'93 merc 350 magnum/alpha

[t_south91]

Hey guys,

Well I just got myself a new boat and had it out for the 2nd time yesterday and I broke down on me....

I purchased a '93 Webbcraft, 21ft with a 350 Magnum, Alpha One drive. Its CLEAN, or thought it was. Has 267 hours, and I am the third owner.

The previous owner never had it out on the water this season. Its first time in, was when I test drove it. Took it out the following day, had it out for 6-7 hours. Ran like a BOSS. Took a little while to crank up but figured that because it hadn't been used all year.

Take it out yesterday, fires right up. The lady wants to hop in the lake and cool off. So we park and I shut it down. Well that's where it all started.

When I shut it down, it probably took 20-40 seconds for the engine to totally shut off. It kept running until it eventually lost gas supply and died. After 20 minutes of swimming, we decided to pack up and cruise. Go to turn the key and this horrible clunking noise came from the engine. 2 Clunks and then nothing. Tried a few more times to crank it, got the same result. Luckily I got towed in.

Key info, the previous owner did put a new starter on it at the end of last season. It sounds as if something is bound/hung up. Its not the battery, the noise is far too loud and violent for it to be that.

Any thoughts or help is greatly appreciated! Need to get this thing back up and running!!

Thanks!
TS

 

[Bt Doctur]

the dieseling caused water to be sucked back into the engine. you need to remove the spark plugs and crank the motor to clear the cylinders. Then start the motor on muffs to dry things out.
High engine temp or incorrect timing or poor fuel causes it.

 

[t_south91]

the dieseling caused water to be sucked back into the engine. you need to remove the spark plugs and crank the motor to clear the cylinders. Then start the motor on muffs to dry things out.
High engine temp or incorrect timing or poor fuel causes it.

Thank you so much!

I will give this a try when I get home this evening.

 

[Bondo]

Ayuh,..... BD's on it again,.... Right on the money,....

Dieselin' is Bad, really Bad,.... Turn the key back "On", don't let it stutter, 'n die,....

That last gasp is the motor runnin' Backwards,....

 

[t_south91]

Well you guys were right! Took the plugs out, manually cranked the motor and water came out. Put new plugs in, reconnected everything and she fired right up. Thinking that its bad gas causing this. Checked both the engine temp, and timing. They were fine. So the gas is the last culprit. Which would make sense, since the guy I bought it from hasn't run it in over a year.

Thank you both again for your help!!

 

[Alumarine]

If it diesels in the future turn the ignition key back to run as quickly as possible to avoid the same problem.
Let it idle for a minute and it might shut off fine.

 

[t_south91]

Will do.

Thanks for the advice guys!

 

[NHGuy]

Yep, and if the timing is correct it's likely that the idle is too high, and the temp too high also. You can run it at a fast idle to get the temp down if the temp is above normal. Idle should be about 725 in neutral, 675 in gear. When the idle is too high it provides enough fuel for the engine to diesel.
As a last ditch when dieseling you can shut off the key and then put the shift in gear to help stop the engine.

 

[t_south91]

Yep, and if the timing is correct it's likely that the idle is too high, and the temp too high also. You can run it at a fast idle to get the temp down if the temp is above normal. Idle should be about 725 in neutral, 675 in gear. When the idle is too high it provides enough fuel for the engine to diesel.
As a last ditch when dieseling you can shut off the key and then put the shift in gear to help stop the engine.

Thanks for the input!

Think I have that issue resolved. Only problem I am having now is that it takes the engine a little while to turn over. It will only start if I give it throttle in neutral. No matter when I start it warmed up or cold. Not sure if the carb just needs to be cleaned out from running that bad gas through it or what. Thoughts?

Thanks in advance!

 

[Bondo]

It will only start if I give it throttle in neutral. No matter when I start it warmed up or cold. Not sure if the carb just needs to be cleaned out from running that bad gas through it or what. Thoughts?

Ayuh,..... I concur with yer diagnosis,..... Rebuild the carb,......

 

[t_south91]

Thanks Bondo, that's what I was afraid of.... Its strange though because it runs like a champ, no bogging down when I bury the throttle. Almost as if its running too "rich". But after it starts up you can smell it. It sometimes floods itself starting up...but it does start everytime!