Vacuum Advance Port on a 3/69-9/69 Aisan

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Hi everyone!

I found a pretty good deal (or what I thought was a good deal) on an early Aisan 2-barrel to replace the rochester that came on my 40 from the previous owner. I was cleaning it up and soon realized that it isn't ported for vacuum advance. and after some reading on the forms, it seems that nobody does that for these early 2 barrels. I saw what looked like might be a suitable existing vacuum circuit that I could maybe use as it does not really seem to do much. I have attached some pictures of the carb and what I am talking about below, maybe I could pop out the small metal "rivet" and replace it with a port for the vacuum advance? I have seen something similar on some of the old crowns which seem to have a similar carb.

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I’d call Mark

Aka. @65swb45

Or Jim C.

I know for sure Mark has drilled them into carbs.
 
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65swb45

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1. I believe there was a voicemail on my answering machine yesterday about this.
2. I did not return the call because I don’t know the answer. If I knew it at some time in the past, it escapes me at the moment. I would have to put one of those carbs in front of me to see if it jogs my memory.
3. Form follows function. A properly functioning vacuum advance port has no vacuum at idle. That means it’s vacuum signal would be above the primary throttle plate at idle. I suspect if you trace the path of the passage you are currently focusing on, you will find that it’s terminus is UNDER the throttle plate, and in all probability is the vacuum source for the idle circuit.

Hth
 
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I recently went through this. Here's the thread with all the info you need.

 
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1. I believe there was a voicemail on my answering machine yesterday about this.
2. I did not return the call because I don’t know the answer. If I knew it at some time in the past, it escapes me at the moment. I would have to put one of those carbs in front of me to see if it jogs my memory.
3. Form follows function. A properly functioning vacuum advance port has no vacuum at idle. That means it’s vacuum signal would be above the primary throttle plate at idle. I suspect if you trace the path of the passage you are currently focusing on, you will find that it’s terminus is UNDER the throttle plate, and in all probability is the vacuum source for the idle circuit.

Hth
🙇‍♂️

And here I thought you knew everything… ;)
 
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I recently went through this. Here's the thread with all the info you need.

I saw this the other day when I had some free time and was trying to figure out a workaround. I was hoping to figure out a creative solution, but it looks like I will just get a new carb then, thanks!
1. I believe there was a voicemail on my answering machine yesterday about this.
2. I did not return the call because I don’t know the answer. If I knew it at some time in the past, it escapes me at the moment. I would have to put one of those carbs in front of me to see if it jogs my memory.
3. Form follows function. A properly functioning vacuum advance port has no vacuum at idle. That means it’s vacuum signal would be above the primary throttle plate at idle. I suspect if you trace the path of the passage you are currently focusing on, you will find that it’s terminus is UNDER the throttle plate, and in all probability is the vacuum source for the idle circuit.

Hth
Yep that was me! Looks like I will give you another call tomorrow then and see if I can purchase the proper carb from you!
 

Dizzy

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I'm still in debate as to why I'm using ported vac on my 2F. If I hook my distributor to manifold vacuum, I get more advance at idle. Some folks say that 'ported' vacuum advance is from the era when manufactures were looking to reduce NOx at idle, and that before that, up until the '60s, engines came configured with manifold vacuum connected to the distributor. Setting static timing would still be done capped.

Is manifold vacuum spark advance really a bad thing on a F/2F?
 

65swb45

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I saw this the other day when I had some free time and was trying to figure out a workaround. I was hoping to figure out a creative solution, but it looks like I will just get a new carb then, thanks!

Yep that was me! Looks like I will give you another call tomorrow then and see if I can purchase the proper carb from you!
Okay.😊
 

65swb45

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I'm still in debate as to why I'm using ported vac on my 2F. If I hook my distributor to manifold vacuum, I get more advance at idle. Some folks say that 'ported' vacuum advance is from the era when manufactures were looking to reduce NOx at idle, and that before that, up until the '60s, engines came configured with manifold vacuum connected to the distributor. Setting static timing would still be done capped.

Is manifold vacuum spark advance really a bad thing on a F/2F?
Coming from a guy who’s username is dizzy, it kind of feels like a trick question. :lol: There are plenty of articles online that explain the advantages of ported vacuum over mani vacuum, and the disadvantages of manifold vacuum.

In layman’s terms, you always want to have as much ‘bang for the buck’ advance WITHOUT pre-detonation. The active fuel management systems of EFI have sensors to accomplish this. The next best thing, in a carbureted system, is ported vacuum, precisely because it is load sensitive.

If you run manifold vacuum at idle, you ’run out’ of advance too early in the rpm range.

More significantly, you want the advance to drop off under heavy load before predetonation occurs. Because manifold vacuum is ‘deeper’ in the engine, it does not drop off as quickly as ported vacuum which, being up in the carburetor, is closer to atmospheric pressure to begin with. You can confirm the difference using a cab mounted vacuum gauge.

As a younger man, I contemplated running a modified manifold advance with a T fitting that would come into the cab. That way I tho I could install a manual bleed off to release vacuum when I heard the engine pinging. Now I am too hard of hearing (from decades of driving a Landcruiser)to risk that.☹️
 
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. . . More significantly, you want the advance to drop off under heavy load before predetonation occurs. Because manifold vacuum is ‘deeper’ in the engine, it does not drop off as quickly as ported vacuum which, being up in the carburetor, is closer to atmospheric pressure to begin with. You can confirm the difference using a cab mounted vacuum gauge. . . .
☹️

Your first sentence above is 100% correct. However, I hate to disagree with a master but I feel I must in this case. From everything I've read and experienced, manifold vacuum drops off as the throttle is opened and decreases where ported vacuum is above the butterfly(s) and shows no vacuum at idle but increases as throttle opens. Therefore, load is sensed better with manifold vacuum and actually decreases advance as less vacuum is detected where ported vacuum actually produces more advance at full load instead of decreasing it.

If I'm wrong please point me to documentation to the contrary.

UPDATED: I need to retract part of what I've said above. My comment about your first sentence still stands and is 100% correct. In doing some additional research I have discovered that ported/timed vacuum and manifold vacuum are basically the same, the only difference is there start point. Manifold vacuum is there at idle when ported/timed vacuum is at zero. Ported/timed vacuum starts about 1000 RPM and is the same as manifold vacuum. They stay the same until you back off the throttle all the way and manifold vacuum goes high while ported/timed vacuum goes to zero.

I ran across a thread regarding when to use manifold or ported/timed vacuum. This was his response: "One question that continues to crop up is do I connect my distributor vacuum advance canister to full time vacuum or ported vacuum? As far as I’m concerned it all depends on the distributor that you’re using and if your engine likes the additional timing at idle. Your initial timing setting is based on total timing, with a distributor that has its initial timing down around 5 degrees or below I would consider hooking the vacuum up to full time vacuum and with the initial timing at about 15 degrees I would use ported vacuum. Ported vacuum becomes full vacuum at about 1000 RPM as the throttle is increased so I don’t think that having additional advance between let’s say 600 – 1000 RPM is that important unless your engine likes it." The poster Bruce88 has additional posts, although aimed at SBC's, regarding tuning and other issues that relate as well to the FJ40.

65swb45 I bow to the master!
 
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Dizzy

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So, for the later half of '69, Toyota used a VSV to control the advance diaphragm in the distributor? The VSV was remotely controlled by a speed sensor, throttle position, or temp sensor, or some kind of combination? It would have been hooked up to manifold vacuum, fuel tank vapors from the charcoal canister, and the distributor? In a stock configuration, for the later half of that year, when would vacuum advance kick in?
 
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So I might have found a carb that I could get ported, but I am not sure if the linkage would work with my accelerator cable. My fj40 is a 64 with a 1969 motor in it and it has the cable-type accelerator set up.

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That one will work, you just need to add the correct bracket for the cable and replace ball/turnbuckle linkage with the throttle cable connector that accepts the barrel ended cable. Add your ported vacuum tube and you'll be all set.

Should look like this:
i-qzkR2St-L.jpg
 
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That one will work, you just need to add the correct bracket for the cable and replace ball/turnbuckle linkage with the throttle cable connector that accepts the barrel ended cable. Add your ported vacuum tube and you'll be all set.

Should look like this:
i-qzkR2St-L.jpg
Sweet, thank you for the clarification! Any idea where I could find those parts? I don't see anything like that in stock at SOR.
 
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I think marksoffroad has repro throttle cable and return spring brackets. He might have a used cable connector for the primary throttle plate shaft. I would give him a call. Or watch the classifieds for parts. 👍
 
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Yep, looks like I see the parts on his site.

@65swb45 If I buy the carb and send it to you to rebuild it and port it for the vacuum advance and bought all the parts for the linkage, would you be willing to change those pieces out for me? For extra of course :).
 

65swb45

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As long as you can get the correct bellcrank ( what the barrel on the end of the accelerator cable attaches to) I can handle the rest.😉

BTW, did I, or did I not predict that there was a good chance the base may have been swapped…without seeing or having any description of the carb other than the date code? 😉
 
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