Evinrude Big Twin 40 HP fouling one plug only

soccoach · May 26, 2012

I recently replaced the plugs, points and condensor. I did a pressure test on both cylinders and registered over 90 lbs on both. One pug is badlyfouled. The other is very clean. This was after only 10 minutes of running the engine in a water tank.
What would cause on plug to foul and not the other?

Thanks in advance.

nwcove · May 26, 2012

Re: Evinrude Big Twin 40 HP fouling one plug only

bad coil, or plug lead. ( possible head gasket issue tho)

boobie · May 26, 2012

Re: Evinrude Big Twin 40 HP fouling one plug only

Or a bad fuel pump leaking fuel into the cyl it runs off of.

tx1961whaler · May 26, 2012

Re: Evinrude Big Twin 40 HP fouling one plug only

Or the inner exhaust cover leaking water into the "clean" cylinder.......

Quack kills · May 26, 2012

Re: Evinrude Big Twin 40 HP fouling one plug only

What yeAr?

soccoach · May 27, 2012

Re: Evinrude Big Twin 40 HP fouling one plug only

Quack kills said:
What yeAr?

1968. I looked at the coils. No cracks, infact they looked brand new. I checked the spark on the plugs and they seemed to be OK. The fact that the cylinder pressure held for several minutes rules out the head gasket.
I will run the boat again today after doing a thourough inspection yesterday. If I have th same symptoms, I will replace the coils.

Thanks

kenmyfam · May 27, 2012

Re: Evinrude Big Twin 40 HP fouling one plug only

soccoach said:
1968. I looked at the coils. No cracks, infact they looked brand new. I checked the spark on the plugs and they seemed to be OK. The fact that the cylinder pressure held for several minutes rules out the head gasket.
I will run the boat again today after doing a thourough inspection yesterday. If I have th same symptoms, I will replace the coils.

Thanks

What kind of pressure test did you do ???

soccoach · May 28, 2012

Re: Evinrude Big Twin 40 HP fouling one plug only

I did a compression test over 5 minutes to see if there was any leakage. Pressure held at 95 lbs.
I took the boat out yesterday and ran WOT. Had a good run, but the car began to spit gas out the front. Will have the carb rebuilt this week. Thanks for all the help.

silver_bay · May 28, 2012

Re: Evinrude Big Twin 40 HP fouling one plug only

Is the fouled plug on the cyl with the fuel pump? If so, check the pump diaphram for leaks.

Dirtscooter · Jun 18, 2012

Re: Evinrude Big Twin 40 HP fouling one plug only

Been a couple weeks. I'm wondering if the problem was resolved and if it was the fuel pump. Also I was curious if it was the top cylinder that was missing...

kfa4303 · Jun 18, 2012

Re: Evinrude Big Twin 40 HP fouling one plug only

fuel out of the carb throat usually means there's an issue with the float getting stuck and flooding the engine, but I'm curious to know how it turned out too.

soccoach · Jun 19, 2012

Re: Evinrude Big Twin 40 HP fouling one plug only

Quite a story. I finished all of the work. I pulled the intake manifold to check the leaves and gaskets. OK.
I rebuilt the carb. I ran the boat three times without a problem.
I advertised to sell the boat. On the test run, itran fine until we returned to the dock. The engine stalled. The choke lever had moved to half choke. Once again gas flooded out of the carb. I could not restart.
I have replaced the float (again), changed te coils and plug wires.
I won't be able to test for a couple of days.

Dirtscooter · Jun 20, 2012

Re: Evinrude Big Twin 40 HP fouling one plug only

soccoach said:
Quite a story. I finished all of the work. I pulled the intake manifold to check the leaves and gaskets. OK.
I rebuilt the carb. I ran the boat three times without a problem.
I advertised to sell the boat. On the test run, itran fine until we returned to the dock. The engine stalled. The choke lever had moved to half choke. Once again gas flooded out of the carb. I could not restart.
I have replaced the float (again), changed te coils and plug wires.
I won't be able to test for a couple of days.

When you say you've replaced the float again, are we to understand that the float removed from it just now was new? If so was it installed into the carb as it came out of the package without being coated to withstand ethanol added fuel? We found it helpful to weigh the float immediately when it comes out. It should weigh slightly less than 3 grams. If it is bad and you weigh it quickly enough before it has a chance to dry it might weigh nearly 4. After being double coated with por15 and dried for 96 hours it should weigh 3 grams.
Not that we are jumping the conclusion to assume the float to be the culprit but like to eliminate it as a suspect with the coating. Could be needle or fuel pump or ??? I'm wondering though if it were the float, how long it took for it to go bad and what kind of fuel did that.

1946Zephyr · Jun 20, 2012

Re: Evinrude Big Twin 40 HP fouling one plug only

I would get a plastic float, if the float is giving problems.

Dirtscooter · Jun 21, 2012

Re: Evinrude Big Twin 40 HP fouling one plug only

1946Zephyr said:
I would get a plastic float, if the float is giving problems.

I agree..........Do you have a source or a part number for that big twin float in plastic? I think it would be the answer to a lot of Big Twin prayers. We made a brass float last weekend from a dual pontoon brass float out of an old tractor carb. Hours with a dremmel and solder.

soccoach · Jun 22, 2012

Re: Evinrude Big Twin 40 HP fouling one plug only

Well, I took the boat out yesterday and all went fine. I think I need to adjust the throttle a little. One of the sparkplug wires was cut too short so I will replace that today. I found that if I push the throttle a little more on the start, it will start easier. Just 2 pulls.
I put two paddles in the boat in case I get stuck again.

Thanks for all the advice. I will take it out again tomorrow to test it. If I have more problems, I will come back!

kfa4303 · Jun 22, 2012

Re: Evinrude Big Twin 40 HP fouling one plug only

Making progress. All these old motors have their own unique way they like to be started. Mine likes lots of throttle upon start up, but then idles right down. Good luck. Keep us posted!

Dirtscooter · Jun 23, 2012

Re: Evinrude Big Twin 40 HP fouling one plug only

kfa4303 said:
Making progress. All these old motors have their own unique way they like to be started. Mine likes lots of throttle upon start up, but then idles right down. Good luck. Keep us posted!

Considering how every Big Twin seems to have a character of it's own when it comes to starting and it's transition to high circuit in the carb, I've decided to experiment with different fuel mixtures this weekend.

We have a 6 gallon tank which is mixed at 12-1 with 33% of the oil being Marvel Mystery Oil. We've been using it for a couple of months to wake up long sleeping Big Twins and Elgins. All seemed to benefit from it as the longer they were hooked up the better they acted, at the expense of out eyes around the test barrels.

Another 6 gallon tank starting today will have a 32-1 Klotz Mixture, a smokeless synthetic oil. I'm wanting to document how much the carb adjustment, Idle, and high needles change.
and naturally how the character of the starting and idling manners change. I will start a new thread on it if anyone thinks it might be of interest, although I still haven't figured out the correct link in order to start a new thread yet.

soccoach · Jul 2, 2012

Re: Evinrude Big Twin 40 HP fouling one plug only

If it isn't one thing it's another. A screw came loose and lodged between a coil and the magneto. I fixed it, but didn't realize it had also bent one of the points. After pulling the harmonic balancer AGAIN, I think I have this thing solved. I will test it again tomorrow, crossing my fingers!

Evinrude Big Twin 40 HP fouling one plug only

Cadet

Admiral

Supreme Mariner

Vice Admiral

Recruit

Cadet

Supreme Mariner

Cadet

Petty Officer 3rd Class

Cadet

Banned

Cadet

Cadet

Vice Admiral

Cadet

Cadet

Banned

Cadet

Cadet