Carb? Timing? 90hp

[Hemitt]

hello all, so I have a 1990 90hp Force. I recently purchased the boat. I had the boat in my driveway on muffs and it started fine and throttled fine. I put it in the water and it would idle fine but putting it just in gear it would die out. I could throttle it up from idle fast and have it spit to get it going but would run fine at full throttle. Figured fuel issue? Drained the tank put fresh fuel, new spark plugs, new fuel line and filter. I pulled carbs which were fairly clean (just bottom carb had a few flakes in bottom of the bowl). Put new gaskets and cleaned them up. I put it all back together according to sticky on here for synchronizing them. Well I had to adjust roller so notch on cam is Id say half of inch below roller to get it to even start. When running at idle I’m get a bad almost like a backfire but more of a sound like a hit and miss motor like it’s stumbling. I’ve adjusted everything almost every which way I could think of but doesn’t seem to get better... any ideas or am I looking at a different problem? Thanks.

 

[Nordin]

First check for spark on all 3 cylinders, and then check compression on all cylinders.

If one cylinders fail in either spark or compression the link and sync at top of this site would not fix anything.

Comression should be 140-150 PSI as from factory. It should run pretty faily with down to about 110-120 PSI and most important is that all cylinders are even.
Not more then 10% in different, soo for example all three at about 120 PSI is better then two at 140 PSI and one at 110.

If the spark and compression checks out okey then do the link and sync.
Initial setting of the air fuel mixture screws are 1 1/4 out from seated and after done the link and sync the roller can be 1/4 in above the mark at idle.
If it is 1/2 in above....something is wrong, The idle will be to high and the clutch dog will worn out.

 

[jerryjerry05]

What's the idle set at?
On the hose, it should be about 1150-1200 rpm's
In gear in the water about 750-800 rpm's.

You said:

When running at idle I’m get a bad almost like a backfire but more of a sound like a hit and miss motor like it’s stumbling.

That sounds like it's sucking air somewhere??
Make sure the carbs are tight.
Set them at 1 turn out(factory recommendation).
Start the motor and spray starting fluid around the intake side of the motor.
Not in the carb but around the packs and the fuel pump.
If that makes the motor stutter,cough, stall then there's an air leak or bad gasket
somewhere.

The plenum has a hose connected to the bottom make sure it's still connected to the intake base.

The dirt in the carb, install a filter. Fram G-2 G-3 G-12
It's clear and collects the tiny stuff that can block the jets.

The trigger leads can break under the shrink wrap.
Pull on them gently and see if they separate.​

 

[Hemitt]

Welp, did a compression check. Top cylinder was about 110, bottom cylinder was about 112 and middle one was 70. I would assume that’s my problem. Wouldn’t think it would run so good in WOT... how much of a pain is it to dig in and rebuild? Or should I count my losses and try to find a new outboard?

 

[jerryjerry05]

Take the head off and check for damage??
The gasket might be bad??(hope)
Usually any damage is gonna get worse.

Sometimes the rings carbon up and cause a low compression problem.
You can remove the port cover on #2 and check the rings.
Use a new gasket and silicone if the cover goes back on.

If your any good with tools and have a good place to work a rebuild isn't that tough.
First thing is find a machine shop that can bore the hole.
LOT'S of shops won't touch one