Top cylinder runs weakly in Force 50 hp 1989 motor

[Lenmoy]

I am stumped! The engine runs ragged during idle and into mid range. Runs like on 1.5 cylinders instead of a 2. It is slow to plane off the 15 ft. Maxum boat with only the driver inside. A test using a standard spark tester shows a somewhat cooler color spark on the top cylinder (bad one-red/blue color rather than white/blue color-good one) but they both pull at least the prescribed distance of about a 1/4 inch or more. Visually the bad cylinder spark frequency seems to not be as fast as the good one althought the different color may be misleadiing and of course the engine is idling slower due to the miss anyway. I have switched coils, plugs and spark plug wires but the same results on the top cylinder. Nothing changes. When I run the engine on the bottom cylinder only it idles well but when I run the engine on the top cylinder only it runs very roughly or stalls. After this individual cylinder test the top or bad cylinder spark plug color is slightly darker than the good one. Although it could not be classified as too dark! Visual inspection of fuel pump diaphram is O.K., carb has been cleaned several times and is super clean, Wot timing is at 28 degrees as called for, compression on both cylinders is 130 psi, with the carb removed the reeds look fine as well as they can be seen, without any breaks or holes and they can be heard to snap back when opened slightly manually using my fingers and it has brand new 50/1 fuel. When first started up and for at least 10 minutes or until I open the throttle up to clear it out, the engine smokes blue white smoke out the exhaust as though I put too much oil into the gas which I did not do. Once cleared it does not do that again when used. Hardly have to use the choke to start the engine in summer temps. I am not familiar with the trigger mechanism. Considering the mention above regarding the spark not seeming to be as fast in the bad cylinder could one, if there are two triggers, not be firing often enough? If there is a trigger for each cylinder could that be the problem and if so, does anyone know how to test this? FYI this is a model F07A9B with a WE 17C carb.

Any and all suggestions would be greatly appreciated.

Len

 

[bubbahemi]

Re: Top cylinder runs weakly in Force 50 hp 1989 motor

did you look at the rigs or plug wrires

 

[Jiggz]

Re: Top cylinder runs weakly in Force 50 hp 1989 motor

If you already switched plugs, coils and plug wires then the only thing left is the module. Which could mean half side of the module is not working properly. But before jumping on that conclusion check the voltage output of the module using a DVA equipped voltmeter. Orange wire to ground and then red wire to ground. The voltage reading should be around 150V+.

 

[Lenmoy]

Re: Top cylinder runs weakly in Force 50 hp 1989 motor

did you look at the rigs or plug wrires

Thank you. I have switched wires and tried a new one on the poor running cylinder.

Len

 

[Lenmoy]

Re: Top cylinder runs weakly in Force 50 hp 1989 motor

I am not familiar with DVA equipment. What is it? Can I use a multi volt/ohm meter that is capable of reading this voltage? Also, is this voltage while the engine is running?

Can you address the trigger or triggers?

Tks

Len

 

[Jiggz]

Re: Top cylinder runs weakly in Force 50 hp 1989 motor

The DVA is an adapter for reading transient voltage or spikes. Since the CD module only feed voltage spikes to the coils it is very hard to read using a conventional voltmeter. Google it and probably find some for sale on ebay. The trigger seems to be working although you can try reading its output with a regular voltmeter. The voltage output is really small 0.5V~5VAC. These readings are taken with the engine at least idling.

 

[Lenmoy]

Re: Top cylinder runs weakly in Force 50 hp 1989 motor

The DVA is an adapter for reading transient voltage or spikes. Since the CD module only feed voltage spikes to the coils it is very hard to read using a conventional voltmeter. Google it and probably find some for sale on ebay. The trigger seems to be working although you can try reading its output with a regular voltmeter. The voltage output is really small 0.5V~5VAC. These readings are taken with the engine at least idling.

I noticed something while getting comfortable with ign. wiring. On the output of each coil at rest from the spark plug lead connection to the input wire on the back, not the ground, one reads about 1K while the other reads around 300 ohms. They are different as one probably has been replaced. One is black and the other is blue. Do these resistance reading tell us anything?

Tomorrow I intend to pull the flywheel off so I can better identify the wires by color and then do some testing. I may not be able to do the DVA test yet.


Tks

Le

 

[Lenmoy]

Re: Top cylinder runs weakly in Force 50 hp 1989 motor

The DVA is an adapter for reading transient voltage or spikes. Since the CD module only feed voltage spikes to the coils it is very hard to read using a conventional voltmeter. Google it and probably find some for sale on ebay. The trigger seems to be working although you can try reading its output with a regular voltmeter. The voltage output is really small 0.5V~5VAC. These readings are taken with the engine at least idling.

I have used my digital volt/ohm meter just to see what I actually could observe knowing that it would not act like a DVA. However, I did notice different voltage spikes from each side of the CDI. One side seemed to be lower than the other. Do you think this indicates something?

Thanks for you help

Len