5.7 liter sluggish when given full throttle, fine if I ease into full throtle

[wadyadoing]

1993 5.7 liter competetion ski #0f025486. direct drive sea ray spitfire comp ski boat

the boat is runnig ok but in the last year Ive noticed a drop in power. It will not allow full throttle to be applied fast but if you ease into it it is fine. I think it must be a carb issue and have considerds rebuilding it but dont want to if not needed. the boat is slow spooling up in rpm if you give it to much throttle to fast. it kind of feels like the secondarys arnt opening up or somthing like that. and ive had it not run well at all if given full throttle fast when pulling a skier it wont come up on plane and after such an event it will smoke like crazy. Anyway thats about the best I can describe it. any suggestions will be appreciated. Im a skier and power is my friend.

Thanks

 

[SS MAYFLOAT]

Re: 5.7 liter sluggish when given full throttle, fine if I ease into full throtle

I'm guessing that it is black smoke? this would mean unburnt gas. Could be bad timing and or the springs for the advance gone bad.

 

[Flukinicehole]

Re: 5.7 liter sluggish when given full throttle, fine if I ease into full throtle

With the engine off look down the carb. Have someone push on the throttle. You should see a nice steady stream of gas. If you dont you need an accelerator pump. This is where you should look first. Post back with your findings.

 

[Maclin]

Re: 5.7 liter sluggish when given full throttle, fine if I ease into full throtle

Sounds to me more like the secondaries are opening too fast or as mentioned above, the accelerator pump shot has deteriorated.

Do you know what type of Carb you have? A Rochester Quadrajet or a Holley?

There is an external adjustment on the Rochester QJ's for a spring that controls the secondary airvalve opening rate. Sorry I do not know exactly where it is, my expertise on that type of carb (springloaded airvalve secondaries) is with Carter Thermoquads, but the concept is identical. It is easy to check to see if that has happened. Just move the airvalve manually and see if it has spring tension that resists movement and can keep it all the way closed when you let up.

A Holley secondary opening rate normally will not change at all during the life of it's rebuild. The secondary opening rate is controlled by air rushing into the primaries causing a vacuum, this vacuum acts to pull a diapgram up. On the other side of the diaphragm is a a spring that resists this vertical movement. All of this is in a closed housing, there are several different springs available from Holley to tune this rate. To change the rate the housing must be opened and the spring changed out.

 

[Coors]

Re: 5.7 liter sluggish when given full throttle, fine if I ease into full throtle

acellerator pump. Rebuild the carb.

 

[Mkos1980]

Re: 5.7 liter sluggish when given full throttle, fine if I ease into full throtle

I had same problem. I thought it was athe accelerator pump. I rebuilt the carb and had same problem. Ended up being the secondary airflaps opening too fast. I tightened up the spring on it and now it runs awesome.

 

[Flukinicehole]

Re: 5.7 liter sluggish when given full throttle, fine if I ease into full throtle

I had same problem. I thought it was athe accelerator pump. I rebuilt the carb and had same problem. Ended up being the secondary airflaps opening too fast. I tightened up the spring on it and now it runs awesome.

This is why you should check the accelerator shot first. It can be a few different things this is the easiest to check. If there is no shot of gas it's not working. If you get a nice stream of gas then the secondaries are not working properly.

 

[Haut Medoc]

Re: 5.7 liter sluggish when given full throttle, fine if I ease into full throtle

This is why you should check the accelerator shot first. It can be a few different things this is the easiest to check. If there is no shot of gas it's not working. If you get a nice stream of gas then the secondaries are not working properly.

I agree^^^^^^......

 

[QC]

Re: 5.7 liter sluggish when given full throttle, fine if I ease into full throtle

It's called troubleshooting, not guessing and swapping parts ^^^^^

 

[Maclin]

Re: 5.7 liter sluggish when given full throttle, fine if I ease into full throtle

If the airvalve does open too soon then even a good accel pump shot can't help. Have to look at both things. The secondary airvalve is right there, easier to check than the accel pump shot, don't even have to hit the throttle.

 

[Coors]

Re: 5.7 liter sluggish when given full throttle, fine if I ease into full throtle

good point, I didn't think about a hole-shot.

 

[wadyadoing]

Re: 5.7 liter sluggish when given full throttle, fine if I ease into full throtle

Thanks to all who replied. This is the first chance Ive had to read the thread. Ill print it out and conduct the tests this weekend. Ill repost with my findings. It is black smoke I took it out on saturday and it ran good but., It still has the same problem. And my fuel economey is suffering as well. This is A great forum best on the net for boat issues.


Thanks again Ill repost with my findings.

 

[rad1026]

Re: 5.7 liter sluggish when given full throttle, fine if I ease into full throtle

I have the exactly the same problem. Mine isn't as bad, it never gets to the point where it feels like its going to stall, just a big cough and then it usually picks up nicely. But if you are trying to get a skier up it can be frustrating. I can't wait to get out to the lake so I can play around with the carb a little. So here are some details about the Secondary Air Valve adjustments:

The AV is the flap the covers the secondaries of the carburetor. The AV flaps only open when the demand for more air is present (WOT). When decreasing the tension on the AV spring it allows the secondaries to open faster and allows them to open wider due to lower spring resistance against airflow.
To adjust the AV Tension you will need a small allen key and a very small flat headed screwdriver. That's all that's required.
Make sure never to turn the adjustment screw more than a 1/8 of a turn at one time. If the tension is over tightened the spring will be destroyed leaving your carburetor in pretty bad shape. The carburetor will have to be removed and a new spring purchased and installed - which is no easy task.
As long as you only make small adjustments you will be safe. Never adjust the screw more than 1 turn!
On the port side of the carburetor toward the rear you will see the linkage for the secondary air flap. If you look close through the slot in the air flap linkage you will see a very small screw.
Don't turn it just yet! There is an Allen key set screw positioned on the underside of the overhang on the air horn. Loosen the setscrew very carefully and just enough to allow the AV tension screw to turn. Turn the AV tension screw counter-clockwise until the AV flaps open up.
Now turn the tension screw clockwise until the AV flaps just close shut. This is considered the "0 tension" point. If you are setting your carburetor to OEM specs you will turn your AV tension screw the specified amount of times either tightening or loosening from this point.
If you are going to tune the carburetor yourself then just tighten your setscrew down at the "0 tension" point. Now comes the fun part.
As always, make sure your engine is warmed up. It is always important to make sure your timing is set to optimal and your ignition system is up to date and operating correctly.
When the engine is warm go for a test ride. The purpose of this testing is to correctly tune the secondary operation under WOT. With the boat at a complete stop stab the accelerator all the way open.
If your engine bogged (sputtered and then picked up) you have 2 options available. Ideally you should step up to a richer secondary rod pair. This will provide you with more fuel to overcome the bogging lean condition while providing the fastest AV opening rate.
If you do not want to change the rods, you can go ahead and adjust your AV tension clockwise in 1/8-turn increments until the bog goes away.

Hope that helps!

 

[Coors]

Re: 5.7 liter sluggish when given full throttle, fine if I ease into full throtle

Have you checked the choke for proper operation?

 

[rybad]

Re: 5.7 liter sluggish when given full throttle, fine if I ease into full throtle

I had a similiar problem a couple years ago. I had everyone tell me I needed to rebuild the carb. Then, my uncle (who's been boating fo 40 years) asked me if I changed my fuel filters lately.

I change the water/fuel seperator every year, and the carb filters every few years. Oddly enough, I had replaced it that Spring so I told him I didnt believe that would b the problem.. Then he asked if I used the "cardboard" filter, or the plastic.

I told him, I used whatever the local marina parts department gave me for my engine. We pulled the filter, and saw that it was in-fact the cardboard type,and that it had collapsed, basically restricting the fuel flow.

At low speed, enough gas was getting through, but throttle up quickly, and it would bog down.

..Just my story, maybe you should check this too.

 

[Maclin]

Re: 5.7 liter sluggish when given full throttle, fine if I ease into full throtle

That would not cause the rich condition wadyadoing has described. His problem is choke or secondary airvalve settings more than likely.

 

[Bondo]

Re: 5.7 liter sluggish when given full throttle, fine if I ease into full throtle

I think it must be a carb issue

Ayuh,......

I Agree........ A complete Carb Rebuild will probably cure it.......

Changing the Fuel Filters should be an Annual event, at the least,+ the 1st thing to do when a Fuel related Issue crops up......

Most of the ideas presented above are merely points of a Complete Carb Rebuild,.....
Which really isn't alot more work than just hitting the single various systems of the Carb........
Do it All,.. Do it Once,.... And Fine Tune it,.......

 

[Maclin]

Re: 5.7 liter sluggish when given full throttle, fine if I ease into full throtle

Ayuh brother, Ayuh!

 

[Coors]

Re: 5.7 liter sluggish when given full throttle, fine if I ease into full throtle

Sometimes it takes too much typing, over and over, to convince people.
What Bondo and I said.
The carb.

 

[Destin]

Re: 5.7 liter sluggish when given full throttle, fine if I ease into full throtle

Check the vacuum canister on the side of the carb. On a Q-Jet it controls the choke and secondary air valve. If it fails it won't pull the choke open when the engine starts and you will get black smoke until the choke warms up. It also delays the secondary air valve from opening fully for about a second. If it's not working you will get a severe bog if the throttle is opened rapidly.