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realistic expectations for fuel mileage w/carbs

I am currently having my carbs rejetted. They're 40 idfs, with the stock jets and venturis that Weber supplies with the kit for a 73 2.0L 914, installed by the PO ( I'd change back if I knew what a pain this was). I was probably getting 10-12 mpg overall with previous jets ( WAAAY too rich for street driving). I'm aware that a rich conditon can wash down the cyl walls, shortening life of the motor. I have the stock dist, recurved for this motor, and probably the stock cam and lifters, etc, stock exhaust, fresh rebuild. When this thing is jetted properly, what would be the range of MPG that one can reasonably expect for normall street driving with this setup? ( I was expecting 20+. Is that realistic?)
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Old 04-09-2003, 01:19 PM
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I'm not an expert, but I have the same type of setup as you do. I'll bet I get 20MPG on the highway doing 60. In the city...well I'm sure it's quite a bit lower. Carbs always seem to run rich from what I've heard here. The relative lack of fuel metering compared to FI (I don't know how efficent the 914 FI was but it was surely better than dual Webers) must play a big part in why we tend to get fairly poor gas mileage, I'd think.

Experts feel free to chime in and squash me like a bug if necessary!
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Old 04-09-2003, 03:11 PM
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I have same set up as you w/ a set of DRLA 40's. Best mileage I have seen is 20 mpg on the highway. Around town I get 15 or 16 mpg.

Daily driver 98 4x4 Suburban gets 13 around town and 17 on the highway. Got to love modern fuel injection.

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Old 04-09-2003, 03:31 PM
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I had well-tuned 40IDF's on a 2.2 for years. I got about 15-17 in the city and about 22 to 24 on the highway.
Old 04-09-2003, 03:34 PM
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do you have bosche oo9 distributor or fuel pressure regulator?
Old 04-09-2003, 03:44 PM
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I am running Bosch 050 distributor & a rotary pump, no regulator.

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Old 04-09-2003, 03:58 PM
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I have one of those cheesey round, chrome regs.
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Old 04-09-2003, 05:13 PM
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I have Weber 44IDF's and discovered I can fill up, drive about 100 miles to the track, drive laps throughout the day (1-2 hrs of track time), and then drive 100 miles home...on one 1 tank of gas. I have no idea what mpg it works out to, but it's good 'nuff for me!
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Last edited by campbellcj; 04-09-2003 at 07:21 PM..
Old 04-09-2003, 07:19 PM
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I have an stock injected '73 2.0 and I was wondering about mileage too. I don't think mine does any better than 20 on the highway--haven't verified this yet, but it sure does need to be filled up frequently.
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Old 04-09-2003, 08:07 PM
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my tailpipe is black, sooty

My tailpipe looks black and sooty, andI always thought that a white tailpipe was indicative of a good fuel mixture. Is this baloney?
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Old 04-09-2003, 08:32 PM
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My 44s witha 34mm venturi, 125 main jet, 200 air and F11 emulsion get me 38MPG on my 2056cc 912E engine. Thats running 85-90MPH most of the time with stock gearing. This engine is very efficient, with 9:1 static CR, tight deck, balanced chambers, larger intake valves, split duration symmetrical lift cam, but no port work. Makes 120BHP(dyno) all day long.

Try resetting your float heights, and playing with vent sizes. larger vents are much better for midrange and top end and slow down the velocity in the carb, for more volume- a good thing for MPG.

Stock 40 IDFs come with a 28mm vent, thats okay for a 1600 engine, but not for a 2.0. Try a 32mm vent, 125-130 main, 175 or 200 air and an F11 emulsion.

No matter what you should get 25-28MPG with carbs on a stock engine. Most of my 2270 engines average 30MPG, even my 2316 making 180 ponies will get 30 if I drive it like a sane person (that has only happened once)

Timing also has a huge impact on MPG, sometimes more so than the jetting in most cases.....
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Old 04-09-2003, 09:04 PM
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Jake, those are pretty amazing numbers.
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Old 04-09-2003, 09:47 PM
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Sometimes it amazes me as well...Its all in efficiency with a built engine, but stock is far from efficient, especially with the FI cam still installed. Itry to calculate peak Torque in my 914 engine recipes to occur at 4,000RPM, this puts the engine at its peak efficiency, where it should use the least amount of fuel at an 85MPH cruising speed, and still have torque if you stomp the throttle.

The other key is keeping the engine cool. I have found that keeping the heads constantly at 325 degrees and below gives a huge boost in MPG, another reason to invest in better cylinders!

Even my old 74 Bus that weighs 5K pounds with crappy gearing gets 27MPG running 75MPH on the highway(thats 4200RPM) The engine is a 2109"Powerstroke" and has CIS injection. Before I added the CIS I averaged 20MPG.
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Old 04-09-2003, 10:00 PM
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guards,
You are using stock cam/lifters, right? Shouldn't... The stock cam is made for FI. I know, I know; it works. But not as good as it could.
Jake, what cam/gear do you prefer?
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Old 04-09-2003, 11:17 PM
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I recently did a topend rebuild. The lower unit was fine, so I left it. It would be difficult to determine if I still have the stock cam w/o cracking the case. I'm the 3rd owner, the first guy set it up for autox, did the carbs, ss brakelines, heaters, exhaust, 14" ats wheels, konis. The next guy drove it and did nothing mechanically but painted it red and parked it for 14 years
I unstuck the brakes and motor and drove it and dropped a valve seat, so I did a clutch, trans synchros, brakes, rebuilt starter/alt, carbs, and got 15" wheels, so now I really dont want to double my investment by buying a crate supermotor. I just want to make it run well and drive it, it's a fun car, solid and it looks very good.
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Old 04-10-2003, 06:32 AM
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Back when mine was running, stock 2.0L, 40 IDF's, 28mnm venturis, and replacement stock cam, I was getting an average of 20 mph. The carbs where still not quite right and I know now it was the venturis, change you carbs to the specs listed by Jake and try to figure out a way to isolate the vibration in the linkage that causes the accelerator pumps to constantly dribble a little. In addition to the carbs, read as much as you can about timing and you should be happy with the resulting milage.
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Old 04-10-2003, 12:38 PM
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Quote:
Originally posted by chrisreale
Jake, those are pretty amazing numbers.
That's putting it diplomatically.

The day I see a worked T4 with 44IDF's going 90 mph that gets 38 mpg, it's probably going to be driven by one of those Raelian clones.

What do the skeptics say? "Extraordinary claims require extraordinary evidence"?
Old 04-10-2003, 02:03 PM
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http://www.germanlook.com/Forums/showthread.php?s=&threadid=1692

Thats the link to a test I did on a 1400+ mile trip......(yes, I have nothing else better to do than keep averages on my excel spreadsheet in the laptop as cruise along)

I fully understand people to question it, it seems extraordinary, even to me, but it does happen. Saying that I average 90 is an exaggeration, but cruising 80 all the time is not. I run along at 4K RPM until I see a cop for a 3 hour freeway trip atleast once a week going to see a Blonde......Thats how this engine has racked up 18000 miles since september 2002.
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Old 04-10-2003, 02:15 PM
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BTW, Swapping to Royal Purple 10/30 full synthetic got me from 32 to 38 as one change.

Doubt me if you want, just don't call me a liar.
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Old 04-10-2003, 02:18 PM
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Quote:
Originally posted by Jake Raby
BTW, Swapping to Royal Purple 10/30 full synthetic got me from 32 to 38 as one change.

Doubt me if you want, just don't call me a liar.
Hey, you've got all the figures there, but I'll believe it when I see it. I owned a 914 with a 2.2L motor built by Garrettson's w/40 IDF's, ran like a top. Best mileage I ever got on a highway trip was in the mid 20's, just like everyone else who I've known who had one of these beasts. 38 mpg on 44IDF's is way out of anything I've ever heard or seen.

You've got to admit, it's a pretty incredible claim.
Old 04-10-2003, 02:39 PM
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