75 hp no fuel #3 cylinder

[Archer59]

1994 Mercury 75 hp 0G014879

On the water motor surged a couple of times as I accelerated then cleared up.
Was running fine until I slowed down for a bit and tried to accelerate but could not get over 3200 rpms.
To make a long story short pulled #3 plug wire while running and no change, running rough.
Checked spark, looks good, checked plugs and #3 had less fuel/oil on it than the other two.
The fuel pump had been rebuilt, and looks like there is plenty of spark.
So needle in carb?
I rebuilt them earlier this spring and left the old needles in with the rubber tips.
The needles in the kit all metal without rubber.
Will be checking things over tomorrow afternoon.
Please advise.

Thanks,

 

[achris]

Re: 75 hp no fuel #3 cylinder

If you are getting spark, and the compression is good, then all that leaves is the carb, and the fuel pump base gasket, or the lower crankshaft seal....

Personally, I'd try the pump first, then the carb...

Chris.....

 

[Archer59]

Re: 75 hp no fuel #3 cylinder

Smelling an awful lot of gas when I took the cover off.
Checked compression on all three cylinders 120 on my tester.
Didn't do a leak down test though.
Since there was no change since I rebuilt the fuel pump looks like I'll be tearing the carb apart.
I can't see any leaks any where.

Oh what fun....

 

[1nebel0]

Re: 75 hp no fuel #3 cylinder

Change the needle..Ethanol is playing hell with floats and needles....even plastic floats are warping from the fuel so nothing is immune form the damage...

 

[Archer59]

Re: 75 hp no fuel #3 cylinder

Took bottom carb off and all looks good.
I have fuel to the bowl, needle and seat operating.
At least when I tip it upside down cannot blow air through intake.
I checked all passages and blew them out.
I have spark but don't know if it's weak or not... don't think so.
Running out of ideas.
Trigger perhaps?

 

[achris]

Re: 75 hp no fuel #3 cylinder

When the engine is running, put you hand close to the opening of the bottom carb. You should only feel sucking. If you feel ANY blowing, you may have a reed problem....

Chris....

 

[Archer59]

Re: 75 hp no fuel #3 cylinder

Thanks will try that tonight.

 

[James R]

Re: 75 hp no fuel #3 cylinder

That carb could be flooding. Dont mess about, replace the needles and make sure the floats are set correctly.

 

[Archer59]

Re: 75 hp no fuel #3 cylinder

If it was flooding wouldn't the plug be fouled?

 

[achris]

Re: 75 hp no fuel #3 cylinder

When you pull the plug is it wet or dry?

 

[Archer59]

Re: 75 hp no fuel #3 cylinder

Not much of anything on it.
And the bowl is full of fuel

 

[achris]

Re: 75 hp no fuel #3 cylinder

Do the test I suggested. If you are unsure of the carb, #3 and #2 can be swapped for diagnostic purposes.

 

[Archer59]

Re: 75 hp no fuel #3 cylinder

Looks like all carbs are sucking air.
Good idea on the swap, will do that tomorrow.

Just hoping it's nothing internal.

 

[James R]

Re: 75 hp no fuel #3 cylinder

Lower crankshaft seal failure will provide these symptoms. If the seal fails the cylinder sucks air in past the seal and not sufficient to pull the fuel from the carb.

 

[Archer59]

Re: 75 hp no fuel #3 cylinder

Well I thought I had good spark until I tested with an air gap set at 7/16.
#3 will not make the jump.
#1 and #2 did.
I disconnected the stop wire from the switch box and still no spark.
Glad I found the issue ... now to find the solution.

 

[achris]

Re: 75 hp no fuel #3 cylinder

On that engine you have 3 separate coils. Swap the wires between #3 and one of the others. If the #3 coil is now firing properly, then the switchbox is the problem, If the weak spark stays with coil, then buy a new coil....

Chris......

 

[quicktach]

Re: 75 hp no fuel #3 cylinder

Service carbs. Carefully check the needles for any sign of wear (rings where seat occurs). If in doubt, put in the metal tip needles. Check all fuel filters too ...especially if there's a water separator. The way it happened so fast, makes me think it's a carb issue.

 

[achris]

Re: 75 hp no fuel #3 cylinder

Service carbs. Carefully check the needles for any sign of wear (rings where seat occurs). If in doubt, put in the metal tip needles. Check all fuel filters too ...especially if there's a water separator. The way it happened so fast, makes me think it's a carb issue.

We have already proved it to be a coil/switchbox problem... Now we are just determining which... Please read the entire thread, not just the opening post...

Chris......