Vacuum?

[PussyPusher]

I have an AMC 360 in an older jet boat. My question is I have a Holley 4Barrel carb with Vacuum Secondaries and a vacuum advance on my distributor. When I get on it, it seems that the second the secondaries open I lose my ignition curve and it goes out of time. What can I do???

[Nubbs]

The vacuum in your manifold will decrease when your secondaries open. With decreased vacuum, your vacuum advance distributor will not be as advanced as it was before the secondaries opened. When you step on the throttle, two butterflies open. The manifold pressure (vacuum) will be at a certain level. The distributor will be at a certain advance because of the vacuum. When the secondaries open, the pressure drop across the carburator will be less. As a result, vacuum will decrease. With less vacuum, your distributor will have less advance.
You can advance the base timing of the distributor or you can adjust the internals of the distributor to alter the advance curve. I don't know what will work best for you.
Good luck!!

[PussyPusher]

Im not quiet sure whats going to best either. I understand the physics of it all. I just was wondering if I should try to go to a mechanical advance or somehting

[Nubbs]

You could try blocking off the vacuum port on the manifold or carb and setting your timing to work with just the mechanical advance of your distributor. It wouldn't cost you any money to experiment. You could also try opening your secondaries at a lower vacuum.

[PussyPusher]

How do I adjust the secondaries?
Will the distributor advance without the vacuum hooked up?

[Havasu Hangin']

PussyPusher:
How do I adjust the secondaries?Different secondary vacum spring.

[PussyPusher]

OK I am a little uninformed when it comes ot this so... How do I change the spring on the secondaries? I really appreciate your guys help on this.

[Havasu Hangin']

PussyPusher:
OK I am a little uninformed when it comes ot this so... How do I change the spring on the secondaries? I really appreciate your guys help on this. There's a vacum plunger on the side of the carb, which is connected to the secondary linkage. I think it's held by 4 screws on my Holley...
..or have a carb expert do it for you- it's not expensive.
[ January 08, 2003, 01:11 PM: Message edited by: Havasu Hangin' ]

[Craig]

The vacuum advance on a distributor is strickly there to enhance fuel economy. The moment you barely crack open the throttle from a steady state, the vacuum going to the distributor drops off. Plug that puppy off if you want.
You can change the carb secondary spring easily in 15 minutes, max. Unbolt the cover, pull the spring out and put a light one in. Remember if your carb is set up right you won't feel the secondaries "come in" like you do on a mechanical carb. http://free.***boat.net/ubb/Avatars/Gearhead_Garage/Other_Equipment/carb2.JPG

[PussyPusher]

Craig,
Thank you for the diagram. I was also told to try using the ford vacuum inline diaphrams that are supposed to hold a little more vacuum for just a few seconds longer. So let me get this straight, what you are saying is that when I jump on the gas and secondaries open I lose vacuum to the distributor and that is what is supposed to happen? I thought that the vacuum help with the ignition curve under hard throttle???

[Craig]

The only thing the vacuum advance does is while you're cruising at steady state down the highway, vacuum is high. Since the motors really not under any load, the distributor kicks in more degrees advance, which will aid fuel economy. Too much advance under a load is bad, so when the vacuum drops, due to the throttle being opened, the distributor backs down the advance. You can get adjustable vacuum canisters if you really want to play with it. I used to run a distributor on my GS at the drgas that had vacuum advance. Sometimes I wouldn't disconect the vacuum, sometimes I would, I never saw any difference in et or mph with regards to the vacuum advance. I might be missing a point or two here, someone help me out if I am. But most of the "performance" distributors from MSD etc, don't have the vacuum advance canister even on them.
Craig

[DUCKY]

Where is your vacuum line for the dist. connected? It should be connected to the small port on the right side of the primary metering plate. If it is connected below the throttle plates, It shouldn't be and that will cause the problem you are describing.

[Craig]

Like Ducky said, the vacuum needs to be to a ported source. One that is not active at idle.

[PussyPusher]

Well to tell you the truth the vacuum line comes off the top of the manifold and goes to the vacuum port on the carb. There is a little "T" in that line that runs a line up to the distributor. There is only 1 port on the carb and it is being used to supply vacuum to the secondaries. It does look a lot like the image that Craig attached. Just a different finish. Am I missing something?
[ January 12, 2003, 08:39 PM: Message edited by: PussyPusher ]

[BK]

The carb in the picture looks to have a quick change kit on it? is that the part that looks differant? BTW the vacume secondary springs are color coded for lighter or hevyer on the ends. Dont see to many people running vacume advance distributors on boats, the HEI I was running previously had vacume advance and I was advised to remove it before I installed it.

[HOSS]

First off, are you running a PCV?
Second, if you are running vaccum for distributor from a nipple located in the diagram, you have it wrong. Hook line to nipple off side of metering plate.
Gotta love those bench racers! They never learn!

[PussyPusher]

Well there is a PCV. When I removed it I found a hole in the side of it too. So that will be replaced with a non-PCV fitting. As far as connecting to the side of the metering block, I would if there was a GOD DAMN nipple. I only have ONE nipple on the whole frigin carb. This things is really buggin me. I will try to get some pics of it so you can all see my frustration.
Thank you all
Shawn

[HOSS]

Is it PCV or PVC, I can`t remember?
Gotta love those bench racers! They never learn!

[PussyPusher]

PCV! :D

[HOSS]

What does PCV stand for?
Gotta love those bench racers! They never learn!

[PussyPusher]

piece of crap valve!
[ January 16, 2003, 08:46 PM: Message edited by: PussyPusher ]

[PussyPusher]

Im really not sure but I would guess positive crankcase ventilation?

[DUCKY]

PussyPusher:
Im really not sure but I would guess positive crankcase ventilation? You are correct sir!
If there is no port on the right of the primary metering plate, then it should have a removable plug in it. But I wouldn't worry about it. Disconnect it and make the necessary adjustments to the distributor for more centrifugal advance. You probably have the same dist. I have (GM Single point) All I did was grind a little off the trailing (SMALL) edge of the advance weight, and put in lighter springs. I now have 10deg at idle and 34deg at 3000 rpm.
I also would lose the pcv system all together. Just put good breathers on it. There is no reason to suck blowby down the intake if you are not subject to emission control. Don't just put a fitting in there to replace the pcv valve. The valve prevents liquid oil from being sucked down the engine.
[ January 16, 2003, 09:13 PM: Message edited by: DUCKY ]

[HOSS]

So PCV really means "suck and vent"?
Gotta love those bench racers! They never learn!

[DUCKY]

HOSS:
So PCV really means "suck and vent"?
Gotta love those bench racers! They never learn! Actually it's just SUCK! Like most other emission control devices!!!