Weber Carb performance

[Eric_C]

What kind of performance (gas milage) can one expect for a 1980 or so MGB that has a single downdraft Weber carb? /ubbthreads/images/graemlins/confused.gif

 

[schutnik]

I'm getting 25-30 depending on how I drive. That's with a 38DGES.

 

[Eric_C]

Thanks for the reply! Wow! If I am calculating it correctly I am only getting around 12-15 miles, so clearly I have some adjusting to do. Any suggestions? Did you adjust your own carb?

 

[schutnik]

I did. But I just followed the weber instructions. Its still running a bit rich, so I think I'm going to adjust it again, this time using a vacuum gauge...

 

[Eric_C]

I am so amazed at the difference, is 25-30 highway miles? If so, do you have an idea about your in-town mileage?

 

[schutnik]

In town is about the same for me. But, I don't drive in traffic much. Where I am, and where I typically drive, there's very little stop and go, so driving around town means driving about 35-40mph and stopping at the occasional stoplight or stopsign.

 

[Eric_C]

Thanks again. There must be something way out of adjustment in my car. I will let you know if I get around to it soon.

 

[Guinn]

I am still not sure what I get with my 78B and a DGV carb but it seems to be around 22, mixed town and country but mostly country, mostly less than 10 miles per trip. Be sure your engine is tuned, tires properly inflated and lead removed from foot. The best indication of proper tune is spark plug color. Be sure you are using the proper plugs. Also check compression. Under 90 +- 10 could be a culprit.

Guinn

Guinn

 

[ecutr6]

I have ridden with you!! Get your foot out of the carb, and come to a complete stop at those stop signs. By the way, I will take you up on the windscreen volunteering!! See you Monday. On the way to Yoders'.

 

[Eric_C]

You have a point Ron, today I will try a regulated 50 miles trip to see the maximum I can get out of my car and will report back, w/o the lead foot!

 

[Eric_C]

Thanks, I had not thought to look at the plugs, but I believe I am running rich.

 

[Eric_C]

I just did a road test today, ran the car for 57 miles,around 60 mph, mostly in overdrive, all highway and then checked the gas useage and found I got 18.56 mpg, that seems below what your saying. Any suggestions?

 

[Jay_Nickell]

I have a 1980 with OD, Weber 32/36, great compression numbers, and I get 22.5 mpg all city miles, burning 89 octane. I drive my car like someone is chasing me, and I'm not sure someone isn't, so why take a chance?

 

[Guinn]

Eric, you haven't said anything about how well the car runs, idles and accelerates. Also, does the exhaust smell rich when warm and idling? Black tail pipe? What are you using for an air filter?

If you haven't already tuned per this document, you should do so. It really is simple. You do need a fairly long slot type screw driver. Mine is about 8". If the car won't idle with the idle screw not touching the stop, screw it in the minimum that lets it idle at all.
Document: https://www.webercarburetors.com/ppw/html/tech/carburetor_set_up_and_lean_best_.htm

Guinn

 

[Eric_C]

Jay, Thanks for your reply, from the sounds of it your cars performance it what I expected from my own, therefore I think it is time to find the problem.

 

[Eric_C]

Thanks Guinn,
I rebuilt my carb about a year ago, use a foam filter that came with a custom filter and cover from Moss Motors. Have around 140 compression on each cylinder. It does smell gasy but all my MG's have smelt that way, perhaps that is why I haven't taken the hint. The tail pipe is black and what I have noticed is during the night driving when I step on the accelerator it looks very dusty in the rear view mirror, cannot see it during the day. Car idles evenly more or less around 800-1000rpm. Thanks for the link I am pretty sure I know what the problem is now that I have gotten the various replys.

 

[Eric_C]

Guinn,

I replied to you message but it I did something wrong, did not show up. Wanted to say thanks as I think I will be able to solve the problem now and will definately look at the link. Eric

 

[Guinn]

Let us know how it does after you re-tune it, Eric. By the way, old mechs like my uncle Bud, a race car mechanic/driver back in the 30's and 40's, always smelled the exhaust before trying a new tune-up. Probably told him more about the engine condition than I would ever know. Might be why he only lived to be 86! /ubbthreads/images/graemlins/lol.gif

Guinn

 

[Simon TR4a]

Hi Eric, I hope you don't mind a Triumph guy jumping in on the MG board!
There is very little that can be adjusted on Weber carbs without changing internal parts, main jet, emulsion tube,air correction jet, pump jet etc. Only when these items are correct for the application will the car run properly and get reasonable gas mileage.

You probably need to take your carb apart and note down the tiny numbers on all the parts, then compare with the recommendations for your car on a website like Teglerizer or Pierce Manifolds.
A cutaway diagram of the carb is helpful, and again, can be found on the internet.
I do not have much knowledge of your carb, as my wifes Spitfire has a 40mm DCOE, but I think the principles are similar.Perhaps someone else with a similar setup to yours can give more detail.
Simon.

 

[DrEntropy]

Leaves me out... All DCOE, all the time.