1990 Force 50 Starts/runs great, bogs down then stalls at WOT, starts right back up

Jlesinski

Seaman
Joined
Aug 22, 2009
Messages
52
Hello,

I just obtained a Spectrum boat with a 1990 Force 50hp motor on it. It starts up and runs great in the driveway. It has sat for a while, but was stored indoors and looks to be in great condition. I got it from a friend, who was given it from his uncle so I don't have anything into it really yet. When I first got it I knew it was bogging down at wide open so it would need some tinkering. Supposedly the carbs were cleaned, but that was years ago when it was being run.

The first thing I did was switch out the impeller to make sure I wasn't going to get any overheat issues. It was worn and needed it. Then I took it out for a test run and sure enough it would run at wide open, then bog down and sometimes stall. Then it would fire right back up and run again. It seemed to run at up to half throttle for a long time without issue, but sure enough if I open it up it would maybe run for a bit and then bog down again. I did this several times and each time it fired right back up without issue.

I am thinking this is a fuel issue.
  • Fuel Vent is open
  • The gas in it was old so I am cleaning the tanks and getting non ethanol.I will put seafoam in there also.
  • I pulled the fuel filter which appears to be a screen only and it looks clean.
  • I am replacing the fuel lines and bulb with 5/16 hose. It appears to be 3/8 on there but the fitting seems like 5/16. It was held on with wire ties and I think it may be sucking air on the fuel pump line in.
  • I am looking at carb rebuild kits, but the serial number is not legible on the sticker so I am not sure if there is a huge variation. It seems like there are a lot of serials for this boat. I can clean it and see how that goes if I can't figure out which kit to get.
  • Going to order some plugs as well. I figure this won't hurt.
  • I just picked up an actual service manual.
  • I can do a compression test if that makes sense, but it seems like it wouldn't run fine for a bit and bog down if there was bad compression.
Is there something else that could be causing this kind of behavior? Am I on the right track? I am not sure if it's ok to put muffs on it and try to replicate the stalling by opening it up in the driveway. I had run it in a barrel full of water to test the impeller but I obviously can't open it up in the barrel.

Thanks for your suggestions!

Jim
 

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
My bet is on fuel delivery system. The best way to troubleshoot this is to install a clear fuel filter between the fuel pump outlet and the carb inlet. It doesn't have to be the expensive ones since it is mostly for troubleshooting purposes. Fram G2 from WM costs less than $5 and even comes with hose clamps. After installation prime it and make sure it is at least half full. Now do a test run again with the engine cowling off. Have a second person drive the boat while you monitor the clear fuel filter.

If the clear fuel filter empties, the problem is with the fuel pump, fuel hose or leaking priming bulb or leaky suction hose. If it stays at least 1/2~3/4 full, then the problem is with the carb's float setting, leaky float or partially clogged inlet.
 

Jlesinski

Seaman
Joined
Aug 22, 2009
Messages
52
Thanks for the suggestion! I bought new lines and a bulb today as they seem older anyway. I plan to install them and test this weekend. Also, one thing that seems off to me is that this is the 1990 motor and the plugs are the NGK BUHX non? electrode plugs. When I was looking up plugs for this motor, inoats says the plugs are NGK BUHW which have the electrode. Could that be causing the issue or compounding it? I am picking some of the BUHW plugs. It looks like BUHX is for 1991 and up.

Is there any way to identify the motor other than the serial sticker? I cant make it out at all and wiping it off with wd40 to "clean it up" just made it worse...
 

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
Both BUHX or BUHW are gapless type plugs, i.e. there is no protruding center electrode. The only difference between the two is the gap of the perimeter anode to the center electrode. I don't have the exact gap numbers but if memory serves me right the BUHX has the smaller gap.

I do not believe the plugs are the problem if the motor is able to go WOT, bogs down and then stall especially if the plugs are still new. You can post pic of the plug tips for diagnosis. Like I said, my bet is on fuel delivery and it's mostly a minor leaky hose or connection upstream of the fuel pump.

And yes, the right plugs for your 90-50HP is BUHX. The 92 and later model uses the BUHW.
 

Jlesinski

Seaman
Joined
Aug 22, 2009
Messages
52
Thanks Jiggz. I ordered the BUHX plugs right from this site: http://www.iboats.com/mall/partfind...gd_poid=175593&gd_row=15&session_id=997298772

I figure it won't hurt to have an extra set. The photo does show the gapped plug, but it's probably just a stock photo.

So far, I have replaced the fuel lines, bulb, put in fresh fuel 50:1, and added in Seafoam. Compression on both cylinders is 120. I haven't had a chance to take it out yet, but I did make a video of it running here: https://youtu.be/OAka82GtBEE

One thing I have seen is that it will sit there and idle for a long time, but sometimes will just die like someone turned the key off. Then I can go hit the key and as soon as I turn it, it is running again. Could that be the same issue as running wide open?

I hope to get it out this weekend or sooner to see if it will run wide open with the changes I made. If that doesn't work I will post back for next steps.
 

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
Before going out to test, take my $5 suggestion for the clear fuel filter. This will help in your current and future troubleshooting by eliminating the "fuel" cause. As soon as you get the fuel out of the way, at least you can focus if the source of the problem is electrical or mechanical. From the video it seems to be running fine.
 

Nordin

Commander
Joined
Jun 12, 2010
Messages
2,428
I suggest you to take a look at the fuel pump diaphragm.
As you says it run at lower RPM.s but bog at WOT then it sounds like the pump do not deliver enough fuel at WOT.
Changing the diaphragm is a regular maintainence and I bet it is stiff from age and ethanol.
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
17,923
The inline fuel line connectors have a rubber seal in them.
It can go bad and cause the problem you describe.
​The tank vent line can be clogged too

​Check the temp and see if it's getting hot.
​Test the buzzer and see if the sending unit is working?
 

Jlesinski

Seaman
Joined
Aug 22, 2009
Messages
52
No Title

I think I have this one solved. I did end up rebuilding the fuel pump and had replaced all fuel lines. I ended up ordering some gaskets for the carb on ebay and pulling it all apart. Look at the inside of the carb! I am guessing that this black stuff is from ethanol breaking down the fuel line... I soaked most of the parts and the carb in cleaner overnight and cleaned it up and blew it out really well. We were out on the lake topping out at 25mph by GPS yesterday with 2 adults and a kid. I think that will be about as good as it get's with this Force 50HP!

I probably should have gotten into the carb sooner. Thanks for all the help and suggestions!
 

Attachments

  • photo266329.jpg
    photo266329.jpg
    75.8 KB · Views: 0
  • photo266330.jpg
    photo266330.jpg
    130.1 KB · Views: 0
  • photo266331.jpg
    photo266331.jpg
    125.4 KB · Views: 0
  • photo266332.jpg
    photo266332.jpg
    144.8 KB · Views: 0
  • photo266333.jpg
    photo266333.jpg
    231 KB · Views: 0

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
Great and thanks for posting the final cause and solution to the problem. This greatly helps others with similar symptoms.
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
17,923
If there's no filter between the carb and the pump, install one.
Fram G2 G3 G12
​Stops a lot of problems.
 
Top