VSV question Pin_Head?

[IDave]

So, I believe it was Pin_Head who in a recent post mentioned that the VSV was not only for smog issues, but actually made the engine run better. That, and the fact that I found an appropriate '71 emmision control manual got me thinking about my own setup.

My rig came with a VSV that was plugged into the speedmarker, which was plugged into nothing, since the speedometer cable and the attendent speed detector was missing. Two of the four vacuum hoses were hooked into the carb, to what purpose I have no idea. Ultimately, I have changed out to a "NonUSA" carburetor.

Things seem to run FINE, but I would always be happier if things ran GREAT. It would require a speed detector and the attendent short speedo cables, and, perhaps, a speed marker if mine turns out not to be functional.

So, if Charlie or someone out there can give me some guidance, I would appreciate opinions on whether adding this back would make a detectable positive difference.

 

[Poser]

If it works....don't mess with it.

But that is just me.

Good luck!

-Steve

 

[cruiser_guy]

If you decide to go that way I've got some of that stuff from a '71 F engine as well as a '2/76 2F. The VSV for the '71 doesn't look like the one in the picture though, it looks like the box found in the later model trucks.
If I've got what you need it'd be $40 + shipping for the VSV, etc. etc.

 

[IDave]

Hmm. The picture I posted is from the 71 emissions manual and is labeled "F engine". It is the one that came with my 71, and is the one SOR shows for up to 9/71. SOR shows the box you have for 9/71 through 9/72, so that would be the 1972 model year. Probably not much different, but I would stay original. The speed detector is probably different for yours, too. Here is that figure from the SOR catalog. Look like yours? Thanks for the offer though!

 

[cruiser_guy]

I guess my F must be a '72 then! The guy I got it from called it a '71.

 

[IDave]

Yeah, my '71 is registered as a '70 for similar reasons.

 

[Pin_Head]

With a non-USA carb, I don't think that there are any issues for your VSV to worry about. On the models that have a vacuum line from the VSV to the top of the carb, the line runs the "power valve". This valve is an auxiliary main jet and it is open when you need the power and closes for the "lean burn" cruising cycle. The problem is that I don't remember what its default (eg no vacuum) state is. If the jet is open when there is no vacuum, then it will never run lean. If it is closed with no vacuum, then it will always run lean. I'm too lazy to take my carb apart and look, but if I had to guess I would think that the default is open.

 

[IDave]

Thanks, Charlie. I suspect I don't want to mess with it, but the vacuum setup looks the same as the stock setup to me. SOR's literature says it doesn't need or want to run with antipollution devices, but I thought I'd ask after your comment. I am assuming that you mean to the diaphragm when you mention a "line from the VSV to the top of the carb." This was the state of my original carb. The NonUSA came with a line from the vacuum nipple at the base of the carb to the diaphragm. It obviously could be hooked up like the original was, and, in fact, looks just like the original to me. Here's a photo from SOR of the NonUSA I have:

 

[Pin_Head]

No, the line you are talking about appears to go to the throttle positioner. The one I was talking about is line #8 in this diagram. I have only seen it on 2Fs.

 

[IDave]

Gotcha. Thanks!