1986 Merc 115HP Stalls With Load

[akendall]

Specs:<br />1986 Merc 115HP (Standard Prop) on a 1979 17ft J-Craft.<br /><br />Symptom:<br />-Motor runs great free of load (no waterskier/tow) from slow to full throttle (~5800RPM) even when hammering it, idles great as well. However, when trying to pull a waterskier out of the water it stalls.<br /><br />-I have changed the gas and spark plugs but problem still persists. Only when gas bulb is sqeezed during the initial waterskier pull is the motor sometimes successful.<br /><br />-Please give some suggestions if possible

 

[akendall]

Re: 1986 Merc 115HP Stalls With Load

Let me add to the specs on the motor - it is an inline 6 cylinder

 

[DJ]

Re: 1986 Merc 115HP Stalls With Load

akendall,<br /><br />More than likely, the check valve in your primer bulb is no longer fuctioning.<br /><br />Also, if your fuel connection (at the engine) is of the long bayonett type, these were notorious for having the O'ring seals go bad. There is also an O'ring in the fuel inlet (where the connector plugs in) on the side of the engine.<br /><br />Essentailly, your engine is sucking air when it needs the fuel the most.

 

[letsbarbq]

Re: 1986 Merc 115HP Stalls With Load

hey djohn long time no see. sorry akendall. dont mean to get off the subject.<br /><br />Letsbarbq

 

[akendall]

Re: 1986 Merc 115HP Stalls With Load

Thanks a lot for the advice djohns19! I checked the fuel lines and there were air leaks - I have now replaced them... but the problem still persists.<br /><br />I would like to also mention the following:<br /><br />-when spraying carb cleaner into the three carbs I noticed that when spraying into the bottom carb it made little difference compared to the top two (which would lead the motor to a close stall during the carb cleaner injection) Is this normal, or does it mean that the bottom carb may be running poorly? ...and would this possibly contribute to the issue I'm experiencing?

 

[JB]

Re: 1986 Merc 115HP Stalls With Load

Howdy, AKendall.<br /><br />It probably means that your bottom cylinders are not making power.<br /><br />How a multicylinder 2 stroke engine seems to start and run without a load tells you nothing except that at least one cylinder is making power. BTW, never rev a 2 stroke without load. Thermal runaway will take control away from you and blow it sky high unless you get the fuel cut off soon enough.<br /><br />Pull or short out each spark plug with the engine at idle. If the idle speed drops that cylinder is okay. No change and the cylinder is dead.<br /><br />Check spark on dead cylinders. You already added "fuel" and got no change.<br /><br />Good luck

 

[Bob Blair]

Re: 1986 Merc 115HP Stalls With Load

I rebuilt my fuel pump in anticpation of fixing my problem. Which is similar to yours except I don't get the RPMs in the water only out of the water.<br /><br />My engine is the 90 HP and the rebuild of the pump was very simple.

 

[akendall]

Re: 1986 Merc 115HP Stalls With Load

Thanks for the advice JB! - I'm going to try that this weekend - at the cottage ;^)... and let you know how it went. Oh, and by the way I never throttle it too high in idle - 5800 is the RPM I get in full forward without a skier (sorry if I confused anyone in the explanations...) And I should add that I can pull up skiers successfully sometimes - it's a sporadic incident - errrrr!<br /><br />BTW - Bob Blair, did the fuel pump rebuild fix your problem with torque even though you still have an issue with RPM's in the water?

 

[Bob Blair]

Re: 1986 Merc 115HP Stalls With Load

It made the boat run much better. But, no it didn't completely fix my problem. I noticed the diaphrams were worn and sand had made it all the way to the pump. So it had an impact rebuilding it.<br /><br />I'm now debugging the cylinders. <br /><br />They are all firing but one may not be getting enough fuel from the carb. I need to try JBs suggestions and debug the cylinders once more.<br /><br />I'll rebuild them this weekend.<br /><br />Good luck with yours.

 

[akendall]

Re: 1986 Merc 115HP Stalls With Load

I just want to thank you guys first for the advice you have given me above.<br /><br />I'm off to perform the compression test and I was just wondering what kind of compression I should be seeing in all of the cylinders (couldn't find that value in the Seloc manual)<br /><br />As well, after the compression test is completed I'm going to perform the spark (ignition) test - all I do is simply touch the threaded part of the plug to the engine block and crank the motor to see spark? Should this be done with all of the spark plugs disconnected or can they be in the motor at this time? Never done this kinda stuff before - I know... it's pretty sad! <br /><br />...and you can tell how sketchy the Seloc manual can be at times...<br /><br />Thanks...

 

[what200]

Re: 1986 Merc 115HP Stalls With Load

when performing compression tests or spark tests the wires your not testing should be ground to the block. It is stressful on the switchbox otherwise.<br /><br />Good compression numbers would be around 130 and acceptable would be above 100. More importantly is the difference between cylinders. A difference of 5 or less is good. A difference of 15 is less good. More than 15 means something is wrong like sticking rings, scored cylinder walls, scuffed piston, etc.

 

[akendall]

Re: 1986 Merc 115HP Stalls With Load

Hello fellow boat lovers!<br /><br />I know it's been two months but I'm back and happy to say that the motor passed the compression and iginition tests - thanks "what200" for the values. (hard to diagnose motor all the time - 3hrs away!)<br /><br />-I then pulled the plugs as "JB" (thanks) suggested and found power loss on all cylinders (while running) as well as a spark test and that suggested (to me) that at least I was getting good ignition.<br />-Had the stator tested both low and high windings and it passed.<br />-Now I've been told to look deeper into the carbs, one method is to actually to cover each carb up with a rag for a short duration, one at a time while running - and if I see gas flow onto the rag that means that the carb is getting gas - if not then the carb isn't and it needs to be everhauled - does this sound like a good test to you guys?<br />-One more question I have, I noticed that if I drag the waterskier first (at between 900 - 1500 RPM) before hammering the throttle, this stalling condition doesn't happen at all. Any of you guys have any suggestions on what this might mean or what it may lead me to next in fixing this problem?<br /><br />Any replies appreciated!

 

[Miskwabi]

Re: 1986 Merc 115HP Stalls With Load

Hey - this is akendall back after 10 years (I created a new account because the email for my old account is no longer in use) - just to provide an update on this problem I had... as I see there are others out there still with similar issues with this engine. This may not be the root cause for this kind of issue for all, but this ended up being the low speed winding in my stator. Once my stator was replaced, the problem went away - and hasn't come back since. Funny thing is, one mechanic said that the stator tested fine as per one of my updates previously.... but evidently it was defective.
I still recommend taking the troubleshooting steps that have been well methodically written out within this site however before going straight to the stator - as their are so many causes for this type of issue.
I'm glad to be back!