How the Spark Control Valve (SCV) Works

I've got a Ford Service Handbook for single barrel carburetors dated August 1962. It's got all the details on all the internals, adjustments, specs etc. for the 1 bbl carbs used in 1963 on the 144, 170, 223, and 262. Since there is so much discussion about how the SCV works, I thought I'd post some illustrations and text that show it in action. If there's other info people would like to see, let me know. I'd post the whole thing on a web site if I wasn't worried about the Ford copyright issue.

Good stuff. Thanks.

Steve-O

Interesting. I would like to know the best way to plug the hole up if you take the valve out. ( I have an early carb with a later dist and do have misfiring at higher rpms due to excessive advance) I went to a specialty nut and bolt store today, and they did not have a bolt with matching threads to screw in there to plug it up. There are holes outboard of the threads in the hole that I assume need to be plugged up, but since the threaded area is a smaller diameter, sticking something like a cork in there will not cover those holes.

Can I just fill the whole cavity with silicone and let it cure before I run it?

S-man

After reading that the scv will give too much advance (and was doing so) with my late distributor on my "old" 1100, out of curiosity I checked timing before and after removing the valve and plugging the hole on the 1100 I just installed. There was no differance in total timing/advance. Maybe the valve itself is malfunctioning?

S-man

mustang6, did your 68 distributor give you any problems? wanting to go with an h/w 5200 carb and clifford adapter but worried about the distrubutor on my 68.

I run the later style Duraspark II electronic distributor in my car, but the stock 68 distributor is OK with the H/W 5200. 1967 and earlier load-a-matic distributors are the problem ones that require the carbs with SCVs. See the sticky right below this one for a rundown on that subject.

At a gathering over the weekend, sedanman noticed I had a SCV on my 1100 (thanks for noticing!) but I mentioned that the engine was a `68 200 and the distributor had centrifugal advance. I had my carb rebuilt 3 years ago at Pony Carb and I was sure I had given them the numbers off my engine. I did some searching and found this from the Pony Carb website:

"1968 carburetors differ from 65-67 in 2 ways. First: They do not have a spark control valve (looks like a power valve). For the engine to function properly with this carburetor - the distributor must have centrifuged advance (spring loaded weights inside) along with the vacuum advance unit. 67 and older engines (except 66 and 67 California Emissions) utilized the load-o-matic distributor which had vacuum advance only."

I emailed Pony and told them the situation. I got a quick response and they agreed that it should not have the SCV. I sent them my invoice number so they could look up their records. I'm waiting for a response but they did say:

"No you should not have the spark control valve if it is a 68. There are 2 vacuum ports behind the spark control valve that would need to be plugged, we'd use epoxy."

I'll post more information when they respond again but I hope they can explain in detail how I can properly plug up the ports without having to send them my carb. My car is a daily driver so I can't be without it for weeks while they correct it.

Thank You for your explanation of the SCV. I have a '67 mustang 200 with the original distributor and a rebuilt Carb I got about 7 years ago from a parts store. The rebuilt carb does not have a SCV on it and always looked different from my original carb.
When I go up large hills the engine seems to be very under powered. In fact on a hill in West Virginia I topped out at about 65 MPH going up the hill. Under normal driving conditions the car has plenty of power, but I guess going up the hills the manifold vacuum is low and the venturi vacuum is not present so there is no spark advance.

Now I am planning to upgrade to the Clifford Weber 38-38 kit, so I guess I should upgrade the distributor to a post '68 model. I assume any upgraded carb will not work correctly with the '67 dist.
Or could I get the latest pertronix II module and would the new module add the centrifugal advance electronically?

Greg

Greg,

All you have to do if you want to keep things simple is get a post '67 distributor- they are only about $40. In fact, I hear just a vacuum cannister is about $25, so it's not a bad deal. Just make sure you get the one with single vac. advance, not with the vacuum retard. If you want to get more complicated, there's plenty of guys here that can insruct you on installing a duraspark distributor with the factory electronic module or something else aftermarket.

Thor

just put the dsII on my girlfriends '67Mustang with the 1100 w/scv. to keep the dsII from seeing too much vac. could i just tee into the manifold line going to the pcv valve? would i have to also pull the hard line off the carb and put a plug into that port on the carb? all help will be appreciated.

Hi...and welcome to the forum.

I think the vacuum port on the carb only opens at a certain point during acceleration (thus only advancing at higher RPMs). You wouldn't want to just hook the distributor advance up to direct, constant vacuum from the manifold.

You'll need to just disable the SCV. If you take the carb off and look from the bottom up into the venturi, you'll see a small hole just opposite the SCV. You can just plug that up with some epoxy.

You could also remove the SCV and plug that if you can find something with the same threads.

Hope that helps...

Hi Kenny and all,

It's funny how old threads appear again and again....Speaking of threads, I went to the local Nut and Screw shop and they did not have anything that would thread in the scv hole. I think kenny's suggestion of epoxy is the only way. Or find an old scv valve that is frozen and does not work and just screw it in- I've seen many of them. When you rev the engine you should see it work (at least on some of them - the design in varies from rebuld kit to kit) if it doesen't it's bad.

Thor

I chose to plug an old spark control valve with epoxy and use it on the carb, looks stock and I can return the carb to original condition if I ever choose to,don't like the idea of making a mod to the carb that can't be easily un done!