Force 120 Idle rough

[Josh P]

OK i need help, i have a 1991 force 120, problem is it has a rough idle kinda like its only firing on 3 but trying to fire on the 4th. I have checked compression, dry test came up with 150 all across the board, so i replaced plugs , no change so i pulled the carbs and cleaned them, they had some junk in them. Set my idle screw at lightly seated to 1 turn out , fired it up same problem. Tried adjusting the idle screws it doesn't smooth out but it dies so they are doing something. If i try to rev it a bit by the linkage ( i know its not advancing the timing but it should still rev up to a point) and it dies but fires right back up> I have included a video sorry its from a cell phone, crappy quality. But you only really have to listen to it. I need help please. forgot to put have checked spark while cranking and all was good are this known to not fire when under compression? but fire when cranking?
Force 120 rough idle

 

[jerryjerry05]

Re: Force 120 Idle rough

Check the fuel pump diaphram.Then the reeds.You can see them when you remove the carbs.
What condition on the plugs?.
Get a spark tester.It measures the strength of the spark.Set it at 7/16 gap. Available at Auto Zone $5.99.J

 

[brianvolt7]

Re: Force 120 Idle rough

What are the reeds?

 

[Josh P]

Re: Force 120 Idle rough

crap forgot to put that to,i replaced the fuel pump diaphram and the 3 check valves in the pump, when i had the carbs off i checked the reeds they didnt look broken or missing maybe they still could be bad or stuck? plugs didnt loook bad they were a little black not bad tho the porcelin had some white showing i figured that they were fouled, what brand plug should be ran in these motors? i know in cars some manufactures dont like bosch as they make them run worse etc etc. IM gonna do the spark test later today. I cant explain well what reeds are but the do almost the same job as a regular valve in a 4 cycle engine, just a little different. When i wen to trade school 5 yrs ago we breifly touched on it, i just dont remember that most i mainly repair and hop up cars. I have a 88 fiero with a 425hp 3800 v6 supercharged Thanks again jerry helping me out tons

 

[Josh P]

Re: Force 120 Idle rough

ok checked spark looks like no 2 has no spark while running and no 4 has interminette ( how ever you spell it) so sounds like coils? i think so i found 2 new in box on ebay for 39 so im gonna grab them later unless its said otherwise. thanks

 

[jerryjerry05]

Re: Force 120 Idle rough

Before you buy anything change the coils around.#1 on #2 #3 on #4 or whereever you change them .Then try and see if the no spark follows the coil.J

 

[Josh P]

Re: Force 120 Idle rough

do you think it could be the trigger or cd if not coils (please say no please say no please say no)

 

[brianvolt7]

Re: Force 120 Idle rough

Sorry for butting in JerryJerry05 but would I be able to use this spark plug tester on my boat if the plugs are the flat style without a gap setting?

 

[Josh P]

Re: Force 120 Idle rough

ok i swapped coils. I swapped 1 with 2 and visa versa. now no 1 is dead cool i need a coil. but i swapped 3 and 4 and 4 with 3, i still have an intermittent spark on 4, my number 3 coil had good consistant spark, now its on 4 and it doesn't so any way to test trigger, or cd box?

 

[Josh P]

Re: Force 120 Idle rough

ok thanks to pnwboat he has helped me determine i need a stator one side ohmed out 750k the other set or side was only 500 ohms, values should be 680-850ohms, so off to get a stator anybody know where to buy a good used one or a decently priced new one

 

[Josh P]

Rough Idle 120 I really need help now.

Rough Idle 120 I really need help now.

OK so got the flywheel off, removed stator and trigger for testing. Before when i tested each of the above i removed all the wires from the terminal block and tested them came up with trigger ok, 50 ohms on all. Stator 790 on the 1/2 box wires and 510 on the 3/4 box wires. so that explains my intermittent spark on 4 right?. Well now that the flywheel was off i re tested everything. heres what i got
Stator - 790 ohms and 790 ohms. Now im lost.
Trigger- Pair 1: 52.8 Pair 2: 52.8 Pair 3: 52.7 Pair 4: 52.5.
Coil #1 Primary: .5 ohms Secondary : 999 ohms
Coil #2 Primary: .4 ohms Secondary : 2500ohms(found my dead coil)
Coil #3 Primary: .5 ohms Secondary : 999 ohms
Coil #4 Primary: .5 ohms Secondary : 1000 ohms
I know i have a bad coil but that is on a different cd box. Plus when i swap cd boxes i still have my intermittent spark on 4. but i lose cylinder 3 OK so now my question i need to do DVA testing what do i need to convert my multimeter to a dva? Need some help guys thanks

 

[pnwboat]

Re: Force 120 Idle rough

You need a DVA adapter for your meter. I don't think I would go out and by one just yet.

http://www.iboats.com/Boat-Parts-Accessories/dm/*******.883584158--keywords.DVA%20adapter--searched.1--**********.047598790--submit.Search--submit.x.0--submit.y.0

As far as the coil goes, it may not be bad. The connector for the spark plug is basically a piece of wire that is poked through the insulation on the spark plug wire, and makes contact with the metal conductor inside the wire. A lot of times corrosion gets in there and makes for a poor connection when reading with an OHM meter. If you pull the boot off, you'll see what I mean. Use some liquid soap or WD-40 to make it easier to get the boot off.

When you say you swap the CD Modules, are you swapping them with each other, or do you have another replacement CD Module?

Disconnect the "Kill Circuit" wires that go from the CD Modules to the terminal block on the starter side of the motor. I believe it's the third position down. They should be either White or Black/Yellow. Tape them up and see of that has any affect. NOTE: To stop the engine after you start it, just engage the choke to kill the motor. Hook them back up if it has no affect.

 

[Josh P]

Re: Force 120 Idle rough

i swapped the cd modules with each other, im gonna put the flywheel back on, check that coil and disconnect the kill wires, i did that before but i dont think i checked spark on no 4. thanks illl post my findings

 

[jerryjerry05]

Re: Force 120 Idle rough

Yes.J

Sorry for butting in JerryJerry05 but would I be able to use this spark plug tester on my boat if the plugs are the flat style without a gap setting?

 

[Josh P]

Re: Force 120 Idle rough

ok i dunno what i did but, i cleaned and regreased the trigger for when it turns, i cleaned the mounting surface of the stator after i tested it again befiore installing it. It tested good 795 ohms ohms on both sides, .9 for the rectifier. Anti-seized the bolts holding the stator, bolted it down, anti-seized the flywheel key it looked a bit rusty, then installed and torqued the flywheel, wired the ignition setup per the label above the exhaust cover, took my time double checked everything. Took the end off my no 2 coil no corrosion snipped some of the wire off to maybe get rid of the high resistance, no , luck its about 2200 now, reinstalled coil wire and terminal, the installed onto motor. Ok now i hooked up the hose turned on the water, it fires after 4 secs , had to drain the carbs and reset one of my float heights before this, it was spitting gas out the vent on the carb, wasn't off by much. fired it up instantly sounded better, now get this my coils and cd's are in the original place when i first had this issue. #4 spark is solid not intermittent, 3 is good 2 is firing, SOB no 1 is dead. so i got the multi-meter and while its running i set my meter on ac 200 scale and check all my wires on my terminal block to ground they are all getting signal of some sort, i dont have a dva so cant tell exactly but they are getting something. I am going to replace my number 2 coil cause it still has high resistance in the secondary side, and im gonna start with one cd box. Let me know if im thinking right. I will eventually replace my other CD box . Thanks guys sorry so long had a lot to touch on.