu.be/YKMyhE6lE0U

this link will take you to the video I recorded. You’ll hear the miss or whatever it is

 

[flyingscott]

Use a timing light on each cylinder as it is doing that. That will help you narrow it down to which cylinder is the culprit. Make sure all the linkages are moving correctly and buy a factory manual.

 

[flyingscott]

I have that engine. WOT stuttering can be caused by your fouled #3 or 4 or both from too much low speed operation. Before you do anything else, change the plugs, make a run and report.

Something that helps to keep the plugs clean for low speed running is to tilt the rear of the engine up 10-15 degrees anytime you are running OFF plane. Only takes a minute to prove my point......have the engine in gear, idling around or running at low speed tilted down where most folks have it set to do their hole shot and get on plane. Expect the engine to be vibrating. With your new plugs installed, just tilt the rear up as stated and give it a minute and notice how smooth it idles/runs slowly. Additionally, when you punch out of the hole it will come out clean and accelerate to WOT throttle without misfiring and having to clean up #3 and 4 plug to get them to fire properly.

If you do mostly slow speeds and cruising, limiting time at WOT, I have an Iridium plug that works really great as an aid in keeping the plugs clean.[/

Stop adding so much unnecessary information to these posts. All it does is confuse things.

 

[Texasmark]

You need to buy a manual for your motor a good FACTORY one. Then you need to look at your fuel system. The only way that 3 and 4 can foul out at an idle is if the accelerator pumps are leaking. Because on you 2+2 motor the bottom carbs have no idle circuits just a small hole to provide enough lube for the cylinder.. It is not uncommon for the accelerator pumps to fail on those. BS on the low speed operation I trolled my 125 Merc all day one day and skiid the next and never had a problem. I changed my plugs pnce in 10 yrs. I also never had to tilt my MERC 125 to get it to run right either. Do a compression test before anything and buy a manual. You should not have to do anything special to get your motor to come out of the hole correctly.

Great. I guess I'm chasing butterflies but it works for me and that's what's important. My compressions are 3 at 129 and 1 at 130 done at the dealer where I bought the used boat. He marked the numbers on the water jacket.

I have the 2015 revision of the OEM manual published back in 1998. Some things have changed from the previous OEM manual. It was not a revision. Accelerator pump, and fuel pump have new kits. Fuel filter and secondary filters are new. Carbs are clean and lines aren't degrading.

Acceleration kicks in around 1800-2000 like the manual says it is supposed to. Plugs are gapped to 0.040 as stated in the manual. Fuel is 91 gasoline and oil it Pennzoil Premium TC-W3 semi-senthetic, engine oiler works. Engine doesn't smoke. Acceleration is more than needed to plane out a 17 ½' Crestliner Fish Hawk in a couple of seconds. Running a square port 20P Laser II. Boat ran 47 early in the year when it was cool at rev limit of 5250 and has dropped a couple of k with the water temp at 81 and air at 95. The engine is 18 years old.

If the engine is idling in gear and is moving back and forth, with the trim sucked in and all you do is to raise the rear and it smoothes out like my towers used to idle, There IS something to tilting and as I said before, Mercury designed that into some of their fishing engines....Mark 10A, 15A and 28A, 1959 to name 3.

 

[Levie17]

Thanks. I did put a timing light on each cylinder a few days ago. Nothing was cutting out. I did pull the stator today and bench tested it. Two weeks ago I did the same thing. It tested 600 ohms. Tonight it tested 720. CDI has the range at 500-700.

 

[Texasmark]

Thanks. I did put a timing light on each cylinder a few days ago. Nothing was cutting out. I did pull the stator today and bench tested it. Two weeks ago I did the same thing. It tested 600 ohms. Tonight it tested 720. CDI has the range at 500-700.

Copper has a high temperature coefficient so changes in ambient or component temperature can make for wild readings on the Ohm scale. Note that a lot of postings of resistances, especially in transformer circuits....which this happens to be, the magnet on the flywheel is the primary.....list an ambient temperature for the measurements. Recalling my manual, there is an ambient mentioned....forget just where, or they give you a large spread of resistance. I wouldn't be concerned about your new reading.