Another Mileage Thread

Just wondering what everyone's thoughts are about my mileage.

After my engine rebuild last summer, my mileage has gone way down and I'm only getting about 18MPG. Before the rebuild, I was getting around 22. My mechanic tells me that 18 is about right and that anything over 20 is too lean, but I see lots of you posting that you are getting 25 plus! So what's up?

My engine was a typical Vintage 1915, but with 40IDF Webers before the rebuild and I was getting around 22MPG back then. It is now a 2054 with a 7.95 compression ratio, wedge cut ported and polished CB Performance heads and matching intakes, with a W110 cam and a header.

The timing is set to 28 degrees at 3000RPM and as I posted in another thread, Larry Jowdy just tuned my ignition and adjusted my carbs, but we did not have time to get inside the carbs or play with the main jets.

The car runs great, but I would love to get it back up to at least 20MPG. What do you think?

Troy, You know my running gear. Around 17 mpg. In the process of rebuilding carbuerators(weber 48s). Hope to improve on gas consumption.

Bob

Troy--with an 8 gallon tank that MPG limits you---maybe you have a larger tank?

I had the Vintage 1915 engine in my Speedster ---I guess similar to yours byt with Solex-Kadrons. I saw 27-28 mpg highway commoly going interstate speeds and was always happy with that. The Kadrons never gave me a bit of trouble---never.

Now, with a larger Type IV engine and Dells I'm averaging exactly 25 on the highway which is very acceptable to me even with an 8 gal tank.

Are the 40 Webers on the large side for a 1915?

I'm no expert but hope one will chime in here for you but I did want to offer the above thoughts.

Good luck with it!

CB Performance 2110 with Weber 44's and 3:88...... I get an easy 25MPG if I keep my damn foot out of it! 30 on highway with top & side curtains.
Just Sayin'

My Spyder had 1915cc CB engine 44IDFs Freeway flyer tranny and 205R70 rear tires and delivered over 30 mpg on the interstates and 25/27 cruising the back roads.... And if I bent the gas pedal, 20/22..... Danny P. gets good milage from a bigger engine than that....

I have the same engine that Leon had in his Spyder, and I get ~25 around town when I'm gentle. I averaged 27-28 on the way home from Carlisle.

Same 1915cc and same 44IDF Webers.

I forgot to mention that I have a Freeway Flyer transmission. The comments are all interesting, but I was also hoping for some suggestions about what might be causing the poor mileage.

Troy..... It would sound like way too large idle and / or main jets.... If you do not have the Weber manual from CB Perf., get one.... It will make sorting out the problem easier.... As with ANY problem, its difficult to diagnos if you can not be there with it.....

Your tail pipe is a soft sooty black even after a blast on the freeway, right??

I'm always a bit surprised that every time this comes up, everybody talks about looking at the main jets.

Next time you are driving, observe how far you are pushing down the accelerator- it'll be "just barely". That's idle jets. You won't be into the mains until you're foot goes down a whole lot more, and the engine speed picks up quite a bit.

The order for setting up carbs, which is pretty much universally agreed up (over on the Samba, where such things are discussed at length) is: 1) idles 2) airs 3) mains. This flies in the face of the Tommlenson books (yo, DUDE!), which advocate doing airs last- but seems to make a good deal of sense.

Everybody is worried about going too lean, so we're all running around pig-rich. I'd bet a dozen donuts that 95% of the hobby is running the jets that came in the carbs. I was, until I bought a wideband A/F and about $500 worth of jets.

If you run CHT gauges, and look at the A/F while setting stuff up- it all becomes clearer. Most of us are running idles at least 2 sizes too big.

The only 44IDF tune-up issue that I've had in some 24,000 miles was float levels. I'm certainly no expert but my "wrench" seems to be.
He found that my floats were out of sink. He adjusted them correctly and everything got better.

Troy: You might check and post here what size idle, mains and air jets you have, then you can compare to what others are running.
Doug

No doubt you need to set up those carbs and jet properly. First verify your fuel pressure, then make sure the floats are set up properly, then what size venturi's/idles/mains/and air jets are you running? I would re-check all of the jets with a gauge since they may have been reamed out and are larger then the size they are marked. From there work on the idles then airs then mains as discussed above. Like mentioned above there is a lot of info on the samba serch for a wideband jetting thread. John at aircooled.net is a good source for advice and sells the webber jets-go to him he will steer you in the right direction after you pull your jets and check your venturis to verify what you are running.

Hey Troy,

I have 2332 type 1 engine and I used to get only 14 mpg in the city no mater how gently I drive. I play a bit with the idle jets, however, that is more because I had a lot of problem off idle, it just doesn't run well and the mileage stayed poor. One day my electronic ignition decides to quit on the 405 in the morning rush hour when I was driving my kid to school. So I replaced whatever module that I had in the car with Computronix electronic ignition. To my surprise my mileage increased to around 19-20 mpg without any change of any jets on my carburetor.
Now I am using CB Magnaspark digital distributor because I hate the slight stumbling due to the retarded timing at low rpm with the mechanical distributor, and I am still able to maintain 19-20 mpg in the city and I have a lot less problem with rough running at low rpm that usually is attributed to clog idle jet. I am now convinced that the spark timing have a lot to do with the mpg of any engine and how the engine runs.
So maybe you want to check your ignition system.

Good luck

Eddy

So Stan.
Do I understand you correctly? If I'm not depressing the gas pedal very far, I'm getting most of my fuel delivered via the idle jets? I paid attention to that today and I really don't have to depress it very much to get up to speed. Also, I checked my mileage again today after all around town driving and it was 14mpg. My 19mpg mileage included some freeway driving.

Messing with the jets on my carbs is something that I don't think I am up to doing, but I don't know anyone in this area that really is an expert at it.

I've had both Compufire and Petronix breakless points in my distributor, so I don't think that is the issue, but maybe a better distributor would help.
Troy

Troy,
Mark Harney is a wiz with Webers and wrote several tech articles about the IDF.
Unfortunately he is no longer in the business, but his website is still up sporadically. I just checked and it's working.
My advice? Get on the site and COPY all his tech articles.
You won't regret it.

http://www.carburetorclinic.com/weber_tech.htm

Troy-

You understand that correctly- the idles are where you spend 95% of the time driving around. Fortunately, the idles are the easiest of the jets to set up (if not to get to).

In order of things- the float height and fuel pressure need to be correct, or all kinds of funky stuff is going to show up. If you've got a CB electric fuel pump- the pressure's right. Setting up the float height is nowhere near as hard as it sounds. The link Terry posted should have an article.

After you are sure the floats and fuel pressure are OK- look at a couple of your idle jets, and order a set each in the next two smaller sizes. After you drop down a size, you'll need to reset your mixture screws for "best lean idle" (the procedure is probably in one of the articles in Terry's link). Check your sync (buy the more expensive "snail" synchronizer from some place in the back of "Hot VWs"- the "uni-syns" are not sensitive enough), and head out. You're engine will likely be snappier, and get better mileage.

Everything Stan says is correct, but before all that, you need to be sure your valves are all adjusted properly, COLD, and your carbs are synched. Then you can start to play with the carbs. I agree about float height and fuel pressure also, along with spark. I ended up going to a crankfired distributorless system and that cured my off-idle stumble, along with careful accelerator pump adjustments.

Everything mechanical needs to be certified as good before you even look at carbs.