Dizzy Venting, Need Some Insight

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ProwlerDriver

ProwlerDriver

10 Year 15 Year
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Aug 12, 2008
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Camano Island, WA
Alright, getting down to the nitty gritty with my front end overhaul...
The "Radiator Leak" Rebuild

Originally i had thought about capping the dizzy vents, as every other distributor ive seen isnt vented. But i figured the brains at toyota know whats going on, so im figuring out how to apply this to my situation.
Weber desmog going on.
So i know one end goes into the cab. Easy enough.
The other end that supplies the vacuum- I was looking at hooking this up to the intake manifold, on the same port as the brake booster. I had mentioned this before in another thread and JimC said it might need a restrictor as to not be a huge vacuum leak (at least thats what i took from it).

Soooo....
Is this a good location for vacuum? (intake manifold)
If not what alternate places do i have for vacuum(not using stock air cleaner)
Do i need a vcv on the vacuum line?
How would you restrict the vacuum? (if needed)
 
So the stock installation is to connect to the manifold vacuum at the three-nipple connector (called a gas filter). Are you removing this device as part of your desmog/carb change out?

However, the intake manifold connects to a diaphragm on a VCV, which implies to me that the distributor cap is not purged with manifold vacuum, but that the manifold vacuum opens the VCV which allows some ventilation into the air cleaner. Perhaps the air cleaner operates under slight vacuum conditions which will generate a flow through the distributor cap. Is there any reason you are not keeping the rest of the components used in the cap venting system?
dist cap venting 01.webp
 
2mbb said:
So the stock installation is to connect to the manifold vacuum at the three-nipple connector (called a gas filter). Are you removing this device as part of your desmog/carb change out?
Click to expand...

I was just going to plug the gas filter hole in an effort to simplify. The port on the other side of the manifold that the brake booster utilizes has an unused vacuum port due to the desmog (think it was for A/C idle up), i thought i could use that instead.

doesnt the manifold operate under vacuum? I assume hooking it up the way i describe would pull air through the cab, through the dizzy, and put it into the manifold. The only problem i can see is that this might be too much of a vacuum draw.
 
Last edited:
Yes the "gas filter" sees the same vacuum as the AC idle up port; these are both "manifold" vacuum. I guess my point is that in the stock system that vacuum is applied to a VCV, not directly to the distributor cap. The distributor cap seems to either be naturally vented to the air cleaner, or the small vacuum generated in the air cleaner is used to flush a small amount of fresh air through the distributor cap. I inferred from your initial post that you were going to not use the VCV and try and connect manifold vacuum directly to the distributor cap. If you do this I would follow Jim C's advice and use a restriction orifice. But I think it would be better to use the VCV.
 
Cool. Im not using the stock air cleaner so i dont know how id hook up the vcv to get it to work as stock- as their are 3 ports on the thing.
i guess that narrows it down... so now my question is

How would i restrict the vacuum hooking up the dizzy straight to the gas filter? Is their a common part i could grab for this?
Or, maybe a better idea--
Instead of connecting to manifold vacuum can i fab a port up on the aircleaner and run the vacuum side of the dizzy vent there?
 
There was a restriction orifice as part of your stock choke opener system. It's circled in green in the schematic, and I've shown where it is usually installed--on the vacuum tubing going to one of the air cleaner ports. A restriction orifice is just a restriction in the line, meaning a small cross-sectional area for flow. It should be easy to fab something if you don't have the stock one.

Here's a post with the part number for the stock restriction orifice if you want to try to purchase one: IH8MUD Forums - View Single Post - Stock F2 Choke system confusion
dist venting.webp
2f carburetor 03.webp
 
Perfect! I will find that part in the miles of tubing i have! Thanks for all the help 2mbb. Now i can hook it up where i wanted it too and not have to fab something on the aircleaner.

On a side note-- do you know anything about the "filter" inside the firewall the other end of the dizzy vent is hooked up to? I sucked on it (i know, i know) to see if it was clear and got a mouthful of dirt. I know i dont need that going into my dizzy. If its to hard to get to/clean can i leave it open to atmosphere?
 
Alright i found it connected to a ton of metal spaghetti. now upon closer inspection one end is a big hole- the other is a small hole with 2 holes on the side. The side holes will be covered by the hose so it should work as advertised-- in a big hole out the small. now which way to hook it up...

were trying to get less vacuum pull so my guess is.... that it really doesnt matter right? either way it will be restricted as the manifold trys to pull the air through it. regardless of how i hook it up it will have to go through that small hole. let me know if im looking at this wrong.
 
it doesn't matter which way to hook it up, just use the proper size tubing (3mm).

Regarding the filter, I've never tried to replace or remove mine. However, you should use a filter because the air will go directly into the engine, and you want that air to be filtered. You might be able to find a small breather filter (or maybe even one of those cheap in-line fuel filters) at your autoparts store.
 
2mbb said:
There was a restriction orifice as part of your stock choke opener system. It's circled in green in the schematic, and I've shown where it is usually installed--on the vacuum tubing going to one of the air cleaner ports. A restriction orifice is just a restriction in the line, meaning a small cross-sectional area for flow. It should be easy to fab something if you don't have the stock one.

Here's a post with the part number for the stock restriction orifice if you want to try to purchase one: IH8MUD Forums - View Single Post - Stock F2 Choke system confusion
Click to expand...

If ever there was a strong argument for desmogging, this picture is it.
 
Just go with a cheap fuel filter to cap the fresh air source, mount it high on the firewall and you'll be good. I once had the in-cab filter become plugged and crankcase fumes were being pulled into the distributor. Killed two distributors before I figured out the problem.
 
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