Vacuum from distributor.

[michael_cini]

hi guys,

is it mandatory to have the vacuum line from the distributor feed into the carb? the car idles too high when the line is hooked thru the carb. when i remove the line and plug it off at the carb i can get the car at a lower idle and get better throttle response. can i cause any harm by having the distributor line unhooked? thanks.

michael

ps - see my signature for setup details.

 

[fordconvert]

It sounds like you have it hooked to a 'manifold' source on the carb. Factory usually hooked it to a 'ported' source which the biggest difference is at idle there is no vacuum. If you have full vacuum to the dizzy at idle it will advance the timing and one of the results will be a higher idle speed. The later the carb model the more ports there were to control various devices on the engines. You may have to get an exact ID so people can tell you what ports are what or you can do some testing with a vacuum gauge and at least determine what is 'proted' and what is 'manifold'. Manifold will be high vacuum at idle, ported will typically be very low or even no signal at idle but as soon as you come off it should go high and almost match the manifold. Under load it will be different but just revving in the driveway should pretty much respond on and off. If you snap the throttle quick both ported and manifold should drop momentarily but then stabilize with a medium to high reading.

 

[Eric Rose]

Your sig doesn't say what distributor you are using (LoM, dual advance, DsII or DUI?). Also, did you set your static timing with the vacuum advance blocked off?

I'm running a Carter YF and a DSII on my 200. I set my static timing to 12 degrees and then tried both manifold and ported sources. I got better results with the ported source, if that helps. The venturi vacuum may be less with your 2v, so you might do better with a manifold source.

It may be a good idea to see how much vac. the manifold and the venturi are pulling at idle by hooking a T fitting into your vac. lines. You can also see how the vac from each source rises/falls and where the peaks are.

 

[66 Fastback]

It also depends on the distributor. Do you have the Load-O-matic distributor or the l1968 and later version?

As mentioned, you can run it on a ported vacuum source. I prefer manifold source. You may need to re-set the idle speed with the throttle plates with the vac line connected. You could have your idle speed up there high enough where some of the centrifugal advance is kicking in (if you have the later type distributor). When you connect the vac source, idle speed increases and may be adding in additional centrifugal advance too. You may have to decrease the initial timing. What Distributor are you running and what is your initial timing set at?

Fuel mileage and part throttle response at cruise will likely suffer if you keep the vacuum line plugged. Temperatures could also increase if the ignition is not advanced enough.
Doug

 

[michael_cini]

thanks guys,

i have a dsII dizzy. sorry for forgetting that. its been a bit since we set the timing, i think around 12-14 degrees. yes, we set the advance with it blocked off.

on the carb, there is only 1 place to plug the line in, there is not another choice?

thanks.

michael

Your sig doesn't say what distributor you are using (LoM, dual advance, DsII or DUI?). Also, did you set your static timing with the vacuum advance blocked off?

I'm running a Carter YF and a DSII on my 200. I set my static timing to 12 degrees and then tried both manifold and ported sources. I got better results with the ported source, if that helps. The venturi vacuum may be less with your 2v, so you might do better with a manifold source.

It may be a good idea to see how much vac. the manifold and the venturi are pulling at idle by hooking a T fitting into your vac. lines. You can also see how the vac from each source rises/falls and where the peaks are.

 

[michael_cini]

there is only 1 port on my holley carb, according to the manual it is the "timed spark vacuum port." which according to what i have read and been told it should not affect the idle speed, but it does. i have tried it with the line hooked up to this port and then plugging it and hooking the line to direct manifold vacuum. the result is the same, too high of an idle. i'm quite perplexed, suggestions please!

 

[fordconvert]

If you have a vacuum signal on a ported port that sort of indicates the throttle blades must be at least slightly open. Is the throttle actually hitting the stop screws? If its not it could be something choke related or worn throttle shaft and bore not letting it close all the way. If the throttle is closing all the way and there is still vacuum there it could be something simple like a bad or wrong gasket used at some point in its life.

 

[michael_cini]

thank you fordconvert for all of the tips, looks like i have some investigating to do! i will let you know what i find.

If you have a vacuum signal on a ported port that sort of indicates the throttle blades must be at least slightly open. Is the throttle actually hitting the stop screws? If its not it could be something choke related or worn throttle shaft and bore not letting it close all the way. If the throttle is closing all the way and there is still vacuum there it could be something simple like a bad or wrong gasket used at some point in its life.

 

[jamyers]

Manifold vacuum will increase the idle speed. Just turn the idle speed screw out until the idle comes back down to spec. Perfectly normal on engines meant to use manifold vacuum.