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Ibm going to call her cantankerous

dhyams

Regular Contributor
"Put boat in at ramp; started

"Put boat in at ramp; started right up, idled over to dock to tie up. Engine died on the way, and would not restart. Sprayed starter fluid in carb throat, and cranked, and after a few tries, started up and stayed cranked.

Drove boat about six miles, cruising speed. All was fine. Slowed to an idle to allow a friend to catch up, and when I did, engine died. Same story; after cranking and cranking, many pumps of throttle, and sprays of starter fluid, boat finally caught and we were off cruising again. I did up the idle speed a little, because I had decreased it a couple of weeks ago trying to deal w/ dieseling.

Drove boat back six miles. I was starting to slow a little because I was getting a little closer to the dock (the one I started at), so I pulled the throttle back a tiny bit. Engine died. Same thing again. Pump throttle, spray lighter fluid, try not to spew profanities, and about 15-20 minutes later, it finally caught and ran again. Went to dock and pulled out boat, and it acted fine.

On the last incident, I did notice, after the boat had died, that the temperature was 175 or so, which was weird...never seen it that high. The temp did fall immediately after I got the boat cranked finally (fell back to 150 where it always is), so I think the high temp was just a result of the boat dying while underway (latent heat from the engine all transferred into water that was not circulating any more).

This same behavior has happened once before, about a week ago. Died at near-idle, and would not recrank until about 10-15 minutes later. Who knows if all of the throttle pumping and starter fluid spraying helped. Although, that time, it did recrank right after spraying the starter fluid, but it might have been a coincidence.

I know that this is only partial info to go on, but I thought I'd throw it out there and find out if the symptoms fit something like vapor lock, or something else. Or, what can I check on the water when the boat does this?

1996
4.3LX Mercruiser
Alpha One
2 bbl Mercarb (rebuilt last year)


Thanks a million,"
 
"This sounds like a vacuum lea

"This sounds like a vacuum leak to me.

Temp issue is what you say, latent heat after shut down.

You eed to get a vacuum guage/teater and find a threaded hole in the intake manifold and screw in a fitting to connect to the guage and get it started and record the vacuum readings at idle, 1000 rpms, 2000 rpms and take special note on the behavior of the needle if is erratic or steady when at each rpm setting. Let us know what it is.

Also pay close attention to the shift bracket and the V notch/micro switch. This is the shift interuptor switch and as you are backing down the throttle if your cable (s) are out of adjustment or the short shift cable is old and binding you could be causing the switch to be engaged wich would shut the ignition off.

Just some more posibilities......"
 
"Thanks Kghost; I'll secur

"Thanks Kghost; I'll secure a gauge to check the vacuum, and I think I see the threaded connector on the manifold that you're talking about.

I tightened down the bolts on the carb a little bit, just to make myself feel better mainly. I'm just about at the end of my rope on this boat.

I'll also keep an eye on the shift cutoff switch; didn't think about that one.

I pulled the dist. cap and checked it, and the cap/rotor both look fine to my untrained eye. Theere was a weirdish orange fluid (not much of it) below the rotor, though...don't know what that is.

Could a bad ignition coil cause a problem like this?

The erratic nature of the problem makes me think that it's loss of spark and the problem is electrical in nature."
 
"If the coil may be bad, feel

"If the coil may be bad, feel it, is it HOT?

Also look at night time. If you see arcing between the posts of the coil it will show at night. This would reveal a crack.


What you need to find out when it dies is what is NOT happening when you try to restart.

1. Is there spark? Use spark checker or timing light immeadatly

2. is it flooding? pull a couple of spark plugs and see if they are wet as soon as it dies, If so the carb is flooding!

3. Is there fuel? Pump throttle/linkage and see if fuel is sqirting from accelorater pump circut.


One more thing is you say when running all is well till you come to a stop.

Have you pulled the fuel pick up?
The end of a pickup tube sometimes has a screen on it and if has come dislodged it could be sealing off the pick up tube.
You can remove the fuel guage sender and looked inside with a good strong flash light. ***BE CAREFUL WORKING AROUND THE GAS TANK*** if you find anything questionable replace it.

Have you checked the anti siphon valve?

As far as the antisyphin valve you can TEMPORARLY replace it with a striaght barbed fitting to see if it is bad BUT you must put it or a new one back in!!!

One other thing, your engine has a electric fuel pump, correct?

If so if it dies again you can jump out the oil pressure switch I belive they are light blue wires (someone correct me if I am wrong here) that attach near/on the same location as the oil pressure sending unit. If the pressure switch is bad it will shut down the fuel pump as it needs ~ 15 psi of oil pressure to make the switch.

This and bad fuel pumps and bad fuel pump connectors were a common problem with very similar complaints as yours...

That is about all I can think of today...........WHEW......"
 
"Kghost: once again, thanks a

"Kghost: once again, thanks a million.

I really have no reason to believe that it's the ignition coil, other than it's a part that I don't know when it was replaced last, or how long they are supposed to last. I don't even know why I keep thinking of that as a possible source of the problem. I guess because it's an easy part to replace.
uhoh.gif


Yep, I'm going to be prepared the next time that I take the boat out, and have a checklist of stuff to do immediately upon dying. The things you list will definitely be on there. I didn't have my wits about me that night it died 3 times, because there were about 15 people waiting on me and I all I could think about was get this $#$#@#$ boat started quick! [Here the scene: a bunch of people in my friend's brand new Chaparral 26-footer, all waiting on me and another friend in my dinky (by comparison) little '96 18-footer)]


Re: the antisiphon valve, and the fuel pump: I replaced it with a new one last year when I had a dead elec. fuel pump. I replaced the valve, pump, and put a water-sep fuel filter in too.

Re: fuel pickup: I'll check.

Re: oil pressure switch. Will have jump wire ready ;)

Re: is there fuel: I get strong squirts from the accel pump when I pump the throttle, but I'll double check when the boat dies again.

Re: timing light to check spark...now that you say it, the last time the boat died, I pulled out the timing light and had a friend turn the boat over. I could have sworn that the light didn't strobe during the cranking process, but then, as luck would have it, the engine whirred to life (and the timing light popped on too at the same time, showing me that the timing was still at 8 BTDC). I immediately put down the light and took the boat to dock. I can't think of any reason that the timing light wouldn't have worked during cranking though? That might tell me right there that it was a spark problem and not a fuel system problem."
 
"Guy:
Going from memory (


"Guy:
Going from memory (I looked at it last night) it looked OK; no rust. The bit of orange fluid in the bottom was oily-like and not water-like.

Just in general (trying to learn here), let's say that you had some electrical problem that caused you to lose spark while underway. Boat engine dies, and you drift to a stop. What would the carb have done right after the engine died? Would it pull in enough of a glob of fuel to flood you out, and you would have trouble starting until enough gas evaporates?"
 
"The orange fluid; it's no

"The orange fluid; it's not loctite dribbled down from the rotor? Rotors are loctited in place from the factory.

When the engine is turning say 3800 RPMs and suddenly loses spark, the engine is still rotating and sucking fuel from the carb until it stops cranking. Think of a lawn mower when you turn it off. The engine should not draw too much fuel by vacuum to flood it."
 
"If you think the engine is fl

"If you think the engine is flooded when trying to start it, open the throttle all the way and crank it until it clears out or starts."
 
"Thx Guy:

I forgot about th


"Thx Guy:

I forgot about the choke unloader in the heat of the moment


I worked on the boat for a while tonight, and here's what I found:

Hooked up vacuum gauge to intake manifold. At idle, gauge was steady at 18 in. Hg. At 2000RPM, gauge was steady at 19 in. Hg. Didn't go any higher than that, because boat was in driveway.

Idle mixture screw: in inspecting stuff, I noticed that it was a little loose, even to the touch. Screwed it all the way in, and counted 2 3/4 turns (ACK!) I do not know how it got that way. I screwed it back out 1 1/4 turns, and the engine definitely sounded different. Reset the idle speed to 650 (neutral in driveway), and reset the timing, as it had shifted a little bit.

I didn't think to retest the intake manifold vacuum after the mixture screw/timing/idle speed was reset."
 
The steady vacuum numbers are

The steady vacuum numbers are excellent. Next time the engine is running and warm adjust the mixture inward slowly until the engine stumbles; make a mental note of that point on the screw. Now back the screw out slowly until it stumbles again and then split the difference between the two stumble points and turn the screw in to that point.
 
I have the non-vortec 4.3L eng

I have the non-vortec 4.3L engine and Mercarb and can only get 14-15" of vacuum at idle.
 
"Took out on the water this ev

"Took out on the water this evening, and she ran perfect except for dieseling at every opportunity. I'm thinking the mixture screw that was grossly wrong was the culprit...or at least I'm hoping so. Time will tell, I suppose.

I'm more prepared now to diagnose in the event of a "dead on water" scenario."
 
"An update on this; the boat h

"An update on this; the boat has run just great (well, except for the dieseling) after several outings on the lake. The mixture screw I think was the problem; I think it was set so wide open that I was flooding out whenever I pulled the throttle back.

Thanks to all who helped me out!!"
 
Try to back your timimg off to

Try to back your timimg off to 4 degrees btdc from 8.

If you are running marginal gas quality timimg will affect your issue.

If 4 helps but does not eliminate it completely try 2 to see if it solves your deiseling.
 
I'll try setting the timin

I'll try setting the timing to 4 btdc. But just curious...won't that decrease the engine efficiency? More unburned fuel in the exhaust?
 
I would not worry about effici

I would not worry about efficiency at this point.

You are trying to solve a problem of dieseling not high end performance.

Gas has changed a fair amount since 1996 when that motor was biult. Many marine specs have also changed with the changes in fuel quality.

This issue although is not very common it is also not unique. It could have something to do with your specific engine biuld and that is what seperates it from a motor of the same year and size that does not have that problem.

When you adjust the a/f mixtures screws can you get the engine to stumble when turned almost all the way in?

You may want to try to lean them out (turn in) 1/4 turn at a time and see if that can assist in stopping the dieseling. If you go to lean it most likely will stumble on acceleration. Then you know you have gone to far.......
 
"All good points and good info

"All good points and good info kghost...when I can, I'll make these adjustments and report back, in my quest to vanquish the chugs from the engine when I cut the it off ;)"
 
"As a follow on to this, my sc

"As a follow on to this, my scattered brain just remembered something else...

Somewhere along the way, it was said that I might need to adjust the throttle mechanism in order to have it push harder against the little cam that the idle screw bumps against (sorry for that horrible explanation).

After a towing run one time, I popped the hatch and grabbed the throttle arm (connected to the carb) and pushed it hard against that cam. The rpm dropped by about, say 50-75.

I did make sure before pushing on that linkage that the idle screw was flush against the cam, and it was.

So I know that I probably need to adjust that linkage in some way, but I'm not quite sure what to do. Any guidance, or any pictures floating around the web?"
 
"Daniel , i posted some inform

"Daniel , i posted some information on the other post you had for the diesling issues . I have the same motor and adjusted the timing it did not cure the problem . I adusted the trunion two turns to lower the idle speed and keep it consistant . Also changed brands of fuel and used 89 octane I changed the spark plugs to the next lower heat range . It runs good and doesnt diesel anymore ."
 
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