Logo
FULL SITE MENU

Merc 260hp surging in the midrange rpms

K

knollwoodworker

New member
Just purchased a boat with a 1998 230hp Alpha package. The motor seemed to run fine until we hit a pretty good wake series, than would only run at idle. I changed the fuel/water filter and now the boat runs fine at idle and will run wide open but surges in the 2500-4000 rpm range. I emptied the fuel/water filter again and added a fuel treatment but that hasn't seemed to help the problem. Looking for some experienced knowledge to ask more questions or send me down the right road to fix the problem. The boat had about 30 gals of gas from last year, I topped it off and added marine stabil and gumout fuel system treatment. Any help would be appreciated.
 
the filter in the fitting that enters the carb needs cleaning over and over till the fuel is clean.

the fuel pump have a filter in it ? And yes keep dumping the fuel water sep.

Finally the carb may have to be cleaned out over and over for a few weeks till it's all clean.

Just don;t get any carb cleaner on any rubber or you will be looking for new ones.

Just disassemble soak and then clean all the holes and remove the jets.

Mine after getting the motor running after sitting for eight years i just kept at it till it ran strong.

Meaning the carb was takin apart and cleaned 3-4 times i can't remember.

Below is a copied and pasted post i made on a different website:

[FONT=Verdana, Helvetica, sans-serif]
[/FONT] Detaled carb rebuild:[FONT=Verdana, Helvetica, sans-serif]

Get yourself down to a auto parts store, get a can of berrymans carb soak comes with a screen in the can, like a deep fryer.

Also get a can of compressed carb cleaner.And a carb rebuild kit.

With a clean area on a table or bench i place a old cookie sheet with sides.

Break down the carb and remove all the rubber.

Remove the jets they should just screw out.

Everything goes into the berrymans, let soak for a few hours.

While it's soaking turn your attention to the motor.

Remove the fuel pump from the motor, the screen clean, all hoses good no cracks.

Re-install the fuel pump, and remove the t-stat, that good, i would replace it.

ok time to drain and refill the lower drive.

Well it should be a couple hours a beer and a little work another beer and a little more work hell might be 5 hours who knows.

Remove the parts from the berrymans, start with the lower carb housing and blow it dry with compressed air, it clean?

Piece by piece build it, make sure every passage is clean blow it dry and use compressed can carb clear blow it dry again.

Jets clean, Float, floating no gas in it ?

Push the float under water and if you see bubbles it's time to replace it.

Ok when you install the pin in the forks that hold the float are they pressing on the float tounge and not allowing the float to move freely ?

So if you did your job correctly the carb should operate freely, and when you install the adjustment screws be gentle.

Do not bend the tips. All the way in with them gently and out 2 turns to start.

Final adjustment on the water.

Have someone else drive about 2000 rpm maybe a little more and you do the final adjustment.

If you take your time and there are no distractions, you should be ok.

Good luck !
[/FONT]​


​


​
 
Chiefalen,
Can you explain why if it is a fuel issue it will run wide open yet seem to have fuel fluctuations in the mid ranges? Guess I don't completely understand the carb principal.
 
You might be sucking garbage off the bottom of the tank.

That's why i first posted the pump post.

Then there are different circuits in a carb.

You have the idle then, " my words " midrange and high circuit.

Those are my words the tech terms i can post a site for you to read on carbs.

Now let me ask a question to try to help you. Maybe more then one.

You did a tune up on this boat last when ?

You did look under the cap. ?

98' should have electronic ignition.

Thunder bolt ?

The thunderbolt system in it's day was the very best in my humble opinion. Yea there's a but.

20+ years latter they break down.

Not saying it's your problem, and not saying your into alot of money if it does cause there is a way to bypass the whole business.

But say you go theu the whole fuel system clean from the tank to the carb.

Rebuild the carb, cause if water sits in the bottom of the bowl you will always have problems till the carb is rebuilt. But say the whole fuel delivery system is clean then whats left ?

1- your ignition.

2-Your timing chain

3- compression

4-vacuum

Clean the system run it..... still not running right carb rebuild.... run it still not running right we look at the other possible causes.

I could also be full of c--p.
 
I had a similar issue with the 350 cu. in. 260 (rated) engines in my Chris Craft Stinger. It turned out the brass reusable filters that were located inside the carbs - remove the fuel line and then the large nut that houses the filter and threads into the carb - had to be cleaned on a frequent basis. I could not find anyone locally that was a quadrajet expect but got very good help, advice, and parts from the Carburetor Shop in Onterio, CA.
 
Back
Top