Fuel pressure??

[skynyrdcat]

88 Evinrude V-4

Newly rebuilt power head with new power pack, plugs and wires, still loads up and misses.
Also getting lots of oil / gas residue in silencer cover.

I pulled the carbs during rebuild, the floats were level and all was very clean.
Checked synchro at least 5 times, all is good.

Also, the plugs are wet when I pull them (not water, just gas and oil).
I by passed the VRO (during rebuild) with an after market fuel pump, but would like to know the max fuel pressure for this application.

The needle and seats sealed up well by the way when I had the carbs apart.

Any thoughts?

 

[skynyrdcat]

Re: Fuel pressure??

By the way, I only get about 4100 RPM at WOT

 

[ezeke]

Re: Fuel pressure??

Sounds as though you are still getting fuel past the float valves. You only need fuel pump pressure enough to lift fuel from the tank to get the float bowl full - about 1.5 psi on a conventional pump for a crossflow V4; at that point the float should rise and close the float valve so that no more fuel gets in the carburetors until the vacuum created by the pistons has drained enough fuel to lower the float.

When you have a carburetor off the engine, turn it upside down so that the float drops. In that position, you should not be able to blow air or fuel into the carburetor.

BTW, I would be trying for 5800 RPM at WOT. Need more information about the whole setup to make a guess as to what is going on. Were you getting better RPM before?

 

[Dhadley]

Re: Fuel pressure??

Describe "an after market fuel pump".

 

[skynyrdcat]

Re: Fuel pressure??

Sounds as though you are still getting fuel past the float valves. You only need fuel pump pressure enough to lift fuel from the tank to get the float bowl full - about 1.5 psi on a conventional pump for a crossflow V4; at that point the float should rise and close the float valve so that no more fuel gets in the carburetors until the vacuum created by the pistons has drained enough fuel to lower the float.

When you have a carburetor off the engine, turn it upside down so that the float drops. In that position, you should not be able to blow air or fuel into the carburetor.

BTW, I would be trying for 5800 RPM at WOT. Need more information about the whole setup to make a guess as to what is going on. Were you getting better RPM before?

I checked the needle and seat again (I can not blow thru with carb upside down).
I did find that when running I can remove the port side plug wires (one at a time) and little difference is made. I'm getting good fire and compression to both port cylinders, so my question is does one carb run both the port cylinders and one the strbrd cyls, or does one carb run the top two and one the bottom two?
The engine was in bad shape when I got it, have never got 5500rpm. I'm hoping when I get this corrected I can get my full 55-5800 rpm.

By the way if I remove plug wire from either starboard side cyl it makes a big difference so I'm getting good results from both of those.

 

[skynyrdcat]

Re: Fuel pressure??

UPDATE!!!

Fuel system seems OK but I did find that the spark on the top port cyl is intermittent.

Sometimes I check it and it's firing, sometimes it's not firing.
Has new power pack, what else could cause this?

 

[ezeke]

Re: Fuel pressure??

First, try to answer DHadley's question, he is the master technician around here.

The ignition system has to have good clean connections all along the wiring system, especially the ground wires. It amazing how many times folks have written on this forum that their problems disappeared after they cleaned all of the connections.

My first choice when only one cylinder is misbehaving is to swap the ignition coil. If you even think someone might have used auto spark plug wires on that engine, replace them with solid core. Make sure that you have the right spark plugs.

The top carburetor serves the top two cylinders.

I would remove the cylinder head on the port side and see what's up.

Get a new gasket so you will not be tempted to reuse the old one.

 

[skynyrdcat]

Re: Fuel pressure??

First, try to answer DHadley's question, he is the master technician around here.

The ignition system has to have good clean connections all along the wiring system, especially the ground wires. It amazing how many times folks have written on this forum that their problems disappeared after they cleaned all of the connections.

My first choice when only one cylinder is misbehaving is to swap the ignition coil. If you even think someone might have used auto spark plug wires on that engine, replace them with solid core. Make sure that you have the right spark plugs.

The top carburetor serves the top two cylinders.

I would remove the cylinder head on the port side and see what's up.

Get a new gasket so you will not be tempted to reuse the old one.

Cool, as far as the after market fuel pump, by that I mean it's not the original set up. It's a pump to by pass the VRO.

I took it out today and get up to 4800 rpm by trimming the motor up.
It does OK and can be used as is, but I'm a perfectionist and want my full performance, plus I can't rest if I can't get the problem fixed. I have brand new wires (silid core) and power pack.
I bought the boat at a good price but it had problems, I have rebuit the engine 100% with new plugs, all ignition except coils and stator.