94 force 120 no spark on top 2 cylinders

dirtyrice23

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Hey guys, my boat is not getting spark on the top 2 cylinders. It cranks up fine but is only running on the bottom 2 cylinders. I ordered a replacement cdi box and no change. Any ideas on what to troubleshoot next? Any help would be greatly appreciated!
 

pnwboat

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Re: 94 force 120 no spark on top 2 cylinders

You might want to check the stator. There were a couple of ignition systems used around that year. If your stator wires are Blue and Yellow, disconnect them and you should read 680-850 OHMs across them. If your stator wires are White/Green and Green/White, you should read 500 - 700 OHMs across them.
 

jerryjerry05

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Re: 94 force 120 no spark on top 2 cylinders

Do a compression test just to make sure?
Outboard ignition . com or CDI ignition both sites have test procedures for the ignition system.
 

dirtyrice23

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Re: 94 force 120 no spark on top 2 cylinders

Ok great I will start there and post my results. Thanks for the help!
 

dirtyrice23

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Re: 94 force 120 no spark on top 2 cylinders

I got spark on all four last night. Cleaned up the connections for both cdi boxes, added a ground from the motor to the 2nd cdi box and they all work now. Checked compression 108 99 110 115. I am going to take her out this weekend and run some new gas. It has been sitting for a while. Hopefully my problem is fixed but I will update after the water test. Thanks for the help.
 

pnwboat

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Re: 94 force 120 no spark on top 2 cylinders

If the problem returns, check for broken wires. Especially if your spade lug connectors have a small piece of black heat shrink tubing covering the area where the wire is soldered/crimped to the spade lug connector itself. Wire strands can break inside the tubing. You can't see it, and the heat shrink will hold the broken wire to the connector giving you the impression that it's OK.
 

dirtyrice23

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Re: 94 force 120 no spark on top 2 cylinders

Ok thanks pnwboat. I took the boat out on Saturday and it ran great for about 5 min. First, it only ran right with the cover off. It would cut off if i put the cover on. Also it sounded like the top carb was popping. When my brother placed is hand over the carb kind of cupping it, it ran better. Any suggestions would be great? Thanks.
 

pnwboat

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Re: 94 force 120 no spark on top 2 cylinders

Cutting out when you put the cover on is usually an exhaust leak inside the cover. Most common cause is a bad exhaust boot or bad clamp that holds the exhaust boot in place. Boot is item #27 in the diagram below. Spring clamp is #29

Mercury, Mercruiser, Force, etc. - DRIVESHAFT HOUSING - 120 H.P.

There were two types of ignition systems used on your motor. Need to determine which one you have. Do you the Prestolite system which has two light blue CD Modules with 4 light blue coils, or do you have the Mercury style with a single Switch Box and the 4 dark blue coils?
 

dirtyrice23

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Re: 94 force 120 no spark on top 2 cylinders

Thanks! Its the prestolite system but my cdi boxes are black and the four coils are also black. Should there be exhaust smoke inside the engine or just out of the pee holes?
 

dirtyrice23

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Re: 94 force 120 no spark on top 2 cylinders

It was smoking pretty good by the way. Also, I dont have the blow back covers on the carbs. Do they make a difference?
 

pnwboat

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Re: 94 force 120 no spark on top 2 cylinders

There should be absolutely no exhaust smoke inside the engine cover. Only exhaust smoke should be outside of the motor. Just out of the two pee holes and exhaust snout or prop hub depending on what type of lower unit you have.

The missing carb covers are not a show stopper. Shouldn't make much of a difference.

Sounds like at some point the ignition system was changed for the earlier version Prestolite system. It should be fine. Like I mentioned before. Check the wire connections on the spade lug connectors where the CD modules, trigger wires and stator wires are all connected on the terminal strip. Especially if they have the black heatshrink tubing covering the wire/spade lug crimp/solder joint. The trigger wires are more susceptible to breakage since they are smaller.

Make sure the trigger and stator wires that come out from under the flywheel are nor rubbing against the flywheel and shorting out. When you move the throttle, it moves the trigger assy, which in turn moves the trigger wires.

There should also be a ground wire that runs from the Coil/CD Module mounting plate to the engine block. Make sure it's there and making good contact at both ends.
 

dirtyrice23

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Re: 94 force 120 no spark on top 2 cylinders

Great there is def an exhaust leak so I will check those parts and go post results. Thanks!
 

dirtyrice23

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Re: 94 force 120 no spark on top 2 cylinders

Also, what would cause the carb to act better by cupping it?
 

pnwboat

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Re: 94 force 120 no spark on top 2 cylinders

Also, what would cause the carb to act better by cupping it?

Hard to say. My "guess" is that it's causing the carburetor to run richer. If the ignition spark is marginal, it may make it easier to ignite the fuel mixture. If the carb is running lean due to fuel delivery problem, it could temporarily cure it. Might take the fuel bowl off and check for any crud in there. If you don't already have one, there should be an in-line fuel filter between the fuel pump and carburetors.
 

dirtyrice23

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Re: 94 force 120 no spark on top 2 cylinders

"Cutting out when you put the cover on is usually an exhaust leak inside the cover. Most common cause is a bad exhaust boot or bad clamp that holds the exhaust boot in place. Boot is item #27 in the diagram below. Spring clamp is #29

Mercury, Mercruiser, Force, etc. - DRIVESHAFT HOUSING - 120 H.P."


This may seem like a silly question but is the boot connected to the pee hole? I just need to take off the lower cover to get to this part?
 

pnwboat

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Re: 94 force 120 no spark on top 2 cylinders

There is heat resistant plastic insert (#26) inside the boot. There's also a spring (#28) in side the boot. The spring pushes on the insert inside the boot, which in turn pushes the free end of the boot against the lower cover. There is a circular depression cast into the lower cover right at the pee holes to keep the end of the boot in place. When you put the lower cover in place, the boot is compressed and seals and stays in place. There is a circular raised neck that sticks out from the lower housing that the boot slips on to. The spring clamp (#29) holds the one end of the boot onto it.

Once you remove the lower housing cover, you'll see how everything fits together. Hardest part is getting that darn spring clamp on to hold the boot. Just be careful and don't poke a hole in the new boot.
 

dirtyrice23

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Re: 94 force 120 no spark on top 2 cylinders

Ok noted. I will check the boot asap and order parts as necessary. I will comment back with results. I really appreciate the help!
 

dirtyrice23

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Re: 94 force 120 no spark on top 2 cylinders

Also, it seems that my top coil is not getting as strong of a spark as the rest. I want to put a new coil on the top cylinder but since the packs and coils are black and not blue like the book says they should be, I am not sure which coil to purchase. Any ideas on how I can figure out which one I need?
 

pnwboat

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Re: 94 force 120 no spark on top 2 cylinders

Before you buy anything, swap the top coil with one of the others. The coils are not a high failure item. If the problem moves, then buy a coil. If no difference start checking the ignition system. I mentioned on post#2 about checking the stator resistance. Jerry also provided a link to trouble-shooting ignition problems.
 

dirtyrice23

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Re: 94 force 120 no spark on top 2 cylinders

Before you buy anything, swap the top coil with one of the others. The coils are not a high failure item. If the problem moves, then buy a coil. If no difference start checking the ignition system. I mentioned on post#2 about checking the stator resistance. Jerry also provided a link to trouble-shooting ignition problems.

Thanks. I already did the swap test, added a ground wire and made new wire connections for the block which fixed the wiring issue. Im just not sure what coil to buy since my ignition system has been swapped? I did figure out my carbs were bad so I have 2 new (used) ones on order. One of the arms holding the float pin was completely broken off on the bottom carb which was causing it to spit gas out of the side and prob flood. The top carb needle that sticks through the middle (tube-bypass)was also broken off and the main nozzle was jacked as well. The top coil does get spark but the tester showed it was weaker than the other three. I really appreciate all the help.
 
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