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Wed Jul 02, 2014 11:09 pm

Hi my brothers 1973 super beetle, since we bought it, has had terrible gas mileage (Like 12-15 mpg). It has the stock 1600cc engine, 34-pict-3, vacum advance distributor, and from what i can tell no vacum leaks on the intake or carb. I have meticulously cleaned the carb and all the jets. No matter how much adjustment, it still gets crap for mileage.

I notice though that when you give it gas it has a slight delay, but then revs high. My thought is the Main is too big. And the idle, seems we can set it to idle nice when warmed up, but crap at cold (or vice versa). We've set the automatic choke to the specs, and it opens and closes.

So im wondering what some people have their jets at for Denver altitude, 5280 ft. Or if anybody has any ideas it'd be appreciated.

Wed Jul 02, 2014 11:39 pm

Stock jetting on the 34PICT/3 for sea level in a 1600 with a vacuum distributor should be idle 55, main jet 127.5, air correction 80, and power jet 65. That's for straight gasoline. If you have E10 or similar, that changes things.

Alcohol contains about 40% USED oxygen, so 10% ethanol (E10) will run the engine 4% lean. Each main jet size alters the mixture by about 2%, so for E10, you need a main jet 2 sizes (4%) larger - 132.5 for example (at sea level).

THEN consider altitude. For each 5000' or thereabouts, you need a main jet one size smaller than the calculation above, since there is less oxygen in any given volume of air.

For Denver, that means when using straight gasoline, you need you need a main jet of 125 or just maybe 122.5 (1-2 sizes smaller than 127.5 since you are a little higher than 5000'), and you might even find that a smaller 50 idle jet might help too, since the engine runs partly on the idle jet up to around 2500rpm.

If using E10 or similar in Denver, you need a main jet of 130 (one size smaller than 132.5), and stay with the 55 idle jet.

Make sure your timing is correct too. If you have a double vac distributor, it uses 5ATDC (that's AFTER TDC) set at idle with all the vac lines hooked up (the retard line is the one closest to the distributor body and that goes to the vac port low on the rear of the carb. The vac port on the distributor furthest from the distributor body is the advance line and it connects to the left side of the carb, near the throttle arm). If you have a single vac distributor, the rear port on the carb (the retard port) must be blocked off, and the timing is set to 7.5BTDC, either set static (engine off), or at idle with the vac line pulled off the carb and that's blocked at the carb, leaving the line open at the distributor.

Setting the choke is always a little hit and miss, and it will never work just right unless the carb mixture set up is close to ideal. Sometimes it's a compromise to get it to work just right in both winter and summer. Try setting it so it JUST closes with the engine stone cold. If it holds too much choke as it's warming up (sooty exhaust) then open it up a few degrees. If the engine starts to stumble after a few seconds driving, the choke might be opening up too fast, so close it a few degrees more.

And VW Owner's Manuals always recommend driving off straight after starting the engine: DON'T idle it. This ensures that the engine warms up at about the same rate as the choke opens up. If you idle it, the engine stays too cold as the choke opens, so you end up driving on a cold engine with insufficient choke for a mile or two.

At sea level with straight gasoline you should get around 24-26mpg (US gallons), so in Denver you should get around 22-24mpg.

With E10, at sea level you should get around 22-25mpg and in Denver around 20-23mpg.

Hope that helps.

Thu Jul 03, 2014 6:07 am

That's a great explanation from Aussiebug. I live 60 miles north of Denver and drive by 72 super beetle sometimes to Denver and back. It has all original setup with 127.5 and 55. The air correction is 75. Last trip I took two weeks ago, mostly 70mph got me 33mpg. Usually get at least 30mpg. When I check the plugs they are still showing slightly rich.
So you do need to check your carb and the timing. Timing does matter. Also make sure you don't have hot air blasting to your aircleaner fromthe preheated. Sometimes when the flap doesn't close properly this will happen.
If you need any help drop me a line, I've worked with these for over 20 years now.

Thu Jul 03, 2014 11:40 am

Thanks guys, we'll give the carb, and timing a once over. And who knows maybe the PO put in different jets from stock.

Thu Jul 03, 2014 3:00 pm

80z air correction was only used on Ghias in the USA, never on bugs.

I'm at that altitude, and did find one of those jets once and tried it in my 1600DP Baja and it did bump up the fuel economy but I could feel it reduced the power... this was years before I had any kind of oil temperature gauge but I suspect it bumped that up too... and my bugs have always run hot at this altitude to begin with.

VW actually used 130 main jet for some years in the USA. However I'd go with 127.5.

Its been 24 years since I got my first 1600DP Baja bug... The only time I ever got that bad of fuel economy in that car with a 34PICT-3, is when I left it sitting at fast idle for long stretches in the winter, or when the choke heating element stopped working.

I can't imagine just plain driving giving you under 15MPG. Even stop and go city driving I'll get around 20MPG in my Baja.

I never get over 30MPG unless I'm driving slow on back roads or in the mountains... and I log all the fuel I buy.

-Andy

Thu Jul 03, 2014 3:57 pm

you should be around 47-50 idle and 120-122.5 main at 5k'.

Thu Jul 03, 2014 7:13 pm

Living at about 6500 with the stock 1600 generally get 25 ~ 29 just kicking around and on the hy 30+. Stock tranny and tires.
You just need to dial it in more. Time it with a timing light and watch the timing advance.

Thu Jul 03, 2014 7:26 pm

Check the action and diaphragm on your accelerator pump. If the adjustment is off you might be squirting fuel into the throttle body when you just want to open the butterfly a bit. If you have a hole in the diaphragm you could be dumping gas into your intake manifold when parked.

Fri Jul 04, 2014 2:26 am

glutamodo wrote: 80z air correction was only used on Ghias in the USA, never on bugs.

I'm at that altitude, and did find one of those jets once and tried it in my 1600DP Baja and it did bump up the fuel economy but I could feel it reduced the power...

-Andy

SO what DID the US 34PICT/3 carbs use Andy?

From the second para I'm guessing the stock air correction jet was a little smaller than 80 (75?) since you say trying an 80 reduced the power a little. A larger air correction jet will lean the mixture in the middle to high rev range.

John Connolly's suggestions are interesting and since we all consider him a carb guru...worth following. Similar but at the leaner end of my suggestions.

I'd certainly try them if you have straight gasoline, but John doesn't say what fuel he's made those recommendation for, and I've heard before that Denver has/had Ethanol fuel.

Fri Jul 04, 2014 7:19 am

Ah, I thought one of my charts had been posted to this thread but I was thinking of a different recent thread. This the Beetle-only USA-only chart:

Straight gas is hard to find anymore. When I have used it in the last couple of years, I never noticed any difference in power or economy.

Sat Jul 05, 2014 4:34 am

Thanks for the chart Andy.

Here in Australia, straight gasoline (petrol) is still a normal option.

Most servos (gas stations) have
91 RON octane normal unleaded (straight gasoline)
95 RON Premium unleaded (straight gasoline)
91RON E10 (10% Ethanol)
55 Cetane Diesel (Plenty of diesel cars here as well as trucks)
LPgas (which is about 120 RON octane and a very popular alternate fuel).

And a few stations have 94 RON E10, 98 RON E85, and 98 RON Utlimate straight gasoline (higher density too, so more miles per tank in cars with an ECU).

And there is even a few CNG refueling stations. No hydrogen that I'm aware of yet!

More choices than you can throw a stick at.

Sat Jul 05, 2014 8:22 am

If you are running E10 jetting with E0, you are not going to gain any fuel economy. The economy is gained when you jet properly, and need 15% less fuel than E10 jetting.

The fact is that E10 is a complete rip off. The engine will go farther on 9 gallons of straight gas than 10 gallons of E10 (which has 9 gallons of gas, and 1 gallon of ethanol). It's all about politics and payoffs, and we get to suffer with significantly reduced fuel component lifespans.

glutamodo wrote: Straight gas is hard to find anymore. When I have used it in the last couple of years, I never noticed any difference in power or economy.