Drilling for ported Vacuum (1 Viewer)

[ducktapeguy]

Quick questions regarding the ported vacuum. What size hole does it need to be, and how far about the throttle plate should it be? Here are pics of what I am planning on doing. If I locate the hole 25mm above the base of the carb (shown at the cross mark), that would put the hole 4mm above the throttle plate (at approximately the spot marked inside the bore) along the line indicated. Any reason to move it higher or lower?

Background info: 1975 2F motor, half-ass desmogged. I'd rather not desmog it, but at this point I don't want to leave it half done either. PO had cut and plugged the EGR tube so the EGR cooler and valve was removed. The EGR port from the carb spacer has also been capped. The air injection rail had some holes in it, so that was also removed and plugged along with the smog pump. I still have the original equipment, but it's non functional.

The reason I need to add a ported vacuum is because at some point the stock dizzy was replaced with a vacuum advance. I believe the 1975 CA spec should have come with a vacuum retard? At least that is what the #6 port on the black box (VSV?) says the hose should hook up to. The cruiser runs fine, but I'm guessing having the vacuum advance module hooked up to a vacuum retard line probably isn't optimal.

If I add the ported vacuum, should I go ahead and do a full desmog, or can some of it be left alone? I've re-read most of the desmog threads and tech links, but they're usually a complete desmog. Should I leave stuff like the TP, AAP, and black box alone and just cap off the unused ports? Or would they be useless anyway and I should just remove it?

 

[Pin_Head]

The vacuum port is about 1 mm above the closed throttle plate. I don't know the size, but I would guess about .025 inch from eyeballing it. Personally, I think vacuum advance is nice but not necessary. I will run fine with just mechanical advance.

 

[BDelling]

I'm thinking of doing this as well - so your photos are great!. I read about this in the tech links section and the article had drill sizes. It is here: Cruiser Carb Info - Land Cruiser Tech from IH8MUD.com

It says:

"1970-74 USA OEM TLC carb does not have "ported vacuum" port for vacuum advance distributor. Cast iron throttle plate housing has boss ready made for ported vacuum port (AD). Entrust machine work with good machine shop, or be willing to waste a few housings. Find brass tube ~.156" x .75" to press into depth of ~.25" (hobby shop or old carb). See figure II. Center punch a mark near center of boss and .96" above bottom surface of cast iron throttle plate housing. Drill thru with .020-.032" drill, radial to bore cross-section and perpendicular to throttle bore axis. With drill wander, lowest (optimal) hole centerline entry position is ~.90". assuming you've hit oil, drill hole for press fit of ~.156" brass tube into cast iron. This port should read 0 inches Hg vacuum at hot idle."

Let us know how it goes. Bruce

 

[ducktapeguy]

Thanks for the input. I can't believe I missed that paragraph. I was actually reading that same page last night when searching for the answer and remember reading the paragraph right below it about the 70-87 carbs. My eyes are getting old.

I have a spare carb, so I might try it out on one and see how it goes. Eventually I want to upgrade to the FJ60 vacuum advance dizzy to eliminate the points. I'm hoping to get everything tuned up correctly, my goal is to acheive 17 mpg on this motor. I've already averaged about 15.5, and that was before fixing a few of the vacuum leaks and other stuff.

 

[FJ40Jim]

The markings for vac advance port look about right.

Connect vac advance dissy to ported vac fitting on carb base.
Connect power valve and AAP to manifold vacuum fitting in front of carb.
Connect TP (choke breaker) to manifold vacuum under carb on driver's side.

That's about it.

 

[BlackDiamond72]

Did you ever do this? How did it come out? If so, where did you get the little brass nipple?

James

 

[ducktapeguy]

Funny you should ask this now, I just happened to be working on it tonight. I did drill for ported vac a while ago, but I haven't installed it on my cruiser yet. I just picked up a rebuild kit from FJ40jim so by next week I will know whether I did it right.

The brass nipple is just some brass tubing I picked up at a hobby store. See the paragraph above quoted by Bdelling. I basically followed those instructions. You can see the hole in the second pic, I'm shining a light through the tube from the outside, it's the little pinpoint of light

 

[BDelling]

Timely Post!

Thanks for posting the results. It's funny, because I was digging out my carb I was going to do this to the other day, and I was thinking, I wonder if I can find that post on the ported vacuum drill...

 

[BlackDiamond72]

Did you use a drill press or hand held drill? Hardened steel drill bit? How did you press in the brass nipple? I have called every decent machine shop and carb shop in denver and no one is willing to try. I guess I will have to take matters into my own hands......again.

 

[ducktapeguy]

I used a drill press, regular drill bit. It'd be near impossible to drill a hole that small using a handheld drill. It's cast iron, so it's pretty easy to drill, I think I spot drilled the surface just to break through the rough surface and center the drill bit, from there its was just slow speed + plenty of lube. The brass tube was just tapped into place with a mallet after I chamfered the front. The first half of the hole is a .157 counterbore, and the bottom half might be a .155 so only the bottom half is press fit. I did that just in case I needed to remove it at some point in the future for whatever reason. Not sure if it was necessary because it's still a pretty tight fit.

I don't know why a machine shop won't do it for you, it's pretty simple. You may need to get a precision chuck to hold the drill bit, I think the standard chuck on a drill press won't grip a pin drill.

 

[BDelling]

Blackdiamond72:

JimC or Mark's Offroad will drill it for you.

 

[BlackDiamond72]

Yeah, I thought about it too late though. I'd like to have this rig running well to make the trip out to moab for the safari in a few weeks and don't want to risk not having it back in time. I've got 30 other projects going on this rig at the moment so maybe I'll just use mechanical advance and send it to mark afterwards.