Brand new fan clutch - overheats at idle?

[burnin oil]

Sounds like you got it fixed. If you need to get the radiator fixed check out Beach Radiator in Virginia Beach. A really nice guy owns the place and the work is top notch. Avoid the place on Military Highway that has a good rep with the old timers. The quality went down hill and you can actually see them working on radiators at the car wash next door because they rented out their shop! Two attempts to fix a radiator there only resulted in a bigger leak. Beach radiator fixed it right up.

[davepl]

Originally Posted by davepl

Make a note of what your initial timing is as well. If it's retarded it'll run warmer, and may only be noticeable at idle.

Well, I was correct about the timing being retarded, but for the wrong reason (I guessed initial and not vacuum).

I bring it up not (only) to brag but because there shouldn't BE any vacuum advance at idle.

[JJorgensen52]

Originally Posted by davepl

Well, I was correct about the timing being retarded, but for the wrong reason (I guessed initial and not vacuum).

I bring it up not (only) to brag but because there shouldn't BE any vacuum advance at idle.

Yes you were, good call sir.

This gets into a whole other topic I was researching last night. My truck is non-emissions (No A.I.R.), so as I understood it I should be using manifold vacuum for the distributor, not ported. Thus, I have full vacuum at idle (which is why you set initial with the module disconnected). I read a superbly good write-up by a GM ignition engineer who helped design the systems and why they did what they did.

That makes the most sense to me, since you only want to retard timing under high load (low vacuum) scenarios, and idle is about as low load as it gets. It definitely idles a lot more smoothly with the manifold vacuum.

[mechanicalman]

Originally Posted by JJorgensen52

Yes you were, good call sir.

This gets into a whole other topic I was researching last night. My truck is non-emissions (No A.I.R.), so as I understood it I should be using manifold vacuum for the distributor, not ported. Thus, I have full vacuum at idle (which is why you set initial with the module disconnected). I read a superbly good write-up by a GM ignition engineer who helped design the systems and why they did what they did.

That makes the most sense to me, since you only want to retard timing under high load (low vacuum) scenarios, and idle is about as low load as it gets. It definitely idles a lot more smoothly with the manifold vacuum.

The only time manifold vacuum is different than ported vacuum is before the carb butterflies clear the ported vacuum port enough to get past the venturi effect (very small window) at very low throttle angle, after that the two ports are exactly the same. So in function, manifold vacuum vs ported vacuum (with equal base timing specs) for the dist advance, it's six of one and half dozen of the other, except you put out a lot more emissions at idle with it on manifold vacuum and waste more fuel at idle only. It's mainly a crutch for poor mechanical advance characteristics.

Obviously I don't know your engine combination or your local emissions law, and none of what I've said disputes anything you said about how your vehicle runs and responds but I know for certain it will cause your CO readings to increase at idle if you use the same base timing specs with the pod dis-connected, due to incomplete combustion. The idle mixture screws will allow you to set the engine to idle smooth with either set-up in most cases, unless the engine has been modified to the point the carb needs modified.

[davepl]

There were in fact attempts at combating emissions by using full manifold vacuum for timing control, but I'm pretty sure those didn't come along until the late 70s or early 80s.

Unless there's something really special about that motor, and a lack of Air Injection isn't it (all mine lack it too), I don't think this is the case.

Remember vacuum advance advances the timing under light load. Your initial timing is appropriate for idle, but once you start adding load at low volumetric efficiency you need more lead time to get it to burn.

If you used manifold vacuum you'd have whackadoo idle timing and then less as you tipped in load, which is the opposite of what you want.

Where's mechanicalman when you need him? He can likely back me up on this (again, unless there's something weird about the post-70 trucks).

[davepl]

Never mind, we posted at the same time! I call the vacuum port he refers to as the transfer slot (the transition between idle and drive circuits) but otherwise what he wrote sounds right to me!

[mechanicalman]

Originally Posted by davepl

Well, I was correct about the timing being retarded, but for the wrong reason (I guessed initial and not vacuum).

I bring it up not (only) to brag but because there shouldn't BE any vacuum advance at idle.

"Timing sounds right; 6-10 should be OK. If it were at part throttle I'd check vacuum advance but sounds like it's only at idle.

Weird that only the bottom half of the rad gets hot. Are you sure it's not plugged and needs to be boiled out? Maybe it's been like that a long time, but didn't matter until the clutch fan relied on it for temp sensing.

Unless you had a fancy two-pass radiator I can't picture a scenario in which a factory rad wouldn't heat evenly. In fact it should be hotter at the top and cooler at the bottom by whatever temp drop (maybe 30-60 degrees) that your rad can manage".

Spot on, Dave. Who would have known he was running manifold vacuum? And, I didn't pick up on the radiator being cooler at the bottom, yeah that didn't make sense unless it was low on coolant.

[JJorgensen52]

In the interest of learning and education, here's the information I read last night (borrowed from the HotRodders.com forum):

Originally Posted by HotRodders.com

As many of you are aware, timing and vacuum advance is one of my favorite subjects, as I was involved in the development of some of those systems in my GM days and I understand it. Many people don't, as there has been very little written about it anywhere that makes sense, and as a result, a lot of folks are under the misunderstanding that vacuum advance somehow compromises performance. Nothing could be further from the truth. I finally sat down the other day and wrote up a primer on the subject, with the objective of helping more folks to understand vacuum advance and how it works together with initial timing and centrifugal advance to optimize all-around operation and performance. I have this as a Word document if anyone wants it sent to them - I've cut-and-pasted it here; it's long, but hopefully it's also informative.

TIMING AND VACUUM ADVANCE 101

The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.

The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.

At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).

When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.

The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.

Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.

If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.

What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.

Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.

For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts.

That said, it seems to me that using ported vacuum would cause a drastic change in the amount of advance the engine sees immediately on tip-in (when the blades open and ported becomes equal to manifold). At least in my understanding, since my mixture *should* be going rich (due to the accelerator pump) on tip-in, I would not want to be advancing my timing, because the fuel rich mixture requires additional time to mix and compress before it will burn evenly (thus preventing knock).

Again, not meaning to be arguementitive, just trying to understand what's at play here, what is correct, and why - we all know the internet is full of mis-information so it's best to be sure!

[mechanicalman]

Originally Posted by JJorgensen52

In the interest of learning and education, here's the information I read last night (borrowed from the HotRodders.com forum):


That said, it seems to me that using ported vacuum would cause a drastic change in the amount of advance the engine sees immediately on tip-in (when the blades open and ported becomes equal to manifold). At least in my understanding, since my mixture *should* be going rich (due to the accelerator pump) on tip-in, I would not want to be advancing my timing, because the fuel rich mixture requires additional time to mix and compress before it will burn evenly (thus preventing knock).

Again, not meaning to be arguementitive, just trying to understand what's at play here, what is correct, and why - we all know the internet is full of mis-information so it's best to be sure!

But how could there be an increase in vacuum induced timing "when the blades open and ported becomes equal to manifold"? Think about it. A person tends to think that ported vacuum starts to advance immediately when the throttle blades open because manifold vacuum advance decreases when the blades open, which is true if you open the throttle gradually like in normal driving (how EGR is able to work). But the same is true even connected to manifold vacuum. Only time when vacuum advance sees no vacuum (ported OR manifold) is when the blades are opened quickly and wide, (heavy load needs less timing so it works) and it's the same with ported or manifold in that instance as well. However, "when the blades open and ported becomes equal to manifold", then the ignition timing in that instance is the same even with your pod connected to manifold vacuum.

So, "when the throttle blades open and ported becomes equal to manifold", six of one and half a dozen of the other, it's all the same then.

I'm not trying to be argumentative either, and I used to make the same assumption.

BTW, very good link I saved it on my favorites. Thanks.

[mechanicalman]

Originally Posted by JJorgensen52

In the interest of learning and education, here's the information I read last night (borrowed from the HotRodders.com forum):


That said, it seems to me that using ported vacuum would cause a drastic change in the amount of advance the engine sees immediately on tip-in (when the blades open and ported becomes equal to manifold). At least in my understanding, since my mixture *should* be going rich (due to the accelerator pump) on tip-in, I would not want to be advancing my timing, because the fuel rich mixture requires additional time to mix and compress before it will burn evenly (thus preventing knock).

Again, not meaning to be arguementitive, just trying to understand what's at play here, what is correct, and why - we all know the internet is full of mis-information so it's best to be sure!

"If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more".

This I know to be "internet mis-information". No distributor from the factory ever had near that much centrifugal advance.

Yes, ported vacuum was initiated for the purpose of heating up the exhaust and lowering the emissions on both AIR and non-AIR engines along with the low base timing specs. And yes, you want as much advance as you NEED at idle without making it crank slowly if emissions are not on your list of to-do. But you don't need manifold vacuum to do it, you simply set the base timing for as much as you can without cranking hard (I run 15 degrees base with ported vacuum and still barely pass Arizona emissions without changing the settings). I have a true 8.7:1 compression ratio (flat-top pistons with 80cc combustion chambers), my mechanical advance curve is correct (after much fuss) and I get 37 degrees total timing (15 base plus 22 mechanical) and 54 cruise advance (15 base plus 22 mechanical plus 17 vacuum). Stock HEI (I did replace the shaft with a GM part don't remember the number) with aftermarket pod and advance springs, my vacuum pod is adjustable and is just barely all in at cruise, I'm running a 373 gear without overdrive, headers, and I get 12 MPG city and 15 MPG highway at 65 MPH. I know, I need an overdrive. No excuses.

"For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts".

This too is untrue, and conceited at best. This too is just someone talking on the internet, not straight from the pages of a GM engineer, unless it's the engineer that got fired for printing things that were untrue. Yet I admit a lot of the stuff he said is true, but not all of it.

And, I'm just someone talking on the internet LOL. You never know who to believe, and really, trial and error and your own satisfaction and happiness is all there is. Good luck and stay safe.

[davepl]

Originally Posted by mechanicalman

So, "when the throttle blades open and ported becomes equal to manifold", six of one and half a dozen of the other, it's all the same then.

It helps to see a diagram of this, which is actually in this month's Hemming Classic Cars and worth reading.

At idle, the transfer slot is above the mostly-closed throttle blades so there is no ported vacuum but lots of manifold vacuum (because the blades are closed).

As you tip into the throttle, this uncovers the transfer slot and you start to get vacuum there. Manifold vacuum drops just as a function of the blades now reducing restriction as they open.

Once both are open, unless its a carb design that routes one to a venturi, they are exposed to the same conditions and hence, as he says, six of one half dozen of the other.

But as you read in the article above vacuum advance is for part throttle. At WOT it's zero. At idle its zero. Only during part throttle does it do anything.

A frequent mistake I see made is for people, particularly with older higher compression engines, to experience pinging under part load. They then back off the total timing, thinking its a function of high compression. What they actually could do is change the vacuum curve (some are adjustable with an allen key, otherwise replace) to bring in less part throttle advance. After all, that's where it was detonating. But the approach of backing off mechanical timing hurts the engine's performance at every RPM.

[JJorgensen52]

Originally Posted by mechanicalman

And yes, you want as much advance as you NEED at idle without making it crank slowly if emissions are not on your list of to-do. But you don't need manifold vacuum to do it, you simply set the base timing for as much as you can without cranking hard (I run 15 degrees base with ported vacuum and still barely pass Arizona emissions without changing the settings).

So this leads to yet another question - I'm base timed at 6 degrees BTDC right now. If I bring it up towards 12 or 15, the truck has a tough time starting, cranks real slow like it's got high compression (which it definitely does not!). I've also noticed that I'm getting what feels like knock/an intermittent miss at WOT under load, when I'm timed with more advance. That may be a different issue, but the ignition components are only a few years old.

I'm beginning to wonder about my balancer.

As far as the ported vs. manifold - my thought (perhaps incorrect) was that as soon as I uncover the transfer slot (so small throttle increment), I now am seeing port = manifold, and since my throttle percentage is still low, my advance would jump right up. It makes good sense that if I go from idle to WOT that the vacuum advance never has a chance to get involved.

There only appears to be one ported vacuum location available on my 2GV, and it's currently hooked to the charcoal can. I presume that's where I should be getting my timing vacuum? The vacuum fitting on the rear of the carb base, closest to (and I had assumed, for) the distributor is manifold vacuum.

Thanks for the info folks!

[mechanicalman]

Originally Posted by JJorgensen52

So this leads to yet another question - I'm base timed at 6 degrees BTDC right now. If I bring it up towards 12 or 15, the truck has a tough time starting, cranks real slow like it's got high compression (which it definitely does not!). I've also noticed that I'm getting what feels like knock/an intermittent miss at WOT under load, when I'm timed with more advance. That may be a different issue, but the ignition components are only a few years old.

I'm beginning to wonder about my balancer.

As far as the ported vs. manifold - my thought (perhaps incorrect) was that as soon as I uncover the transfer slot (so small throttle increment), I now am seeing port = manifold, and since my throttle percentage is still low, my advance would jump right up. It makes good sense that if I go from idle to WOT that the vacuum advance never has a chance to get involved.

There only appears to be on ported vacuum location available on my 2GV, and it's currently hooked to the charcoal can. I presume that's where I should be getting my timing vacuum? The vacuum fitting on the rear of the carb base, closest to (and I had assumed, for) the distributor is manifold vacuum.

Thanks for the info folks!

Not sure what set-up you have, but found this picture showing kinda where the dist vac hose goes. I'm going to do some research and maybe get back to you on the other (transfer slot).

http://repairguide.autozone.com/znet...5280252293.gif

[mechanicalman]

Originally Posted by davepl

It helps to see a diagram of this, which is actually in this month's Hemming Classic Cars and worth reading.

At idle, the transfer slot is above the mostly-closed throttle blades so there is no ported vacuum but lots of manifold vacuum (because the blades are closed).

As you tip into the throttle, this uncovers the transfer slot and you start to get vacuum there. Manifold vacuum drops just as a function of the blades now reducing restriction as they open.

Once both are open, unless its a carb design that routes one to a venturi, they are exposed to the same conditions and hence, as he says, six of one half dozen of the other.

But as you read in the article above vacuum advance is for part throttle. At WOT it's zero. At idle its zero. Only during part throttle does it do anything.

A frequent mistake I see made is for people, particularly with older higher compression engines, to experience pinging under part load. They then back off the total timing, thinking its a function of high compression. What they actually could do is change the vacuum curve (some are adjustable with an allen key, otherwise replace) to bring in less part throttle advance. After all, that's where it was detonating. But the approach of backing off mechanical timing hurts the engine's performance at every RPM.

Dave-here is a self-quote of myself from 1144 today:"The only time manifold vacuum is different than ported vacuum is before the carb butterflies clear the ported vacuum port enough to get past the venturi effect (very small window) at very low throttle angle".

Well, I'm not sure that during transition to ported vacuum if the is actually any venturi effect from the pinched airflow, and if there is if it's enough to measure or cause a spike in the ported vacuum vs the manifold vacuum. I think we are all pretty sure once past this point it's all the same, but I'm wondering if the transition is an issue regarding advance operation. Your thoughts? I don't get Hemming Motor News, could not find a link if you have one I'd love to read that article (learning op).

[JJorgensen52]

Originally Posted by mechanicalman

Not sure what set-up you have, but found this picture showing kinda where the dist vac hose goes. I'm going to do some research and maybe get back to you on the other (transfer slot).

http://repairguide.autozone.com/znet...5280252293.gif

That looks like what I thought:


The labels are hard to read, but the port facing forward from the baseplate is currently to the air cleaner, and the ported vacuum (pointed at camera) to the charcoal can.

It appears the charcoal can should be connected at the front port, the air cleaner at the rear port, and that leaves distributor to the ported vacuum.

The truck is bone stock 307 2 barrel

[mechanicalman]

Originally Posted by JJorgensen52

That looks like what I thought:


The labels are hard to read, but the port facing forward from the baseplate is currently to the air cleaner, and the ported vacuum (pointed at camera) to the charcoal can.

It appears the charcoal can should be connected at the front port, the air cleaner at the rear port, and that leaves distributor to the ported vacuum.

The truck is bone stock 307 2 barrel

It appears you have your charcoal can attached to where the ported vacuum for the dist would have been, and your distributor where the thermac goes (I think that's the air cleaner, but not sure) and the one at the top for a "TCS clean air tube"? I'm confused as to what a TCS clean air tube is and a thermac, hoping someone will chime in and help us. I know there has to be some 307 purists out there.

But if you want to keep manifold vacuum your set-up might be OK, not sure. I agree you might want to check your balancer, or you might have a carbon build-up lighting the fire early. I know a real good way to clean the carbon out, but on an old engine with questionable valve seats it might end up needing a valve job. The valve seals ever been replaced?

[mechanicalman]

Here's a cool link, Jorgie. OK I call you Jorgie?

https://www.google.com/search?q=port...gQsAQ&dpr=0.95

Not sure "transition slot" pertains to ported vacuum, seems to only have to do with idle and part throttle fuel circuit, but always willing to listen to good info from whatever sources.

[JJorgensen52]

Jorgie works for me

So I just got wrapped up rebuilding the carb (I have a separate thread going on that issue), which has improved a few things I was seeing, but:

1. Thermac (I would assume) refers to the thermal air control valve in the air cleaner.

2. TCS clean air tube I'm clueless on, but my carb does not have that port so no worries!

3. I swapped the distributor, Thermac and charcoal lines around so it's now using ported vacuum to the distributor.

I just took it out for a quick test drive, and seat of the pants tells me it's happier this way. I've no other way to quantify that. But improvement is good no matter how I came by it!

[mechanicalman]

Originally Posted by JJorgensen52

Jorgie works for me

So I just got wrapped up rebuilding the carb (I have a separate thread going on that issue), which has improved a few things I was seeing, but:

1. Thermac (I would assume) refers to the thermal air control valve in the air cleaner.

2. TCS clean air tube I'm clueless on, but my carb does not have that port so no worries!

3. I swapped the distributor, Thermac and charcoal lines around so it's now using ported vacuum to the distributor.

I just took it out for a quick test drive, and seat of the pants tells me it's happier this way. I've no other way to quantify that. But improvement is good no matter how I came by it!

You might try edging up the base timing now, but it might start cranking slow again. If it does, and you want my de-carbon trick, let me know.

[mechanicalman]

Originally Posted by JJorgensen52

Jorgie works for me

So I just got wrapped up rebuilding the carb (I have a separate thread going on that issue), which has improved a few things I was seeing, but:

1. Thermac (I would assume) refers to the thermal air control valve in the air cleaner.

2. TCS clean air tube I'm clueless on, but my carb does not have that port so no worries!

3. I swapped the distributor, Thermac and charcoal lines around so it's now using ported vacuum to the distributor.

I just took it out for a quick test drive, and seat of the pants tells me it's happier this way. I've no other way to quantify that. But improvement is good no matter how I came by it!

OK, found out what TCS clean air tube is, just don't know why they say "clean air tube". It's transmission controlled spark. My 72 had it, and it killed cold drive-ability. It consists of a third gear switch, an electrical activated vacuum switch, and a thermal sensor of what kind I don't remember but probably a metal temp switch. When the engine was cold, it did not allow vacuum advance until you hit 3rd gear, and it was supposed to lower tailpipe emissions. Just something on the diagram that's not on your truck.