Acceleration problem

[Stephane]

Donzi Ragazza 23' 1988

I have a GM 350 (OMC) 260 hp with a Rochester 4 bbl equipped with point ignition system

The dwell is set at 30 deg and the timing is at 8 deg.

When i put the trottle from idle to full trottle the engine hesitate at the mid trottle position. (It sound like a fouling carb)

The problem is the same if i run at 3000 rpm and i put the trottle to full trottle firmly. (there a lack of power at mid trottle)

I send the carburator to a carb specialist and he change the gasket kit et re-adjusted.

The problem was not solve.

I don't like this prolem especilly when i toe a skier

Somebody know what append and what can i do to retreive a linear acceleration

[Lenny]

My carb did that on my 18 as well. At any throttle range (short of WOT) you could hammer it all the way down and it would all but stall then jump to where it should be. I assumed it was the carburator and it was either starving or dumping vast quantities of fuel into the motor. Then it would catch up. Went away with the carb change out so that was the extent of my "trouble shooting". :rolleyes:

[Mr X]

Replace the accelerator pump in the rochester carb........

[Sam]

Lenny, what carb did you end with ?

Sam

[Lenny]

Sam, Barry Grant Sea Demon 650 Mechanical. Out of the box, it works fine :)

I am at sea level.

[MOP]

Assuming this is a Quadra Jet Carb!!!

It could be that the secondaries damper plate is not set correctly, it is surprising how many forget to adjust it. There is a specification for it though I quit using it, reason all boats seem to react a little different. If you are handy you should try adjusting it, if the tension is to light it allows to much air ans not enough fuel and boggs down and if to tight it causes to much gas and not enough air which also boggs the engine. He is what to do, remove the air cleaner the back set of venturies have a plate that is spring tention controled as the plate has air sucked by it it will open an lift the fuel metering rods, the rods must for lack of better wording move in unison with the engine sucking to controll air and fuel mixture. Anyway with the engine off apply a little throttle to release the damper plates lock this must be done before each adjustment, now facing the engine from the cockpit push down on the plate with your finger and watch in the left side where the plates shaft come out you will see the small arm move as you push down, this is where the adjustment is done. Stop and look at it you will see a small flush housing right by the tip of the shaft this screw sets the tension of this spring, right next to it is a knurled blue steel allen head screw this screw is the screw that holds/locks the adjusting screw in place. You will need a very small screw driver and an allen wrench to do the job, what I usualy do is to release the tension while holding the adjust screw from turning once the lock is loose I slowly let off on the adjusting screw. When the screw stops turning all by its self I then turn it in about 3/4 of a turn applying light pressure to hold the plates closed and lightly tighten the lock screw. I start at 3/4 turn as most will not run right with less tension, now go and test it see how it reacts it should be a little late or lean delivering fuel. Depending on how the boat reacts I reset the screw with a little more tension about 1/4 turn, as the engine starts to feel like it is starting to run better I only give about a 1/8 turn until it is smooth and responsive. The plates may not be your total problem but that is your final running adjustment and one thing to be checked out.

Phil

[Stephane]

Hi Phil (MOP) your answer sound good for me,

I will try to adjust the secondaries damper this afternoon and i willl comeback with my comments

Hope to see a difference !

Thansk

[Ralph Savarese]

Also before you make major assumtions. Try looking down the carburetor with the engine off and flame arrestor off and pump the gas see if you have nice steady streems of fuel from the accelerator pump jets if not either you have a clogged jet or a bad accelerator pump . I have had experence seeing both.

Ralph

[Moody Blu']

sounds like accel pump or the attaching rod is disconnected?

[Stephane]

OK Phil you had the answer.

The problem was on the same part of the carb.

First the spring of the air valve was too smooth, we fix that by torquing a 3/8 turn more than the seating.

Secondo the air valve dashpot ajustement distance was to long

Now the performance of the engine is normal with a linear acceleration withour any drop.

Thanks

[MOP]

Glad I came up with a good one for you, hope to hear some nice boating reports.

Phil

[Ed Donnelly]

Hey Mop; pretty good for an old fart :biggrin: :biggrin: .........Ed