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vacuum advance disabled Just noticed that the vacuum advance inlet on the distributor of my '39 V8 85 was plugged off by the former owner. He had installed a 3X2 setup and the intake does not have the vacuum port like on the stock manifold. Am I crazy or does this engine not require the vacuum advance? The engine runs rich and cuts out under load. I thought it was a carburetion issue.
Your thoughts are much appreciated.:) Phil |
Re: vacuum advance disabled The vacuum piston is a vacuum retard system not advance like later cars.
The piston is pushed down on a retard ring on the advance weights , when the engine is started the vacuum pulls the piston upward againt spring tension allowing the advance to function normally. when you accelerate the vac drops off allowing the piston again contact the ring retarding timing to prevent spark knock. Many unhook the vac line and disable thinking this runs better , probably doesnt run better at all. The piston also keeps the distributor in static time for starting as well and shouldnt be removed....:eek: Car run good ??? leave it as is...........:D |
Re: vacuum advance disabled You have to wonder how well that vac helps. If working at its full potential it has an effect.
If the curve is set up by a professional like bubba I would bet a vac less dizzy would be just fine. More so it ha crab setup. Maybe not... |
Re: vacuum advance disabled Tinker: You sound like my buddy in town that has an older 350 Chevy that gets 6 MPG and always is on the verge of overheating. 10 years ago he asked me to look at it , and I discovered then that the vacuum advance was not working and strongly suggested that this most likely was his problem. Now 10 years later it still gets 6 MPG and overheats just the same because he read somewhere in a glossy magazine about some hot-rod with a distributor that did not use a vacuum advance, so thinks his street machine can do just fine without one also.
To operate properly and get decent fuel mileage ,any older street driven vehicle needs vacuum advance, even flatheads that require a maximum of only 24 degrees total. If a flathead or anything else seems to run better without it, then it has way too much initial timing advance already. Listen to Bubba, he knows what he is talking about. Bruce |
Re: vacuum advance disabled Since this is a brake, without the vacuum the advance is not happening correctly. It is in full brake all the time unless internal parts have been removed such as the spring, or even the piston. It would be very easy to drill and tap one of the intake manifold intake runners for the vacuum you need. I suspect the big problem may be fuel related. Too big of main jets resulting in rich mixture. "cut out under load" also check fuel pressure, too high or too low, want 2-2 1/4# at Carb.
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Re: vacuum advance disabled Besides there not being a port available on the 3x2 set up, is it not a factor that with more than one carb on a f/h there is not adequate vacuum to operate advance or brake? Installing one of Bubba's Chevy distributors on my 8BA I got an Accel adjustable advance can for it so that it can be set as low as possible. I have yet to get the can on it, but seems like there was discussion about that a while back. (I need to get the can on there because the thing runs great with Bubba's dizzy on there but I only get about 11 mpg.)
PS, I added a plate with a vacuum port under the center carb to have a source available. |
Re: vacuum advance disabled I am sure that the retard brake will still function with multi carbs but it has to be tuned to the system anytime there is a modification made. The manifold pressure is at its lowest (highest vacuum) when the throttle plates are closed no matter how many there are. With multi carbs, the throttle plates don't have to open as far as a single carb with the same rpm. The carbs do have to have lower setting power valves though so you don't get too much fuel flow during accelleration.
A person can set up a Ford/Mallory ignition to work with it's centrifugal flyweight system only but it can not retard when vacuum drops as the throttle is opened so it won't get as good a fuel milage and could tend to run warmer. |
Re: vacuum advance disabled Bruce, my comment was for discussion purposes :). I do use the vac brake on my flatheads. One setup by bubba and the other by skip.
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Re: vacuum advance disabled Quote:
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Re: vacuum advance disabled Take it apart first and see that there is a piston and spring in there! And, as noted above, if the innards are still there with no vac they are putting an anchor on your part throttle operation at least. Hook it back up to vac when checked out for innards, run the adjust screw all the way out BY HAND so you don't pop the do-dad spring seat off of the screw, then back in maybe a turn and a half. Usually with modern gas you want it backed way out like that. You want some drag from this as the brake disc can float radially without a slight drag, giving you slightly erratic timing.
While messing around, look at engine end of the distributor shaft..."68" or "11" stamped there?? Find it an 11 shaft and advance for slightly quicker and longer curve that will add a bit of response. |
Re: vacuum advance disabled The vacuum brake system is primitive, at best. We set them up on our Sun machine and find hitting the retard specs is tentative, at best. Most of these distributors have piston pads that are badly worn, usually with a deep groove where they rode the point disk, and pistons that flop around in the chamber permitting a vacuum leak. This results in a constant drag on the point plate, degrading the advance. They were designed to prevent preignition knock with the gas of their day. Now, the fuel is very different, and "spark knock" is very rare. If you can detect difference in performance when the adjuster is backed off, something else is out of whack, such as weak or broken springs in the weight assembly, or a badly worn distributor shaft and bushings. Ford made a great improvement when the 8BA engines came along by using vacuum only, drawn by a port above the throttle plate, instead of raw vacuum from the intake manifold.
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Re: vacuum advance disabled Wow, Thank you all for the great info and suggestions. As suggested, first I will tear the dizzy down and see what's inside. If all is still intact, I'll re-establish the vacuum line to the brake and see what happens. This forum is a life savor. I'll post the results in case you're all interested. Thank you all again, Phil
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Re: vacuum advance disabled Quote:
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Re: vacuum advance disabled Ford made a great improvement when the 8BA engines came along by using vacuum only, drawn by a port above the throttle plate, instead of raw vacuum from the intake manifold.??????
Really? The loadamatic an improvement? Good Lord never thunk I'd here that! I'll give my opinion here, I think the loadamatic ain't that bad in good fettle, and set up right, with the right stuff around it, in a heavy car or pickup. The pre 8BA ignitions are great! Really really good ignitions. One paragraph had "ain't that bad" the other had "great, and a couple of really's" thrown in. Pre 8BA ignitions work great in any guise on a Flathead. 8BA ignitions turn to poo if you look at a dual carb manifold! To original poster, yes you should have vacuum connected to the brake. As above have said, if only to stop the advance plate skipping around and to stabilise the timing. I doubt you'd need much more than just touching as Bruce stated. "cutting under load" confirm the coil and condenser are good. These can give these symptoms. Easy swap on know good ones. "runs rich" how have you come to this conclusion? What carbs are fitted? Martin. |
Re: vacuum advance disabled Settle the ignition before worrying about carb; misfire and retarded spark (and you have part throttle retard if brake is in there with no manifold vac) can imitate richness on the plugs. You want brake hooked up to manifold, using ported spark here is inferior but possibly a justifiable temporary kludge if you aren't up for removing and drilling the manifold this weekend.
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Re: vacuum advance disabled Quote:
Normally I an very proud to be a "Barner" and also proud of the answer we all send to those asking,,, but today :confused: "" never I thunk I'd say it too"" Phil; Yes go in to the dist. do what you can ?? the vacumm plate under the center carb is a good way to go.. send the dist to Bubbas for the best re-do and timing set up you can get. and stay with us..... Stock market down 285 points, going to 300 under ?? thing I'll have a beer too?...............OLD..............BILL:cool: |
Re: vacuum advance disabled Old Bill, read all the posts and there content. My comments on the 8BA ignition was a comment to another posters comments on the 8BA ignition being referred to as am improvement, And relevant to that.
The second part of my post related directly to the original post. It is completely relevant to the posters question, backing up other posters comments 're the vacuum brake, aswell as pointing out coil and or condenser if faulty can give the symptoms he has. Also asking for carb type to help diagnose his rich condition. All fairly clear if you read the posts properly. Thanks for your input, Martin. Ps, I don't drink beer, only cyder. And very rarely drink coffee, just tea. I know shmit about stock markets, so can't comment on that remark. |
Re: vacuum advance disabled Just to digress here a bit. I always see it said that the vacuum piston stabilizes the rotating disc in the distributor. With vacuum applied, the piston is withdrawn from contact with the plate. So how can it do any stabilizing? I think if the spark is erratic, it is due to worn parts in the distributor.
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Re: vacuum advance disabled Sounds like Old... Bill and scooder are just friends that haven't met yet. Did someone mention beer? It's my birthday today and ...... don't mind if I do.
PS. All of your input on this problem I'm having has been the best (so far) birthday present I've received. Thank you all again X 1000 |
Re: vacuum advance disabled Flatjack, I see your point re the brake piston, I makes sence, I think that the piston doesn't completely lift of the plate except on the over run. I've seen with the piston removed, the timing flicking about when using a timing light. With the piston in, at idle the timing stabilised.
Wether they all do this, I don't know, but the one I seen did just this. Mr topless, you got some things to look at an try, do report back your findings. Martin. |
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