Had some intermittent problems last year while boating. I could be out fishing for hours perhaps going wide open, then all of a sudden the motor would cut to half power. It would continue like this for a few mins then go right back up to full power. Due to the intermittent nature of the problem, I guessed it was ignition related.
I hadn't done it ever, so I rebuilt the fuel pump and carburetor. But the motor was still very difficult to get started. It did finally start after installing new plugs. It seemed to run fine, but after stopping it, I couldn't get it to start again. Checked the spark and it seemed a little weak.
Model: Mercury 402 (2cyl, EL - Electric Start, Long-Shaft)
Serial Number: 7102322
Year: 1977
Started testing the ignition system.
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Compression
CYL1: 120PSI
CYL2: 120PSI
Ignition
Trigger Resistance:
White to Brown = 830 Ohms
Stator Resistance (Merc OEM)
(LS) Blue/Ground = 5600 Ohms
(HS) Red/Ground = 60 Ohms
CDI DVA - Stator and Switchbox output to coils
(LS) Blue/Ground = 114.4V
(HS) Red/Ground = 35V
Switchbox to COIL #1 = 80V
Switchbox to COIL #2 = 82V
.#####################################
DVA reading from Stator LS (Blue/Ground) should have been 180+ Volts. I took the flywheel off to inspect the stator. Found there was a crack and something bubbled out of it. Likely overheated.
I installed a new stator CDI 174-5255. When I turned it over, it started but was running really rough. For a short while it would run ok then back to rough (rpm seems to affect how rough it was - lower was so so, mid range really bad, high rpm it seemed not too bad).
Took some new readings with the new stator.
Trigger Resistance:
White to Brown = 830 Ohms
Stator Resistance (CDI 174-5255)
(LS) Blue/Ground = 2840 Ohms
(HS) Red/Ground = 52.3 Ohms
CDI DVA - Stator and output to coils
(LS) Blue/Ground = 177 to 181 V (this dropped to 120 when it was running really bad)
(HS) Red/Ground = 135 to 142 V
Yellow 1(Rectifier lead 1) = 0.34V
Yellow 2(Rectifier lead 2) = 28V
Switchbox to COIL #1 = 146V (dropped to 108-112 when really rough)
Switchbox to COIL #2 = 145V (dropped to 108-112 when really rough)
Trigger CDI DVA
Brown/Ground = 1.7V
White/Ground = 1.7V
Coil Resistance (Sierra 18-5186)
COIL #1 - Primary = 0.3 Ohms, Secondary = 594 Ohms
COIL #2 - Primary = 0.3 Ohms, Secondary = 246.6 Ohms
I'm at a loss as to what might be going wrong. Voltages are low according to the documentation. When my old stator was working (notes from July 2013), it put out 307V & 207V - output from the switchbox to coils was 208V & 198V.
- disconnected the rectifier - no difference
- swapped out switchbox - no difference
Video of motor running.
https://www.youtube.com/watch?v=b2TEDej4iZg
Could this new CDI stator be bad? Flywheel? Output to coils is supposed to be at least 180Volts. Anyone know what the resistance specs should be on those Sierra 18-5186 coils?
Thanks,
Cambo
I hadn't done it ever, so I rebuilt the fuel pump and carburetor. But the motor was still very difficult to get started. It did finally start after installing new plugs. It seemed to run fine, but after stopping it, I couldn't get it to start again. Checked the spark and it seemed a little weak.
Model: Mercury 402 (2cyl, EL - Electric Start, Long-Shaft)
Serial Number: 7102322
Year: 1977
Started testing the ignition system.
.#####################################
Compression
CYL1: 120PSI
CYL2: 120PSI
Ignition
Trigger Resistance:
White to Brown = 830 Ohms
Stator Resistance (Merc OEM)
(LS) Blue/Ground = 5600 Ohms
(HS) Red/Ground = 60 Ohms
CDI DVA - Stator and Switchbox output to coils
(LS) Blue/Ground = 114.4V
(HS) Red/Ground = 35V
Switchbox to COIL #1 = 80V
Switchbox to COIL #2 = 82V
.#####################################
DVA reading from Stator LS (Blue/Ground) should have been 180+ Volts. I took the flywheel off to inspect the stator. Found there was a crack and something bubbled out of it. Likely overheated.
I installed a new stator CDI 174-5255. When I turned it over, it started but was running really rough. For a short while it would run ok then back to rough (rpm seems to affect how rough it was - lower was so so, mid range really bad, high rpm it seemed not too bad).
Took some new readings with the new stator.
Trigger Resistance:
White to Brown = 830 Ohms
Stator Resistance (CDI 174-5255)
(LS) Blue/Ground = 2840 Ohms
(HS) Red/Ground = 52.3 Ohms
CDI DVA - Stator and output to coils
(LS) Blue/Ground = 177 to 181 V (this dropped to 120 when it was running really bad)
(HS) Red/Ground = 135 to 142 V
Yellow 1(Rectifier lead 1) = 0.34V
Yellow 2(Rectifier lead 2) = 28V
Switchbox to COIL #1 = 146V (dropped to 108-112 when really rough)
Switchbox to COIL #2 = 145V (dropped to 108-112 when really rough)
Trigger CDI DVA
Brown/Ground = 1.7V
White/Ground = 1.7V
Coil Resistance (Sierra 18-5186)
COIL #1 - Primary = 0.3 Ohms, Secondary = 594 Ohms
COIL #2 - Primary = 0.3 Ohms, Secondary = 246.6 Ohms
I'm at a loss as to what might be going wrong. Voltages are low according to the documentation. When my old stator was working (notes from July 2013), it put out 307V & 207V - output from the switchbox to coils was 208V & 198V.
- disconnected the rectifier - no difference
- swapped out switchbox - no difference
Video of motor running.
https://www.youtube.com/watch?v=b2TEDej4iZg
Could this new CDI stator be bad? Flywheel? Output to coils is supposed to be at least 180Volts. Anyone know what the resistance specs should be on those Sierra 18-5186 coils?
Thanks,
Cambo
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