75' 70hp evinrude strange ignition problem

[xjdriver]

Hi guys, I have a 1975 70hp evinrude 70573E. It sometimes runs rough and stumbles, and other times it seems to run fine (on muffs) so i fired it up one nite and saw a bright blue spark jumping from the plug BOOTS to the base of the spark plugs, and it was running bad at the time to, so I start it up again the next nite and it ran fine, no spark jumping from spark plug boots. I just dont get what could be cousing this. I attempted to take it out on the water but it ran pretty bad at low RPM the idle was rough and mid range RPM had a stumble, just like it did on muffs when I saw the spark jumping. I have no way of running it in water at home, just on muffs, it seems like one cylinder will randomly drop out and then kick back in it will run rough, then cough and start running smooth again, then start to stumble again, then sometimes it seems to run fine. I am open to suggestions other than ignition. but the sparks jumping was pretty strange. Its got new plugs and had spark on every cylinder when I tested it, compression is 120 on all cylinders to. mabey its some kind of ground issue? or foulty plugs? I dont Know

 

[Daviet]

Re: 75' 70hp evinrude strange ignition problem

I would start by replacing the defective plug wire boot, it is leaking to ground and causing the cylinder to misfire.

 

[xjdriver]

Re: 75' 70hp evinrude strange ignition problem

Ya thats what I was thinking, but the wierd thing is that I took all the boots off and just ran it with the metal coils, and no sparks jumped and it seemed to run good! do you think that somehow the boots are defective and they are acting as a conductors and is allowwing the spark to go through it? its still pretty wierd becouse they are RUBBER. is there some kind of tub that I could get to run it in water at home?

 

[MACH1SCJ]

Re: 75' 70hp evinrude strange ignition problem

That is generally caused by carbon tracking. Once it starts the only way to fix it is to replace the boot & spark plug at the same time. Look on the plug does it look like someone has drawn a line down the porcelain with a pencil? But it wont wipe off, or in the boot a thin burn line. A big trash can??? I have a 55 gal plastic barrel I cut down.

 

[xjdriver]

Re: 75' 70hp evinrude strange ignition problem

Ya, the spark plugs have black lines/marks on them, but dang there brand new! or were new. I have a metal 55 gal drum that I cut the top off to run my 6 horse in, but the 70 wont quite fit, mabey if I cut the top lip of the barrel it just might fit ill have to try it tommorow. Im thinking of running it with just the metal coils on the plugs and somehow get it in the water and see if this solves my problem, I guess new plugs and boots are in order anyways.

 

[xjdriver]

Re: 75' 70hp evinrude strange ignition problem

Got it running in a drum, seems to be running fine except shifting at dead idle, it will run for a couple seconds then stall. If i just raise the idle a hair using the warm up lever it shifts fine. How do you properly raise the idle?

 

[Daviet]

Re: 75' 70hp evinrude strange ignition problem

#41 is your idle adjust screw, make sure to check the cable adjustment when you are done, idle should be 700-750 with the boat in the water and in gear warmed up.
http://www.ishopmarine.com/ishop/js...CatFilter=BRP&eCatSupFldr=supplier-100-005-EJ

 

[xjdriver]

Re: 75' 70hp evinrude strange ignition problem

OK but I heard that it needs to idle with all carbs closed and the first hash mark on the throttle cam lined up with the roller, and if I adjust using that screw im pretty sure it will just begin to open the carbs up. I could be wrong tho. unless I need to disconnect the throttle cam from the linkage and adjust the idle with that screw using timing only, then adjust the throttle cam to the first mark?

 

[Daviet]

Re: 75' 70hp evinrude strange ignition problem

Anytime you change the linkage you need to check the link & synk to make sure all the linkages are adjusted properly.

 

[xjdriver]

Re: 75' 70hp evinrude strange ignition problem

Ok, is there any way of using a automotive style multimeter/tach on the engine? Couse the boat doesnt have a tach. And if i let it run in the drum for awhile will that warm it up? It doesnt seem to really warm up much, it does have a new t-stat, thanks for the help guys

 

[xjdriver]

Re: 75' 70hp evinrude strange ignition problem

Raised idle, and she seems to be running fine now. In the drum anyways, i might be taking her out this weekend.

 

[Daviet]

Re: 75' 70hp evinrude strange ignition problem

Good luck on your test run. You have to have a 2-cycle tach to use on your engine, an automotive tach is usually for a 4-cycle engines.

 

[xjdriver]

Re: 75' 70hp evinrude strange ignition problem

Thanks, my last test run didnt go so well. I adjusted idle by feel, just high enough to idle in farward gear smoothly. I also noticed that it took less effort for the motor to idle in reverse, is this normal?