2001 40HP Mercury 2 stroke losing power after a short time

[hrbeck2000]

Hi,
I have a 2001 Mercury 40HP 2 stroke serial number 0T475589 2 cylinder single carb. The motor is on a pontoon boat.

Sorry for the novel but I should start with a little background. A couple years ago the top end seemed to be diminishing. The boat would start fine every time and run well enough it just wouldn't achieve the same RPMs as it used to. 2 Years ago it started to idle poorly and would stall when you put it in gear. If you throttled it up a hair and put it in gear it was fine once you got moving still having the problem at top end. So last spring I had the repair facility look at it when they pulled it out of storage. They rebuilt the carb and replaced the fuel filter but said after starting and running it a while it quit. They decided it was still fuel related as the compression and spark were good when it quit. This time they replaced the fuel line from tank to motor including primer bulb as well as the fuel pump. Bottom line is they kept the boat for the entire season never fixing it. I finally had to demand they return my boat as it was clear they were never going to get it right.
This year After trying to get several mobile repair services to come and look at it and not even returning my calls I decided to dive in. Based on the new gaskets and appearances it does look like the replaced the parts they said they did. I installed a new battery and new plugs and it fired right up. It ran on the water muffs for a while and then stalled. After cranking it a little bit and choking it the motor started back up and ran again for half an hour at 1/4 throttle on the muffs. I figured it was unlikely but maybe it had an air lock that they never cleared out and it was good. Dropped the boat in the water and it started right up. I backed away from the launch no problem and started across the lake at about 3/4 throttle, It seemed to have more top end then before and was running great until after about 200 yards it started losing power. I pulled back on the throttle and it would come back and I could throttle up again for short periods but it would start bogging down after a very short distance. I was able to take it down to just above idle and it ran OK and I was able to get it back to the dock. So at this point I'm hoping someone has experienced something similar and can provide some advice.

Thanks, Rich

 

[Texasmark]

First thing I would check is the primer bulb on the fuel line. You need to know if the engine is getting fuel when running. Start out like you described in another trip to the water. While the engine is still running properly and at a reasonable speed...faster the better, reach back and squeeze the bulb, paying attention to what it feels like. It should be soft, not flat, not hard but soft....continue running till it stops and immediately feel the bulb again. If it doesn't feel soft but feels and looks flat, you are not getting fuel to your engine and that's a clogged tank vent possibility. It may not be completely clogged which allows you to run at lower rpms but when the fuel consumption exceeds the air replaced in the tank from the fuel vent it will develop a vacuum and stop delivering fuel.

 

[hrbeck2000]

Thanks for the advice!

I was able to spend a little time messing with it last night. It started right up without hardly any choke which is better than it has been in years so that's encouraging. As I was warming it up I noticed the amount of water coming from the site hole was a weak stream. This was way different than when I was running it on the muffs and much less than it use to have. I'm suspecting an overheat problem at this point. It might not be my entire issue but I have to get that fixed before I go any further. I suspect the guy I had work on it last year ran it without the muffs and fried the impeller. I'll replace that this weekend and report back.

Thanks

 

[hrbeck2000]

OK, I was able to get an impeller today and installed it. I've not done one of these but I have done others without any issues. I watched a couple videos and went after it. Everything seemed exactly like the videos and it went together very well. It went all the way up into place without forcing it and I bolted it together. The water stream seems unchanged. Maybe it never was that strong off the muffs and I didn't notice. I suspect not though and I may have misaligned something going back together. I am adding a video of it draining when I lift the motor and it seems to be leaking from areas I don't remember it leaking from. But before I drop the housing again I figured I would post the video and get some opinions. I also attached a video of it running. The prime bulb seems soft and there is no change to engine RPM when I squeeze it.

Ideas???

 

[Texasmark]

Where is your tell tale stream in picture #2. I can't tell if the engine is cutting out in the video or your recorder is picking up interference...sounds rough.
Picture #1 just looks like normal draining from several points...I assume the engine wasn't running with the LU out of the water.

On what you may have missed, the pipe from the water pump outlet to the bottom of the block is what there is to miss if you missed something...didn't get it stabbed or if it had seals, didn't get the seal installed or in the right place.

If you are thinking about a over temp problem, the engine wouldn't crank if it stopped due to actual OT. It would be seized...pistons to the cylinder walls and wouldn't even rotate with the starter or by hand. Subsequently it wouldn't start and run.

Dirt dobbers, corrosion, mud and sand, and salt deposits can clog your pee line. You need to go back to the source of the pee hose and remove the adapter and do a quick muffs run to see ifwater spurting out of the engine block. If not find out why. Then running on muffs at like 1500 rpms, run it for a bit and hold your hand on the rear of the block. If it doesn't get so hot that you have to remove your hand your thermostat must be working ok.

I see the bulb check passed your test but you need to check it when it cuts out with your running in the boat on the water where you have the problem.

 

[Faztbullet]

Replace the fuel lines and bulb the clean the carbs. Bet the fuel line liner has degraded and restricting fuel supply and blocking high speed jets. Looks like a aftermarket grey line...

 

[hrbeck2000]

Thanks for the replys

The fuel line is aftermarket but it's brand new along with the bulb. I shot the video with the front of the boat up against the shore and powered up to about half throttle. It will take off initially and then just bog down and stay there until you throttle down for a few seconds and then back up. The carb has been rebuilt and the fuel pump replaced. It really does feel like it's starving for fuel to me but I'm not sure how with everything new. The odd thing is I had the guy do the carb because it had lost a little top end and was idling poorly. It never had this loss of power issue before he worked on it.

 

[Faztbullet]

Revisit the carb repair..

 

[hrbeck2000]

Okay, I'll pull it and go through it. Who knows for sure what kind of job he did?

What about the hoses under the hood? I was thinking maybe I should replace those as well when I'm in there. Is that just standard bulk fuel hose from the auto parts store or something specific to marine use?

Thanks again for the suggestions.

 

[Texasmark]

The hose visit is a valid question. I had a 2002, 90 hp triple 2 stroke that spent it's life on Ethanol. At 10 years of age I was having similar problems. In cleaning out the carbs, I found little black specks like I found by using a cotton swab and swabbing the inside of a fuel line to check for degredation (which I found...little black specks).

I messed with that thing for quite awhile till one day I had the bowl of one in my hand and shot it with 100+# of compressed air. Lo and behold, a tiny black speck of fuel line came out of the cavity where the high speed jet is located on one of my carbs. Put it all back together, did the link and sync on the carb linkage and never saw that problem again.

That's one reason I asked if you cut your fuel filter open...the other was to see if any of the brown residue was in there from the engine to tank fuel line.

On what fuel line to use, the fuel pressure is single digit PSI and the space is limited. Finding a suitable diameter at an auto parts store is questionable...a marine dealer, probably.

On the Zip ties used on the fuel lines, regular ZTs aren't used. Merc uses a special tie that has a curved locking section such that when pulled up tight, the curved part closes up the little gap that regular zip ties leave and could cause a fuel leak. I got mine off ebay.

 

[hrbeck2000]

Thanks for the great info.
I'll pull the carb and clean it out and blow through everything with compressed air. I won't take any chances and just replace the fuel lines under the hood with the correct zip ties as you outlined. It might be a couple days before I report back. We have rain in the forecast the next few days.

 

[hrbeck2000]

Hi Everyone,

Sorry it has taken so long to report back. I was out of town and today was the first opportunity I had to work on the motor.
While I was away I was thinking about this and it dawned on me why not do the same thing I did when I was working on cars? When I had a low power/bog down issue I would hit it with a squirt of carb clean to see if the additional fuel made a difference. Well that's what I did and this thing just came alive with the smallest hit of carb clean. I think it is safe to say we have a low fuel issue.
I went ahead and pulled the carb and will go through it but the parts store is closed today so I won't be able to get fuel line or zip ties until tomorrow.

Stay tuned.............

 

[hrbeck2000]

OK, I disassembled the carb for cleaning and there really didn't seem to be any dirt in there. I went ahead and shot carb clean through all the ports and followed up with compressed air. Everything seems to be open. One thing I did find is the round gasket at the power valve is missing. I assume Mercury put it in there for a reason. Could that really be my entire problem?

 

[hrbeck2000]

Well, I decided to make a gasket out of some gasket material I had in the garage and put this thing back together and see what happens. Apparently Mercury wants that gasket in place because the boat runs great! It's always something little like that. I wish I would have just worked on the boat from the start instead of letting the boat mechanic do it.

Oh well. Lesson learned.

Thanks to those that provided feedback and advice. Maybe someone else will find this helpful down the line.

Take care!