120hp rough idle

[slim6969]

need some help guys i have a 1990 rude 120 that has a rough idle heres a video please note i did not give it gas in the video i put a new fuel pump and spark plugs on it any help would be greatly appreciated

 

[Bosunsmate]

you should compression test it and test for spark on each cylinder, if thats ok i recommend a carb clean

 

[ThomW]

I agree. See if you have good spark on all plugs. One could be cutting in and out causing the rise and drop of rpm's. if that's okay, and compression is good. Most likely a gas issue.

 

[slim6969]

That's guys. Will post what I find out

 

[slim6969]

So update. Compression is all around 140 give or take a few. Have spark on all but one cylinder I changed the coil and still no spark.

 

[slim6969]

I have tested the orange wire that powers the coil with the key on and it has the same voltage as the rest of them.

Should I be testing it well cranking the engine over ??

 

[racerone]

It should be tested while cranking it over.----But what voltage shows there when key is in " on " position ?

 

[slim6969]

12. Battery voltage. Even when cranking I get voltage. Can't remember off the top of my head what it was but it was the same as the rest of the orange plugs

To me I waould think if there's voltage there and the same voltage as the rest it should be sparking.

When I move the orange wire to the coil above and the no spark fallows

 

[racerone]

What meter are you using to check this voltage ?----Tester as per a factory manual ?

 

[slim6969]

What meter are you using to check this voltage ?----Tester as per a factory manual ?

a digital multimeter

 

[racerone]

Perhaps a factory manual will suggest a different / proper meter for testing on this type of ignition system.

 

[Bosunsmate]

Well if it follows it thats a good enough test for me to say its whats up stream of that orange wire

 

[cfauvel]

can we assume that the stator is fine as three of four plugs have good spark?
you changed out coil and that didn't help, so to me the only thing possible is the power pack or a bad wire going to the coil (sometimes the wire can break inside the insulation). I don't recall the expected voltage come from the power pack to the coils, I would guess in the 200-300 v range whilst cranking....and you'll need a DVA adapter to accurately read that.

 

[Bosunsmate]

Dont forget the timing base, that could be poked

 

[cfauvel]

Dont forget the timing base, that could be poked

yes indeed...best to start from timer base and stator and work your way down in the testing....I see a DVA adapter in someone's future.