'85 Mercury 25HP XD (0A136185) won't run above 2000ish RPM's on the water/under load.

[FirstTimeSeaLegs]

Hello all,

(Please, if this post/topic has been discussed for the year/make/model of my outboard, I apologize as I did not see it when I searched the forum and this may be deleted)

I Bought a 1985 Bass Tracker that came with a factory installed Mercury 25HP XD on it. I have fiddled with running the motor on muffs, and as per norm, seemed to me at least, to run "okay". Ran a little rough at first but as it warmed up the idle would improve and eventually stabilize. Put into forward/reverse and tried to give it some throttle, and it would bog down and die. Restart the motor and repeat that process 2-3 times and it evetually would let me throttle up in both forward/reverse as long as I feathered the gas/throttle. All the above is while motor is on muff's.

Decided that I would just take it to the lake and see if it was simply something that I could "run out of it" while out on the water. After about 30 minutes of messing with it, I was able to get the boat off the pier and heading out into the lake. I twisted the throttle as far as it would go, the motor rev'd up some, but it was NEVER hitting above/around 2000ish RPM's. Now, the RPM's is just a best guess on my part, but based on watching videos of well running motors just like mine. Top speed was between 5.5 and 5.6 mph by GPS. Pulled the cowl off and tried to run the boat again, this time trying to pay attention to the throttle linkage and the opening/closing of the butterfly valve in the carburetor. Everything appeared to be opening/moving as it should with no binding etc, but no matter what I tried, I could not get the motor to run in the 5000 RPM range. Loaded the boat up and headed home after spending 3 hours on the water, accomplishing nothing.

Did some research and found several topics related to my symptoms possibly being a fuel issue. So that said, I emptied my fuel tank, replaced the fuel hose, cleaned both strainers/filters and then made up 5 gallons of fresh 50:1 fuel. Took the boat back out to the lake the next day and had a repeat of the same problems as before, very very poor performance/no RPM's at WOT. Filled a water bottle with fresh fuel and poked holes in the cap and tried spraying the fuel directly into the carburetor while holding the throttle at WOT. The RPM's never changed.

I am here in hopes that someone has come across this before or something very similar and may be able/willing to help. I tried to keep the story short and sweet as best I could. If more info is needed please let me know.

 

[FirstTimeSeaLegs]

Hmm, guess I shouldn't have posted this.

 

[flyingscott]

Need a Serial #. Compression and spark test need to be done report back with those #s. Sounds like you are running on 1 cylinder.

 

[FirstTimeSeaLegs]

Need a Serial #. Compression and spark test need to be done report back with those #s. Sounds like you are running on 1 cylinder.

Thanks for the reply man. The serial number is (0A136185), in the thread topic. Compression is approximately 110 in each cylinder. Spark test is great. Leak down test, great. I'll have exact numbers for the spark test and leak down test tomorrow.

 

[flyingscott]

Do a cylinder drop test. You may need to rebuild the carb get the kit that has all the gaskets.

 

[FirstTimeSeaLegs]

Do a cylinder drop test. You may need to rebuild the carb get the kit that has all the gaskets.

Thank you! I'll try that.

 

[FirstTimeSeaLegs]

Ok so I ended up taking my boat to a Marine Mechanic. The following information is directly from the diagnostic report:
1.) Spark was good
2.) Compression was 135 & 140 on cylinders 1/2 respectively.
3.) Leak down was 100-92 cylinder #1, and 100-90 cylinder #2.
4.) Carburetor rebuilt
5.) New spark plugs
6.) Reed Valve assembly checked/cleaned.

I dropped by the shop today to pay my bill thinking my boat would be done. It wasn't. I asked what still seems to be the problem and he stated that he hasn't figured that (the problem) out yet. He believes it may be a gasket/o-ring somewhere between the carburetor and the reed valves. He claims the motor idles rough on muffs but gets better if you feather the throttle, so he tore the carb back apart and double checked everything again. He said he was going to see if the gasket/o-ring is leaking/damaged and replace it if needed. If that isn't the problem he stated that the carb could have stress/micro fractures in it preventing proper fuel flow and if that is true he has another carb on site that he will try on my motor to see if the problem goes away.

I know this guy is a decent mechanic too, so I've placed my trust in his diagnosis, but I have to admit that it worries me that he has had my boat since Monday and we still don't know what's wrong with it.

Will update here as I know more. I sure hope once this is all done that someone can benefit from this post at some point haha!

 

[FirstTimeSeaLegs]

Went back out to see my marine mechanic today and he believes he has found the problem. The 2-piece gasket between the carburetor and the reed valve assembly is what he thinks has malfunctioned. He took me back and showed me one half the gasket and it indeed was extremely spongy and you could see where the lower half of it was/had not been sitting correctly.

Unfortunately, we won't be able to test this until next Tuesday or Wednesday as he had to order this gasket.

I sure hope this is actually the problem as there isn't anything left to check haha. Will update once I know more.

 

[FirstTimeSeaLegs]

No Title

#28 is one of the gaskets/seals he is going to replace. #29 and #33 are also being replaced.

 

[FirstTimeSeaLegs]

Ok here's the latest:
Went to my mechanic today after waiting almost a week for a gasket to come in to see how it was going. I got there and he was still working on it. The motor still will not run right. He said that there is a leak in the crankcase. He started the motor up and sprayed starting fluid along where the two halves of the crankcase meet and the motor would stay running. When he stopped spraying the motor would sputter and die.

At this point, it's going beyond what my wallet can afford so I've decided that I'm going to bring the boat home and work on the motor myself for awhile.

Just wanted to let everyone know what's been done so far and what is still to be done. If anyone has any suggestions, please post them here.

Thanks!

 

[Bobbywolf]

A crankcase leak on a 2 stroke will definatly cause you greif. Its pretty involved to split the block, but worth it if you are handy. Probably cost prohibitive to pay someone to do it.

Hopefull you dont find it cracked.

 

[flyingscott]

A crankcase leak on a 2 stroke will definatly cause you greif. Its pretty involved to split the block, but worth it if you are handy. Probably cost prohibitive to pay someone to do it.

Hopefull you dont find it cracked.

You don't split the block to replace intake gaskets. There is also no gasket on the block halves.

 

[Bobbywolf]

You don't split the block to replace intake gaskets. There is also no gasket on the block halves.

The OP never said the intake gaskets. Also, just because there is no gasket, does not mean it isn't leaking. I know the block to crank housing seam is usually sealed with an adhesive rtv only.

 

[flyingscott]

The OP never said the intake gaskets. Also, just because there is no gasket, does not mean it isn't leaking. I know the block to crank housing seam is usually sealed with an adhesive rtv only.

Read post #8 and #9.

 

[Bobbywolf]

They were replaced, but the issue persists. And he specifically mentioned the leak at the case halves.

 

[flyingscott]

Did you do a cylinder drop test on the motor? The problem with spraying starting fluid on the crankcase on those is it can get sucked into the carb. Simply because it sprays all over and there is no silencer on that carb. A better test for the crankcase is use wd 40 with the tube on and spray it slowly on the seam.