96 150 Saltwater Series

[skyeman]

Hello, I just purchased a 1996 150hp Saltwater series 2. When we went to look at the boat and motor, the motor seemed to idle fine on the hose. So the next day we brought it home and went to take it out on the lake. The motor was somewhat difficult to start. Once started, the motor wont idle and runs very rough when up to speed. When you drive it, you can feel 1 or more of the cylinders cutting in and out. So I rebuilt all 3 carburators to no avail. Next we confirmed spark on all 6 cylinders. After fiddling around with it all day, we came to the conclusion that it doesn't run any different without the bottom two sparkplug leads on. We confirmed again that they both have spark. Both cylinders are fed fuel by the same double barrel carburator. I took it apart and went through it again making sure this time to check every little thing. Cleaned it again, put it back on, No results. At this point I am stumped.... The fuel pumps seem to be fine and all the carbs seem to be getting proper fuel supply. The compression is all good. No idea. Was looking for a "Had the same problem, try this" sorta thing. Any help would be greatly appreciated!!!

[cyrillefrenchy]

if you are sure 100% the IDLE JETS are clean, you should look for carb synchronizing.carb sync should be done every time the carbs have been removed.
if your bottom carb is closed a little bit more than the 2 others, the 2 bottom cylinders won't fire at idle, but they should work as soon as you give some throttle.

[99yam40]

Check the fuel pump diaphragms, if they are leaking they will dump too much fuel into certain cylinders,causing them not to fire.

As always when troubleshooting a motor make sure compression is good on all cylinders and check spark and timing, if all is good then look at the fuel/air mix.
Too much fuel and the cylinder will not fire.
Too little fuel and the cylinder will not fire and lean running will eat pistons

[cyrillefrenchy]

[QUOTE=99yam40;48132]Check the fuel pump diaphragms, if they are leaking they will dump too much fuel into certain cylinders,causing them not to fire.

yes i forgot that one and when it happenes, usualy you can see soaked wet spark plug on certain cylinders.

[skyeman]

Thanks for the replies... I confirmed that all the cylinders are getting gas. As for getting too much gas I'll have to check that one... I think I'm going to just give the plugs a change even though even though they aren't very old. I see the spark plugs are definately a little wet.... How would I go about adjusting the "fuel to air" mixture?(That would be how to solve this dilemma correct?) Never really adjusted them before. As of now the motor wont even plain the boat due to bogging itself out...

[cyrillefrenchy]

it could be the fuel pump diaphragm then, the fuel is going to the cylinder , flooding it and when you try to go fast, the fuel pump is not pumping enough gas to feed the bottom carb.
try to remove the fuel pump at the base of these cylinders and open up the pump, when you split it open you will see a diaphragm on the back part, a spring and a washer pushing the diaphragm, inspect this diaphragm , it could be cracked,and can be replaced, cheap part.let us know

[skyeman]

This is getting frustrating...

Today bought 2 new fuel pumps for it coming out at $120. Installed them, And no change. So we did some calling around and heard that the plate that the coils are mounted on might not be getting proper ground. So we tested the ground by taking a jumper cable and connecting it to the ground on the block. No difference. But basically at this point, there are 1 or more unproductive cylinders and they tend to move around. Each time the unproductive cylinder will be different. I've never seen this before... Hopefully not the coils :/ ... That's where it stands for now. Thanks for the replies, Keep 'em coming!

[aluxury1]

Blow the carbs out.

Remove the front airbox, and start with a cylinder, remove the bowl drain nut on the bottom outboard side of the carb. 12mm I remember. Then carefully rotate idle mix screw in (clockwise) and count the turns til it gently seats. Write down how many turns as exact as you can. Back screw out all the way and set aside. Now blow air through mixture screw hole for a few seconds. Replace mix screw all the way in and back out correct amount of turns. Replace bowl drain nut. I have to do this once a year, but it is the only bad mark against the carbuerated models. I have heard many stories of fuel problems and injection systems.