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I did my time searching, no specific answer..

  1. #1
    in the works MAD GREEK's Avatar
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    Default I did my time searching, no specific answer..

    I got one of those HEI distributors on a stock 350 chevy motor. Its got that "vacuum advance" deal on it. I know i need to take it off but how? or what do i replace it with? i have seen on Summit.com the vacuum lock outs but it doesnt specifically say for MSD, just for "Proform GM HEI".
    Just a little confused. Does running the motor with it on there and not hooked up to any vacuum make it run different or badly? Had an issue with the motor lean popping and was kinda wondering if that could be an issue..

    Any advise or thought would be appreciated.
    Thank you,
    Troy
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    gn7
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    Quote Originally Posted by KeepItOn1 Productions View Post
    I got one of those HEI distributors on a stock 350 chevy motor. Its got that "vacuum advance" deal on it. I know i need to take it off but how? or what do i replace it with? i have seen on Summit.com the vacuum lock outs but it doesnt specifically say for MSD, just for "Proform GM HEI".
    Just a little confused. Does running the motor with it on there and not hooked up to any vacuum make it run different or badly? Had an issue with the motor lean popping and was kinda wondering if that could be an issue..

    Any advise or thought would be appreciated.
    Thank you,
    Troy
    If you timed it according to some manual, it most likly told you to unhook the vac, and time the motor. Then when you hook up the vac, it will advance the timing right there. So yes, if you follow the directions, and do not hook up the vac, it will run like shit. You can just leave it unhooked but it is better to remove it all together. Just unscrew the thing and unhook it from the advance plate. then time the motor at what ever RPM where the timing stops climbing. 3000-3500 should be plenty.
    The dizzy really should be setup for non vac with different springs, but it will work. Either that, or hook the vac up. But if you have a lumpy cam, it isn't going to advance much on the vac.

    No matter. The main thing is to set the timing to your desired max advance.

    Your trying to set the initial timing at an idle aren't you?



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    in the works MAD GREEK's Avatar
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    Quote Originally Posted by gn7 View Post
    If you timed it according to some manual, it most likly told you to unhook the vac, and time the motor. Then when you hook up the vac, it will advance the timing right there. So yes, if you follow the directions, and do not hook up the vac, it will run like shit. You can just leave it unhooked but it is better to remove it all together. Just unscrew the thing and unhook it from the advance plate. then time the motor at what ever RPM where the timing stops climbing. 3000-3500 should be plenty.
    The dizzy really should be setup for non vac with different springs, but it will work. Either that, or hook the vac up. But if you have a lumpy cam, it isn't going to advance much on the vac.

    No matter. The main thing is to set the timing to your desired max advance.

    Your trying to set the initial timing at an idle aren't you?
    i dont think so.. i think my buddy, "Flat Footn", was setting it at 3k rpms. When u say just unhook the thing, thats where i am a little confused... so, literally just unhook it and dont replace it with anything, just take it off and thats it? sounds too easy, haha. Also, if it were to be hooked up, where does the vac hose run to?
    As u can see, i have no freakin clue. I am new the the sport and am learning something new everyday, i appreciate the new knowledge ur giving me
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    gn7
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    Yep, just unhook it, and remove it. 2 places it can hook depending on what you want it to do. The first is anywhere on the manifold or a port at the base of the carb. They refer to this as manifold vac. That simple. When you time the motor with it disconnected, the only advance is the mechanical, if the Rs are raised, or none if timed at an idle. When you hook up the vac canister, it will advance the dizzy from the idle timing. When you floor it, the vac drops and it like you disconnected it. The timing retards. Nice for road cars so they don't detonate. Not so good for boats. You will never get all the way back to full advance because this thing will cancel some of it out as long as the vac is low, which is the whole time your floored.

    The second place you can hook it up is in a port that exist in the side of some Holley metering blocks, just above the idle mixture screw. This ports advances the timing as the engine speeds up, and retards it on throttle closed. Kind of reverse. Not all Holleys have this port. No performance carbs do.

    Best to do away with the vac timing altogether. In most cases with boats, specially small jets, its best to do away with all the advance mechanism and just lock it out at the desired max.



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    Quote Originally Posted by KeepItOn1 Productions View Post
    I got one of those HEI distributors on a stock 350 chevy motor. Its got that "vacuum advance" deal on it. I know i need to take it off but how? or what do i replace it with? i have seen on Summit.com the vacuum lock outs but it doesnt specifically say for MSD, just for "Proform GM HEI".
    Just a little confused. Does running the motor with it on there and not hooked up to any vacuum make it run different or badly? Had an issue with the motor lean popping and was kinda wondering if that could be an issue..

    Any advise or thought would be appreciated.
    Thank you,
    Troy
    The logic behind removing the vacuum advance unit when you don't use it connected to a vacuum source is that the plate can move around due to vibration, causing the timing to vary.

    Different brands of HEI type distributors will undoubtedly have different mounting for the vacuum advance unit, so if you can't determine brand, you may need to fabricated something yourself to "lock" the plate in place, unless you want to try buying a few different ones until you get lucky and find one that fits. It's not uncommon to just put a vacuum cap on the unit and call it good. Kinda doubt that it has anything to do with your popping.
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    gn7
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    Hard to tell from your post, but if its a MSD HEI, go here, and go to page 7

    LINK: MSD HEI manual



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    Last edited by gn7; 11-10-2010 at 07:14 PM.
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    Quote Originally Posted by obnoxious001 View Post
    The logic behind removing the vacuum advance unit when you don't use it connected to a vacuum source is that the plate can move around due to vibration, causing the timing to vary.

    Different brands of HEI type distributors will undoubtedly have different mounting for the vacuum advance unit, so if you can't determine brand, you may need to fabricated something yourself to "lock" the plate in place, unless you want to try buying a few different ones until you get lucky and find one that fits. It's not uncommon to just put a vacuum cap on the unit and call it good. Kinda doubt that it has anything to do with your popping.
    Back in the day when I ran an HEI in a car application, all I would do is dissconect the vacuum pod's source of vacuum, advance the timing to my desired setting and then plug off the pod. I would always remove the stock HEI module and replace it with the MSD unit as well as install a centrifical advance curve kit utilizing the weekest springs and heaviest weights.
    All the vacuum advance does is assist at part throttle. By using the curve kit in conjuction with the mechanical advance setting at 3,500 RPM there was never a need to run the vacuum advance.
    Last edited by Quickjet; 11-10-2010 at 08:14 PM.
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    Quote Originally Posted by obnoxious001 View Post
    The logic behind removing the vacuum advance unit when you don't use it connected to a vacuum source is that the plate can move around due to vibration, causing the timing to vary.

    Different brands of HEI type distributors will undoubtedly have different mounting for the vacuum advance unit, so if you can't determine brand, you may need to fabricated something yourself to "lock" the plate in place, unless you want to try buying a few different ones until you get lucky and find one that fits. It's not uncommon to just put a vacuum cap on the unit and call it good. Kinda doubt that it has anything to do with your popping.
    ok, ill get that thing off since i know they're made basically for auto.
    about the popping.. We're gonna put it on the water this weekend and put some load on the motor and see what happens. Also, bought a carb rebuild kit just to make sure everything in there is all right and tuned correctly.

    Quote Originally Posted by gn7 View Post
    Hard to tell from your post, but if its a MSD HEI, go here, and go to page 7

    LINK: MSD HEI manual
    Thanks, saw that but since the HEI was giving to me, i dont have any of the lockout parts. oh well, it was FREE!!!
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    Quote Originally Posted by Quickjet View Post
    Back in the day when I ran an HEI in a car application, all I would do is dissconect the vacuum pod's source of vacuum, advance the timing to my desired setting and then plug off the pod. I would always remove the stock HEI module and replace it with the MSD unit as well as install a centrifical advance curve kit utilizing the weekest springs and heaviest weights.
    All the vacuum advance does is assist at part throttle. By using the curve kit in conjuction with the mechanical advance setting at 3,500 RPM there was never a need to run the vacuum advance.
    I got the thing for free when i got the motor.. Eventually, it will have the right one on there.. plus that thing is huge, as big as the carb, haha
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    Lean Popping!! Maybe another problem!............... Flat lobe WT
    Last edited by Widetrack; 11-11-2010 at 05:34 AM.


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    The vaccuum advance serves a purpose of giving additional advance under light load conditions.
    Removing it just because others do is not a valid reason.
    Just like locking the timing solid because many others do is not a valid reason either.

    Whatever someone runs on a race boat is a whole different application than what's best for a lake boat.
    That kind of reasoning is why some get such awful fuel economy.

    It would serve you better to understand how to optimize the timing rather than limit it's range.

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    gn7
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    Quote Originally Posted by Unchained View Post
    The vaccuum advance serves a purpose of giving additional advance under light load conditions.
    Removing it just because others do is not a valid reason.
    Just like locking the timing solid because many others do is not a valid reason either.

    Whatever someone runs on a race boat is a whole different application than what's best for a lake boat.
    That kind of reasoning is why some get such awful fuel economy.

    It would serve you better to understand how to optimize the timing rather than limit it's range.
    Well theres a blanket statement for you.

    Not all vacuum advance mechanisms advance timing under light loads. Some retard the timing under loads. All loads. Bigger the load, more the retard. depends on if the vac is hooked to the manifold, or a spark port in the carb. Very few factory marine engines are equiped with a vac advance, and when they are, they are almost always a spark port connection.
    Your right, he should learn what the motor wants. And in almost every performance situation, a locked, or very fast mechanical will be the best suited condition. Only large, heavily loaded boats ever seem to want a vac advance or a slow curve.



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    I knew you would have something to say about that Bob

    I learned a lot about ignition since I have been running EFI.
    It's easy to make it whatever you want with a laptop so there's no reason not to optimize.
    Baseing your timing curve on load is much preferred over baseing it on RPM. Mechanical advance is old school.

    I've been through the removing the vaccuum pot and locking in the timing years ago. It mainly was because I hadn't read up enough to understand what the engine really wanted so I just followed the crowd,
    .............."This was how we did it in the 1970's"...............

    Optimizing the timing is one of the things that I credit to being able to use the SAME PLUGS for 5 years straight on something that's wrung out to this degree and run for 50 hours + per season.

    Now I'm all primed up for a COP rant

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    gn7
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    If I had a electrons controlling my fuel and spark, I would be all over a some crazy ass spark curve myself. Thats the beauty of controlling both the fuel and the spark. The worse possible sceniro for a timing curve has to be a turbo. Thats why turbos for you and me didn't really catch on before EFI and CPUs. Now, turbos are the chit. I wouldn't even consider a turbo without either. I know Impatient will argue that, but blow thrus are old news and old tech. If they were the chit, Buick would have never moved over to EFI.
    And you would need to have your head examined to run one I a closed engine compartment.

    In carb deal, in a light jet or v-drive, it is almost universially better to go with a fixed advance or just a mech. Remember, he doesn't have electrons controlling his carb. Its pretty linear. Linear or lock timing works pretty damn good in those conditions. specially if the thing is never floored below 3000 Rs. Which we have discussed before, is all but impossible to do in a boat.
    I may be floor, but it isn't at 3000 anymore.



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    Last edited by gn7; 11-11-2010 at 04:10 PM.
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