Logo
FULL SITE MENU

Late 80's 80HP 2 stroke won't go over 2,000 RPM after 25 mins of use

T

The Hammer28

New member
About 2 weeks ago, after jamming around on my boat at an average of about 4,000 RPM for 30 mins or so, the boat started to power down, like I was running out of gas. It ran fine at about 2,000 RPM, but if I tried to push it higher, it would start to sputter and hesitate like it was going to die out. Figuring that I was just low on gas and my gauge was busted, I took it out again after throwing some gas in about a week later. Again, after about 25-30 mins, it did the same thing. While putting gas in again, I overflowed the tank, so I now know I'm not low on fuel. Today when I took it out, I only managed about 10 mins before it began choking over 2,000 RPM. I then docked it for about 20 mins and ran it again, but it immediately started doing the same thing. My buddy suggested that it could be the fuel filter, which I will replace, but in the meantime, does anyone have other possible causes? Thanks.
 
Thanks. That sounds like an expensive problem. Is there an easy way to test for that? It has the Thunderbolt ignition, if that means anything to you.
 
I don't think it's overheating. I just had a boat shop replace the impeller/water pump and it's shooting water out of the side pretty nicely. It's a 4 cylinder.
 
Check for spark on all 4 leads.----------Belt driven distributor on it ?---------------Fuel pump checked ?--------Gas oil mixed at 50:1 ?
 
Thanks for the replies. I haven't done any troubleshooting, yet. I was hoping this might be a common problem and I'd get an idea of where to start. I'm pretty careful about mixing 50:1. I use a measuring bottle. I'm not sure about the belt driven distributor. I've attached a couple photos of the motor, which might give you an idea of what I'm dealing with.

https://www.flickr.com/gp/141392619@N04/09331Y
https://www.flickr.com/gp/141392619@N04/N5F29j
https://www.flickr.com/gp/141392619@N04/S64p06
 
ADI Merc (no distributor).

You need to immediately check for spark after it dies. Got to eliminate possibilities.

Jeff
 
I might be misunderstanding what you're saying, but the boat always has spark, at least as long as it's under 2k rpm. If I slam the throttle forward, it'll stumble significantly, but it will never actually die out. For instance, if I push the throttle to wide open, it'll stumble, then rest at about 1500 rpm. As I pull the throttle back (less throttle), it'll find a sweet spot and actually increase rpm and rest at about 2200 rpm. That "sweet spot" is now as high as that engine will climb. Anywhere between idle and 2200 rpm, the boat acts normally. I had it out for about 45 mins yesterday with it acting like that. Should I be trying to take it over 2200 and then pulling a plug wire to check for spark? On a side note, I traced the fuel line from the motor all the way back to the tank and it does not have a fuel filter anywhere, at least in-line. Have any idea where that might be?
 
Check the resistance of the stator high and low-speed windings when the motor is stone cold. Then, check the resistance after you have run for a while and it acts up.

I'd venture to say a bad stator and if the resistance readings are in spec and change drastically after warming-up, you've got it. They may be slightly out-of-spec even cold and that's a good indicator of a problem.

It certainly could be other things, but stator issues are extremely common on the ADI systems.

Here's some troubleshooting info from CDI Electronics:

https://issuu.com/cdielectronics/docs/practical_ouboard_ignition_troubles

The Merc ADI section starts on Page 74. You may need to pick up a DVA (Direct Voltage Adapter) to measure the high-voltage outputs at the switchbox and coils, for further troubleshooting if your stator resistance measurements are inconclusive. This site sells a CDI-Electronics DVA as I recall.

Measuring with a good meter and DVA in most cases will absolutely pinpoint the problem. But a bad stator can usually be picked up with a resistance check.

HTH & let us know what you find..........ed
 
One other possibility. Check the fuel system. I had an issue a couple years ago with my 70hp, one of the retaining pins for the one way valves in the fuel pump broke off and found its way into the carb feed. If the engine was shut down for awhile the piece would work its way back out and the engine would run great until it moved back up to a point where it would restrict the fuel flow enough to slow the engine down. Drove me nuts trying to figure out what was going on.
 
Thanks for the suggestions. Based on the stuff I've been reading, I'm also leaning towards the stator being the issue. The engine did overheat recently before I had the water pump changed and it was smoking a bit from the top. I'm thinking that was probably the stator plastic melting. I'll also pull the fuel line to check on that.
 
Okay, definitely not the stator. I took a chance and just changed it. Based on what I've been reading, it seemed like the stator was definitely the issue. It wasn't. Luckily, the stator was very easy to change on this motor. One thing worth mentioning is that the issue has been slowly getting worse. A few weeks ago, I was able to go full throttle for a half hour before the boat went into "limp mode." Now, I'm lucky if I get 10 minutes. Also, once the motor starts acting up (won't go over 2k RPM), I cannot put it into neutral without it dying out. In other words, it won't idle. Any new theories? I'm going to buy a DVA and get out there this week to try and get some readings. I'm about 1.5 hours from the boat and there's no internet access or cell signal there, so it makes it difficult for me to troubleshoot on the fly without printing a bunch of stuff. Thanks again.
 
You need to find out if it's ignition of fuel related. Make it run best as you can, then cut it off cleanly--no idling--and do a plug check. You might simply have a bad coil, or even a bad plug.

Jeff
 
ive been having the same issues for weeks now - here is something ive learned (probably the hardest way) - Find out EXACTLY what model you have. The stators can differ from year to year with completely different specs (ie red to ground readings). If your serial number plate is missing, look near the right side between the wires coming down from the flywheel, there is a small round silver plug in the ehad with a big M, a serial number will be stamped on that. Confirm what year you have -

THEN start doing stator tests, otherwise u will spend ALOT of time going in circles like me, and possibly removing / damaging a working stator.

I bought the manual and it has different specs.. your 2k + rpm are controlled by the red wire (oem stator), the blue handles idle - 2000. Build yourself a cheap dva adapter for about $3 and connect it to a digital multimeter and measure the wires although the red is tricky - best to do it on the water while running. iirc the blue should do around 100volts and red about 30-40.

Might be heat related if it runs fine - however these thigns are that easy to troubleshoot. I would do a good long run on the water and shut down motor and inspect plugs.. before it acts up -

fyi your symptoms re EXACTLY what i am going through. I have just received a bag full of stators, coils and switch boxes to go back and test with..

Also - disconnect the yellow wires from the reg/rect and see if your issue goes away, a faulty one could also cause these problems..

Your reed valves could also be on the blinck - only way to test is remove all 3 plugs, get bottom dead centre on pistons, open throttle at controls and blow cigarette smoke thru plug hole with tube, get a friend to see if smoke is soming out of carbs. do all 3 -

compression test always good.

Im looking at switch box and lower crank seal next as im out of ideas here!

All the best!
 
ive been having the same issues for weeks now - here is something ive learned (probably the hardest way) - Find out EXACTLY what model you have. The stators can differ from year to year with completely different specs (ie red to ground readings). If your serial number plate is missing, look near the right side between the wires coming down from the flywheel, there is a small round silver plug in the ehad with a big M, a serial number will be stamped on that. Confirm what year you have -

THEN start doing stator tests, otherwise u will spend ALOT of time going in circles like me, and possibly removing / damaging a working stator.

I bought the manual and it has different specs.. your 2k + rpm are controlled by the red wire (oem stator), the blue handles idle - 2000. Build yourself a cheap dva adapter for about $3 and connect it to a digital multimeter and measure the wires although the red is tricky - best to do it on the water while running. iirc the blue should do around 100volts and red about 30-40.

Might be heat related if it runs fine - however these thigns are that easy to troubleshoot. I would do a good long run on the water and shut down motor and inspect plugs.. before it acts up -

fyi your symptoms re EXACTLY what i am going through. I have just received a bag full of stators, coils and switch boxes to go back and test with..

Also - disconnect the yellow wires from the reg/rect and see if your issue goes away, a faulty one could also cause these problems..

Your reed valves could also be on the blinck - only way to test is remove all 3 plugs, get bottom dead centre on pistons, open throttle at controls and blow cigarette smoke thru plug hole with tube, get a friend to see if smoke is soming out of carbs. do all 3 -

compression test always good.

Im looking at switch box and lower crank seal next as im out of ideas here!

All the best!
 
Thanks for the responses. FstaRockr, it sounds like you have a 3 cylinder. I have a four cylinder with a 4 wire stator hook up. Not sure if that makes a difference. Based on the photos of the parts break down on Merc's website, I'm fairly certain that I'm getting parts for the right motor. I did pull the serial from the plug in the motor. Also, the motor is behaving in the exact same way, so I figured the new stator was the right one. The old stator did have a plastic covering over all the coils though, while the new did not. 2 questions: Can I check for spark using an automotive timing light on each one of the wires? What exactly do you mean by "check the plugs"? How am I checking them and why do I check them before the motor acts up? It would be almost impossible for me to approximate a time that the motor will start acting up. Thanks in advance.
 
The Hammer28 said:
2 questions: Can I check for spark using an automotive timing light on each one of the wires? What exactly do you mean by "check the plugs"? How am I checking them and why do I check them before the motor acts up? It would be almost impossible for me to approximate a time that the motor will start acting up. Thanks in advance.
Click to expand...


Yes automotive light works fine - by checking the plugs i mean take them out (bit tricky over the water!) but the only way to really "know" whats happening is to run the motor at full / as fast as possible for 2 minutes at least. immediately shut the motor down, and remove the plugs - when i did mine the top one was a tan brown, and bottom 2 a bit more wet.. take some good pics as well. careful the plugs might be hot, and dont drop em in the water :) I have a stout ski bar hich really helps, otherwise rtating the motor all the way helps..

You might get a good tan reading on all of them - and still have heat related issues, but at least this will eliminate a bad coil, switchbox, crank seal, reed valve or something else.. if they all burn good before the problems show up it will eliminate ALOT of electronic tests!

Either way - you can also try this when its runnning bad to try eliminate a bad coil..

Basic tools that really work are:

Digital multimeter (cheap is fine) with a dva adapter (5 cheap elec components soldered together
Spark gap tester (can also make one DIY with a grounding clamp and old plug..

compression test will confirm good compression, not sure if it will rule out bad reeds but i guess so.. bad reeds = smoke / fuel coming out of carbs at the front. bad crank seal will have a wet/dirty drive shaft as well as bad burning on cyl3 and a bit on 2 (my symptoms) - although im still troubleshooting! having a spare stator is never a bad thing, wrap your old one up for the future :)

hope it works out! fyi the reg/rect test is super easy, basic diode test with all the cables removed.. if yours is the diamond shaped one with 3 terminals iirc you should ONLY get a one way reading from the yellow top two down to the red OUT, and not vice versa - also none should touch ground either.. but dbl check online..


I got caught up in all the tests and variable information - but after doing a few they are actually quite simple. Best thing is to write down results, at least you can build up a page with alot of info.. resistance checks, dva voltages, etc..
 
Thanks for all the great suggestions and info. I don't have much (any) experience soldering electrical components, so I went ahead and just bought a DVA today, as well as an in-line spark tester and compression gauge. I already have a Craftsman multimeter. I'm going to head out there this Friday to pull every bit of info I can and I'll post it up here. I'm going to use the CDI troubleshooting manual that was posted in this thread. One other thing I have to mention: I changed the plugs from NGK's to Champions recently and the boat has been hard to start ever since. Both Champions and NGKs are listed in the Merc parts breakdown for the motor. I have to crank the motor at least a half a dozen times to start it now, where as with the NGKs, it would start on the first or second crank. Not sure if the plugs are that much worse or if the same ignition component that is causing my initial problem is getting worse and affecting starting.
 
Very odd about the plugs.. are they the same heat range? If anything clean the old ones with some diesel injector cleaner (it rmoves carbon REALLY well, use an old toothbrush) - and pop em back in. If the starting is instantly better return the other plugs..

Anyway- dont forget to ID your year / model exactly before running tests. Also bear in mind some tests are run while cranking.. Im putting a video together of a complete run through of tests after I get back to the motor next week -

All the best - At least your stator is new :) wish I had that luxury :)
 
Very odd about the plugs.. are they the same heat range? If anything clean the old ones with some diesel injector cleaner (it rmoves carbon REALLY well, use an old toothbrush) - and pop em back in. If the starting is instantly better return the other plugs..

Anyway- dont forget to ID your year / model exactly before running tests. Also bear in mind some tests are run while cranking.. Im putting a video together of a complete run through of tests after I get back to the motor next week -

All the best - At least your stator is new :) wish I had that luxury :)
 
Okay, well i performed the tests, but they were inconclusive, as I think I had no clue what I was doing. Some of the wire to wire tests gave me no reading whatsoever. However, something interesting happened. I took all the plugs out to do a spark test and while I had them out, I cleaned them. They were all dark and a bit wet. I started the boat up and it ran fine for 20 minutes until I was pressed for time and had to dock it again. When I went back out to start it next time, it took about a half hour to start and when it finally got running, it went into limp mode after about 5 minutes. I'm pretty convinced I have the wrong plugs in. I don't think they're burning correctly, which leads to the buildup on them. Though, the "limp mode" problem started when I had the NGK BUHW-2 plugs in, I never had a problem starting cold. The parts list for my motor on the Merc website is confusing. It has AC Delco V40FFK (I have these in there now) listed as a spark plug to use, but when I click on that part, a sub menu comes down that says NGK BUHW-2. Underneath that, there is another listing for a spark plug, which is NGK BUZHW. Anybody know which NGK I should be using? The Z stands for some sort of radio frequency blocker. The -2 is for some extended gap. I don't know why it would list both. Why wouldn't the BUZHW include the -2, if that is the required gap? Any help is appreciated. I put a pic of the part screen below, so you can see what I'm talking about. Thanks.

https://www.flickr.com/gp/141392619@N04/K5b01Q
 
so - not sure about 4 cyl, look on the cdi website - localte your model and look at the specs, to break it down, there are 2 wires that control the operation of the motor, on mine the blue wire is starting / up to about 2000 rpms, then the red wire kicks in from there up..

so focus on the red wire testing - unfortunately you will have to be in a body of water to reach those rpms for testing (ohms can show you some indication - but DVA is king with these things).

U need to get the boat to the higher revs (where the high wire kicks in) and take readings.. you could tie the nose of the boat to a tire on a mooring and motor in gear against it.. this was recommended to me by an old timer - use with care haha..

i found having crocodile clips as extension on dva meter means you can hook it up before its running - also bear in mind its safer to remove the yellow wires from reg/rect and see if the problem goes away - a faulty reg/rect can also cause issue.. in fact isolating the stator by removing these is recommended imo while troubleshooting -

Busy putting my whole motor back together - pulled powerhead to change crank seals and rebuild rubber mounts (from door stops of all things).. so soon as mines up and running im back to testing..

also - i baked my switch box in the oven, a tiny bit of moisture can make these malfunction.. i found some hairline splits between casing and rubber, so cleaned it impeccably with brake cleaner on the outside and rtv siliconed around every metal/rubber join AND i coated all the rubber as well as i had a small split in that too - will see if it works! heck - i even had tiny pitted corrosion holes in the actual aluminium!

You really have to look carefully at these old components!

ill be making a video on front to back testing when im done!
 
Back
Top