TL;DR: Rebuilt mercruiser 140, idles great but doesn’t have enough power to plane. Going to replace fuel pump, and rotor cap. Anything I’m not thinking of?
Numbers:
Engine: mercruiser 3.0 - 4779114
Carburetor: Rochester 2GC - 7043184
074 7 1
Outdrive: I think it was a pre alpha or early alpha 1 gen 1 at some point. But now it has a sterdrive engineering 106.
Alright, this might be a doozy. I’ll try to include everything that’s happened.
I bought a 1978 Bonito 8CBR last summer. It seemed like it was old, but it ran pretty well on the water. Around 32mph top speed. Then I found out that oil was spewing out of the dipstick. I did my compression test and it was low (I don’t remember the numbers now), but shot up to normal after I added some oil. Therefore, long story short, I decided to rebuild the engine as a project. A local machine shop confirmed the block was worn and bored it .030” over. They also rebuilt the head for me which included pressure testing, resurface and lapping the valves. They purchased a full kit for the engine and sent me on my way. It has a new cam, timing gears, pistons, bearings, lifters, the whole shebang all new gaskets, everything. I put the engine back together and torqued everything to spec from the service manual I have. I rebuilt the carburetor, got new plugs, wires, coil, condenser, and rotor. I did the break in procedure of running it at a few thousand rpm for 20 minutes when I first started it up. Then it mostly sat in a carport because the season was over. Now, I’ve taken it out a few times and it starts up easily, idles well. I’ve verified the idle speed in gear with a laser tachometer. It runs around 760 rpm in gear and about 900 rpm when out of gear. The timing is set between 6-10° btdc at idle. I set the point gap to .022” with feeler gauges. I’ve even checked compression just to be sure and it is 150 psi on all cylinders.
Now for the problem, it sounds like it wants to run. But if you give it throttle while in gear on the water, it won’t get any higher than about 2800 rpm. Once you get above 1500 rpm or so, it starts to sound a little like a lawn mower. If you give it more throttle, it gets louder, but engine speed doesn’t increase.
I don’t have the right timing light to verify the advance, but I can tell that it does advance. I have verified spark on cylinders at idle and even bought a secondary ignition pickup. Although I haven’t tried using an oscilloscope while on the water.
The only things that are still original on the engine are the distributor cap, the fuel pump, and the distributor assembly.
I’ve considered all sorts of options and I just can’t figure it out. I have taken the carburetor out and re-cleaned passages but nothing changes. I even bought a little kit from Amazon to clear out carburetor passages.
I’ve been able to get the boat to plane a few times and it sounds alright. It wouldn’t go much faster than about 3000 rpm, but it would at least plane. Now I can’t get it to go much faster than a few miles an hour.
I have scoured the forums for someone with a similar problem and I can’t find anything. I’ve found results for bogging, but mine doesn’t seem like bogging down and dying. It seems like the engine is pushing, but just can’t push any harder.
It has a Rochester 2GC carburetor. The carburetor is definitely suspect. The bowl was a little corroded when I rebuilt it. But I did my best to clean it. However, I am wary of buying another rebuilt carburetor in case that one isn’t in any better condition. I tried to purchase a new Chinese mercarb (by National Carburetor), but the mounting bolts were too far apart.
I have considered switching to a Holley 2300 marine, but I figure the adapter plate and modifications to the throttle linkage would be a hassle.
I figure it can’t hurt to buy a new fuel pump just in case, but I wanted to check if anyone else had experienced something similar. I have a fuel pressure gauge, but there’s no way to check the pressure with the hard fuel line.
I did align the engine with the outdrive when I put it back in. All of the bellows have been replaced along with the gimbal bearing. I’ve probably replaced more things that I’m forgetting.
I have not replaced the distributor cap, it looked okay though. I can replace that pretty easily and no harm in replacing it.
I have also not run the engine on an external tank yet.
Here are two videos showing what the engine is doing on the water. It will rev up pretty well in neutral, but not under load. They are both showing I under load.
https://youtube.com/shorts/yjDJFPywF1s?feature=share
Numbers:
Engine: mercruiser 3.0 - 4779114
Carburetor: Rochester 2GC - 7043184
074 7 1
Outdrive: I think it was a pre alpha or early alpha 1 gen 1 at some point. But now it has a sterdrive engineering 106.
Alright, this might be a doozy. I’ll try to include everything that’s happened.
I bought a 1978 Bonito 8CBR last summer. It seemed like it was old, but it ran pretty well on the water. Around 32mph top speed. Then I found out that oil was spewing out of the dipstick. I did my compression test and it was low (I don’t remember the numbers now), but shot up to normal after I added some oil. Therefore, long story short, I decided to rebuild the engine as a project. A local machine shop confirmed the block was worn and bored it .030” over. They also rebuilt the head for me which included pressure testing, resurface and lapping the valves. They purchased a full kit for the engine and sent me on my way. It has a new cam, timing gears, pistons, bearings, lifters, the whole shebang all new gaskets, everything. I put the engine back together and torqued everything to spec from the service manual I have. I rebuilt the carburetor, got new plugs, wires, coil, condenser, and rotor. I did the break in procedure of running it at a few thousand rpm for 20 minutes when I first started it up. Then it mostly sat in a carport because the season was over. Now, I’ve taken it out a few times and it starts up easily, idles well. I’ve verified the idle speed in gear with a laser tachometer. It runs around 760 rpm in gear and about 900 rpm when out of gear. The timing is set between 6-10° btdc at idle. I set the point gap to .022” with feeler gauges. I’ve even checked compression just to be sure and it is 150 psi on all cylinders.
Now for the problem, it sounds like it wants to run. But if you give it throttle while in gear on the water, it won’t get any higher than about 2800 rpm. Once you get above 1500 rpm or so, it starts to sound a little like a lawn mower. If you give it more throttle, it gets louder, but engine speed doesn’t increase.
I don’t have the right timing light to verify the advance, but I can tell that it does advance. I have verified spark on cylinders at idle and even bought a secondary ignition pickup. Although I haven’t tried using an oscilloscope while on the water.
The only things that are still original on the engine are the distributor cap, the fuel pump, and the distributor assembly.
I’ve considered all sorts of options and I just can’t figure it out. I have taken the carburetor out and re-cleaned passages but nothing changes. I even bought a little kit from Amazon to clear out carburetor passages.
I’ve been able to get the boat to plane a few times and it sounds alright. It wouldn’t go much faster than about 3000 rpm, but it would at least plane. Now I can’t get it to go much faster than a few miles an hour.
I have scoured the forums for someone with a similar problem and I can’t find anything. I’ve found results for bogging, but mine doesn’t seem like bogging down and dying. It seems like the engine is pushing, but just can’t push any harder.
It has a Rochester 2GC carburetor. The carburetor is definitely suspect. The bowl was a little corroded when I rebuilt it. But I did my best to clean it. However, I am wary of buying another rebuilt carburetor in case that one isn’t in any better condition. I tried to purchase a new Chinese mercarb (by National Carburetor), but the mounting bolts were too far apart.
I have considered switching to a Holley 2300 marine, but I figure the adapter plate and modifications to the throttle linkage would be a hassle.
I figure it can’t hurt to buy a new fuel pump just in case, but I wanted to check if anyone else had experienced something similar. I have a fuel pressure gauge, but there’s no way to check the pressure with the hard fuel line.
I did align the engine with the outdrive when I put it back in. All of the bellows have been replaced along with the gimbal bearing. I’ve probably replaced more things that I’m forgetting.
I have not replaced the distributor cap, it looked okay though. I can replace that pretty easily and no harm in replacing it.
I have also not run the engine on an external tank yet.
Here are two videos showing what the engine is doing on the water. It will rev up pretty well in neutral, but not under load. They are both showing I under load.
