1980 200HP Johnson V6 Rough Idle (Sensor Coil?)

[Randy W.]

Hi All:
I'm working through a very rough idle issue. I have rebuilt the carburetors with kits and replaced one fuel pump. I feel comfortable that the fuel system is now solid. As background, compression is 90 lbs. on 5 cylinders and 95 lbs. on one. I'm moving to the ignition area supported by a clymers manual and the original shop manual. The sensor coil (part #581487) registers 18.5, 33.9, and 18.5 ohms on terminal a,b and c respectively. On the other side we have 33.8, 18.6, and 18.7 ohms across a,b and c respectively. According to both manuals these values should be 17.5 ohms +/- 5. Do you think this could be causing my rough idle issue? BTW, several weeks ago I did a spark check and had spark at all six wires via a spark checker at 7/16"....however I didn't think it was that strong? I built a DVA adapter with specs from this site, however I was not able to get cranking voltages from the meter out of the power packs prior to going into the coils. Maybe someone can point me in the right direction. Thanks again! Randy.

 

[jonesg]

Re: 1980 200HP Johnson V6 Rough Idle (Sensor Coil?)

I think you'd have to have a good spark to jump 7/16th gap.
A timing light might show non spark better while its running.

 

[Randy W.]

Re: 1980 200HP Johnson V6 Rough Idle (Sensor Coil?)

Thanks Jonesg:

I've missed something, so I think your advice to go back to the timing light is a good start (or restart). I'll recheck timing also. Thanks again!

 

[emdsapmgr]

Re: 1980 200HP Johnson V6 Rough Idle (Sensor Coil?)

As mentioned by jonesg, I'd probably start the engine up on the garden hose and check each plugwire for spark using an inductive timing light. That light will show weak firing, no fires and intermittent. First guess is that if the engine runs ok at high rpm's the ignition is ok. Idle problems are unique on carbed engines. They idle with the butterflys closed. (Visually check to make sure that they are all closing properly at idle.) In so doing, they draw fuel through the special idle circuits (passages) in the carb bodies. If it won't idle, could be you have some dried fuel in one of more passages. Once you crack the throttle just a little (butterflys open slightly) the carbs will draw on other jets and may run fine all the way to top end. When overhauling these carbs, best to spray an aerosol carb cleaner through one passage in one carb, then compare the outflow spray pattern with that same passage from the next carb. Repeat on all passages, all carbs to make sure they flow fuel equally between carbs.

 

[Randy W.]

Re: 1980 200HP Johnson V6 Rough Idle (Sensor Coil?)

As mentioned by jonesg, I'd probably start the engine up on the garden hose and check each plugwire for spark using an inductive timing light. That light will show weak firing, no fires and intermittent. First guess is that if the engine runs ok at high rpm's the ignition is ok. Idle problems are unique on carbed engines. They idle with the butterflys closed. (Visually check to make sure that they are all closing properly at idle.) In so doing, they draw fuel through the special idle circuits (passages) in the carb bodies. If it won't idle, could be you have some dried fuel in one of more passages. Once you crack the throttle just a little (butterflys open slightly) the carbs will draw on other jets and may run fine all the way to top end. When overhauling these carbs, best to spray an aerosol carb cleaner through one passage in one carb, then compare the outflow spray pattern with that same passage from the next carb. Repeat on all passages, all carbs to make sure they flow fuel equally between carbs.

Thanks! That's the procedure I used on the carbs. Reassembled the stator and sensor unit and it runs great! Must have had a ground, connection or coil wire problem. I'll be doing the timong light check also.

 

[emdsapmgr]

Re: 1980 200HP Johnson V6 Rough Idle (Sensor Coil?)

Good deal. Easy fix. Bad ground cause of a lot of problems. Many expensive ignition parts have been unneccarily replaced due to bad grounds, esp on older equipment.