Engine stalls afters running

[CSUGDEN]

I have a 1990 Merc 150 XR4 Outboard engine. It runs fine at full throttle and seems to start and idle fine (after startup) but after driving the boat at half or full throttle and then throttling down to neutral, the engine stalls every time.

Any suggestions on how to troubleshoot this?

Charlie

 

[Windykid]

Re: Engine stalls afters running

Is the primer bulb flat at this point?

 

[CraigC]

Re: Engine stalls afters running

Need a few details, so I'm going to go the fun route!

Also, I'm sure you said this is the case, but I want to be 100% clear...you can run as long as you want, this problem only happens when you bring it back to an idle by yourself. Correct?

Ok fun time, I've got 2 questions for you about some further info on this condition...answer mine and I'll try very hard to help answer yours!

1.) This is right after you have the problem - i.e. you just did a half/full throttle run for a while, then tried to bring it back to an idle, and it stalled on you, like you said above.

Now, if you turn the key to start it back up (right after it stalls on you - like 10 seconds later...or without waiting a significant period of time).....
What does it do?
Does it:
a.) start right back up and idle ok?
b.) start right back up and NOT idle ok? (won't idle now that it's fully warmed up)
b.) hard to get to restart but idles ok once restarted?
d.) hard to get to restart AND NOT idle ok now?
e.) NOT restart at all now, and you have to wait a while?
(If somehow there should be an f. needed below because of something very strange that I missed, please explain that also)

2.) Has anyone done any work on this lately? By that I mean, did you NOT have this problem prior to ANY tune-up and/or repairs, and now after something's been changed, poof - it's doing this? OR has this problem just come out of the clear blue?

Let me know,
Thanks.

 

[CSUGDEN]

Re: Engine stalls afters running

WindyKid
Dont know aqbout the buld but I will check it out.

The engine has been purchased, used and run primarily on a lake for many years, so I am told and has only seen salt water for 1 year prior to the sale where it has been standing for a single season unused.

CraigC

I would say the answer is more likely 1c. It restarts but the idle struggles but I think I have seen the gamut of what you mentioned. I've got new gas in there and it still does happen but perhaps a bit less.

I've put some gas enzyme into the tank to work out any impurities within the delivery system. I dont know if that will do any good. My mechanic says the carbs wull need cleaning at the end of the season but he is new to the shop and I dont entirely trust his diagnosis.

Today I'll give it a better test.

Charlie

 

[CSUGDEN]

Re: Engine stalls afters running

WindyKid

Yeah the fuel bulb is firm.

CraigC

The engine holds idle after full throttle first time after use. After that it stalls every time. Restarting immediately is possible but idle gets shakier as the day wears on.

Charlie

 

[CraigC]

Re: Engine stalls afters running

Ok, sounds like it's a little different. There could be a few things going on here. Here's a few thoughts...
Ok, not idleing correctly when warm could just be the carbs. I would say that you should clean the carbs, I've seen similar running problems caused by dirty/gummed up carbs. (Couldn't hurt to change the inline fuel filter while your at it also, tho it won't fix the problem by itself.)
It also sounds like this could possibly be heat related, as when the engine is fully warmed up it doesn't idle well. Again, could be carbs need to be cleaned out, but could be more severe, for instance could be that it's running a bit hot. An overheating engine will almost certainly never idle correctly. Check to be sure it's not overheating! Also, make sure that you're overheat alarm is working, and check the temp of the tell-tale stream with your hand - it shouldn't ever be too hot to hold your hand under. Do you know when the last time the impeller was changed in the water pump? If overheating a bit, that would be the cause most likely.
Last thing, and granted this kind of a long shot here, but I've heard of it happening, and again is heat related. Make sure you've got spark on all 6 cylinders when this engine is hot/having the problem. I've heard of problems with electrical components where after they get hot they stop functioning properly. If possible take it out and get it to the point where it won't idle well and run a spark test on it to make sure your bad idle isn't caused by it trying to idle on less then 6 cyl's! (Note, there are lots of ways to do that, I'd simply bring a friend and a spare plug, pull off plug wires 1 at a time, connect wire to spare plug, ground plug to head and have friend hit the key and see if you've got spark...repeat for all 6.)

Let me know how it goes.

 

[CSUGDEN]

Re: Engine stalls afters running

The engine I bought used so I had my mechanic:
1. Give it a compression test
2. Tune it up
3. Changed the impeller
4. Checked the water flow


On this particular engine, the installation of a water pressure sensor seemed not to work (where it was spliced in) though on my oldMerc it worked fine.

We had a problem with the oil sensor. We changed it and the alarm went off.
As far as I know, the beeping alarm will change if there is an overheating problem.

Cleaning the carbs is an off season type of task isnt it?

I'll check the temp soon.

Charlie

 

[CraigC]

Re: Engine stalls afters running

It's good that you had those things done initially, those are all good ideas when dealing with a used engine.

Where did you try to hook up the water pressure gauge to? It should be connected to a spot directly directly behind the flywheel - there should be a plug in the block there - it's got a 3/8" drive female head on it, you should remove that plug and put a fitting in there for water pressure. On these motors that's the only reliable place to hook one up, at least to my knowledge anyway.

On the alarm you're correct, if it's an oil problem it'll go "beep-beep-beep" and if it's an overheat condition it'll be a constant "beeeeeeeeeeeeeeeep" sound.

As for cleaning the carbs, normally it would be a pre-season thing...unless you're having problems with how it runs...then it's an "as needed" thing! The more info I get here, and the more I think about it - the more I think you've most likely got dirty carbs.

 

[CraigC]

Re: Engine stalls afters running

Oh, by the way - did you check to make sure it's got spark when it's hot?
It's possible you that you could have a coil on it that's bad...when it heats up the resistance inside the bad coil could be changing, which can cause it to lose spark on that cylinder. With that condition (running on on 5 cyls) it won't want to idle very well...however, it would still run pretty good on 5 when you've got it opened up, so it might seemingly run ok when you wind her up.
Checking spark when it's hot/having the idle issue is the best way to know for sure what's going on.

Hope that one of these ideas I'm tossing out there helps you out, as I know from past experience how frustrating it can be to have an engine that doesn't want to idle!