1986 175 blackmax problems need help

gschultz05

Cadet
Joined
Aug 15, 2010
Messages
24
i have a 1986 champion bass boat with a 175 blackmax outboard on it and the problem i am having is this..... took the boat out 2weeks ago and the boat ran great then last week took the boat back out and as soon as it fire off in the water i could tell something was wrong.....the engine was missing.....got back to the house and fired it up and found 3 dead cylinders, cylinder #2,3, and 5.... checked the obvious and found spark on all 6 cylinders. checked compression and had 125-130 on all 6 cylinders. suspected trigger and changed with no difference on the outcome. changed rectifier with no difference. reversed coils for 1 and 2 to 3 and 4 to isolate the problem and same cylinders still dont fire. checked plugs and plugs are wet so there is fuel getting there......any ideas or help would be great.......

thanks
 

fisherman81654

Petty Officer 2nd Class
Joined
Sep 5, 2011
Messages
135
Re: 1986 175 blackmax problems need help

Sounds like you have a bad switchbox to me,swap them around and see if it makes a difference on which clinders are fireing.
 

gschultz05

Cadet
Joined
Aug 15, 2010
Messages
24
Re: 1986 175 blackmax problems need help

Have spark on all six cylinders. Would suspect that indicates the switch boxes are ok. After reversing the upper 4 coils and restarting the motor, same cylinders didn't fire. Compression is 125/130 across the board and the non firing cylinders are wet on the plugs. Have changed the stator/trigger, and recitifier, but problem same. Ideas??
 

j_martin

Admiral
Joined
Sep 22, 2006
Messages
7,474
Re: 1986 175 blackmax problems need help

Does not compute. It's missing spark, fuel, or compression. If all 3 are good, it'll fire.

Do you have good spark on the missing cylinders, as in 7/16" gap in free air? Jumping across the plug in free air proves nothing.

Is your wiring all correct?
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: 1986 175 blackmax problems need help

Have spark on all six cylinders. Would suspect that indicates the switch boxes are ok. After reversing the upper 4 coils and restarting the motor, same cylinders didn't fire.
This is a lile confusing as you state you have spark on all 6 but then you have cylinders not firing. Do you have spark on all 6 when cranking but lose it when engine starts? If so check the bia's circuit on both packs...
Intermittent firing on one or more cylinders:
Disconnect the white/black wire between the packs on a 6 cylinder and retest. If all cylinders now fire, replace both packs as there is a problem in the bias circuitry. On all others, check for low voltage from the stator and trigger. Disconnect the rectifier and retest. If theproblem disappears, replace the rectifier. On 3 and 6 cylinder engines, disconnect white/black wire and check the bias circuit (white/black terminals) resistance to engine ground. Readings should be approximately 15,000 ohms for standard packs and 9600 ohms for racing units. If the readings are correct on the
packs, index the flywheel and check timing on all individual cylinders. If the timing varies, replace BOTH packs.
 

gschultz05

Cadet
Joined
Aug 15, 2010
Messages
24
Re: 1986 175 blackmax problems need help

Truly appreciate the response. Checked the bias circuit and seems ok. Don't know how to index the flywheel and check timing on individual cylinders.

What I did do today was switch the switch boxes to see if the dead cylinders would change, and changed the rectifier. Nothing changed. Still have strong spark on all six cylinders but 2, 3, & 5 won't fire (plugs are also new). I then reversed two of the coil packs for 1&2 and 3&4, again no change. Then fired the motor and lightly sprayed some engine start fluid in the dead chylinders. #3&5 briefly fired, but #1 stubbled. My next move is to tear down & rebuild the carbs, however not sure this is the problem. Sure acts like ignition timeing to me. Just wierd, ran great last time out (two weeks ago) and now this. Maybe if you can explain the indexing issue I can zero this in. By the way, did try a different trigger with no change. Also tried my old stator with no change. Again, the puzzling part is having spark/compression and fuel and these three cylinders don't want to fire. Any thought or suggestions would be greatly appreciated. Thx Gary in Yuma AZ
 

gschultz05

Cadet
Joined
Aug 15, 2010
Messages
24
Re: 1986 175 blackmax problems need help

p.s we figured out indexing (we think) and it all checked out ok
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: 1986 175 blackmax problems need help

It sounds like a carb problem since you sprayed the intake and the cylinder lit off. If it still actsup after carb rebuilds, disconnect the wht/blk bia's wire from packs and retest but do not run engine over 3000 rpms. Also run a jumper wire from a known good ground to the rear divider plate to ensure coils are grounded.
 
Top