carb question.

[jp89bayliner]

well I finally got my fuel system working correctly. But I have a question about my quadrajet of my 1985 omc. The motor is a 305 with a 4 bbl quadrajet. I pulled the carb apart to do a rebuild first time. It went well and was not that hard to do as I thought. My question is that I rebuilt it becuase when I go to wot from a slow speed it falls on it's face for a few monents then picks up and goes to top speed. I thought my rebuild would take care of it but it did not still there. My question is I found a great tech artical on the quadrajet and while I was reading it and looking at the pics I saw were they were talking about power valve springs and how you can change them to flow more fuel. When I had mine apart I did not see any spring under the power valve? I wonder if some one has been in the carb before or due marine carbs not have them? I think that would explain my bog when going to wot. Am I correct in thinking this.

When I rebuilt the carb I soaked the carb in carb dip over night, checked all surfaces were flat and they werent so I took it to the machine shop and they made all the mounting surfaces flat. I then replaced all parts that came in my kit including a new brass float set to correct level.

I also noticed that in the tech articale that I read that they epoxy all the plugs cause they are known to leak fuel from the bowl. I did not do this and that would probley explain why when it sits off for awile that when it starts It is hard to start that I haft to wait for the bowl to fill up before it will start. I know this because while I was at the carb after the boat was off for some time I had friend pump the throttle I heard air coming from the accelerator pump but no fuel until you crank the engine and gas fills the bowl.

Any pros got some tips I would really appreciate them, and also were can I get a power valve spring from what I read they are calibrated for each aplacation Thank's for any help in advanced.

 

[John_S]

Re: carb question.

Yes there is suppose to be a spring under the power piston. I think you can get a kit of all different springs for $10.

 

[jp89bayliner]

Re: carb question.

Ok now I know that there is sapost to be a spring under there can any one tell were to get these from? Does napa carry them? Second what type of epoxy should I use to seal up the the plugs on the bottom of the carb? Can I just use jb weld? Thank's for any help JP.

 

[Maclin]

Re: carb question.

Have you tried adjusting the spring loaded secondary airvalve opening rate? Many QJ bogs can be tuned out that way.

 

[jp89bayliner]

Re: carb question.

Have you tried adjusting the spring loaded secondary airvalve opening rate? Many QJ bogs can be tuned out that way.

I am a first time quadrajet owner and the first time I have ever worked on one.can you go into detail on the proper way of adjusting the the secondary air valve, or point me in the direction of a tech page to do this? Or is this some thing I can find in my manuel thank you for any info jp.

 

[MikDee]

Re: carb question.

The power valve is under the air horn (top cover) in between, and slightly behind the primary barrels, it holds the 2 metering rods for the jets in the bowl, suspended. (There's a little plastic donut that holds it in place once the cover is put back on) it is narrow hollow brass cylinder, that is held up in place by a spring inside, and moves up, & down, against the spring pressure, depending on engine vacuum. It needs to work freely,,, or else havoc! These springs are application specific. You need to have the right one for your boat, I believe they are color coded.

 

[Maclin]

Re: carb question.

The airvalve is spring loaded and has an adjustment, I was hoping it would have been mentioned in the technical article you found and my post would prompt you to look into that!

The airvalve is at the top of the secondary barrels and should not be confused with the throttle plates. The secondary throttle plates open with the throttle linkage but the airvalve plate at the top opens as the engine's airflow demands increase. If it is not tight enough then it opens too soon it will cause a lean bog. If it is too tight your engine may not be getting all the flow it wants.

I do not know where the QJ adjustment is specifically. I must apologize for not being able to give detailed instructions, my expertise is in Carter AVS and Thermoquad automotive performance models. They have the same type of spring loaded airvalve. They use a small coil spring held in place with a set screw, the adjustment is right on the side inline with the airvalve shaft.

 

[MikDee]

Re: carb question.

Sorry,I don't know how to adjust the airvalve on a Qjet for best performance, But I do know that the heaviest power valve spring will run the richest through the RPM range, because it will try to overcome the vacuum on the power valve, lifting the metering rods up out of the bowl jets more, faster, and more often. This may also make your carb run too rich, causing more fuel use, and other issues.

 

[jp89bayliner]

Re: carb question.

The power valve is under the air horn (top cover) in between, and slightly behind the primary barrels, it holds the 2 metering rods for the jets in the bowl, suspended. (There's a little plastic donut that holds it in place once the cover is put back on) it is narrow hollow brass cylinder, that is held up in place by a spring inside, and moves up, & down, against the spring pressure, depending on engine vacuum. It needs to work freely,,, or else havoc! These springs are application specific. You need to have the right one for your boat, I believe they are color coded.

I know the spring you are talkign about mine was grey if I remember correctly. They do work very free. I am guessing that changing the spring is what is going to correct my problem. But I am not sure what spring to go to. I am thinking about calling marine carb .com and asking them to send me a rebuild for my boat I feel like I am getting over my head here. I boat the boat this way but my first drive did not show the problem cause I slowly went to wot listening for noises and what not. So Iam not sure if this the orginal carb for the boat or if it is already a rebuild, a very poor rebuild before I got it.

Or my other option is going to a edelbrock carb. Unless some one can point me in the right dirction of what color springs to buy. I know I still need to get a spring for the power valve. Does any one know what size jets they have in there QJ. Thank's agian for the info JP

 

[Uraijit]

Re: carb question.

I know the spring you are talkign about mine was grey if I remember correctly. They do work very free. I am guessing that changing the spring is what is going to correct my problem. But I am not sure what spring to go to. I am thinking about calling marine carb .com and asking them to send me a rebuild for my boat I feel like I am getting over my head here. I boat the boat this way but my first drive did not show the problem cause I slowly went to wot listening for noises and what not. So Iam not sure if this the orginal carb for the boat or if it is already a rebuild, a very poor rebuild before I got it.

Or my other option is going to a edelbrock carb. Unless some one can point me in the right dirction of what color springs to buy. I know I still need to get a spring for the power valve. Does any one know what size jets they have in there QJ. Thank's agian for the info JP

With Q-Jet carbs, there's a lot more to proper setup than just jet size. (IE Metering rods, etc).

I'd start by fixing the issue you KNOW is there. Replace the missing spring, and then go from there. You can keep making guesses at what else MIGHT be wrong, but the best course of action is to fix the known issues first, and then see if anything else needs fixing. You should be able to get springs from NAPA.

If the spring doesn't fix it, for less than the cost of a new Holley or Edelbrock, there are several Q-Jet experts who will build you the ultimate Q-Jet carb, custom suited to your specific application, elevation, and "driving" habits. I'd go that route before dumping a bunch of money in a different carb that's still going to need to be tuned/set up to your app.

A properly tuned Q-Jet will kick the snot out of just about any other carb out there.

 

[chiefalen]

Re: carb question.

I was gonna post the same thing. Send it to a expert. 4 barrels are a b-yatch.

Worth the money, you tell them how you want it setup and thats it. You'll get it back and bolt it on and enjoy whats left of the summer.

Good luck

 

[MikDee]

Re: carb question.

I know the spring you are talkign about mine was grey if I remember correctly. They do work very free. I am guessing that changing the spring is what is going to correct my problem. But I am not sure what spring to go to.

Wait, I thought you said you had no spring under your power valve? Yet you say yours was gray? and the power valve works freely?

I was only trying to give you an idea of what the power valve looks like, and how it works.

If it's a marine carb, and the right type for your boat, chances are it's an orig. equip. carb, or even if it was a o.e. replacement carb, I doubt it has the wrong power valve spring?

I wouldn't mess with it then! I doubt that's your problem. I'd keep everything the way it is till the hesitation issue is resolved. You might want to check your accelerator pump, or Air valve setting.

 

[rad1026]

Re: carb question.

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.

 

[sarantis]

Re: carb question.

This may help you.Instead of the gauge you can use any weight from 70-90gr.

 

[John_S]

Re: carb question.

Here is a Merc Q-jet of similiar vintage. Please point out which spring you think you are missing. After what you said and Mikdee pointed out, you may be talking about the Accelerator pump return spring, but don't know.

http://www.mercruiserparts.com/Show...=1077&bnbr=110&bdesc=CARBURETOR+(228-230-260)

 

[jp89bayliner]

Re: carb question.

Wait, I thought you said you had no spring under your power valve? Yet you say yours was gray? and the power valve works freely?

I was only trying to give you an idea of what the power valve looks like, and how it works.

If it's a marine carb, and the right type for your boat, chances are it's an orig. equip. carb, or even if it was a o.e. replacement carb, I doubt it has the wrong power valve spring?

I wouldn't mess with it then! I doubt that's your problem. I'd keep everything the way it is till the hesitation issue is resolved. You might want to check your accelerator pump, or Air valve setting.

I am sorry I was refering to the rear cam on the secondaries not the power valve. There is definetly no spring under my power valve, that is for sure.

 

[jp89bayliner]

Re: carb question.

Here is a Merc Q-jet of similiar vintage. Please point out which spring you think you are missing. After what you said and Mikdee pointed out, you may be talking about the Accelerator pump return spring, but don't know.

http://www.mercruiserparts.com/Show...=1077&bnbr=110&bdesc=CARBURETOR+(228-230-260)

The piece I know I am missing is number 6 on that daigram. Thank's for the response JP.

 

[jp89bayliner]

Re: carb question.

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.

I spoke with napa today and gave them the number of the carb and they set me up with a power valve spring. I am going to replace the spring and try the above this weekend. Hope fully I can get out real early before any one else hit's the lake and do some adjusting and see how it goes. Thank's for the ideas I feel like I can do almost any thing with the help and knowledge around here. Thank's JP

 

[MikDee]

Re: carb question.

Wait, do you have the 2 metering rods #7 in the Pic.??? I did not think the engine would run without a power valve spring? Are you sure it's not there?
This I gotta see? You've gotta figure the metering rods are being sucked down by vacuum, closing off the main jets with no spring to hold them open. If this is the case, please don't mess with anything else on the carb till you get this done, & try it! If this is as you say, I'd bet it's your only problem.

Many, yrs ago, when I was much younger, I was looking for performance, and I removed the primary metering rods from my Qjet, leaving the jets wide open
Big Mistake! The car ran, but a total bog, with black smoke out the exhaust, and I could see the gas gauge go down, as I drove it! It was the opposite of what you have, running Way too Rich! I couldn't get the metering rods back in fast enough, and decided not to try that again :redface:

 

[John_S]

Re: carb question.

With no power piston spring, he would be running in the cruise mode all the time. This would be cause a lean condition (bog or backfire) on accelleration.