ignition testing question

[DukeDelago]

I've used an in line ignition spark tester to verify that all 4 plugs are getting spark on my 1990 force 120. My question is, does this necessarily mean that the plugs are firing, or just that they are getting power from the coils. The engine starts and idles fine, but maxes out at just over 4000 rpm and has a very hard time planing. At WOT it will occasionally "blip" up a few hundred rpm on the tach, but never gains full power. Is it possible that I have a faulty plug, or should I be looking elsewhere in the ignition system? If I remember correctly, the CD modules fire multiple times per cycle at low RPM, but only once above 3500 or so. If this is the case I am wondering if I am only getting actual spark sometimes on one cylinder, but that it's only noticeable at high rpm where there isn't multiple sparks on the power stroke. Any suggestions would be helpful, it would be nice to know if I am even in the ballpark on this!! Thanks all.

 

[Josh P]

Re: ignition testing question

I would try plugs as they are cheap, clean your carbs and replace your fuel pump diapharm. if you find alot of crap in the bowls maybe install a filter. but plugs foul out easily i would try a set and get ngks for replacments.

 

[jerryjerry05]

Re: ignition testing question

You could have a bad plug.Did you do a compression test?All the plugs burning right? Any wet/oily or water on any,anything odd???
Tell us about the prop,load,boat size.Anything???
Spark test.$6 gap tester at any auto zone etc. Spark should be 7/16"
Fuel pump diaphram?
Do the tests and get back.Read my signature.It could be swollen gaskets in the needle/seat. Diaphram or pump valves not operating right.J

 

[DukeDelago]

Re: ignition testing question

compression is good, 135, 135, 135, 129. Top two plugs look a little oily, bottom two look a little dry. replaced fuel pump diaphram this season, have torn down and cleaned carbs multiple times in pursuit of this with no difference. Boat is a 1990 maxum 2100 ldc (l-drive). Not sure on prop pitch, but I think it is 13" and the original. My work is by no means fool proof, so all these items are still possibilities!! Jerry do you recommend the gap tester over the in line version? I assumed the in line was more idiot proof, but I'm always happy to add a tool to my collection if it's going to be the right one! I bought a new set of Champion ul18v's just to rule plugs out of the equation. The set I'm replacing is fairly new, but you never know