Logo

1980 50hp Thunderbolt Ign. Issue

Greg5494

New member
Hi folks,

I'm going to be as thorough as possible in giving this post as most background information as possible. I've explored many avenues, and searched far and wide on the Youtube and Google for the obvious answers on this issue; needless to say I've come up short. I am therefore looking for and grateful for the infinite wisdom of all of you who may either have experience with this specific motor or the older 2-stroke outboards (as it is my understanding they're a pretty basic gig when it comes to a motor?)

Early May 2017, I purchased a bass tracker equipped with the above mentioned motor.
While an in-lake test was not done, a 55gal drum test was done (@ high rpms, in gear and out). There existed no issues.

First use (or two/three) - Noticed there were two small transom welds that had cracked and therefore made decision to not operate the boat at a high rpm (defined over, say, 2000, maybe 2500rpm. It performed well for the short duration of motor-use (as I was mostly trolling with an electric unit, not needing much boat motor).

After the boat stalling out at idle RPMs (or just above) the boat would cut out and shut off- I noticed there was a "hairline fracture" in the Carb Diaphragm (a Blue cap that connects fuel line to the upper carb). This was causing me to lose fuel pressure and fuel to flow out. I took it to the nearest shop it Waterbury, Dons Marine Center, to which he fixed it, pat me on the back, and said she's good for a few years- take care of it.

June 2017 - After gaining a little more confidence in the transoms structural integrity, I took a couple people out fishing and decided, lets get to the spot sooner than later. This would be the first time I pushed the motor past prior-stated RPMs. After sitting at the spot and fishing for an hour, the boat starts-up, and idles fine. Upon putting it "well in gear", it starts to putter, barely sustaining itself. This occurs for the first fifteen-twenty minutes of a thirty minutes trip back to shore. I called the mechanic and we ruled out things like gas/air mixture screws, as if it were that, it would be a consistent issue.

July (and through august) 2017 - Im highly discouraged. I took time off of working on it and it sat for a while (with the same tank of gas, might I add). I tried carb cleaner for the first time. Spend 30 minutes blasting the motor and running it. I got it back on the water and I'm surprised to find out that my boat would never put as low as it did that day in June. Instead it would max out at about 8-10 mph, with the occasional 12 mph, to which at that point it would bog itself down (but NOT stall out) until I pulled the throttle back and it could "process" it.

Somewhere along this journey I Seafoamed the motor via fuel mixture and for one time and one time only that boat hopped right up on a plane and performed beautifully... but it literally only lasted two minutes, if that.

I checked- Spark, Sparkplugs, Compression, Possible burnt fuses, Pinched fuel lines, Loose connections, Other leaks in fuel line, Exhaust build up of carbon deposits

Thank you for your time! Greatly appreciate any and all knowledge
Greg
 
Plugged exhaust tuner ?----What are the compression values ?----Spark jumps a gap of 1cm or more on all 4 leads ?
 
Sound to me like you may have a stater problem. CDI has a trouble shooting section that will help you diagnose if the problem exists. The stater has a high speed and a low speed section. The 2000-2500 rpm motor speed is about where they transition from one section to the other. Also, Mercs of that vintage are notorious for wiring insulation failures. I have an '86 60hp Merc and I had to repair or replace most of the ignition wiring on the motor. The insulation was crumbling and would fall off the wire if you touched it.
 
Sounds to me like a piece of fuel line or crud of some kind is blocking your carbs main jet. (First part of your explanation) I even had the main jet vibrate loose and eventually had to be towed in. Found the jet in the float bowl. I have a 1977 500 and it now runs like a watch but I fought through rotting wiring a bad stator and fouled fuel lines before I got it back to real life. Our motors are notorious for rotten wiring but with the new parts, they make a wonderful outboard motor. BTW- Mine acted just like what you mentioned at the end of your explanation due to a faulty Stator.
 
Last edited:
Thank you for your input. I value it greatly.
I have yet to entirely rule out a faulty fuel system so it is very possible I am experiencing the Trifecta of Stator, Main Jet, and Fuel Line Issue.
With any luck, I can spend some time with it tomorrow.
Do you recommend against me checking it myself? I see that a Stator is about $200. Lord knows I'd spend Five going to a mechanic. I have the necessary tools, the motors' service manual, and quite a bit of confidence in my ability to Youtube and Do it.

I found the below video that I believe is a Before and After of stator replacement. I need confirmation if anyone can give- the titles are not very clear, but there is certainly distinct sound difference between the two.

BEFORE: https://www.youtube.com/watch?v=tSKSce2LKy4 (This is what my boat sounds like in idle at proper carb setting done by marine mechanic)

AFTER: https://www.youtube.com/watch?v=J1GukHqYHQI
 
If my memory serves me correctly the compression rates were at like 115 I think? I don't recall exactly. If I were to look at a gauge, it landed somewhere around 1030-11oclock (I think)

The distance of spark jump is unknown. Tested it multiple times, not to mention I took a pretty intense shock because I neglected to let go of the lead lol

Can you describe what an exhaust tuner does on a small HP motor and how that might affect the remaining 75% of throttle? This will give me some insight while I search further for definitive answers.

Thanks!!
 
Greg-Racerone is trying to save you some money. Do a proper spark test and get a good compression test before going into your wallet too deep. The old motors can get to the point of spending too much too fast. The work I did on my motor was with the oversight of a retired Merc mechanic. He helped me with the large part of instilling confidence and very little muscle. You will probably need help getting the flywheel off to replace the stator. and rebuilding the carbs and synchronizing them is not a first timers dream. The rest you can do with a good "Mercury" service manual. One thing I can tell you..... running on muffs will not tell you squat about whether or not your stator is bad as it "may" be. If you know how to use a multi meter and test it, you are way ahead of the game. I had to suck it up and throw money at mine before it all came to fruition. The flywheel was the only part of the stator replacement that was hard. The interior wiring harness was not bad at all and some of the other wiring was also replaced. I do have some extra coils I don't need and an extra switch box (keep for spare). Other than that the money was well spent. New fuel lines were dirt cheap as was a new tank bulb and line. All the original rubber components were disintegrating inside out.
 
You can test your stater with a good multi-meter and a DVA. If you are handy and frugal you can build a DVA from part off the internet for a couple bucks, I did or buy one from Amazon for about $40. The first CDI tests are conducted by disconnecting a few wires and checking the resistance of the coils. You don't need a DVA for that. If the resistances are in spec. you are done. If the resistances are really out of spec. you are also done. Time for a new stater.

Then you are going to need a flywheel puller.

https://www.ebay.com/itm/Mercury-Ma...orityMailSmallFlatRateBox!56442!US!-1&vxp=mtr

$23 on ebay. Worth every penny. As for the stater cost shop ebay.

Good Luck
 
I know I said to get a good Mercury Service manual. I have the Mercury Manual I picked up from ebay. Very decent. Glad I have it and would be lost without it. U-tube and forums are great up to a point but you also want fishing and boating to be your hobby and NOT "Boat Motor Tech". Please post updates on progress. There are many here that are real helpful and honestly I don't have much else to add until you start on your lower unit seals and bearings. Another "book" entirely.
 
Last edited:
So long as SELOC is considered a good Mercury Service manual, I'm all set there
I'm more than happy and willing to post updates, as hopefully it'll assist in the solving of anothers' issue(s).
Thank you!
 
Back
Top