JET-A-VATOR Experiment

[vamram]

*I had posted this in the 50 MPG thread a couple of days ago, but decided it would be better served as its own thread. I'll be updating it as I go.*

I'm trying to improve the mileage I get on my '72 Super.

After reading through various of the MPG threads, I got curious and bought a Jet-A-Vator from Gene Berg Enterprises last week. It's the 30% unit and I bought also a 135 main jet for the carb, upping from the "default" 127.5 I had, on their recommendation.

The Jet-A-Vator comes w/longer studs since it sits between the base of the carb and the intake manifold. I didn't install it on my German Solex 34/3 because I didn't want to mess w/the Solex's base studs and this is a carb that runs really well. It was rebuilt for me by Volkzbitz, and I use it w/a matching DVDA distributor.

So instead I took a 3-year old Euromax 34/3 (only 1 year of use, been in a cabinet for 2 years), opened and cleaned it, replaced the accelerator pump diaphragm, adjusted the choke, and set the three screws (volume, bypass, idle/accelerator arm) per Bentley instructions. Then I installed it, w/both vacuum hoses connected. Car cranked right up and stayed on as soon as the bowl got enough gas in it.

After taking it on the first 20-mile Jet-A-Vator cruise, i pulled over because the idle after warming up was too fast. I re-adjusted the carb, w/the setting ending as follows: volume screw is 1.75 turns out, bypass is 1.5 turns out, idle is good and steady around 900.

Today, I drove it again and decided to check the timing and re-adjust the carb. I've got it timed at about 0-2 degrees TDC/BTDC. Even though I'm running w/a DVDA, I find that at 5* ATDC it doesn't run as well and starts hard. I advanced it the point before where it pings under load and then set the idle.

After adjusting the time, I re-adjusted the carb. 3 turns out of the volume screw, 1 out of the bypass. Idle is steady at 900.

Btw - the engine is an AE code case, stock 1600dp setup, stock muffler, heat exchangers, working flaps and t-stat, correct oil bath filter. Only non-factory item on it is the CB Maxi-2 oil pump/filter combo.

One note - I've always had a dead spot upon acceleration w/this Euromax, when it was new and again now that I put it back on after a thorough clean ing, replacing the accelerator diaphragm and installing the bigger main jet. When new, I had the dead spot even w/a new Pertronix SVDA distributor. So my guess is it's just the nature of a shitty chinese-made carb w/a bad accelerator pump or intake vacuum port. I'll eventually swap the Solex back in, w/or w/out the Jet-A-Vator.

Tank is full, I'll report back on the mileage over the next couple of weeks.
Most of my driving is city so it won't be great, but I know what I was averaging previously because I've kept a log of every single fill-up since I bought the car 2 years ago.
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Eventually, "we are what we pretend to be.’”
Give peace a chance - Stop Russian-Soviet Aggression!!

'74 Super 9/16 - present, in refurb process.
'73 Super - 6/18 - Present - Daily Driver!
'75 Super Le Grande...waiting it's turn in line behind '74.
Click to view image
Save the Supers!!

[Quokka42]

Gadgets like the jet-a-vator were popular when fuel prices surged in the 70s. Another gadget that worked about the same was a bolt placed under the pedal to stop you putting it all the way down. That's really how it works, it restricts flow into the cylinders. If you were a lead foot it will save you some gas, if not it won't.
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There has only ever been one man who was perfect, and they nailed Him to a cross.

[SoCalJes]

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Jesse
71 Ghia
______________________________________
Just because it didn't come that way, doesn't mean it shouldn't have.

[Marv [UK]]

Sorry, but I think you've set your timing all wrong.

Disconnect your vac hoses from the canister and plug them with a screw. Time to 7.5 BTDC and go from there. Taking 5 to 7 degrees off your timing has added it onto the top end. If you're getting 30 degrees at 3000 revs when timed correctly, you'll now be getting 37 or so which is too much. No wonder you're pinging.

Timing is a good indicator of tune. If your engine likes more timing it's running too rich. Go down a jet size

You'll likely get much better mpg just from this simple procedure.

Personally, I'd ditch the vacuum retard anyway. Run just SVDA and the distributor won't be fighting itself
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The opinion of the author as expressed does not always reflect that of the author nor does he extend any apologies or assume any liability or responsibility for its content or lack thereof or for any lack of humour of the reader of any content at all, anywhere, ever. The reader agrees to all risk by reading it and is advised that any ‘issue’ is theirs alone as they chose to read it.

[Bruce]

[Marv [UK]]

[vamram]

Thanks for the input. I'm not a lead-foot so if the gadget won't add mpg w/my typical driving, then it will go on the shelf when i'm satisfied that it's just a gimmick. I'll give it a couple of tankfuls at least, what the heck.

As for the timing - if I go 5* ATDC I have to also have the carb running really rich to get the idle right, and cold and hot starts are both hard - i.e., the engine cranks a few turns before starting up. As I have it now, it starts right up on the 1st hit of the key, whether it's 0*F outside as it's been many a time this winter, or today's balmy 50-something.

I will check the total advance w/the hoses both connected and disconnected report back.

Also, to clarify, the engine is not pinging under load. I drove it, and then retarded it to the point where I wasn't getting pinging anymore. Doesn't land at 5*ATDC when I do it this way. I started timing it this way after reading a several other threads where that was recommended by much more experienced samba folks than me, some of them mechanics. Doesn't mean it's correct but...seemed like it was worth a shot.
_________________
Eventually, "we are what we pretend to be.’”
Give peace a chance - Stop Russian-Soviet Aggression!!

'74 Super 9/16 - present, in refurb process.
'73 Super - 6/18 - Present - Daily Driver!
'75 Super Le Grande...waiting it's turn in line behind '74.
Click to view image
Save the Supers!!

[Boolean]

Don't set timing at idle even if it says so in a book. Disconnect all vacuum hoses from the distributor and set fully advanced timing to 28-30. You may have to rev it beyond what same book thinks your advance curve ends at, but that's fine.
Just raise rpm until it is fully advanced. Adjust, and check mileage.
I would not connect the retard diaphragm afterwards. Just plug that hose.
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I strive for perfection. Excellence will not be tolerated!
Build thread here:
http://www.thesamba.com/vw/forum/viewtopic.php?t=529379

[Quokka42]

A DVDA won't advance at all with the vacuum hoses disconnected.
_________________
There has only ever been one man who was perfect, and they nailed Him to a cross.

[Marv [UK]]

[vamram]

Ran out of time to check/re-time. But - in 79 fill-ups over the last 2 years I've averaged 22.15 MPG, mostly city driving. Seems pretty shitty to me. The highest I've ever managed is 31.52MPG, which I think was on last Memorial Day weekend's round trip to the BugOut in VA.
_________________
Eventually, "we are what we pretend to be.’”
Give peace a chance - Stop Russian-Soviet Aggression!!

'74 Super 9/16 - present, in refurb process.
'73 Super - 6/18 - Present - Daily Driver!
'75 Super Le Grande...waiting it's turn in line behind '74.
Click to view image
Save the Supers!!

[Boolean]

The reason behind the "adjust with hoses disconnected blah, blah" is that an old or in our world unknown distributor that may have been badly repaired or modified or just worn - will not have the correct advance curve. The important part of the curve to us is at load and higher rpms. That generates the power, longevity and fuel economy.
The reason we are recommended to adjust at idle is partly because that is the important part for ancient pollution control, and partly because those recommendations refer to new distributors in perfect order inserted in new factory stock engines.
It's been a while since then.
_________________
I strive for perfection. Excellence will not be tolerated!
Build thread here:
http://www.thesamba.com/vw/forum/viewtopic.php?t=529379

[Eaallred]

I'm running a dual vac distributor in my 64 w/ bastard 40 horse and 30pict-1

Left off the vacuum line for the retard, only connected the advance. Timed to total of 32 degrees with vacuum line off, then reconnected the advance vacuum line.

Runs great.
_________________
Eric Allred

You have to remember something: Everybody pities the weak; Jealousy you have to earn.

[vamram]

The D-vac can is a refurbished one, has a sticker on it from the refurb business identifying it as so. So it may be a safe assumption that setting the timing per Bentley at the 5 ATDC at idle is probably long a thing of the past for this dizzy.
_________________
Eventually, "we are what we pretend to be.’”
Give peace a chance - Stop Russian-Soviet Aggression!!

'74 Super 9/16 - present, in refurb process.
'73 Super - 6/18 - Present - Daily Driver!
'75 Super Le Grande...waiting it's turn in line behind '74.
Click to view image
Save the Supers!!

[helowrench]

[Quokka42]

OK, OK. I was confused. This has been pointed out, how about getting back to the original topic?

If you want perfection talk to my ex-wife. Me - I have been wrong before, was wrong in this instance, and will be wrong again in the future. Sorry to disappoint you.
_________________
There has only ever been one man who was perfect, and they nailed Him to a cross.

[mark tucker]

[vamram]

I'm sticking w/my '72 German Bosch DVDA, both hoses connected. I'll try and dial the timing in based on the advice you all have posted, then back to running w/the jet-a-vator to see if it's just a gimmick gadget. Although I was under the impression that items coming from Gene Berg Enterprises where as a rule not gimmicks.

Btw, the DVDA i'm running is VW 113-905-205AJ.
_________________
Eventually, "we are what we pretend to be.’”
Give peace a chance - Stop Russian-Soviet Aggression!!

'74 Super 9/16 - present, in refurb process.
'73 Super - 6/18 - Present - Daily Driver!
'75 Super Le Grande...waiting it's turn in line behind '74.
Click to view image
Save the Supers!!

[Juanito84]

[ps2375]