2001 mercruiser 4.3 - no power, 3600 WOT RPM

[kwaits]

Hello experts, I'm in need of help.

I have a 4.3 carb mercruiser which is acting up today.
The motor has ran great last few weeks but today seems to have no low end power and WOT RPM is 3600 according to the tach. I haven't changed anything during this period besides gas.
Unfortunatly it's not a tach issue or seat of the pants issue since the boat struggled and sometimes couldn't even pull up a wake boarder today.

We drained the gas out (got a big mouthful during the siphon process) and refilled with 93 Octane from a different station but the problem remains.

My plan is to replace plugs, wires, and fuel filter.
Any other ideas?

We have a trip planned for next weekend and hope to get out on the lake for one last wake boarding trip this year.

From searching through the vast iboats.com forums I see it could be a timing issue? could this happen overnight?

Thanks in advance for your knowledge and time.

 

[mthieme]

Re: 2001 mercruiser 4.3 - no power, 3600 WOT RPM

do you have points?

 

[Don S]

Re: 2001 mercruiser 4.3 - no power, 3600 WOT RPM

No points, Thunderbolt V ignition system.
When was the last full tuneup and fuel filter change?

 

[kwaits]

Re: 2001 mercruiser 4.3 - no power, 3600 WOT RPM

not sure when the last tuneup was performed.
We purchased the boat only a few weeks ago.

What's all involved in a complete tune up?
- plugs, wires, fuel filter, oil change????

- should the distrubutor cap be replaced during the tuneup process.

 

[kwaits]

Re: 2001 mercruiser 4.3 - no power, 3600 WOT RPM

Oh yea, I was looking at the motor this morning and saw an "exposed nipple" coming out of the distrubutor cap (not like Janet Jackson).

Should a hose be connected to this or is this left to atmosphere pressure?
Thought perhaps it was some sort of vaccum advance but not really sure.

 

[chiefalen]

Re: 2001 mercruiser 4.3 - no power, 3600 WOT RPM

That nipple supposed to have a wire on it, maybe a spark plug wire?

And maybe your not running on all the cylinders?

Follow each spark plug wire back to the dizzy, any not ending on the dizzy maybe hanging loose?

Oil looks good?

 

[Don S]

Re: 2001 mercruiser 4.3 - no power, 3600 WOT RPM

Oh yea, I was looking at the motor this morning and saw an "exposed nipple" coming out of the distrubutor cap

It's just a vent, nothing goes on it.

For the engine, start with a proper compression test.
http://www.boatfix.com/merc/Bullet/97/97_25.pdf

Then new cap, rotor, spark plugs, check timing and advance timing, adjust idle mixture and speed.
NOTE: To adjust timing and the carb, you must be in base timing mode.
Here is a link to the OEM manual for your engine.
http://www-alt.mercurymarine.com/mnetdata/SERVICE/CRUISER/Servmanl/25/25covr1.pdf
The link opens only the first 3 sections only, you have to go to the index page and download the others sections.

Here is a test for the fuel system you should do also.
http://forums.iboats.com/showthread.php?t=167561

 

[Bondo]

Re: 2001 mercruiser 4.3 - no power, 3600 WOT RPM

Should a hose be connected to this or is this left to atmosphere pressure?
Thought perhaps it was some sort of vaccum advance but not really sure.

Nope,.... That's the Vent.....

 

[Don S]

Re: 2001 mercruiser 4.3 - no power, 3600 WOT RPM

Here is a list of about every possible cause of low WOT there is.

Engine Won't Reach Operating RPM. Check

• Fuel condition. Type and Octane possibly old fuel
• Propeller pitch or diameter, damaged blades
• Restricted fuel pickup tube or anti siphon valve Fuel System Test
• Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
• Marine growth on hull and outdrive
• Wrong gear ratio in outdrive
• Restricted carburetor air intake (clogged flame arrestor)
• Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
• Poor cylinder compression Compression Test
• Carburetor defective, or wrong type.
• Fuel pump pressure and vacuum
• Boat overloaded, improperly loaded, or improperly trimmed.
• Engine Overheating
• Engine timing and ignition system operation
• Remote control cables and linkage for proper travel to open throttle plates fully.

 

[kwaits]

Re: 2001 mercruiser 4.3 - no power, 3600 WOT RPM

thanks, I'll update once the issue is resolved.

This forums is great

 

[98LSWON]

Re: 2001 mercruiser 4.3 - no power, 3600 WOT RPM

I had a plug wire fall off of a 4.3L and only got 3800 RPMS out of it, it still ran smoooth BTW. I'd check all the plugs/wires first.