Losing Power/ Fuel Delivery 1968 18 HP Evinrude

[mobydick]

I have what I think is a fuel delivery issue. I have 100% replaced the ignition system but the symptoms do not seem to me to be ignition related.

I start the motor, let it warm up, get going, open the throttle to full, reach plane for a few seconds, it then bogs down to about 1/3 throttle speed. I let it idle a bit open the throttle again, it almost reaches plane and then bogs to about 1/3 throttle speed again. I can continue this pattern all day.

I have tried to pump the fuel line bulb but it is hard and makes no difference.
I rebuilt the carb about 4 months ago.
I pulled the full line off the carb side of the pump and it seems to be supplying pressure. I have not measured the oz. of fuel per minute.(I do not know a spec).
I suspect it may be a sticking float/float needle/ float adjustment.

Any ideas?

Thanks
Greg

 

[tashasdaddy]

Re: Losing Power/ Fuel Delivery 1968 18 HP Evinrude

ethanol poisoning, http://forums.iboats.com/showthread.php?t=299680

 

[mobydick]

Re: Losing Power/ Fuel Delivery 1968 18 HP Evinrude

Maybe ethanol related but I replace all the fuel lines when I rebuilt my carb as well as the fuel pump. Is it possible that ethanol destroys the fuel pump diaphram? As I mentioned, it does seem to be supplying fuel just fine.

 

[JB]

Re: Losing Power/ Fuel Delivery 1968 18 HP Evinrude

Sounds to me like it is burning fuel faster than it is getting into the carb. That is usually a restriction in the fuel supply system. I have found those exact symptoms when the fuel line from primer bulb to the fuel pump was pinched and when air was leaking into the fuel lines.

I would carefully scope out the crankcase pulse line to the fuel pump for restriction or leakage.

I don't agree that E10 is the culprit.

 

[Doyle Johnson]

Re: Losing Power/ Fuel Delivery 1968 18 HP Evinrude

Seen this problem b 4. Alot of times the person doe's not open the air cap on the top of there gas can. Check to see if you have that little valve wide open b 4 you start her up next time.

 

[14ftgrumman]

Re: Losing Power/ Fuel Delivery 1968 18 HP Evinrude

When you ebuilt the carb, did you remove and clean the carb jets?

 

[Sargent Skiff]

Re: Losing Power/ Fuel Delivery 1968 18 HP Evinrude

I'd check the intake screen inside the fuel tank.

 

[samo_ott]

Re: Losing Power/ Fuel Delivery 1968 18 HP Evinrude

Something you could try is to make a spray bottle of 50:1 premix and when it starts to die spray it in the carb. If it picks up it confirms it is a fuel delivery problem. Just watch out for backfires!

 

[mobydick]

Re: Losing Power/ Fuel Delivery 1968 18 HP Evinrude

Per JBs advice, I checked for any restrictions/ leaks in the all fuel lines from the tank to the carb. I even borrowed a friends tank and hose to eliminate that part of the system. I did not find anything.

Can you better describe the "crankcase pulse line to the fuel pump" so that I can locate and check that?

I also tried samo_ott's idea with the spray bottle. When I sprayed fuel into the carb, it wanted to die similar to what would happen if I put the choke on when the engine is warm.

I had one other idea. Is it possible that the float in the carb is not closing the needle when the bowl is full and flooding the engine?

Thanks
Greg

 

[kbait]

Re: Losing Power/ Fuel Delivery 1968 18 HP Evinrude

Flooding sounds right if spraying fuel into carb made it die rich. Ensure good spark and compression, then check float valve and float level.

 

[KB1]

Re: Losing Power/ Fuel Delivery 1968 18 HP Evinrude

Flooding sounds right if spraying fuel into carb made it die rich. Ensure good spark and compression, then check float valve and float level.

Pull one plug at a time and fire it up to make sure that water does not blow out the plug hole. If a head/exhuast gasket is weak/blown you will drowned one cyl. firing properly. The mix spray in the carb will flood the good one. Both will fire but one will be to moist to give power. Seen this on 3 cyl. 55 hp johnny in the mid 80's.

 

[jbjennings]

Re: Losing Power/ Fuel Delivery 1968 18 HP Evinrude

Since it is not picking up by spraying fuel into the carb throat, I believe that pretty much isolates the problem as spark. It could be a head gasket, but I'd think you would have spotted milky stuff on one of the plugs. I'm thinking of a bad coil from the factory, since this has happened to me a couple of times.
Where's F-R? He needs to get on the job----what are we paying him for???
Also, is the throttle plate horizontal on full throtte?? i.e. linc-n-sync problem? how's the mesh of the throttle gears? Jumped a tooth?

Just some guesses,
JBJ

 

[samo_ott]

Re: Losing Power/ Fuel Delivery 1968 18 HP Evinrude

This is a toughy. So it doesn't sound like fuel starvation. Then as JBJ says it's spark or it could be a flooded carb condition in my opinion.

 

[mobydick]

Re: Losing Power/ Fuel Delivery 1968 18 HP Evinrude

Yes, it is a toughy. I have attached a picture of the plugs, top plug in pic is top cylinder. Maybe this could help diagnose.

Just to clarify, the thing that makes this odd is the symptoms.
1. starts fine
2. idles fine
3. low to mid speed fine
4. high speed fine for about 15-30 seconds then slows way down to about 30% throttle speed.
5. let idle a few minutes the twist to full throttle, it get to about 85% throttle speed
6. kill engine and let sit for 30 monutes and does the same as #4

 

[asdasc]

Re: Losing Power/ Fuel Delivery 1968 18 HP Evinrude

I am going to agree with the team that it is spark related. Probably a bad coil that gets hot and shorts, or even a condensor that does the same.

There is a sure difference in the plug readings, and with a single carb you wouldn't see that if ignition were good.

 

[asdasc]

Re: Losing Power/ Fuel Delivery 1968 18 HP Evinrude

I should also ask, did you take compression readings? I wouldn't think that would be it if it runs smooth at mid throttle and starts right, but you never know.

 

[mobydick]

Re: Losing Power/ Fuel Delivery 1968 18 HP Evinrude

I agree with the way the plugs read it would indicate an ignition issue.

Any idea why it works for a bit and then looses power?

 

[mobydick]

Re: Losing Power/ Fuel Delivery 1968 18 HP Evinrude

Also, which plug shows the correct burn in the cylinder?

 

[mobydick]

Re: Losing Power/ Fuel Delivery 1968 18 HP Evinrude

One more thought.
Any chance it is related to a reed valve since they independently control each cylinder?

As a reminder every single part of the ignition is new. But as JB said, could be a bad coil from the factory.

 

[perkdp]

Re: Losing Power/ Fuel Delivery 1968 18 HP Evinrude

I believe the vaccum port driving the fuel pump in on the bottom cylinder.
Bottom plug looks way too rich to me. The pump may have a pin hole in the diaphram that doesn't allow fuel to pass low vaccum / idle but does at high vaccum / wot flooding the bottom cylinder.

When at idle can you pull plug wires one at a time to see if rpm drops ?