I have a Ford 429 It has a motorcraft vacuum advance distributor. I had a Edlebrock 1411 with electric choke on it. It was timed at 8 degrees timing without the vacuum line hooked up as soon as you hook it up it automatically jumps to 12 degrees timing. Next I bought a Holley 750 bolted that on. Go and hook up the vacuum line it jumps to 14 degrees timing. both carbs had vacuum right off the bat. So now Im getting rid of the vacuum advance very frustrated with the timing. what type of distributor should I put in the engine?? Thanks Bryan
You have your vac advance line plumbed to the wrong fitting on the carb. It should be hooked up to a secondary vacuum port, not primary. You have it hooked to a primary port OR your tune is way off and you have the throttle plates jacked too far opened at the idle setting.
Just set your base timing hook up vacuum advance and drive it and see if you have spark knock if you do back it down a little if not you are ok.
Here's a trick to help you figure out which port to hook the line to on the carb... Start the engine and let it idle. Locate the vacuum port that does not have any vacuum on it when the engine is idling. Briefly open the throttle and allow the engine speed to increase while checking for vacuum on that port - it should only have vacuum when the throttle is opened. This is a secondary vacuum port - the one that the vacuum advance should be hooked to. If you have it hooked to primary vacuum (any port that is below the throttle plate) then it will have vacuum on it all the time and the dist will always be advanced. If you can't seem to find any ports with no vacuum at idle, then your throttle plates are being held opened too far by the setscrew...indicating your carb/engine is improperly tuned.
I fired off a 428 C-J engine today that has the original 735 Holley on it. It had primary vacuum on the distributor port. First time I've seen a Holley do that. Could it have something to do with the fact that originally it was routed through a temp/vacuum port on the intake?
If you have ported vacuum at idle on those carbs you either have the wrong port or the throttle blades are open too far at idle, common with a big cam. You might need to address that, but it's a bad idea to lose the Vacuum Adv.
If there's vacuum on the distributor advance port when the throttle plate is closed, then something is wrong. Either the throttle plate isn't all the way closed or what you think is the distributor port is really not... I have never heard of the vacuum advance being tied to primary vacuum via a coolant temp-controlled vacuum switch. Every engine that I have ever worked on that I can remember - that had a vacuum advance feature on the distributor - had that servo plumbed to secondary vacuum on the carb. The fittings are almost always obviously located above the throttle plate on the carb. In other words, if there's 4 or 5 vacuum ports on the carb, the dist port will always be the one that is highest.
I have worked on many cars that had full vacuum at the dist at idle. The tune up spec says to unhook the vacuum line and plug to set the timing.
There's been a lot of different vacuum advance configurations used over the years, but for a 'street performance' application, connecting to a 'manifold vacuum' source (below the throttle blades) will give the best results if the advance unit only has one vacuum connection. Having the timing jump like that is normal. Running without vacuum advance on the street will kill your fuel economy, with no corresponding performance increase.
Both ports on both carbs do the same thing. Could both carbs do the same thing? I talked to a buddy of mine that races older fords and he said lose the edlebrock and lose the vacuum advance on it. So got the holly 750 bolted on and trying to figure out what distributor to get. burning some extra fuel that's no big deal... Posted using the Full Custom H.A.M.B. App!
It is stock rebuilt motor put brand new bearings in it brand new timing gear set. The guy I bought the truck from had the vacuum vent tube plumed into the second port on the carburetor so the carburetor didn't know what was no vacuum. I honestly couldn't tell you what year the distributorr is I put a brand new rotor cap pertronix electronic ignition in it. Brand new for pertronix flame thrower coil with 1.5 ohms resistance also. Posted using the Full Custom H.A.M.B. App!
Does the engine idle good with the vacuum at the dist at idle? The holley carb may be sending a better vacuum signal at idle.
Yea it seemed to be idling fine and both carbs did have vacuum at idle. But he edlebrock when the initial timing at 8 degrees and then plug the vacuum line in It and jumps to 12 degrees timing...but it was hard starting. Posted using the Full Custom H.A.M.B. App!
No vacuum advance is fine in a racing application, but if you want to run part throttle, you need vacuum advance. Lean mixtures at low cylinder pressure (part throttle) burn slower, and need more advanced timing to reach peak pressure at the best time. Seems a little odd you only get 4° when the vacuum canister is connected. Should get an additional 8° to 12° advance from the vacuum. Some distributors are adjustable, maybe someone cranked the advance down. I prefer to connect the distributor to manifold vacuum. Ported vacuum is to make the engine idle hotter for emissions purposes.
Mr. Cow, If you have a DSII Module be sure to get one with the blue connector. It has a cranking retard feature. To activate it you need to be sure the white wire is connected to the S terminal on the solenoid. Also it is common for Ford distributors to have either 20, 26, 30, or 34 degrees advance. In the one below the 10L slot allows 20 crank degrees, the 15 allows 30. You probably have a 13 slot or 17. With the 13 (26) you would want to use about 12 initial for 38 total and to want that to come in by 2500 - 3000. The crank retard (blue grommet ) module will retard it to 2 degrees during cranking.
Okay ill look into that gonna order a new distributor. my distributor has to be worn. Gonna check on the holley 750 to see if it have a vacuum port on the metering block if it does it will have zero vacuum at idle and there for vacuum adbance proble mm will be fixed Posted using the Full Custom H.A.M.B. App!
You need to know how much advance is in the distributor to know where you set the initial. Some helpful info http://www.reincarnation-automotive.com/Duraspark_distributor_recurve_instructions_index.html
I would set it up with 30 Degrees Crank in the distributor and 6-8 initial plus manifold vacuum to the vac advance. Here are the original specs.
I've looked around a bunch an it seems to come up as 6 to 10 degrees Posted using the Full Custom H.A.M.B. App!
Keep in mind if you have a modified motor, the OEM timing specs may not be the best choice anymore. If you've removed all the emission stuff, you may want to try the 'performance' specs used on a factory motor as your starting point. The factories were generally pretty conservative with their 'tune' on the vanilla motors, you can nearly always go with more advance for more low-end 'pep'.
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