Tuning after EGR hackjob delete (5 Viewers)

[YukonCruisers]

Starting on a refurb of a 40, the PO has "deleted" the EGR.

Is there a good thread on tuning post delete?

I don't want to get into a debate about reconnecting everything, I know if left alone EGR is fine, I don't think I have all the bits now, so am looking to just tune it up.

Truck itself is in amazing condition, April '75, no bubbling at the rear fenders, rockers in good original condition, no rust through on the floor pans etc. I already did the rear sill to 2x2 replacement, swapped out a broken rear leaf. I have to change the clutch master and will swap in a disk brake axle up front.

 

[bhsdriller]

I didn't do anything to mine just go through a lean drop setup on it and has been fine
Adjust timing with it as well if needed

 

[YukonCruisers]

Ah, maybe it needs a good carb clean or rebuild then. will spray in some cleaners and pump some seafoam through,

thx

 

[bhsdriller]

Also make sure everything is plugged that needs to be and no vac leaks

 

[DesertFJ40]

Screw the egr emissions crap.

To get your Fj40 running good:


Adjust the valves of the engine

Set your timing. The book tells you to set the bb at the "7 degree pointer mark." I push mine a bit more and set it at the edge of the window as I'm advancing it. So I think thats like 10mmHg

Get a vaccum advance distributor and hook that up. There's people here that will tell you "you need a special ported carb" to connect it. If you don't have a ported carb (like me and don't want to spend a lot of money to have someone do it for you), you can connect it to manifold vaccum. Theres an old article about a race car driver and he goes into the "science". Anyway, manifold vaccum was the best in his experience. Ive had good experience as well, zero issue. Others will say you're going against the "Toyota gods".

If you can, also get an earlier style carb. Suposedly the 1974 one is the best one. But any of the double barrel carbs from the early 70s are good. They got mechaniccal secondaries instead of vacuum acuated ones.

If you get an early carb, take off all that vaccum egr stuff off. Choke breaker, I forget what else. It's not needed.

you might need to get slightly larger carb jets depending on your elevation. Today's gas sucks and the original jets are ussualy too lean for today's gas. The only way to get around this is to use ethenol free gas. Then the carb works as it should. It's an easy fix to do if you decide to change out the jets

Set your idle screw either by ear or vaccum gauge. You can connect to the highest vaccum port and change your idle and see at what point you get the highest reading. If you do it by ear, turn the screw in so it sounds like it's about to die. Then back it off until it runs good. Then keep backing it off until it start to run rough in the other direction. I think it starts to "pop" and you won't notice any further increase I rpm once you reach a certain point. Zero in on the adjustment until it runs as smooth as you can possibly get.


Don't forget to cap off any unused vaccum ports as well. There should be one at your distributor, and a few around the carb, and any that were ocne connected to you egr

That should be it :]

 

[charliemeyer007]

I like straight mechanical advance, let the rpm of the engine determine the advance. +1 for setting the timing just going out the window in the summer - try that in the winter and it will kick back and eat the starter, maybe more if you aren't lucky.

 

[dmaddox]

My first thought to ask was....how is it running now? What are the symptoms, behaviors, etc? To be able to understand what direction to go.

 

[YukonCruisers]

Thanks folks, I will start to dig into it soon.

@dmaddox - current syptoms are very hard starting , despite fuel in the bowl and good spark. Occasionally responds well to a quick start vapour. Once running idle is a littl high, but fine. Stays started once running. When I first got it, the tank barfed so old fuel through the carb, so it may jest need a good cleaning there or a rebuild.

@charliemeyer007 ; @DesertFJ40 - I haven't checked the timing and advance as yet, but I think in order I will do the timing, clean the carb, maybe rebuild the carb. Altitude is a little high here in Whitehorse at 2200'.

Appreciate the suggestions folks, I was mainly concerned that something tied to the EGR pull was the issue, sounds more like a good tuneup and good to go, thx

 

[dmaddox]

EGR/desmogging may only create vacuum leaks. I agree with you here, @YukonCruisers - get the carb cleaned/sorted and the idle circuit blown out so you can confirm a clean jet during idle. Then go after timing. Valves could likely use an adjustment, but that wouldn't cause these issues, just improve power/efficiency as you know. The vacuum leaks/egr removal - after you get a good idle, even if a tad high, spritz around the base of the carb and around the manifolds to see if vacuum sucks in the cleaner (and the rpm will change) - and then address the vacuum leak. After that, will be easy to dial in timing (assuming the carb is squared away). Good luck.

 

[65swb45]

Get a vacuum gauge and get baseline measurements before and after each step you take. It’s actually quite rewarding to see numerical improvements.

Compression test
Adjust valves
Second compression test
Set timing
Lean drop carb

 

[Pighead]

Set your timing. The book tells you to set the bb at the "7 degree pointer mark." I push mine a bit more and set it at the edge of the window as I'm advancing it. So I think thats like 10mmHg

Get a vaccum advance distributor and hook that up. There's people here that will tell you "you need a special ported carb" to connect it. If you don't have a ported carb (like me and don't want to spend a lot of money to have someone do it for you), you can connect it to manifold vaccum. Theres an old article about a race car driver and he goes into the "science". Anyway, manifold vaccum was the best in his experience. Ive had good experience as well, zero issue. Others will say you're going against the "Toyota gods".

You're saying, then, that manifold vacuum is as good as ported vacuum for your vacuum advance distributor? I'm afraid I'm going to have to disagree. I do not have the benefit of an old story with a race car driver who has "science", all I know is from hooking 2 vacuum gauges to one carbureted F/2F block and driving it around for a few months. I've always had an indash manifold vacuum gauge, then I T-ed into the line between the carb and dizzy with another gauge. Now i know, sorta, how much vacuum my particular engine pulls from where and when. I don't pull a lot of ported vacuum. None at idle but it goes up as I ask for acceleration. But only goes up to maybe 8 or 10"/Hg. with a heavy foot, more usually 5 or 6" with casual driving. If you hook manifold vacuum to the dizzy, you'll be at full advance while at idle and your advance would decrease as you applied throttle. And where my manifold vacuum is weakest, climbing a long hill in 4th, my advance will be least as well. Which might keep pinging down, now that I think about it. I wonder if it might be better to run without vacuum advance than get vacuum at the wrong time. And how much vacuum does a dizzy diaphragm need to give how much advance? That's something we need to know.

And the spot where the BB disappears is more like 17* BTDC than 10mmHg.

 

[pb4ugo]

Vacuum advance is sort of unique to automotive engines, because they are not under load all the time. This is a 2f manual.

 

[DesertFJ40]

@Pighead
You got it right on the head :]
Okay so I had to find that article (actually a forum board) where I read about it. One of the guys name is Dave Rey. He was mechanical engineer that worked for GM doing ignition systems and created his own version of an HEI distributor. The other guy I can only find thst his name is "JohnZ". Another GM engineer. I'll try and paraphrase it more, hopefully tomorrow, since it's getting late where I'm at..... But I will post his reasoning behind manifold vaccum advance being superior to ported carb vaccum on the next post below.

Apparently though, the ported vaccum is best only for engines running the the egr or emissions systems. I can't explain it all right now, and the posted article from the forum board may be a bit confusing. But, what you observed running you vaccum gauge and seeing the drop when you give it gas to verus when you're at idle goes exactly to what this guy is saying. Have a read!!!

And here's the original forum post. The part we are wondering about starts to get answered around the halfway mark of what I posted below
Manifold vaccum johnZ

I also like your gauges. Very mad max like

 

[DesertFJ40]

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.