V6 150, Bottom Falls Out At Wot!

C

cwarren902

Cadet
Joined
Mar 3, 2008
Messages
11
I have a 99' model merc nitro series v6 150. Sometimes at WOT it just falls on its face and I have to back off the throttle and it picks back up. The problem is, it doesnt do it all the time. Also, I have had trouble with keeping it idling a couple of times. I dont know where to start because it only does it periodically. It will run fine for a while, then start in, then be fine again later. Any ideas?
 
j_martin

j_martin

Admiral
Joined
Sep 22, 2006
Messages
7,474
Re: V6 150, Bottom Falls Out At Wot!

I'd be willing to bet it's starving at WOT. Had the same problem on my XR4
From your set of symptoms, I would guess that there's some junk in the fuel. I temporarily installed a fuel pressure guage to shoot the trouble out of mine. When it failed, fuel pres went to zero.

Here's what I had to fix on mine.
1. Fuel pump, valve was warped.
2. Fuel filter, kept partially plugging. I discarded it and put in a Racor system.
3. Fuel line and primer bulb. Aftermarket line just won't deliver enough fuel.
4. Cleaned out gas tank. Found almost invisible white sludge that was causing all the fuss.
5. Fuel bayonet connecter. Aftermarket plastic one wouldn't deliver.
6. I went through the carbs just to set everything right and make sure they were clean.

I had deteriorated fuel lines also. You probably don't as yers is post alky construction.

You need to get it fixed. Running lean at WOT is about the quickest way I know of to melt down that engine.

hope it helps
John
 
C

cwarren902

Cadet
Joined
Mar 3, 2008
Messages
11
Re: V6 150, Bottom Falls Out At Wot!

Hey thanks guys for the info. I have one more question for you. I was told not to run 10% ethanol mix gas through this motor, after I had already run a couple of tanks through it. But, the previous owner also had this problem, he replaced the fuel pump and thought he had it fixed. Does this gas clog filters and damage the motor? Although the previous owner did not use 10% ethanol.
 
j_martin

j_martin

Admiral
Joined
Sep 22, 2006
Messages
7,474
Re: V6 150, Bottom Falls Out At Wot!

Ethanol and water will mix, and then "phase" out of the gas. In the interface between the two, bacterial can grow and they form the almost invisible sludge I mentioned above. That'll get you, up to and including smoking a piston if it goes lean at WOT.

Just a little bit of it will plug up that stupid 100 mesh finger sized filter Murkery puts in the engine. That's why I chit canned mine and put in a Racor 60 GPH water seperating filter between the tank and the engine.

It looks like you ran just enough to wake up the crap in the tank and plug things up. You probably should clean everything out and start over.

I bought a 55 mph sluggard that sometimes crapped out at WOT. I've been in the mid 60's since with just motor tune fuel, and setup issues resolved.

I run 92 octane non-oxygenated gasoline that sold around here for small engine and off road use. That's what I'd use in that motor.

hope it helps
John
 
C

CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
Re: V6 150, Bottom Falls Out At Wot!

The less alcohol the better, however fuel quality is becoming poorer nation wide.

Newer engines are designed with this , older engines have been quite tolerant of the alky, the largest problems have been deterioration of fuel lines, plastic parts and fuel pump diaphragms. Of course there is that ever present water accumulation in fuel tanks.

Some recommend timing retard 2 degrees.

Install a separating filter, keep fuel fresh, some always add stabilizer depending on estimated usage/storage.

Definately size prop correctly, ANY overloading leads to detonation and damage.
 
You must log in or register to reply here.
Top