98 force 90hp problem

[montanan]

It is misfiring between 1k & 2k rpms only Runs perfect above and below those ranges. It is also random while in the 1 to 2k rpm. It may go a few minutes running normally then bam it will misfire sometimes to the point it will die. This is while underway in the water.

I have rebuilt the fuel pump and new lines. I wonder if it is electrical. Could the carbs run perfect except within that range. WOT is perfect power is good startup is good Idle is good as long as it is in gear. If I let it idle in neutral it will sometimes miss because it is within the 1 to 2k rpm range.

I have no history on the boat as far as service etc. Looks super clean. It appear to me that the intake manifold has been removed sometime in the past due to paint damage on the bolts.

Looking for some guidance as a starting point. Compression is good engine appears super healthy when running 2500 and above.

 

[jerryjerry05]

Check for water in the fuel, change the plugs, check all wiring connections, look for bare or rubbing wires.
​
​Reset the fuel/air screws.

 

[montanan]

Drained the fuel, installed new plugs, and looked for wires. I will look at wires again today. I did not mess with air/fuel screws because it runs perfect at idle etc.

When I rebuilt the fuel pump it looked super clean inside. Fuel filter also looked super clean.

Thank you for your input. I will get busy & report back if I see anything obvious. If not I have to wait until I take it back to the lake to test.

 

[montanan]

should the trigger have some slack in it? I grabbed the arm coming out to the linkage & I can wiggle it front to back a little.

My wife and I can find no wires that are questionable.

 

[pnwboat]

A little play in the trigger assy. is normal.

Have you done a "Link and Sync" on the carburetors? There is a "sticky" at the top of the forum called Carb and Timing Tutorial that gives you an idea on how to sync the carbs. That RPM range that you are having issues with is the point at which the throttle plates in the carburetor are transitioning from the fuel flow from the idle ports in the throat of the carburetor to the regular main fuel jet. So it's important to make sure all of the throttle plates are in sync with each other.

It's normal in a properly sync'd motor to notice a slight change in the way the motor sounds as you transition through this RPM range (1000 - 2000 RPM). The motor doesn't run quite as smooth but that's the nature of the beast. It shouldn't stall though.

Also like Jerry mentioned, the fuel mixture screws need to be set correctly. The manual calls for them to be 1 turn out from lightly seated. Usually they end up being anywhere from 1 turn out to 1 1/4 turns out or there abouts depending on the motor for best performance.

If it looks like the manifold has been removed, then I would suspect that someone has been looking at the reed valve assy. The 1996 or so and later motors are famous for broken, cracked or bent reed valves. That could also be a possible cause for your symptoms too, but I would start out by checking the lync and sync and idle mixture first.

 

[montanan]

A little play in the trigger assy. is normal.

Have you done a "Link and Sync" on the carburetors? There is a "sticky" at the top of the forum called Carb and Timing Tutorial that gives you an idea on how to sync the carbs. That RPM range that you are having issues with is the point at which the throttle plates in the carburetor are transitioning from the fuel flow from the idle ports in the throat of the carburetor to the regular main fuel jet. So it's important to make sure all of the throttle plates are in sync with each other.

It's normal in a properly sync'd motor to notice a slight change in the way the motor sounds as you transition through this RPM range (1000 - 2000 RPM). The motor doesn't run quite as smooth but that's the nature of the beast. It shouldn't stall though.

Also like Jerry mentioned, the fuel mixture screws need to be set correctly. The manual calls for them to be 1 turn out from lightly seated. Usually they end up being anywhere from 1 turn out to 1 1/4 turns out or there abouts depending on the motor for best performance.

If it looks like the manifold has been removed, then I would suspect that someone has been looking at the reed valve assy. The 1996 or so and later motors are famous for broken, cracked or bent reed valves. That could also be a possible cause for your symptoms too, but I would start out by checking the lync and sync and idle mixture first.

I have been avoiding the carbs ( not a carb guy) but I guess I will dig in. In my mind I keep thinking electrical. When it misses it misses HARD I feel it in the steering wheel & it dies quite often. I just thought that all 3 carbs failing at once would be rare but maybe not.

I towed another boat for over an hour at 2500 rpms & it ran like a dream I run it 4700 rpms at 34 MPH for long periods of time & it runs perfect. The transition idle ports to main jets may be the problem here. thank you for your input.

 

[pnwboat]

Without being there to experience what you are describing makes it a little hard to diagnose but Jerry suggested that checking the wires that are connected to the trigger assy. is also something you should do. Have someone move the throttle back and forth (don't start the motor) while you look closely at the trigger wires. They will move as the trigger assy rotates as you move the throttle. If they're rubbing against the block, make sure the insulation isn't rubbed off at that point.

As far as the carbs are concerned, they are pretty simple. Other than cleaning, replacing the needle valve and adjusting the float height takes care of most issues, unless you have a clogged port somewhere. If you take the carbs off, you have to do a link and sync to insure good performance.

I doubt that all three are bad, maybe just out of adjustment. Do the link and sync and check the idle mixture screws first. I suggest that you make a note of how far out the idle mixture screws are set right now so you can set them back to the way they were if you make adjustments and want to go back to the original setting.

 

[montanan]

Without being there to experience what you are describing makes it a little hard to diagnose but Jerry suggested that checking the wires that are connected to the trigger assy. is also something you should do. Have someone move the throttle back and forth (don't start the motor) while you look closely at the trigger wires. They will move as the trigger assy rotates as you move the throttle. If they're rubbing against the block, make sure the insulation isn't rubbed off at that point.

As far as the carbs are concerned, they are pretty simple. Other than cleaning, replacing the needle valve and adjusting the float height takes care of most issues, unless you have a clogged port somewhere. If you take the carbs off, you have to do a link and sync to insure good performance.

I doubt that all three are bad, maybe just out of adjustment. Do the link and sync and check the idle mixture screws first. I suggest that you make a note of how far out the idle mixture screws are set right now so you can set them back to the way they were if you make adjustments and want to go back to the original setting.

Top 2 carbs were 3/4 & bottom 1.5 turns. I did the screws only & started on the hose. As always it sounds perfect on the hose & could not get it to skip a beat. I do not have a timing light here at the AZ house. Butterflies were fully open at WOT and the cam mark is pretty much dead on with the roller screw.

I will take it out again as soon as I can & give it another try. I am a snowbird & will be leaving in a couple of weeks. I am going to leave it here for the summer. I sure appreciate all the help.

 

[montanan]

Finally got the boat out this year. I did the link and sync and it ran like a dream. Thank you guys very much.

 

[jerryjerry05]

Thanks for the update.
Glad it's running.