poor acceleration from idle

[mariner man 66]

I have a 91 Mariner 135. It has poor acceleration from idle up to midrange and is worse when I am trying to start out with a skier in tow,having about 3~4 seconds of bad hessiation. Once it has hit midrange though, all is good, with revs peaking at 5600.<br />Things I have tried thus far are: Spark plugs and leads replaced; carbs dissmantled and serviced with float levels checked (found blockage in accel pump circuit which didnt fix problem);tune up and ignition timing checked; replaced blocked fuel tank breather; replaced all fuel filters; cleaned out fuel lines.<br /><br />In replacing plugs I checked that all had spark (although I am not sure how to tell the strength of spark). Looking inside the cylinders, I noticed the piston crowns were wet and covered with carbon. The condition of the plugs were cleanish but very damp with fuel and oil (not burning well)<br />The other thing I have noticed is that the motor sits low on the back of the boat, with the exhaust top vent basically at water level. <br /><br />Advice is appreciated prior to me doing the following: removal of the carbon; removal of the oil injection system in favour of premix;replacing fuel pump diaphram; trying boat with idle stabilizer removed; raising the motor on the transom (which will also help with other problems)

 

[Drybo]

Re: poor acceleration from idle

My 91 115 merc needed fuel bulb, carb cleaned and synched, idle set, timing and still sputters from 2-3000 rpm then takes off. I just live with it, my 2 cents.

 

[mariner man 66]

Re: poor acceleration from idle

thanks byrdog, <br />I'll check the fuel bulb. The other stuff I have done.<br />This is the best web forum!!<br />Any other thoughts would be most appreciated

 

[FiveDog]

Re: poor acceleration from idle

My '91 90 Hp Merc does the same thing. I have replaced the fuel line, plugs, and both filters to no avail. I think I will try to decarb next and then rebuild the fuel pump. My motor didn't do this 3 months ago.<br /><br />If you figure it out, let me know.

 

[Moody Blue]

Re: poor acceleration from idle

Symptoms sound like float level adjusted too high. DOes the problem seem worse when motor is trimmed up high (shallow water operation) then trimmed down and hammer the throttle ? If so I would look at the float levels again.

 

[mariner man 66]

Re: poor acceleration from idle

I have the owners manual and have set float levels to spec.Trim position doesnt make any difference as I have tested out in the middle of the lake with only minor trim changes. Initially one of the floats was way out and thought that this may have helped but to no avail.

 

[mariner man 66]

Re: poor acceleration from idle

The problem is worse when hammered hard or under load. When testing with the muffs on, out of the water, there is no hessitation.

 

[Moody Blue]

Re: poor acceleration from idle

When you did the carbs did you replace the needle valve and seat ? Have you properly adjusted the low speed idle mixture setting on the carbs ? Sounds like its running very rich and fouling the plugs. Proper plugs installed ?<br /><br />I would do a de-carb and rebuild the fuel pump if it hasn't been done in the last few years. Double check the idle mixture settings on the carbs.

 

[timmathis]

Re: poor acceleration from idle

Careful testing with muffs on. You should NOT go much higer than idle out of water! Tim

 

[mariner man 66]

Re: poor acceleration from idle

thanks people for your advice. Rodc, I'll keep you posted on the progress as I get the boat back into the water, Winter is nearly finished down here.<br />Proper plugs installed. will rebuild fuel pump this weekend. Will look more closely at the needle valves. One of the float heights was way out like about 3/8" I adjusted back to spec but cant understand how it could have got that way. Is the centre section of the needle valve that sits on the float tang meant to be spring loaded?? as this is solid. I will remove other carbs to check

 

[mariner man 66]

Re: poor acceleration from idle

Things I have done to cure this problem have been 1. Replace flywheel as magnets had become detatched from flywheel (causing poor spark).<br />Replaced stator at same time.<br />2. Removed oil injection system and went with premix 50:1<br />This boat now accelerates HARD.