Help us before my husband throws our Mercury outboard in the water!

Aug 2, 2018
96
Beneteau Oceanis 40cc Little River, SC
Just to be sure...

if this is a 2-stroke - you do use the right mixture of gas and oil, don't you? I have seen a 2-stroke die when getting hot, when the oil to gas ratio was too low (the engine was seizing).

I would also triple check the fuel filter (I know that you mentioned that you did replace it, but the fact that the symptoms went away after replacing the gas tank and lines (new gas!) could point in this direction). I had very similar symptoms when the filter was clogged.
We did try changing the the mixture yesterday. And cleaned the filter again as well.
 
Aug 2, 2018
96
Beneteau Oceanis 40cc Little River, SC
Rather than put $300 into the old carburetor, he should have replaced it with a new one. Some of these gummed up carburetors cannot be repaired. I'm not saying this is the problem but the carburetor should not be eliminated as a possible source of the problem during diagnostics. Kloudie mentions a good point, check the coils as the symptoms are consistent with fouled coils.
Could you point me in the direction of how to check the coils?
 
Aug 2, 2018
96
Beneteau Oceanis 40cc Little River, SC
Update:
Changed the plugs and cleaned the filter.
Just like it has been in the past, motor started up, and ran well and got up on a plane. Then after 10 minutes, it dies if you accelerate. This happens time after time, seemingly after the motor warms up. After it cools, it can be started again. Rinse and repeat. :banghead::banghead::banghead:
 
Nov 6, 2006
9,885
Hunter 34 Mandeville Louisiana
Unfortunately, the coils are usually checked by replacing with new. A simple check with an ohm meter will show good because of no heat (assuming that is the problem). Not easy because that stuff is under the flywheel, but not too much of a pain.
 
Feb 17, 2006
5,274
Lancer 27PS MCB Camp Pendleton KF6BL
I had the same problem with my Yamaha 9.9 outboard. I was told by everyone to clean the carburetor. I was scared to death to take the carb off for fear of messing something up. But I did so and it worked out great. No issues since. But I read that you had the carb serviced. But you are still having the same issue. The motor boggs down when you increase the throttle. Like I said, mine did exactly the same thing.

The issue was the jets. My motor has two sets of jets; one for low idle and one for open throttle. I am sure the mechanic correctly inserted and adjusted the jets when he/she put them back in. However, if they are not adjusted correctly then the fuel flow will be restricted.

I doubt it is a timing issue because that would show up even in idle. A miss here, a miss there. Or overall a rough idle.

I don't know, but I would take the carb out and remove or replace the jets. Or... check to see if that motor has a specific procedures for adjusting the jets.

JMHO

caveat - I did not read all the replies so if this was already mentioned, my apologies.
 
Aug 2, 2018
96
Beneteau Oceanis 40cc Little River, SC
I had the same problem with my Yamaha 9.9 outboard. I was told by everyone to clean the carburetor. I was scared to death to take the carb off for fear of messing something up. But I did so and it worked out great. No issues since. But I read that you had the carb serviced. But you are still having the same issue. The motor boggs down when you increase the throttle. Like I said, mine did exactly the same thing.

The issue was the jets. My motor has two sets of jets; one for low idle and one for open throttle. I am sure the mechanic correctly inserted and adjusted the jets when he/she put them back in. However, if they are not adjusted correctly then the fuel flow will be restricted.

I doubt it is a timing issue because that would show up even in idle. A miss here, a miss there. Or overall a rough idle.

I don't know, but I would take the carb out and remove or replace the jets. Or... check to see if that motor has a specific procedures for adjusting the jets.

JMHO

caveat - I did not read all the replies so if this was already mentioned, my apologies.
I am very glad you responded. This is all very very helpful
 
Aug 2, 2018
96
Beneteau Oceanis 40cc Little River, SC
Unfortunately, the coils are usually checked by replacing with new. A simple check with an ohm meter will show good because of no heat (assuming that is the problem). Not easy because that stuff is under the flywheel, but not too much of a pain.
The captain responded with Oh F@$k! :whoa: That was Helpful, but he just spit out his coffee at the mention of a flywheel!
 

WayneH

.
Jan 22, 2008
1,039
Tartan 37 287 Pensacola, FL
Coils. Oh, God. Coils. My 2 stroke Johnson would suddenly bog down and then come back and bog down and come back. We checked the fuel, drained the carburetor bowl looking for water, changed the plugs. I finally pulled the flywheel off and you could see the crack in one of the coils.

Getting the flywheel off the Johnson was not hard. I don't have a fully stocked tool chest but managed to get it off without banging up the Flywheel or the mechanic. But this was on a Johnson 1964 6hp.

Your mileage WILL vary.
 
Apr 27, 2010
1,236
Hunter 23 Lake Wallenpaupack
You may also want to post this query on an outboard focused forum. I use iboats.com, where they have brand specific sections. Your Merc may be one made by Tohatsu, and there are a few professional mechanics that give a lot of advice. That said, many of the threads I see there where things die at higher speeds after running for a while are temperature related, where some electronic part (as noted in prior posts) fails when it gets hot. If your issue seems to be when the motor is hot (and it may only get hot enough after running at higher RPM for a while) it may be electrical. As noted earlier, when it starts to die position the fuel bulb with arrow pointing up and pump it. If that fixes it (my guess it won't) then it may be a weak fuel pump. At least on my Honda 8, the fuel pump is fairly easy to service or replace.
 

Rick D

.
Jun 14, 2008
7,132
Hunter Legend 40.5 Shoreline Marina Long Beach CA
FWIW, I went through this for two years on 60 hp OB. Turned out to be the fuel pump despite having it rebuilt twice.
 
Nov 9, 2012
2,500
Oday 192 Lake Nockamixon
I just fast read through 3 pages, and there have been lots of fuel system suggestions that never addressed a fuel pump, until Rick D weighed in. So, definitely check your fuel pump. On a 70 hp 2 stroke Merc we used to have, the fuel pump could be rebuilt with new diaphragms. On my small 5hp 4 stroke Tohatsu, it was simply a whole new fuel pump that gets bolted on. Of course, with my Tohatsu, it wasn't the fuel pump at all, but it was the new fuel line and fittings I had purchased, mainly the motor fitting creating a very poor seal and sucking air. I used the original motor and tank fitting from the old line with the new line and bulb and I've been good ever since. Plus I have the old, good, fuel pump as a spare.

Also, there was a great suggestion to try squirting fuel directly into the carb when it starts to die, as a way to determine if it was fuel system or coil. Did you try that yet?
 
Feb 10, 2004
3,919
Hunter 40.5 Warwick, RI
Regarding the $300 carb service- A friend who owns a marina and services lots of small outboards tells me that the only successful way that he has found to completely clean a small engine carb is by using an ultrasonic cleaner. He says that nothing else will clean out the small passages that become plugged. This is especially true for the newer 4-cycle engines, but I took his advice and purchased a small ultrasonic cleaner for all of my small engines. I guess what I am trying to say is that even though the carb was serviced, maybe the job was not as good as it could have been. This may not be the first thing to re-check, but I would keep it on the list.
 
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jviss

.
Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
Changing the fuel tank and hoses (helped it to work for a while and then went back to the same problem)
I have two of these motors, a 1998 and a 2001. They are very good, and run well, and are repairable. If you give up, I'll buy yours.

First, the OEM fuel tank is garbage. I had one fail because the clear, vinyl-like pick-up tube shrunk and became loose, probably because of ethanol in the fuel. By 'shrunk,' I mean the wall thickness decreased, and it no longer sealed. I had symptoms like yours. I bought a new fuel pick up assembly for $26, and it worked for a little while until the same thing happened. The only thing that fixed this was buying a N.O.S. metal tank on eBay. I still use metal tanks, and no problems in this department.

I have had one electronic module fail. Replacing it was easy, and fixed my running problems.

There is no choke on this carb. It has an integral fuel pump, and a primer. The fuel pump diaphragm and primer parts come with the rebuild kit. A complete new carb $214.41 in 20014. I bought one because I broke one tightening it too hard.

Throw away the Merc tank. Get a metal tank. If problems persist, consider an electronic module ($162.03 in 2015). Maybe coils, but I have never had a problem with them.

Good luck.

p.s. check and change the lower unit oil every year. If it's milky, stop using it, flush it, and rebuild it with new seals. If you ruin the lower unit your options are very limited. It is cost prohibitive for anyone to rebuild it, and a new one is almost as much as a new motor ($1400).
 
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Aug 2, 2018
96
Beneteau Oceanis 40cc Little River, SC
You may also want to post this query on an outboard focused forum. I use iboats.com, where they have brand specific sections. Your Merc may be one made by Tohatsu, and there are a few professional mechanics that give a lot of advice. That said, many of the threads I see there where things die at higher speeds after running for a while are temperature related, where some electronic part (as noted in prior posts) fails when it gets hot. If your issue seems to be when the motor is hot (and it may only get hot enough after running at higher RPM for a while) it may be electrical. As noted earlier, when it starts to die position the fuel bulb with arrow pointing up and pump it. If that fixes it (my guess it won't) then it may be a weak fuel pump. At least on my Honda 8, the fuel pump is fairly easy to service or replace.
Awesome!
 
Aug 3, 2012
2,542
Performance Cruising Telstar 28 302 Watkins Glen
Please excuse my ignorance and this is not meant to be critical...but are you motoring a Bene 40CC with an outboard? Curious minds need to know. Coils should be checked for cracks in the polymeric encapsulant, as well as wire connection being loose. Extreme temperature swings can have a prolific impact on the plastic coating, as well as high humidity or rain ingress upon the coil. I still think this is a fuel flow issue.
No. Dinghy
 
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Aug 3, 2012
2,542
Performance Cruising Telstar 28 302 Watkins Glen
I had my Merc 9.9 do a similar thing. It was a fuel feed problem. It idled fine. It started fine. No miss fires. When I would rev it, it would bog and die. The found the bulb was soft. I tried another tank with a shorter fuel hose. It worked fine. I rerouted the original hose, and it worked. The bulb stayed firm. Check all the fuel connections and the hose route before spending more money.

Good luck!
 
Aug 2, 2018
96
Beneteau Oceanis 40cc Little River, SC
I had my Merc 9.9 do a similar thing. It was a fuel feed problem. It idled fine. It started fine. No miss fires. When I would rev it, it would bog and die. The found the bulb was soft. I tried another tank with a shorter fuel hose. It worked fine. I rerouted the original hose, and it worked. The bulb stayed firm. Check all the fuel connections and the hose route before spending more money.

Good luck!
Thank you!
 

Sumner

.
Jan 31, 2009
5,254
Macgregor & Endeavour 26S and 37 Utah's Canyon Country
FWIW, I went through this for two years on 60 hp OB. Turned out to be the fuel pump despite having it rebuilt twice.
:plus::plus:
I'll bet this is it. If the fuel pump has a diaphragm in it, most do, and it is torn it can still pump enough gas at lower speeds, but not keep up at higher throttle settings. It will get worst to the point it might not pump enough for slow throttle openings,

Sumner
==========================================================
1300 miles to The Bahamas and Back in the Mac...
Endeavour 37 Mods...
MacGregor 26-S Mods...
Mac Trips to Utah, Idaho, Wyoming, Canada, Florida, Bahamas
 
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