'89 Evinrude 40hp 7 mph tops

nurs4kdz

Cadet
Joined
May 25, 2019
Messages
9
We started out the season with a bad controller/switch..something. We replaced, and rewired the switch, and now that is fixed. Next issue was the motor did not seem to be getting enough fuel because the primer bulb was stuck, leaking, or something. We were getting air bubbles all in the inline fuel filter. We had an old tank that was really bigger than I wanted anyway, so we went and purchased a new tank--the Atwood 6 gal that undoubtedly is not vented. We also replaced tank line, bulb and filter. We are still getting airspace in the fuel filter, but it is an air gap, not the millions of tiny air bubbles that make it look milky as we had before.

We still have issues and I am not sure where to go from here. The motor just will not get us above 7mph. It sounds good, and when you first gun it, it will give a burst of power, but quickly backs down and does not return unless you back off and gun it again. We have tried carb cleaner to no avail. Yesterday, we began running Seafoam through it and it did seem to give hope, as we would get more bursts of power, like maybe it was about to pick up, but never did..or did not stay over a two second burst/surge. It's hotter than hell here in bama now, so running the water at 6.5 mph in an aluminum boat is miserable, so we probably only ran about a gallon of the Seafoam/fuel through it yesterday.

Carbs completely rebuilt two years ago. Both hubs and I are shade-tree mechanics, so we have just enough knowledge, skill, and tools to be dangerous. The boat does not have a tach on it, but I honestly have an ear for motors, and the dadgum thing SOUNDS great...other than the sputter caused from the Seafoam yesterday.

Where do we go from here? Could we have messed up the throttle while in the control box, could it be the new non-vented tank, or do we need to attack the carbs?

Thanks in advance!
Tracy
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,964
Many folks jump on carburetors first ??------Do these simple checks.-----Post results of a compression test.----And check health of ignition system too.--- Spark should jump a hap of 3/8" or more.
 

jakedaawg

Rear Admiral
Joined
Jun 26, 2012
Messages
4,275
Above must be done...may I also suggest this:

remove air silencer cover. Advance throttle to full. Visually verify that throttle butterflies are now horizontal. Do this with motor off of course.
 

heypawpaw

Petty Officer 2nd Class
Joined
Dec 12, 2016
Messages
111
We still have issues and I am not sure where to go from here. The motor just will not get us above 7mph. It sounds good, and when you first gun it, it will give a burst of power, but quickly backs down and does not return unless you back off and gun it again.

By quickly backs down, do you mean engine bogs down? Have you tried pumping primer bulb when engine slows down? Some air in inline filter normal.
 
Joined
May 22, 2019
Messages
15
I’m having similar issues I think you have an electrical issue, are you getting spark to both spark plugs? Mine has been running on one cylinder for a long time and the other one would fire on randomly and then id get full port at first I thought it was getting flooded. I have a 1984 Evinrude 40 hp motor, tested the spark plugs today and the one isn’t getting any spark so now I have to trace back all wiring from the top spark plug.
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,226
While I'm not one to automatically assume carburetor, it does sound like one carb is not getting enough fuel for some reason. Kinked hose???
 

JerEazy

Petty Officer 1st Class
Joined
Jul 26, 2017
Messages
234
It really wide open - missing spark on a cyl would limit RPMs and speed - but a carb could easily be an issue as well. Or you could just have the wrong prop on there.

checking spark is cheap or free - would start there
 

nurs4kdz

Cadet
Joined
May 25, 2019
Messages
9
Thank you all for the suggestions. We have good compression with both cylinders @ 140 psi. Spark test was good at 3/8". Both throttle butterflies are horizontal with full throttle. I will try a cylinder drop test in the morning. I am still leaning toward a fuel issue. Is there any way to troubleshoot which carb may be the issue without pulling both? I have rebuilt a few carbs in my life, but really hate doing that as I never feel like I can get them adjusted correctly afterwards.

My husband just mentioned this to me tonight, that I think may be key. He said in the past, the primer bulb was always easy to pump, even to the point of easily flooding if you weren't careful. He said that now, after a few squeezes, the bulb is tight and impossible to pump. Is this telling of something?

Again, much, much thanks to you all!!
 

nurs4kdz

Cadet
Joined
May 25, 2019
Messages
9
One more question, and this is so simple I think we should have already tried this, but could it possibly just be a fouled plug? I also just researched, so I will test the fuel line up to the carbs tomorrow by taking the lines loose and pumping the bulb.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,964
Launch the boat.-----Start motor.-------Give it some throttle in gear.-----Spray fuel into top carburetor.-----Report what happens.----Spray fuel into bottom carburetor.--Report what happens.
 

nurs4kdz

Cadet
Joined
May 25, 2019
Messages
9
It will be next weekend before I get it back in the water. I took out the screws on the bottom of the carb bowls. Both had fuel in them.
 

Kplusten

Cadet
Joined
Jun 4, 2014
Messages
22
If motor sounds right at WOT, and you feel an initial burst of thrust, problem may be spun prop. Mark inner and outer hubs, run motor and see if marks are no longer aligned. Second input: The Atwood tanks with EPA and CARB compliant caps are problematic. I use two 6 gal tanks and had to replace caps with pre-2010 Moeller manual vent cap. Also, experts recommend installing a fuel demand valve if you leave the tank exposed to direct sunlight. Tank can overpressurize carb bowls leading to major gas leaks. Do not discount other expert replies, but maybe it is something simple and overlooked.
 

nurs4kdz

Cadet
Joined
May 25, 2019
Messages
9
I did a cylinder drop test, and it bogged down when I removed each plug, so I take it as both cylinders are firing. Kplusten, I am back to thinking it is the Atwood tank/tubing, too. It IS the the non-vented tank. It has a little relief screw valve on the top, but it does not seem to work as the tank quickly swells as the temperature rises. I am going to order a manual vent cap now. I do not know what a fuel demand valve is, but I will google it now. Again, I sincerely appreciate all of your input and suggestions!!
 

kbait

Commander
Joined
Nov 13, 2007
Messages
2,477
Agree..just loosen the cap a bit for now. Plugs gapped to .030”? Do insulators look black/tan/white? Any difference between plugs?
Are you positive there’s no water in bottom of tank?
Also, if your motor is actually revving up and you don’t go faster, spun prop hub is very likely..
Good luck!
 

nurs4kdz

Cadet
Joined
May 25, 2019
Messages
9
We have run it with the cap loosened--no change. Not likely water in tank as this started with an old tank, we purchased a new one and started with fresh gas. I will check for spun prop tomorrow, but I don't think that's it. The motor is not screaming like it is at full RPM, AND every now and then we do get a surge of power.
 

nurs4kdz

Cadet
Joined
May 25, 2019
Messages
9
Kbait, I'll recheck gap tomorrow. I may just go ahead and replace them. Wires were changed out last year.
 

jakedaawg

Rear Admiral
Joined
Jun 26, 2012
Messages
4,275
Is the arrow on the bulb pointing towards the motor?

also, verify that red lever on primer solenoid is parallel with solenoid body.
 
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