Guests - If You want access to member only forums on HSO. You will gain access only when you Sign-in or Sign-Up on HotSpotOutdoors.

It's easy - LOOK UPPER right menu.

  • Announcements

    • Rick

      Members Only Fluid Forum View   08/08/2017

      Fluid forum view allows members only to get right to the meat of this community; the topics. You can toggle between your preferred forum view just below to the left on the main forum entrance. You will see three icons. Try them out and see what you prefer.   Fluid view allows you, if you are a signed up member, to see the newest topic posts in either all forums (select none or all) or in just your favorite forums (select the ones you want to see when you come to Fishing Minnesota). It keeps and in real time with respect to Topic posts and lets YOU SELECT YOUR FAVORITE FORUMS. It can make things fun and easy. This is especially true for less experienced visitors raised on social media. If you, as a members want more specific topics, you can even select a single forum to view. Let us take a look at fluid view in action. We will then break it down and explain how it works in more detail.   The video shows the topic list and the forum filter box. As you can see, it is easy to change the topic list by changing the selected forums. This view replaces the traditional list of categories and forums.   Of course, members only can change the view to better suit your way of browsing.   You will notice a “grid” option. We have moved the grid forum theme setting into the main forum settings. This makes it an option for members only to choose. This screenshot also shows the removal of the forum breadcrumb in fluid view mode. Fluid view remembers your last forum selection so you don’t lose your place when you go back to the listing. The benefit of this feature is easy to see. It removes a potential barrier of entry for members only. It puts the spotlight on topics themselves, and not the hierarchical forum structure. You as a member will enjoy viewing many forums at once and switching between them without leaving the page. We hope that fluid view, the new functionality is an asset that you enjoy .
  • RECEIVE THE GIFTS MEMBERS SHARE WITH YOU HERE...THEN...CREATE SOMETHING TO ENCHANT OTHERS THAT YOU WANT TO SHARE

    You know what we all love...

    When you enchant people, you fill them with delight and yourself in return. Have Fun!!!

  • 0
Sign in to follow this  
Steve Foss

Sudden power loss on 1988 Merc 90 Hp

Question

So I had the Alumacraft and the tall black Merc out for a workout today. Had last year's gas with Seafoam added last November.

Ran great for awhile. But as I was working up toward peak throttle it suddenly lost power and started missing, and when I maxed out the throttle I could only get about 3/4 the total power I'd been getting, with max RPM of 4400 instead of about 5000.

It idles great and runs smoothly when at highest possible speed, but now it takes several seconds with some stuttering even to build up to the 4400 RPMs I can get out of it. Once there, it runs very smoothly. It's always been fast as lightning out of the hole.

It's a 6-cylinder with two carbs. It has very low hours and has been babied and well serviced its whole life.

Any thoughts?

Share this post


Link to post
Share on other sites

30 answers to this question

Recommended Posts

  • 0

Most likely bad gas. I had gas in mine that went over the winter last year and I had the same thing as far as symtoms. I drained some of the gas and it looked like gelatine from the ethenol in it. I replaced all the gas and it was fine after the rest of that gas got worked out of the carbs.

Share this post


Link to post
Share on other sites
  • 0

Steve, I'd start out with checking the gas.

Crank up the tongue jack and let the boat sit long enough for any water to run to the lowest point in the tank. That'll be by the inlet. Depress the pin and hand pump via the primer bulb gas into a clear glass container. If you see swirlies in the gas that be moister. If there are droplets of water in the bottom of the container then I'd siphon at least 5 gallons off, let the water separate and siphone the water out and then burn the gas in your Datsun.

Next check the fuel line for leaks or a swollen condition from within that could be restricting gas flow.

Share this post


Link to post
Share on other sites
  • 0

Sounds about like what my '96 3-cyl 90hp did a couple years ago.

Ended up being gunk in the carbs that required them to be removed and cleaned out. Dunno how the crud got in there because there were filters in the system...but it did.

Kind of worrysome being out a ways on Rainy Lake when the wind starts coming up, and you have several miles to get home, then you fire up the engine to head back to shore, and find the engine will only rev to 3,000 RPM, and you've got to work it just to get that.

Share this post


Link to post
Share on other sites
  • 0

It could very well be a dirty carb(s).

If the above doesn't check out a carb clean and overhaul is a must.

I'll go on to say that the lack off studder at the higher RPM range is worrisome. That is a symptom of a true lean condition from a dirty jet. Continuous use will scorch a cylinder.

This is sounding like "Free Beer" to me. smile

Share this post


Link to post
Share on other sites
  • 0

Thanks, guys.

I've got a fresh 6-gallon can of gas/oil mix from yesterday I haven't used. I'm going to syphon what's left in the boat tank into other cans and replace with fresh gas. Then I'm going to check the carbs, but I looked them over a bit today and they are very clean.

I'm going to try to rule out an electrical problem by running the motor at idle for a few minutes with muffs on, and then pulling the plugs. If there's a cylinder not getting spark, I'll know because the plug will be sopping wet with unburned gas. If it's a spark issue, could be one spark plug, plug wire, etc, or could be more involved.

Another way to rule out gas is to run the motor up and when it starts to stutter, push in the key choke, and if it runs better for a sec or two it's a fuel starvation issue. If pushing in the choke has no impact, it's likely spark.

We'll see.

I'm going to work on it tomorrow. Good news is I can still troll Burntside all I want, because I just got an old late

'60s 9.5 Johnson, the low-slung round-topped one. My grandpa bought it new, and my uncle just had it rebuilt two years ago. Upon my uncle's death, the motor came to me, so now I've got a bulletproof kicker that has become a family heirloom. gringrin

Frank, if I still lived in your neck of the woods I'd drop off the boat/motor/trailer and a couple cases of Leinies and come back a few days later. The Leinies would no doubt be gone, and the motor no doubt fixed. If I can't figure it out on my own it'll be coming your way even though the drive is long. smilesmile

Share this post


Link to post
Share on other sites
  • 0

Steve, instead of siphoning the fresh gas, hook up your fuel line to that tank. Yep you'll have to take the Johnson end off and put on the Merc end. All long as the dia is the same thats all that matters. Just use hose clamps in place of the bands.

Share this post


Link to post
Share on other sites
  • 0

Frank, I wasn't going to syphon the fresh gas, but the old gas in the Alumacraft tank, which is an integral stern tank. Just seems like a good idea to get it all out of there.

Then the fresh gas will go into the Alumacraft tank so that's good gas from now on. I've got the Johnson 6-gallon tank with fresh gas and another 6-gallon can with fresh gas.

I hear you about swapping Merc and Johnson ends and hooking up the Merc to the Johnson tank. But if there's gunk in the carbs/lines, would running fresh gas through the system clean that out? Seems like it wouldn't. But I suppose if it's an issue of water in the gas, that would take care of business right away. What do you think?

Share this post


Link to post
Share on other sites
  • 0

The remote tank would just eliminate the bad gas and swollen gas line. If you drain the onboard tank thats fine and your Datsun wont mind burning it. You still have to eliminate the swollen or air leak in you onboard tank line.

Share this post


Link to post
Share on other sites
  • 0

First thing I will do is run the motor and pull plugs as I mentioned above, to eliminate spark issues. I will drain the onboard tank no matter what, whether it's a spark or a fuel issue, and replace with fresh gas/oil mix.

If it's spark, I'll deal with that. If it's not, then it's a fuel problem, and I will then swap out so the Merc is running off the fresh Johnson tank and then trailer the boat to the lake to see how it runs. If the problem goes away, I'll conclude it probably was water in the onboard tank gas and hope the problem is solved. If the problem is not spark, but fuel, and the problem persists after running on the Johnson tank, then I'll start looking at tearing down the carbs and/or replacing fuel lines.

I don't know that I have a swollen line or air leak, though. It'll be just one more thing to look for, yes?

Share this post


Link to post
Share on other sites
  • 0

That about it. Might add squeezing up the primer bulb when it acts up. If it takes off then your carbs are fine. That would lead to fuel line or fuel pump.

Share this post


Link to post
Share on other sites
  • 0

Steve, I think you are headed in the right direction. I always stressed, start with the easiest to check. Spark is Number 1, compression is #2 and fuel is #3. Unless the problem started right after adding fuel.

On this model Merc, it will have a tough time running if one carb is acting up. The upper carb runs cylinders #1, #2 and #3 and the lower carb takes care of #4, #5 and #6. This engine will not run on 3 cylinders, or at least, I have never seen it.

This engine will loose 1000 plus RPm from a dead cylinder though.

If you find a dead cylinder, let me know. If it is the distributor-less ignition, I have the test equipment to figure out where the problem is. Could be the power pack or the trigger

Share this post


Link to post
Share on other sites
  • 0

Thanks, shamrock. I'll update when I get a few things done tomorrow. Well, if it gets above freezing tomorrow. gringrin

Share this post


Link to post
Share on other sites
  • 0

It does have ADI ignition and I agree with shamrock that it sounds like it lost a cylinder. Check the compression first however. If shamrock has the Merc o Tronic (or comparable) compresion tester, get that too because you wont get an ordinary tester down into #6. IF it is ignition, you will be able to pinpoint the cylinder acting up by using a timing light while running. Once you determined if it is ignition, using the meter shamrock has and the trouble shooting flow chart, you should have no problem finding the problem. If it is dropping a cylinder, expect a bad Switch Box or Coil but dont over look the high speed side of the stator.

Share this post


Link to post
Share on other sites
  • 0

Guess you won't be getting much done then. Ha Ha Give me a call as I don't get on here that much during the busy season.

Share this post


Link to post
Share on other sites
  • 0

Actually, I've been a busy boy this morning. smilesmile

1. Drained old gas.

2. Replaced with fresh gas/oil, including a can of isopropyl and a can of fuel system cleaner.

3. New plugs.

4. All plugs/wires deliver strong spark.

5. Ran motor at idle, pulling and then reattaching one plug wire at a time. With each of the six cylinders, the motor logged down and ran rougher when the wire was pulled, so they are all functioning.

6. Did a thumb compression test, and all felt equally strong.

7. Drained bowls on all three carbs. Could only get a little jar under the top carb, but there was some water in that bowl.

8. Examined the whole fuel system for cracked/leaky lines. None found.

9. Shot carb cleaning spray into the carbs.

The problem still remains.

Randy (Shamrock) and other guys, thanks for the help. I think I'll take it out tommorrow trout fishing on Bside and see if it was a fuel problem that will work itself out.

If not, more work to do.

Further thoughts, guys? smile

Share this post


Link to post
Share on other sites
  • 0

Steve, It still would be a good idea to try a timing light at higher speeds with a load on it, from what it sounds like, it's a higher rpm problem and could still be cutting out at higher rpm's. Interestingly enough I have a Mariner in the back yard waiting on switch box that loses spark on 1 cylinder above 1500 rpm, and it's certainly not the first one to have that happen. I'm not trying to convince you that IS your problem, but more just trying to completly eliminate the ignition system.

Watch the light and listen and feel for the engine losing power. You may have to go through every cylinder. I agree 100% with Randy that spark and compression are the 2 easiest things to eliminate, if all check out then concentrate on fuel and exhaust. Heck, a critter could have even made nest in the exhaust.

Share this post


Link to post
Share on other sites
  • 0

Thanks, Bruce. Actually, it runs rough and accelerates slowly under load at all but the upper end. Once it reaches its new max of 4400 RPM it smooths out.

Also, it doesn't have a distributor, so how would I use a timing light on it? Randy showed me how to check for a gummed up high-speed jet, in case that's what's causing it to smooth out at higher RPM, so I plan on doing that out on the water tomorrow.

Share this post


Link to post
Share on other sites
  • 0

Just attach it to the plug wires as you would any other plug wire. No doubt at all it could be a restricted high speed jet.

Share this post


Link to post
Share on other sites
  • 0

Just attach it to the plug wires as you would any other plug wire.

DOH! gringrin

What should I do to check the exhaust? We get mice in the fall looking to nest in strange places, and wasps, too.

I suppose that even though the spark on all cylinders looks strong to me, and the compression feels consistent and strong in all cylinders to my thumb, an actual ignition eval and compression test using the right equipment might show a problem in either of those directions. A guy can only go so far trying to do things on the cheap. winkwink

Share this post


Link to post
Share on other sites
  • 0

5. Ran motor at idle, pulling and then reattaching one plug wire at a time.

Dunno if it's an urban legend or not, but I've always been under the impression pulling plug wires can cause ignition modules to blow if the spark doesn't have anywhere to go. I.E, any disconnected plug wire should be grounded or put on a spark gap before starting the engine.

Share this post


Link to post
Share on other sites
  • 0

Pulling plug wires is a very common diagnostic tool. Granted, there are some manufacturers that do recommend that you ground the plug wires before cranking the engine. No outboard manufacturer that I am aware of though.

Share this post


Link to post
Share on other sites
  • 0

I had it out today. Top end now is 3600 RPM. When I punch it, it immediately gets to 2800, then gradually reaches plane and, once planed, adds RPMs to get to about 3600. Idles and runs unevenly until it's punched, and at idle or lower RPMs I get a cough/pause/spit now and then. Once punched, I can't hear a miss, but at higher RPMs I can only detect strong misses anyway, so maybe it's missing and I just can't hear it.

I have one simple experiment to try tomorrow (thanks Frank!). I'm going to put the muffs back on, start her up, warm her up, rev her to about 2000 RPMs and shoot gas/oil mix from a spray bottle into each of the three carbs, one at a time. The butterfly valves at those RPMs should be open enough to allow the spray to enter.

If shooting that mix into the carbs evens out or revs the motor, that will tell me there are some plugged jets/lines in that carb and it's time to remove and clean out all three carbs. If it has no impact at all, I think it's time for a full-blown compression and ignition/spark test.

Share this post


Link to post
Share on other sites
  • 0

Just to throw an idea out there that you may have already ruled out but I haven't seen it mentioned yet....did you try a new primer bulb?

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  



  • Your Responses - Share & Have Fun :)

    • If I leave my 2 lines down when I leave my fishouse and go to my buddies house say 75’ away they are considered unattended and illegal, but what if the lines are on buzzer reels and I use a baby monitor to listen for a bite?
    • Yah, I bet I coulda looked that one up myself, eh? 
    • The Air fryer XL was 120.00 and the Air Fryer Oven was 160.00. If you Google Power Air Fryer or put a .com at the end you should find it. 3 or 4 easy payment of $39.99 depending on model and free shipping.
    • I bought a bag of the hearts and chips because I got sick of the mass of sunflower shells on the ground. Now, it’s only been a couple days, but it sure seems like I have a lot less cardinal activity at my feeders since making the switch. Do cardinals prefer the shelled seeds? 
    • I have a very short driveway (2 car lengths) and I always have 2 cars on it. Couple times a year the city says I cant block the sidewalk. (There is no sidewalk there) But they say thats where it would be if there was one so I cant block it   LOL
    • Ill bump you into 2018. I just picked up a WR250F and put plates on it. Not sure how much riding I will get done now though with the house build.
    •   Just my thoughts on that:   You’ll be glad you poured the edge thicker if you’re planning to stay there awhile.  A good, stable slab will reduce wall cracks and keep your door jambs plumb.     And don’t skimp on the insulation.  My current home is slab on grade with in floor heat.  It has 2 inch insulation under it but not up the side of the slab.  I’ll eventually add that additional inslulation around the perimeter.  The ground is a heat sponge.  Heat migrates to cold no matter what direction it goes.  The insulation will pay for itself in a short amount of time.  The higher the R value, the better.   Good luck. It sounds like an interesting project.
    •   Suzanna, if you had not saw the signs in the ditch on either side of your driveway in the past nor had a snowmobile groomer come through there. It sounds like one of the local snowmobile clubs may have added that stretch of ditch to their trail system. You may inquire around the area which snowmobile club is grooming and maintaining the trails in the area and talk to them. They can talk to their members about driveway jumping but they really can't stop some of the young nonmember folks around there from doing it. Please do not do anything like icing down the ditch, blocking it with things like logs, wire or anything else. If someone gets injured as a result of something you did, you will be liable. 
    •   Im pretty sure we are going to pour the edge thicker but I can not find that it is required. I know we have to insulate down and out from the outside edge but cant find the specifics for that either.   Thanks
    • Still some time to get your entry in!!
  • MWO