Occassional dead cylinder

[interalian]

If the crankcase pulses are not strong eniugh to run the pumo i would be surprised if that cylinder would fire.

What would you expect to see for pulse strength on a good motor?

 

[flyingscott]

Your piston compression has NOTHING to do with your pump pulses. The crankcase pulse is controlled by the reed valves not the piston that is 2 strk 101. Remember the old piston port sleds. If you had a bad reed valve all of the cylinders would be affected because the pump is attached to all 3 carbs.

 

[jakedaawg]

I believe the piston coming down creates the pulse. The piston going up creates opposite and pulls in through the carb. Different set of reeds for each cylinder. In this case the vro gets its pulses from the #3 piston and crankcase. Thats why there are sealing rimgs on the crankshaft. As the piston comes down into the bottom of its stroke it forces the fuel and air that was sucked in through the carb up into the combustion chamber. As the piston goes up to fire it pulls in more. Rinse and repeat for each cylinder. Hence two stroke. I am refering to crankcase pressure and vacuum. Not cylinder compression. Modern outboards are cross flow charged, loopcharged, or direct injetion loopers. I havent seen a piston port outboard.

 

[interalian]

I believe the piston coming down creates the pulse. The piston going up creates opposite and pulls in through the carb. Different set of reeds for each cylinder. In this case the vro gets its pulses from the #3 piston and crankcase. Thats why there are sealing rimgs on the crankshaft. As the piston comes down into the bottom of its stroke it forces the fuel and air that was sucked in through the carb up into the combustion chamber. As the piston goes up to fire it pulls in more. Rinse and repeat for each cylinder. Hence two stroke. I am refering to crankcase pressure and vacuum. Not cylinder compression.

Exactly. 2-stroke 101. But how much pressure on compression (piston coming down), and how much vacuum when the piston is going up at cranking speed? Say for a crossflow V4, or loop I-3.

 

[flyingscott]

I believe the piston coming down creates the pulse. The piston going up creates opposite and pulls in through the carb. Different set of reeds for each cylinder. In this case the vro gets its pulses from the #3 piston and crankcase. Thats why there are sealing rimgs on the crankshaft. As the piston comes down into the bottom of its stroke it forces the fuel and air that was sucked in through the carb up into the combustion chamber. As the piston goes up to fire it pulls in more. Rinse and repeat for each cylinder. Hence two stroke. I am refering to crankcase pressure and vacuum. Not cylinder compression. Modern outboards are cross flow charged, loopcharged, or direct injetion loopers. I havent seen a piston port outboard.

Exactly right, I am only saying that when the fuel charge wants to move as it's being compressed the charge wants to leave the cylinder the reed valves being closed helps stop that process by holding crankase pressure resulting in higher pressure for the pulse.. Sorry I think I worded it wrong. The piston port sleds idled a 1500 or above to get enough of a crank case pulse to work the pump.

 

[TrueNorthist]

Interesting about #3 being the pulse driver, that's the suspect cylinder and it has some pretty scary looking scoring on both sides to boot. Whelp, for $75 (plus 12% tax) the Facet pump is the cheapest option, before even counting the cost of replacing the shaped lines. Using a relay and eliminating several clamps, lines etc should minimize the risk of anything going sideways. I could rig up a switch on the dash for the pump, but it might be best to keep that switched by the key. Key off, fuel off. I will use my long Sierra fuel line -- minus the engine end connector with the pump/filter replacing the primer bulb -- and use the VRO oil line pass-through for fuel instead and run a short length of line up to the existing splitter set-up. Easiest, cheapest and simplest. I like that.

Thanks all.

 

[ondarvr]

The power/safety switch should be wired into the motor so if the motor stops the pump does too, the key should power the pump when it's in the "start" position, not in the "on" position.

 

[jakedaawg]

Exactly, this is different than we used to do it. We ran off batt+ when we went fast.

To run a electric you need to pull power from the lighting coil so that it only gets power when the engine is cranking or running. You will still need a bulb to get it to fire on start up then the elec pump will take over.

On the race boats we rigged a seperate switch. You turned your pump on, started in gear, and flew the boat. We used a mecury switch to shut it off in the case of a blow over.

Your case is different, you dont want the pump running if you forget to turn the key off.

 

[Greg_E]

Just disconnecting the plug wire does not mean that you don't have intermittent spark on a particular cylinder, just that now that it's disconnected you have no spark.
If you have an inductive timing light or can borrow one it is a simple test to clip the lead on each of the plug wires to see if one is cutting in and out.
I'm not familiar with your model engine My oldest engine is a 1987 Evinrude V6 225HP. I'll go out on a limb here and assume the power pack and coils are similar between the two, which might not be the case. I have had at various times a poor connection between the coil pack ground strap and the block, a bad coil, an intermittently bad power pack, all which caused an intermittent spark on a particular cylinder.
Before you spend any money verify all cylinders have good spark. If you have three separate coils you can swap the coils and see if the problem moves to the other cylinder.

 

[TrueNorthist]

I am still working on the many other issues present on this motor, but I have taken aboard all of the suggestions above. Many thanks. I also want to include below a link to some videos I just posted at my Youtube channel. Apologies for the quality of both the videos and the channel etc. Interesting views of the inside of the cylinders. I am amazed at just how badly scored they all are and some metal transfer is actually present in #3, along with a lot of fuel pooling. I think the VRO fuel pump was holed or damaged in such a way that fuel was being drawn into the crankcase through the pulse line.

Prior to tear-down, I confirmed that there is always a spark at all three plugs that jumps a 1/2 inch gap, under all running conditions, misfiring and running "well". I have re-linked and synced just to be safe. I also pulled the reed plate and will be installing new reeds later today, however the reeds looked worn but definitely still serviceable.

I should have some results soon, hopefully positive.

Youtube video of cylinder #3

Cylinder #2 top

Cylinder #2 ports

Cylinder #1 top

Cylinder #1 ports

 

[TrueNorthist]

It's running about as good as I coulda hoped. I ended up tapping into the purple #7 wire at the bus which gives me keyed power for the relay. (5amp fuse as well) I have no idea if I am getting juice during start but there must be enough residual pressure available while it's cranking because she flashes right up smartly now and goes through all revs smoothly. I'm getting 35mph out of the old girl which is more than enough, but a new prop should tweak out a bit more yet.

No primer bulb needed so far as the pump is rated to lift 60" while self-priming and I give it a few seconds to pressure up before cranking. I reckon I'll buy a spare fuel pump in case this one ever goes bust, but my experience with Facet pumps leads me to believe it will last longer than the motor. Now I just gotta make it all look nice and tidy.

Again thanks for the tips etc fellas. Much obliged.

edit: I shoulda noted the system pressure is ~5 to 7psi and I will be swapping out the injection clamps for permanent crimps. Not a single hiccup at speed or at idle, but I'm going to rig up a bypass for times when the engine is trolling for long periods and demand is low.

 

[TrueNorthist]

Update after 50 hours: Not one single problem with the electric fuel pump. In fact it has been a decided improvement in several respects. Cold start is a breeze no matter what conditions and enough flow to run both the main and kicker at the same time if I ever go mad. I keep a spare pump in my tool box but I doubt I will need it for a long, long time.

What's not to like about this?

I can remove the shift link in seconds now and have enough room to sleep 6 in there. Look Ma, no pulse line!

Here's a last look at what I installed before I permanently mount it to the boat:

Over the winter I'm going to tidy things up some more and forget about fuel pumps. All in all it was a very painless upgrade. Total cost: $90 for the pump and a few bucks more I guess for sundries.

edit: btw, I used the primer circuit as a power source for the relay which gives me juice in both start and run.