2 MPG evinrude lark V 40 HP

Bill1974 · Mar 24, 2013

So I took my 16 ft Starcraft out in the Columbia river and It was 5 miles from the dock to my anchor point and back. I used 5 gallons of fuel. While running I looked at the engine and saw no evidance of fuel leaking from the engine at all. Anyone have a Tip for finiding this issue?

boobie · Mar 24, 2013

Re: 2 MPG evinrude lark V 40 HP

That mtr will use 4 gal/hr at wot.

Bill1974 · Mar 24, 2013

Re: 2 MPG evinrude lark V 40 HP

My GPS says I do 18-23 MPH depending if I am going up or down river. This puts me more in the 7-8 GPH block.

F_R · Mar 24, 2013

Re: 2 MPG evinrude lark V 40 HP

Were you running at full throttle the whole way?

Anyway, a bad fuel pump diaphragm will drink gas like crazy. So will a non-working automatic choke. And very few of them worked properly. Most people just open the door an manually put it on choke to start it, then flip it to manual choke off position.

Bill1974 · Mar 25, 2013

Re: 2 MPG evinrude lark V 40 HP

No on WOT the entire way. I always pull back the throttle a few hundred RPMS. This tends to be half of my throttle band before I get any major drop in RPMS.

This may also answer another issue of why my top plug looks like it came from a 2 stroke and my bottom plug tends to be more fuel soaked. So maybe my auto choke is shot?
and very clean. I pulled them last week after a 5 min WOT push to see what they looked like.

What does a bad fuel pump diaphragm issue look like? a external fuel leak?

Chris1956 · Mar 25, 2013

Re: 2 MPG evinrude lark V 40 HP

The fuel pump has a internal diaghram that pumps fuel due to the vacuum/pressure pulses of the crankcase. If is has a hole in it, unburned fuel will get into the crankcase and eventually dumped into the water. This will increase fuel usage.

Bill1974 · Mar 25, 2013

Re: 2 MPG evinrude lark V 40 HP

Thanks for the info. I am going to go take a look at it. While I at it I pull my carb off of my kicker and give it a good cleaning.

F_R · Mar 25, 2013

Re: 2 MPG evinrude lark V 40 HP

Lark V is a 1963. There is a hose running from the fuel pump, around the rear of the cylinder head, and to the lower bypass cover on the other side. Disconnect either end of that hose and give the primer bulb a squeeze while watching for fuel to come from the fuel pump side. It should NOT. If it does, the diaphragm is bad and that's where all your gas is going. That would also account for the flooded bottom cylinder.

Bill1974 · Mar 25, 2013

Re: 2 MPG evinrude lark V 40 HP

I took the fuel pump off. I am going to change the diaghram just for a good peice of mind. I love how the fuel pump works and how simplie the system is.

Anyone have a good idea on how long it should last time wise? 1-5 years or would you rec a change anually?

F_R · Mar 25, 2013

Re: 2 MPG evinrude lark V 40 HP

They are pretty dependable. I'd say 3-5 years. But as soon as I say that, one will rupture in one year. Murphy, y'know.

Bill1974 · Mar 28, 2013

Re: 2 MPG evinrude lark V 40 HP

I gave my fuel pumpa good tear down cleaning and put it back together. It looks great and should funtion well. Since that was not the problem I guess my automatic choke is bad. I will be using it manually next trip out to see how the engine performs.

If the choke is stuck ON. I should see a increase in fuel consumtion and I should get a decrease in power due to the choke resticting air into the engine. Or is my thought on this incorrect?

steelespike · Mar 28, 2013

Re: 2 MPG evinrude lark V 40 HP

That fuel soaked bottom plug is very suspicious.

Bill1974 · Mar 28, 2013

Re: 2 MPG evinrude lark V 40 HP

can you go into detail? Hole in piston? Bad rings? can you elaborate?

F_R · Mar 29, 2013

Re: 2 MPG evinrude lark V 40 HP

"Looked good". Well maybe yes, maybe not. Did you do the disconnected hose like I suggested?

As far as internal engine damage, have you checked the compression? That should have been your very first step. Sorry we didn't suggest it.

Second step should have been an ignition inspection. It could be running on one cylinder. (The non firing plug would be wet). Sorry we didn't suggest that too.

Everybody jumps to conclusion and assumes it is a fuel problem. Including me this time. Sorry again.

Hey, it could be your lucky day and it may be as simple as a bad spark plug.

Oops, you said it is going 18-23 MPH. It probably wouldn't go that fast on one cylinder. That is what is confusing us. A little clarification here. Was performance "normal"? 18-23 is kind of slow for two cylinders. Back to compression.

Bill1974 · Mar 31, 2013

Re: 2 MPG evinrude lark V 40 HP

I am thinking choke may still be the issue. I have good spark plus I only get a little smoke on start up and that goes away within 30 sec or so. Another thing I noticed is and Oil fuel mix coming from the exaust when I pull the boat out of the water.

So I have spark, Good fuel pump, compression unknown, engine does not smke while running.

F_R · Mar 31, 2013

Re: 2 MPG evinrude lark V 40 HP

SOME fuel and oil out the exhaust is normal. Excessive fuel and oil out the exhaust indicates one of the several things we've been discussing. Back to square one---check compression, etc, etc, etc. That motor is either flooding, or running on one cylinder or has a weak cylinder.

Bill1974 · Mar 31, 2013

Re: 2 MPG evinrude lark V 40 HP

I am going to keep working with it. One of the things I will do is break out my compression test kit and see what I can find.

Bill1974 · Apr 11, 2013

Re: 2 MPG evinrude lark V 40 HP

Update.

I took the boat out and used my Auto choke in manual mode. I got a little more power and I no longer get a run of fuel/oil mix out of my exaust and my lower plug looks great.

I have another minor issue and will post it on a new thread soon.

Bill1974 · Apr 14, 2013

Re: 2 MPG evinrude lark V 40 HP

Ok I was just talking to another guy and he was thinking my boat could be under powered and working to hard? input please?

Chris1956 · Apr 16, 2013

Re: 2 MPG evinrude lark V 40 HP

That is a pretty standard boat/motor combo for the mid 70s or earlier. It won't be a speed demon (say 25MPH), but power should be sufficient.

2 MPG evinrude lark V 40 HP

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