4.3 merc. fuel system problem?

[catcatcher]

After blowing a hole in the #6 piston and endeing up replacing 2 piston and 4 valves on a remanufactured motor with around 15 hours on it. I got the motor back in the boat, aligned it, and finished the install of all the engine components. I pumped the 15 gallons of old fuel out and put 10 fresh gallons in to start it and see how it went. After getting the timing set it starts and idled good. So, the next step was to drop the boat in the water and see how it did under a load. Today was the day for that and it went well on the inital take off. The motor came alive but I could only reach 3900 RPM's. I ran up the lake a ways and turned aound which is when the problem started.

Half way through the turn the RPM's dropped below 3000 and slowly climbed back up to 3500 where it stayed for the remainder of the run. When I pulled the throttle back and came off of plane the motor began spitting and sputtering. So, I throtled back up and it took a minute to clear up but once it did again I was only getting 3500 RPM at WOT. When I brought it back to an idle it spit again and died. It started right back up but was ideling much higher than normal. It was turning 1500RPM at idel now so I lifted the motor cover and pulled the throtle linkage forward and it dropped back to 700RPM at idle. When putting it on the trailer it died as the bow was meeting the rollers but, once again started right back up at a high idle.

Could this be caused by a weak fuel pump? My dad rebuilt the carb and I am wondering how well of a job he did so maybe this could be it?

Any other opinions to the problem are greatly appreciated!

 

[Don S]

Re: 4.3 merc. fuel system problem?

More likely a fuel delivery problem to the pump. If you go to the adults only sticky at the top of this forum, you will find a link to a How to check your boats fuel system, might want to give it a read.

 

[Bondo]

Re: 4.3 merc. fuel system problem?

After blowing a hole in the #6 piston and endeing up replacing 2 piston and 4 valves on a remanufactured motor with around 15 hours on it.

Ayuh,....

It sounds like it's been running Lean, for Along Time,... well, 15hrs anyway...

You should inspect the Entire Fuel System,...
The Tank,..
The Pickup Tube,..
The Anti-siphon Valve,..
The Lines,..
The Filter,+ it's housing,..
The Fuelpump,..
And of course the Carb itself....

The link that Don speaks of will explain just what each piece is Supposed to do...

 

[catcatcher]

Re: 4.3 merc. fuel system problem?

Ayuh,....

It sounds like it's been running Lean, for Along Time,... well, 15hrs anyway...

The reason for the hole in the piston was the former owner failed to tighten the #6 plug.

Thanks to all for the advise and the link.... I will get on it first thing in the morning

 

[J JACKSON]

Re: 4.3 merc. fuel system problem?

how does a loose spark plug cause a hole in the piston?

 

[Bondo]

Re: 4.3 merc. fuel system problem?

The reason for the hole in the piston was the former owner failed to tighten the #6 plug.

Ayuh,... Same Question as Jackson,...

Just How does 1 loose sparkplug cause 2 pistons,+ 4 valves to disintegrate,..??..??

I'd sooner think it's been running Lean since it was installed,+ Detonation Smoked the pistons,+ valves....

 

[chiefalen]

Re: 4.3 merc. fuel system problem?

I'm going to ask a slightly different questions, who did the rebuild the first time ?

Who did the rebuild the second time ? And what was replaced both times, exactly ?

Me thinks we ain't getting the whole story ! Like why the first rebuild ?

 

[catcatcher]

Re: 4.3 merc. fuel system problem?

The guy at the mechine shop where I had the pistons put on the connecting rods and the heads checked/valves done asked when I took the piston with the hole in it if all the pistons on the oppisite side of the motor looked OK. He siad when it happens to one piston usually the piston on the other side of the intake will show signs of dammage too. So, I took the head off of the other side and sure enough the #3 piston had marks in the top of it and the valves were tuliped also.

Here is the original post I made back when the motor went. I had a disk in my lower back buldge half way through the rebuild and just got back out to work on it a couple weeks ago.

http://forums.iboats.com/showthread.php?t=230019

The old motor was replaced with a Napa reman.

After being sick all night I am just now feeling well enough to be moving around so my plan of testing the fule system today is being put off til tomorrow.

 

[Bondo]

Re: 4.3 merc. fuel system problem?

Jeeze Louese,....

Everything was lain out for you, in your Other thread,...
What to Check, What to Fix,... The Whole Shebang....

Then you just buttoned up the motor,+ went out,+ Blew it Up again.....
Now,...
You're back here asking the Same Danm Questions.......... WTF,..??

The Answers in your previous thread are the EXACT Same Answers......
To the EXACT Same Questions That you're Asking here Now....

It Appears that you implemented Abolutely None of the suggested Fixes that you were given the Last Time.....

Nothing has changed,... The ANSWERS you Need are in your old thread from a Year ago....

I'm Done here....

 

[chiefalen]

Re: 4.3 merc. fuel system problem?

Did i or did i not sniff the trickster out, huh ???

 

[catcatcher]

Re: 4.3 merc. fuel system problem?

Well, for one Bondo Everything that was said in the other thread has been done.... Over Propping,.......
Timing Too Advanced,.......
Poor Fuel Quality,.......
Or,....
A Lean running Carb ..... These were your suggestions to the fix.

I put a original prop on from a doner 4.3 outdrive, Timing is right, Fuel is new 93 octain, and rebuilt carb.

Buttoned up the motor is what you call it now but, You said nothing about it not being good to just replace what was broken IN MY ORIGINAL POST. So WTF are you saying here? That all the things you said before are the problem when I have attacked everything you suggested?

Thank you for being done with my question and it would be a pleasure for you not to answer any other questions I have on this forum!

If you have this attitude with peoples boats you work on I can tell your new clients are few and far between!

 

[Bondo]

Re: 4.3 merc. fuel system problem?

Well, for one Bondo Everything that was said in the other thread has been done.... Over Propping,.......
Timing Too Advanced,.......
Poor Fuel Quality,.......
Or,....
A Lean running Carb ..... These were your suggestions to the fix.

I put a original prop on from a doner 4.3 outdrive, Timing is right, Fuel is new 93 octain, and rebuilt carb.

Ayuh,...
You Never stated Any of this,+ it Appears you Failed miserably...

Was the donor prop Smaller,... What were the #s of Both,..??

Fresh Fuel,+ a Rebuilt Carb does Not address the Fuel System,+ it running Lean....
Obviously,... It's Still running Extremely LEAN if you Smoked Another Motor in a matter of Minutes.....

Buttoned up the motor is what you call it now but, You said nothing about it not being good to just replace what was broken IN MY ORIGINAL POST.

Ayuh,.... Button Up a Motor, is Mechanic speak meaning to Properly put a motor Back Together......
And,.....
Replacing the Broken Parts was Never discussed.....
Nobody has stated, now, or last year, Anything "about it not being good to just replace what was broken".....
'ell,... That's what I do,.... Replace worn, Broken Parts......

Thank you for being done with my question and it would be a pleasure for you not to answer any other questions I have on this forum!

Ayuh,.... Not a Problem..... Hope it don't get too Lonely for you....

You See,....
Here at the iboat's forums, most of the guys here with the Answers are into Diagnostics,+ Testing....
Rather than just Throwing parts at it til you happen to get it Right.....
If you Ever get it Right...

If you'd had done ANY Diagnostics,+ Testing when you buttoned up that motor the Last time,...
We wouldn't be here Now,...
Because you would have Found the Reason for the LEAN condition that's Smoking your motors........

Everything I've posted in these 2 threads of your's is Spot On.....

I guess it's My Fault you blew up this motor,.....
I Assumed you had a somewhat of a Mechanical Ability..... I Guess I Assumed Wrong....

You are Right once again Don,........ NEVER Assume.......

 

[Don S]

Re: 4.3 merc. fuel system problem?

Well, for one Bondo Everything that was said in the other thread has been done.... Over Propping,.......
Timing Too Advanced,.......
Poor Fuel Quality,.......
Or,....
A Lean running Carb ..... These were your suggestions to the fix.

I put a original prop on from a doner 4.3 outdrive, Timing is right, Fuel is new 93 octain, and rebuilt carb.

I put a original prop on from a doner 4.3 outdrive,

Hate to tell you this, but there is more than one prop for a 4.3. Boats get heavier over time. And original props aren't always right. After you put the prop on, what was your WOT (Wide Open Throttle) rpm with that prop.

Fuel is new 93 octain, and rebuilt carb.

There is a LOT more to a boats fuel system than just rebuilding a carb.
Have you done vacuum and pressure tests on the fuel tank and the fuel pump?

Obviously you didn't fix the problem, you are still blowing up engines, and a loose spark plug will not hole a piston. Maybe after a couple more engines you will learn.

You need to learn to troubleshoot things properly and not just throw a used prop on and think it fixes a possible overprop condition, and rebuild a carb and think your fuel ssystem is all in perfect shape.

 

[catcatcher]

Re: 4.3 merc. fuel system problem?

As of now the motor in it is not blown. The fuel systym test will be done tomorrow.

 

[180shabah]

Re: 4.3 merc. fuel system problem?

As of now the motor in it is not blown. The fuel systym test will be done tomorrow.

Waiting to hear(read) results....

 

[180shabah]

Re: 4.3 merc. fuel system problem?

Well???

 

[chiefalen]

Re: 4.3 merc. fuel system problem?

180 we ain't gonna hear from him for another year, maybe a different name.