Mercruiser 5.0/Chevy 305 firing every other cylinder

VPinzon

Cadet
Joined
Jun 10, 2022
Messages
8
So I've just redid the whole interior of the boat and decided to tackle the engine. It was running okay just was hard to start.

Anyways here's what I've done as a background. To address the hard staring issue I've rebuilt the carb, set ignition timing, and checked plugs/wires. I have also rebuilt the distributor(cap, rotor, ignition sensor).

It was cranking much better and would usually crank after a few turns without issue so I figured I had solved the issue. We lake tested it a whole day and it seemed to run great. It did however start to be harder and harder to crank. (Essentially just took longer)

While on the lake it ran fine otherwise and we tested it from idle to WOT. It ran 41MPH at nearly 5k rpm. Seemed healthy.

Anyways I came home to address some of the minor issues. I found that my electric choke was unplugged. This might have caused my starting issues after a while. But I decided to check the firing of the cylinders. I unplugged one coil at a time while the engine was running and what I found was when removing wires from cylinder 1,7,6,4 it did not affect the running of the engine at all while 2,3,5,8 if pulling even one almost choked the engine to a halt. So now I'm confused.

After so research I believe I have a carb issue. Since 1,7,6,4 are fueled by one half of my Eddlebrock 1409. I have spark and compression on those cylinders. I am not a carburetor wizard and generally hate them as opposed to fuel injection. But I know that in theory they are simple devices. As my knowledge is limited on this maybe some of y'all can help me out. Especially since I just rebuilt the dang thing.

I did make sure to check floats for minimum and maximum hights. Mine are at 7/16 min between top of float and top of gasket and 1" when fully dropped between top of float and gasket.
 
Last edited:

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
42,069
Pull plugs and compare plugs, all should look the same. If they do it could be it's probably the idle circuit in the carb.
 

VPinzon

Cadet
Joined
Jun 10, 2022
Messages
8
Pull plugs and compare plugs, all should look the same. If they do it could be it's probably the idle circuit in the carb.
Pulled plugs on one side(Would have done all but its a challenge to get the out without removing the exhaust), anyways the firing plugs are very similar to those suspected of not firing but those that are not firing are dry compared to those that are. Dont look burnt just dry.
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
42,069
I would bet one side of the idle circuit is clogged, but dang it still runs
 

VPinzon

Cadet
Joined
Jun 10, 2022
Messages
8
I would bet one side of the idle circuit is clogged, but dang it still runs
Took off carb and cleaned every single port. I noticed that the new float needles were sticking a little in the new seats. I still have my old ones so I put my old ones on and they did not stick like the new ones. Anyways I put it back on the engine and were golden. Got myself a V8 now instead of a V4 haha. Thanks!
 
Top