# 8 valves and a carb: Lets talk MPG and dieseling!



## oRANGEJULIUS (Jul 30, 2006)

Looking for a little input on my current setup, any help you could provide would be awesome. 


What I am working with:

obd1 ABA block
Hydro counterflow head w/ 268 cam
mkI vac electronic distributor / icm combo no knock box
Redline Weber 32/36 Progressive DGEV


Important information:

13650 above seal level
fresh carb and jets, properly set float height, no air leaks, carter 5psi pump, regulated down to 3.5psi
Pistons / valves decarboned, 175psi across all cyl
Smog tested the vehicle and I am at 8%co at 2k rpm (pre cat) (rich mixture). Plugs however are reading good (light brown)
majority of driving is highway, (25% throttle or less)

My current jetting:











since this picture i have dropped my primary idle jet down to a 40, and upped my secondary to a 60. A 40 / 50 combo was giving me a dead spot when the secondary opened... the 40/ 60 eliminated it, however i also noticed i did not have a dead spot with the 50 / 60...

Goals:

Best fuel mileage possible / appropriate amount of power with this given setup with the lowest octane fuel possable
No dieseling / run on

The journey thus far:

Jets were picked based on what i could find for similar sized motors producing around 115hp (bmw, MG, etc) so that was my starting point.

Followed the procedure for setting the mixture screw and i am within the suggested limit ( 1 3/4 turn i think is where it sits currently) idle is set right around 800rpm, car runs very well, i am in the low teens as far as MPG is concerned. 

Not happy with the fuel mileage, i switched to the 40 / 60 idle jets that are currently installed. If i am understanding the operating concepts of this carb correctly, the primary idle jet is basically the major player when my throttle is just cracked open less than 20% or so. So the reasoning there was less fuel out where im at the most, better fuel mileage. Car runs the same with this setup, and im up into the mid / high teens. Noticing the 40/50 idle jet setting cause a lean spot, and had to jump to a 40/60, this leads me to think a 40 is about as small as i could go on my primary? 

With this setup:

Originally set the ignition timing running the vehicle on 87 octane. Dialed in, no pre detonation under load car ran fine, dieseled for 5 to 7 sec on shut down, every time on a warm engine. Attempted to lower idle, wont stay running below 800rpm. Jumped right to 93 octane, car does not diesel, bumped timing saw a slight increase in power. Currently running 89 octane, timing adjusted accordingly, car will diesel for about 1sec on shut down with a warm engine. No major change in fuel mileage during these fuel / timing changes

My other ABA engines (in heavier platforms to boot) on factory FI have all got me 30mpg give or take 4 or so. I understand my setup by nature is far, far less efficient than the factory fuel injection but am i out of the ball park to expect Low to mid 20's (MPG)?

Questions:

Those of you on a single down draft ( or heck, IC's, DOCE, etc for that matter) what are you getting MPG wise?

Do you have any dieseling issues? 

If so, what have you done to correct it? IS there any potential for this to cause engine damage due to this condition?

Anyone running 87 octane with success in a similar environmental condition?

Anyone with a webber progressive care to share there MPG / jet settings?

Any suggestions on maximizing my fuel economy?

Engine in question:


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## hardrocco (Mar 2, 2007)

oRANGEJULIUS said:


> Questions:
> 
> Those of you on a single down draft ( or heck, IC's, DOCE, etc for that matter) what are you getting MPG wise?
> 
> ...


I am running a similar setup in my Scirocco with a 2L 3A block with 10.5 to 1 pistons, counterflow GTI head
I am running a early Mk1 distributor (because I like the quick advance) with a Pertronix Ignitor electronic ignition.
I have the Weber 38/38 progressive downdraft carb on a Redline intake manifold

I drove my car up from CA to PNW and roughly calculated I got over 30 MPG. FYI, my car is running the 9A 020 transmission, I think I can get even better mileage with an FF transmission.

I am not running a knockbox so I fill up with 91 octane. Unfortunately, I didn't write down my carb information and it was 6 years ago so I have no idea what jets etc that I used.

I did have some minor dieseling when the car was running very hot, I added a spacer block between the carb and intake manifold to reduce the temp a little. 
Another thing that causes dieseling is small air leaks causing the car to run too lean. 

I am curious what pistons you are using, what compression ratio you are running w/o a knock sensor. If you had no problem with 91 octane, maybe that was part of your problem. I don't think you can run 87 with an engine over 9 to 1 compression.


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## oRANGEJULIUS (Jul 30, 2006)

hardrocco,

Thanks for the info!

Ok, so I am on the right track thinking I should be achieving higher MPG numbers than what I currently am. 
I have a 3/4" polly/ hard rubber spacer between the carb and the manifold, left this info out from my original post. This is a redline manifold that has ports for coolant to pass through, I currently do not have this feature hooked up.
My engine is right around 10.2 :1 cr, so your correct I should leave 87 octane off the table for this engine and stick to 89 +.


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## hardrocco (Mar 2, 2007)

oRANGEJULIUS said:


> hardrocco,
> 
> Thanks for the info!
> 
> ...


I also have the redline intake with the hot water ports and ran it for a while. The ports are for icing, but I figure my car is not a daily and since it is a counterflow head, the exhaust will warm up the intake enough, I never had any problems with icing.

I am not sure regarding your jetting, I am wondering if you have it backwards with the smaller primary jet and larger secondary. 

Also, I think retarding your timing to use the lesser gas is going backwards, you should maximize your power and then try to find a way to get better gas mileage.
What car are you running this on? Is this an Audi? My Scirocco is only 1700 lbs FYI.


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## oRANGEJULIUS (Jul 30, 2006)

hardrocco said:


> I also have the redline intake with the hot water ports and ran it for a while. The ports are for icing, but I figure my car is not a daily and since it is a counterflow head, the exhaust will warm up the intake enough, I never had any problems with icing.
> 
> I am not sure regarding your jetting, I am wondering if you have it backwards with the smaller primary jet and larger secondary.
> 
> ...


I picked up the Weber carb tuning guide (book), and spent a good deal of time looking over quite a few small displacement forums for various cars that typically run the 32/36 as a replacement carb, and the most common setup was to have the secondary main jet 1 or 2 steps larger than the primary main. If I am understanding how these carbs function correctly, this looks like the way to go. My ownly hang up is, the carb is set to lean best idle well within specification ( so this means i am at least in the ballpark with my primary / idle jet selections) car runs fantastic, plugs read fine, but the MPG is dismal... even refraining from opening the secondary. So i am thinking it may be time to keep down sizing the primary main, but i will have to adjust the secondary as well so i dont end up with a huge flat spot... try to go as lean as I can. Ideally, i would spring for a wideband setup and a big box of jets and have at it, but that would total to be more than what i have in the car.

I would agree with you on the timing / fuel situation. After the car was built, i dumped 5gal of what i had in the shop (87) and set the car up to run correctly with it. I am now 4 tanks through on 89 and it does run much better (advanced timing).

Engine is is a vw fox, guessing somewhere around 2300lbs?










Thanks agein for the suggestions.


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## hardrocco (Mar 2, 2007)

If your car is running fine, do you smell any gas or does it smell rich at all?
You may want to re-adjust the float settings maybe a little less than the suggested setting.

Also, I happen to read a post about the 32/36 carbs needing heating intakes (although mine seems to be fine) the article is for aircooled. Not sure how hot your engine bay is in the Fox.

http://www.aircooled.net/making-weber-progressive-dfev-work-aircooled-vw-engine/


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## oRANGEJULIUS (Jul 30, 2006)

She is running well, does not smell rich and the plugs verify. I am just at a total loss with regards to the poor MPG. I put a huge return spring on as well, so i can realy meter my input... Float height is adjusted to spec currently. 

Please dont take this the wrong way, i thank you very much for all the helpful input so far, and i am by no means an expert here, the float height this just dictates the ammount of fuel that goes in the bowl. proper height allows the bowl to stay full so the fuel is there when requested (metered by the main jets) so less fuel in the bowl wont = less fuel through the jets, but could cause some starvation under heavy acceleration / extreme cornering? Anything may be worth a shot at this point... am i thinking of this right? 

Interesting article on the air cooled engines... we are in the 30's just about daily now so this could be something. Maybe the fuel is not atomizing correctly due to lack of heat? Driving me nuts.

Thanks for the help so far :thumbup:


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## hardrocco (Mar 2, 2007)

Merry Christmas OJ, sorry for the slow reply, been pretty busy.
I am not an expert, just forever learning 
The first carb I put on my current toy was a 32/36 DFEV. It was in the trunk of my car, I put it on and the car run better than the original stock carb which was very tired. My fuel mileage was OK, but since I was going to do an engine swap with a refreshed engine, I decided on getting a new carb. In my build I decided to try the 38 DGAS as my head was ported. I feel that my setup ran better than the used 32/36, I am not sure if it was because the carb was worn out.

I know what you are thinking, that the main jets should meter the fuel from the bowl, and yes if the fuel level is too low, you may have other problems. But there are other orifices in the carb to assist in transition that may be affected by the float level.

According to the Weber manual, if your car is running fine but fuel consumption is excessive, you should check the following:

Needle Valve not seating
Leaking or damaged float assembly
Faulty automatic choke
Incorrect float adjustment

My understanding is the float adjustments and fuel pressure are quite critical in the tuning of these carbs to run properly with decent fuel consumption

Anyways, I hope this helps, good luck with it. Let us know if you figure it out.

Cheers :beer:


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## beastinisgr8 (Jun 12, 2013)

I normally get 25+mpg that's city and highway combined. I run mine at 2.5psi fuel pressure. Mods are exhaust,header,TT276 cam and adk cam gear.


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## oRANGEJULIUS (Jul 30, 2006)

hardrocco, 
Merry Christmas! No worries on the reply, I can relate to the busy season! Once things calm down a, i am going to pull the carb back apart and further investigate the float / needle, needle seat and see what I can come up with. Everything checked out when I assembled the carb last, but to be honest, my inspection of the floats were nothing more than visual ( never dunked them to check for a leak), and the inspection of the needle / seat was also visual... worth looking into. I have verified the electric automatic choke, and system is properly adjusted and working as designed. Thanks for the tips! 

beastinisgr8,

Thanks for the info!, i think i am going to follow along with your fuel pressure settings and dial mine back to 2.5psi Mine was set at the upper threshold of what is recommended by Webber, and who knows if my holly regulator is 100% accurate, I could be in fact past where I need to be.... depending on the tolerances of the regulator. I will give this a shot.


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## oRANGEJULIUS (Jul 30, 2006)

Update:

Last tank of fuel (89 octane) netted me 18mpg, a fair amount of idling, average temps in the 20's F. this is before all of this:

Lowered fuel pressure regulator down to 2.5psi.

Split the carb, dunked the floats (floats are good), everything appears spotless inside, no wear on the needle valve or seat, and verified proper seal. I decided to bump the float height 1mm to see if this has any effect.


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## The Dubbernaut (Feb 1, 2010)

Whats up with the car? Did you ever get to the MPG you were wanting?


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## oRANGEJULIUS (Jul 30, 2006)

MPG stayed about the same; no real changes. I recently pulled this engine and placed it in a rabbit truck. Changes: diesel trans, a dual outlet exhaust manifold, 170 deg. thermostat / fan switch and a larger rad. Ill report back once i can log a few miles with the car


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## NoviceMk2Mech (May 3, 2017)

How's the mpg in the rabbit truck so far? I've looked through this post a few times to try and grab any pointers about my setup. I really enjoy the color choice on the block and accessories. Never thought I'd enjoy gold like that. Also love touches on the fox like the shark mouth. 
I've had problems with my Weber 32/36 DFEV for a bit. It stinks, literally, I'm sure it's running to rich and I go through gas like no other. Here's a link to a post I created a bit ago 
https://forums.vwvortex.com/showthread.php?t=9249791#/topics/9249791
Thank you in advance. And I hope things have gotten better with you're mpg.


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