Engine quit suddenly after running perfectly.

[calm like a bomb]

What would cause an engine that is running just fine all weekend to suddenly shut off under little to no load when it ran like a top up to the split second it abruptly quit? 70hp Johnson 3 cylinder(1988). <br /> It acts like it is electrical,as if I had yanked the killswitch or simply turned off the key.<br /> Fuel is fine,carbs taken down and cleaned(already look fine)providing plenty of fresh fuel to cylinders,fuel pump seems fine..plugs are correct,correct gap and were not fouled.Compression is fine.Killswitch,primer bulb,etc,etc were all fine.Waterpump is fine,engine was not overheated or even close. <br /> Plenty of good blue fire from the plugs when tested.Flywheel nut not loose,no pin sheared or any other noticable problem.It has me baffled.<br /> It will not restart or even fire,backfire or give the slightest indication that it will ever start again. <br /> Can the CDI box or ignition coil under the flywheel go out this suddenly and still provide spark but at the wrong time?Could it have jumped time somehow? It still seems to provide plenty of fire to all plug wires when tested in low light(night-time) <br /> My best quess at this point is that the recent full moon did it

 

[Walker]

Re: Engine quit suddenly after running perfectly.

Do a compression test on all 3 cylinders

 

[rodbolt]

Re: Engine quit suddenly after running perfectly.

test compression, test spark for a blue spark at a 7/16ths gap. then insure it has gasoline and not water in the fuel bowls. drain each bowl and collect the drained fuel for inspection. if the inner mag on the flywheel hub is spun it will still have good ignition spark but at the wrong time. easy to check with a timing light.

 

[fireman57]

Re: Engine quit suddenly after running perfectly.

Not totally familiar with your engine but do you have a fuse on the side with a red wire going in one side and a purplish red one out the other?

 

[calm like a bomb]

Re: Engine quit suddenly after running perfectly.

How can it be checked with a timing light when it WILL NOT START?By spinning the starter?I already checked the compression on all three cylinders.The main fuse is fine.<br /> Fresh 91 octane gas about three days old is used.Absolutely no water in fuel,as stated earlier the carbs were pulled off and each individually cleaned.This engine ran perfectly up until the split second it shut down abruptly.No missing,coughing,sputtering,it ran fine.<br /> rodbolt..it gets good blue fire from the plugs now.How can I check for blue fire at an almost 1/2" gap?The normal plug gap setting is .040<br /> It sounds like possibly the inner mag on the flywheel..what would cause it to have spun? <br /> Thanks..this one has be whipped right now

 

[Chinewalker]

Re: Engine quit suddenly after running perfectly.

I have had this happen with a switchbox (powerpack) that was going bad. I was able to borrow the powerpack off a friend's motor and it didn't do it anymore, so I went out and bought a new one for mine. Electronic parts are generally non-returnable, and they're not easily tested without the proper diagnostic equipment, so the borrow/swap method worked better for me.<br /><br />I've also seen this happen with a bad ground in the ignition, so make sure the powerpack ground lead is properly attached.<br /><br />- Scott

 

[fireman57]

Re: Engine quit suddenly after running perfectly.

rodbolt is talking about the spark jumping 1/2# to a ground while you are cranking the engine. Not setting the spark plug gap at 1/2". >40 is a good setting for your plug. I agree with Chinewalker. I know you said that you had them replaced but maybe whatever killed your original packs was not fixed and it killed you new one(s).

 

[calm like a bomb]

Re: Engine quit suddenly after running perfectly.

Scott,<br /> The ground seems to be fine,I don't think that is contributing to the problem.<br /> When you refer to the switchbox/powerpack..do you mean the black box with the plug wires exiting it and a few various smaller wires also?<br /> That seems likely,but when this one went bad,it went bad abruptly with absolutely no warning.<br /> Can they fail that suddenly yet still provide a good blue spark to the plugs?<br /> This one is a real puzzle

 

[calm like a bomb]

Re: Engine quit suddenly after running perfectly.

fireman57,<br /> 10-4 on the spark jumping....I didn't think he meant to stretch the gap to 1/2",I don't believe the plug would respond too well to that treatment The original packs have never been replaced.The engine ran fine until it abruptly quit the other day.The only thing replaced were the carbs after I took them all off and serviced them again..they were fine anyway.Still no go.<br /> it is starting to sound like the powerpack..can it fail abruptly yet still provide fire to the plugs?

 

[Silvertip]

Re: Engine quit suddenly after running perfectly.

Is the spark capabable of jumping the 1/2 inch gap you told about? If not, its an ignition problem. Hold each plug wire 1/2 inch from the block and see if the spark jumps that gap.

 

[Scaaty]

Re: Engine quit suddenly after running perfectly.

If its getting gas, and spark, it will do SOMETHING! You say "it is starting to sound like the powerpack..can it fail abruptly yet still provide fire to the plugs?"<br /> Not any powerpack I have seen. If you get spark, try squirting a touch of gas in the hole, put a plug in, and yank.....

 

[steviecops]

Re: Engine quit suddenly after running perfectly.

I had the exact same thing happen to me whilst I was out at sea last Friday! It had me totally baffled for a good 20 minutes. Tested for a spark, had great spark. Squirted fuel into carbs, didn't even try to splutter. Took out plugs and replaced with new, nothing doing.<br /><br />It turned out it was part of the linkage from the throttle arm to the timing plate that had come off! There is a little plastic ball that fits into a socket attached to the arm on the timing plate, and somehow it had come out. Once I popped it back into place, the engine started up straight away.<br /><br />I hope that your problem is something as simple as that.<br /><br />Good luck.<br />Steve

 

[calm like a bomb]

Re: Engine quit suddenly after running perfectly.

Roddy6950,<br /> That's what I thought too.Fuel + fire = SOMETHING!Believe me when I tell you I gave up on that approach about three days ago.It ain't gonna happen.Should never introduce ether into the equation to check our fuel + fire = SOMETHING theory..<br /> Even that = NOTHING! <br /> No yanking is necessary because it is an electric start.You can spin it over all day and nothing.Remove plugs and turn it over and it will actually spray a fine mist of fuel out of the plug holes as the pistons cycle up and down.Plenty of fuel.

 

[calm like a bomb]

Re: Engine quit suddenly after running perfectly.

Upinsmoke,<br /> What is the correct procedure to hold a plug wire 1/2" from the block while turning the engine over without getting zapped like I'm in an electric chair? Two sticks might work huh?<br /> Or get a really naive neighbor to help..

 

[calm like a bomb]

Re: Engine quit suddenly after running perfectly.

Steviecops,<br /> If I could only be so lucky.

 

[steviecops]

Re: Engine quit suddenly after running perfectly.

Have you checked it?

 

[steviecops]

Re: Engine quit suddenly after running perfectly.

Seems like you know you've got fuel, because you put it there! You have a good spark, so it must just be happening at the wrong time. Sheered flywheel key perhaps?

 

[calm like a bomb]

Re: Engine quit suddenly after running perfectly.

Flywheel key is fine.....it's hard to check from work.

 

[Silvertip]

Re: Engine quit suddenly after running perfectly.

Use an insulated pliers or a clothspin (or clothspeg if you are an easterner) to hold the wire, or make a spark tester. Put two nails in board 1/2 inch apart. Run a wire from one nail to engine block. Put the plug wire on the other nail and spin the engine over. Repeat the test on the other cylinders. You may have spark externally but the ignition may be failing under compression. You should not need to check spark in low light. Good spark is visible in broad dayling and provides a good solid snap when it fires.

 

[Silvertip]

Re: Engine quit suddenly after running perfectly.

You also said compression is good but you didn't provide any numbers.