Could a weak ignition cause this? (updated with test results)

[Joe_the_boatman]

EDIT: [Scroll down for test results]

'85 60hp 2-stroke. I'm beginning to think my bogging problem isn't fuel related, since I've replaced just about everything on the fuel side.

Motor starts and idles fine. Hit full throttle and RPM's jump to around 5K for a few seconds, stumbles a little, then 4K (still at full throttle) and then engine quits unless throttled down, or it may jump back up and then quit. Idling or running slightly above idle the engine runs fine, and gets me back to the dock.

Sounds like a fuel problem, right? Carb bowls have lots of fuel in them after the engine shuts down, though. Pump, carb gaskets, needle valves/seat, fuel lines and filters have all been replaced. Carbs dunked and reassembled, floats set at 11/16", then link'd-n'-sync'd. Timing's 4?BTDC @ 800 RPM. Running Autolite plugs now. Engine missed and stumbled big time when I put NGK's in (weird, I know). Runs great w/ Autolites though. Mixture screw is set where richer or leaner causes idle RPM's to drop (about 3/4 out).

Any ideas? I would think a bad ignition wouldn't let this thing run at all, but again, it starts and idles (trolls) fine.

 

[monk-monk]

Re: Could a weak ignition cause this?

Re: Could a weak ignition cause this?

i don't know that motors coil(s) set-up very well, but you could very well have a coil problem...that change of plug thing...those NGK's could be asking more from the coil(s) to create the right spark and killing the coil! if it has 12 volts to the ignition system with a good battery then the coil is getting 12 volts, but it may be week, and under load may not be able to produce enough spark from the output side to satisfy enough spark to burn off the fuel its being asked to burn therefore drowning or bogging the motor.

 

[emckelvy]

Re: Could a weak ignition cause this?

Re: Could a weak ignition cause this?

Just for a Lark, check stator resistance with a meter. You might even check it when the motor's cold, then again after the motor's been run, warmed up, and then acts up. If the resistance changes drastically, I'd be very suspicious of a cranky stator. Or if the resistance values of either lo-speed or hi-speed windings are out-of-spec, hot or cold.

If you don't have a meter, check the Sears sales paper this weekend. They always seem to have one or another on sale. You should be able to pick up a quite serviceable VOM for $25 or less. Or try your local Radio Shack.

Here's a resistance chart and some troubleshooting info that you may find helpful:

http://www.boatpartstore.com/mercreadings.asp

http://dolphinmarineservice.homestead.com/ign5.html

http://outboardparts.com/mercury/troubleshooting/troubleshooting10.htm

HTH...............ed

 

[Joe_the_boatman]

Re: Could a weak ignition cause this?

Re: Could a weak ignition cause this?

Thanks guys. I also replaced the rectifier. Now my (also new) battery charges....

My (pdf) manual I got off ebay is missing the pages with the stator specs; thanks again for those links.

 

[CharlieB]

Re: Could a weak ignition cause this?

Re: Could a weak ignition cause this?

An inductive timing light or inductive tach should show you if you are have an ignition failure at speed.

 

[Joe_the_boatman]

Re: Could a weak ignition cause this?

Re: Could a weak ignition cause this?

Yeah, I didn't have my timing light with me last time. Good idea though.

My question is, if it is the ignition, why would it only exhibit this behavior when under load, as opposed to just revving it in the bucket at the same RPM's?

Also, it will rev and run fine, but just not for long. What changes in the ignition system in those few seconds that would keep it from working properly from then on? This is why I thought it was the fuel system this whole time. I will do the ignition checks tomorrow morning.

 

[emckelvy]

Re: Could a weak ignition cause this?

Re: Could a weak ignition cause this?

You can have what looks like a good spark, but if one or the other of the ign charge windings in the stator are bad (or going bad and causing intermittent problems), it'll cause running problems.

A timing lite won't give you an indication of this kind of problem, but is a handy tool to check for weak spark or a 'miss'.

But problems with the stator are easily diagnosed with resistance checks of the high-speed and low-speed charge windings........ed

 

[Joe_the_boatman]

Re: Could a weak ignition cause this?

Re: Could a weak ignition cause this?

Test results:

Coils:
(primary=between +/- on coil, secondary=+ or - to high tension lead (spark plug))
#--Primary(ohm)--Secondary(ohm)--[Factory Spec (ohm)]
3--0.3--9510
2--0.2--9190
1--0.2--9240

Factory Spec is 0.2-1 ohm primary, 800-1100 on secondary.


Stator: (disconnected from switch box)
Wires--Tested Resistance (ohm)--[Factory Spec (ohm)]
RED->GND--147--[135-165]* (high side)
BLUE->GND--12,700--[5800-7000] (low side)
WHT->WHT--0.8--[???] (alt current to rectifier)

*my PDF manual says no continuity for high side to ground


Trigger: (disconnected from switch box)
Wires--Tested Resistance (ohm)--[Factory Spec (ohm)]
VIO->WHT/BLK--370M (or open)--[750-1400]
WHT->WHT/BLK--open--[750-1400]
BRN->WHT/BLK--3.3M--[750-1400]


I do electrical work for a living, so I'm fairly confident I took good readings. Trigger readings worry me though. How would this thing run at all with readings like that?

Should I keep checking parts, or start replacing? Since I got no continuity on the trigger, I'll pull it first and look to see if any wires got chewed up.

BTW, my rectifier went out and did this to my stator wires:
http://forums.iboats.com/showthread.php?t=270408
I'm wondering if that affected anything else in the ignition system......

 

[emckelvy]

Re: Could a weak ignition cause this? (updated with test results)

Joey, that stator reading is WAY out-of-spec and I expect you'll find that's your problem. I'd pull the stator for final inspection, if you find arc/burn marks or oozing potting material, that's an absolute confirmation of the problem. Of course that's not saying a stator with bad readings like that and no visible signs of malfunction ain't bad. But it's always comforting to have visual confirmation of one's diagnosis!

Anyway, she ain't gonna run right with stator readings out-of-spec, that's fer sur!

The trigger thing, if it were truly shot you would have no spark at all, so I'm thinking maybe there's an anomaly in the testing instructions. Or maybe it really is bad but somehow is still able to trigger a spark. But you'll be able to take a closer look at the trigger once you've got the flywheel off for the stator job.

Let us know what you find.........ed

p.s. I took a look at the pic in your previous posting and man! does all that wiring look nasty! The one trigger wire looks like it's about to corrode in two, makes one wonder what the wires look like farther back. You may find a mass of corrosion in any/all these wires. Might not be a bad idea to use the "pin probe" trick to check for a break or high-resistance in one or more of the wires. If you do, you may be able to cut back the trigger wire(s) and splice in a good section.

 

[Joe_the_boatman]

Re: Could a weak ignition cause this? (updated with test results)

...The trigger thing, if it were truly shot you would have no spark at all, so I'm thinking maybe there's an anomaly in the testing instructions. Or maybe it really is bad but somehow is still able to trigger a spark. But you'll be able to take a closer look at the trigger once you've got the flywheel off for the stator job.

Let us know what you find.........ed

p.s. I took a look at the pic in your previous posting and man! does all that wiring look nasty! The one trigger wire looks like it's about to corrode in two, makes one wonder what the wires look like farther back. You may find a mass of corrosion in any/all these wires. Might not be a bad idea to use the "pin probe" trick to check for a break or high-resistance in one or more of the wires. If you do, you may be able to cut back the trigger wire(s) and splice in a good section.

Hey Ed...

Those wires in the prev post were the AC coming from the stator to the rectifier (which converts to DC to charge the battery).

I'm thinking the diodes in the rectifier went out (causing an open circuit), then the stator had a ton of high voltage AC looking for a place to go. The only way for the potentials to meet would be to run all the way back through all the windings. Lots of heat.

Stator doesn't look bad at all, minus the 2 AC wires. They were garbage all the way from the rectifier to the stator's plastic housing. I soldered new (larger) wires on, and shrinkwrapped it all.

I was thinking since that was only the charging circuit that was fried, I could still get the rest of the season out of it. Oh well....

Trigger wires look to be in good shape, and aren't kinked or anything. That's why the "open" reading bothered me (plus, it runs). Trigger would be difficult to replace - I'd have to buy the tool for removing the flywheel mounting "pad" from the crankshaft, then worry about indexing the flywheel on installation.

Here's what I'm dealing with, if anyone's interested: (I always take pics. If nothing else, it helps me with reassembly).

Base of the stator, showing wires that were replaced:

 

[Joe_the_boatman]

Re: Could a weak ignition cause this? (updated with test results)

New stator is on it's way. It's easy to replace, who knows what the high voltage windings look like underneath, and resistance is out of spec.

If that doesn't help, we'll look at the trigger next.

 

[Joe_the_boatman]

Re: Could a weak ignition cause this? (updated with test results)

New stator's on. Runs/idles fine in the bucket, so we took it out to Allatoona today. Same problem. Would hit 5400 RPM for a few seconds, then backed down to around 4000 (still full throttle). Throttled down to 1500 RPM, then it conked out after about 20 seconds.

Still sounds like a fuel problem. Next step is to buy a used set of carbs and swap them. I've looked over these carbs 3 times now since they were cleaned and dunked. I would think leaky floats would be the culprit, but they didn't have any liquid in them each time I've removed the bowls.

I'm going to get a DVA meter and test the rest of the electrical system, also, and will test the switchbox next. Any other ideas?

 

[mikeya4]

Re: Could a weak ignition cause this? (updated with test results)

Have you tried pumping the primer bulb? maybe a weak fuel pump, not getting the fuel at higher rpms?
just a thought

edit:
opps just saw you replaced the pump, might be worth trying to pump the primer just in case

 

[hkeiner]

Re: Could a weak ignition cause this? (updated with test results)

Next step is to buy a used set of carbs and swap them

.

Before replacing the carbs or doing other major (expensive) work on the fuel system stuff, you might try using a vacuum gauge and some clear hose to first determine if you have fuel starvation situation or not. The below guide may help you.

 

[Joe_the_boatman]

Re: Could a weak ignition cause this? (updated with test results)

.

Before replacing the carbs or doing other major (expensive) work on the fuel system stuff, you might try using a vacuum gauge and some clear hose to first determine if you have fuel starvation situation or not. The below guide may help you.

Thanks for the guides. I will run through the tests when I get back in town.

I checked the fuel pressure on the outlet of fuel pump - 3.5psi @ 1200 RPM.

Also, carbs have plenty of gas in the bowls when it stalls out. I didn't check every time it stalled out though, since I was busy testing other stuff.

I think the clear fuel line idea will give me a better picture of what's going on.

 

[CharlieB]

Re: Could a weak ignition cause this? (updated with test results)

Before you start spending money on carbs.......

Have you made the determination that you still have spark on this thing dies?

You could still have a temperature related ignition failure, the module failing once to operating temp, which is NOT the same as just running it 'on the hose' or 'in a bucket'.

When the engine is under load, in gear working moving water with the prop, iintake vacuum falls off, progressively lower with additional throttle opening, until WOT when maximum volume of air enters each cylinder.

The more air in a cyl the more electrical load/voltage is required to bridge the plug gap, ignition systems begin heating to their operating temp.

Which is where YOUR engine fails.

Take along a spark tester, inductive tach or timing light to monitor spark up to and during failure.

Does the engine lose spark? If no THEN proceed to the fuel system.

 

[jerryjerry05]

Re: Could a weak ignition cause this? (updated with test results)

Do you use a built in tank or a portable? You said new hoses does that include a new bulb? New bulbs can be bad from the factory.The pickup in the tank could be getting something at higher speed.The air vent could have a clog.Jerry

 

[j_martin]

Re: Could a weak ignition cause this? (updated with test results)

I had a high speed misbehave problem with an XR4. Put on a fuel pressure gauge and dogged the problem to all of this:
Bad fuel line and primer bulb
Plugged fuel filter (many times
sludge in tank, plugging screen
fuel pump
carb adjustments
the fuel connector (bayonet)

All these faults were in the system. Found them one by one, and proved the repair with the gauge.
I wound up discarding the fuel filter on the engine, and putting in a Racor fuel/water seperator and filter. Also discarded is the bayonet fitting. Makes winterizing more of a chore, but eliminates a common problem.

I took out the fuel pressure gauge. One less thing to look at when I'm laboring at keeping the metalflake up and the prop down while at speed.

hope it helps
John

 

[Joe_the_boatman]

Re: Could a weak ignition cause this? (updated with test results)

Thanks for the replies everyone.

Yeah, I know, I DO need to check for spark when it dies. My reasoning for not doing it yet is that the engine dies instantly when given throttle, so I didn't think the timing light would show me much, since it would all happen so quickly. Worth a shot though. The weak spark theory fits my symptoms best, so that does need to be checked. I'll do it next time out.

I've owned 10 cars (all used and high mileage), and 6 (vintage) motorcycles, and never had an ignition problem. Car/bike problems like this have always been fuel related (i.e. bike sits in someone's garage for 5+ years). Guess I've been lucky up 'till now.

I use portable tanks. I blew out the lines w/ compressed air, all the way to the carbs. 3.5psi fuel pressure to top carb, at idle. Carb bowls have fuel after the engine dies. I admit, they WERE running out of gas the first few times out with this motor.

After it'd die, and wouldn't rev past idle in gear, squirting premix into the carbs would cause the engine to surge, so I knew it was a fuel starvation problem. Now, after rebuild, fuel sprayed in when idling (after the engine's "run well then die" cycle), causes it to choke out and quit.

I have not replaced the bulb, but the check valve works as it should. I also need to put in a (temporary) clear gas line off the pump to see if there are air bubbles.

If it's nice out this weekend, hopefully we can launch again and test this stuff out.

 

[CharlieB]

Re: Could a weak ignition cause this? (updated with test results)

Search this site for the CDI Ignition Troubleshooting Guide, or get it from the CDI site.

A very informative, step-by-step guide to testing and tracking down an ignition problem, complete, detailed down to which color wires for your specific motor.

A DVA Meter is critical to load test stator and triggers.

I suspect you are going to find a component failing once up to operating temp.