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MG MGB Technical - poor gas mileage

Can anyone tell me why I am getting such poor gas mileage. I seem to only get around 150 miles to the tank full. Everything seems in order. Timing is fine, idles perfectly, engine sounds good. I did notice, after driving a friends B, that mine seems to be lacking in torque. Pick up is a little slow. It feels a little sluggish, like I was pulling a trailer or something.

Any suggestions greatly appreciated.

Ken
70 B
Ken Harris

Hi Ken.

Assuming that the engine is in good tune, it could be something like binding brakes or maybe a tight bearing somewhere in the drive train.

Does it roll easily when pushed by hand ?.

Are any of the wheels hot after a run ?.

HTH.. Don
Don

I was experiencing poor gas mileage when I purchased my MGB last year. Did all the normal things, checking brakes, tune up, adjust idle, etc, etc. It still didn't improve. Just by chance I was taking a drive to a car show on Cape Cod and had printed directions from Mapquest. The round trip was to be about 150 miles. When I returned I was surprised to see the trip odometer only registered about 110 miles. I took the car out to a measured mile and found that the odometer was not registering accurately, about a third less miles than traveled. (Which isn't a totally bad thing since my classic car insuarnce limits me to 2500 miles a year, I know what you are going to say, that's not enough miles to drive.) By the way, I havn't fixed it yet.
Good luck,
John
John

Ignition timing...and in particular dwell angle on your points? I reset my points the other week...got them wrong apparently and my B performed really poorly...it seems I lost the setting upon retightening the pinch screw...ended up with 40 degrees of dwell instead of 50...made a world of difference once set correctly.
P J KELLY

I will say dwell angle as well. I was getting about 13 mpg until I checked my points. dwell angle was well out. Timming was OK but car was sluggish and didn't pull well under load.

Reset to correct value 66.67% (60deg) and now getting 23 mpg (I have hole in my exhaust which I need to fix) normally I get 26mpg on average and the cars acceleration is much improved.

It could also be timing related. The book values assume the car is relativley new. Over time engine wear will effect the deg BTDC. Mine should be 13 deg BTDC but I have to set it to about 17deg BTDC (72 B with 120K miles on the clock) to get good timimg.

Andrew
andrew.horrocks

You sound like another candidate for a distributor rebuild. I bet 75% of all MGBs on the road could use distributor repairs of one sort or another. Check the points first, but if things don't improve, consider a rebuild.

Jeff Schlemmer

This is why I cannot stay away from this BBS. So much help available when needed, and most, have experienced the exact same problem at some point.

Great info, I will be checking those points tomorrow, and I will let you know the results.

Ken
70 B
Ken Harris

Check your fuel lines. Those old rubber lines may have cracks and minor leaks.
Kimberly

Also check your float valve needles. It may also be that you have a bigger problem (sorry) fuel burn rate is used on aircraft as an indicator of engine health, if it drops suddenly it is telling you something has changed.
S Best

The biggest problems we see on a regular basis are usually ignition and poor carb setting (in that order).

Everyone's advice about the distributor is right on.

Check also that the cap and rotor are not worn.

The wires are a good quality wire and not in poor shape. I recommend MSD wires or Moroso Blue Max, because if properly made, will outlast the car and give optimal performance forever. They do not cause radio interferance.

Spark plugs should be in good shape. We use NGK BP-6ES.

The biggest problems we see with carbs are simple adjustment problems. Usually one float is high and the other low, and then someone has adjusted the idle and jet heights trying to compensate for that, which sends everything off. Once, we saw a pair of SU's where one was missing a dashpot spring and often we see them either out of oil or somewhere in-between.

Start by getting the float level right and follow your manual from there (if you don't have a manual it's probably time to get one). Don't listen to the carbs to set the balance, use a proper airflow meter instead.

Cheers,

Sean
Sean Brown

Ah, so much info to glean, and apply to my B. Thanks to all who dont just read, but add as well
t Wall

I got rid of the points problem on my 73 B by going with an Igniter eletronic ignition system, been so long i can't remember but it's been virtualy trouble and maintence free, also use the Lucas sport coil. I believe it's 40,000 volts. Well worth the investment if you like to drive your MG alot. Tend to get about 27 mpg no matter how i drive it.
LUVMYMG

Ken

I filled up after a 200 mile drive today and calculated 34 mpg (equiv 27 US).

Barry
73B
B.J. Quartermaine

I'll bet distributor. After a head gasket replacement I deceided to do things right. I set the dwell and then timed my car with an timing light. It started and ran fine but seemed to lack mid range power and gas mileage was poorer. What I found was the light advance spring in the distributor was so weak that even at an 600 RPM idle it was giving me some advance. In timing with the light according to the spec's I was actually retarding the timing. I went back to static timing and then adjusting by ear. It runs great and I get 25 to 27 MPG at highway speeds 65-70 non-overdrive. And yes my harmonic balancer was good I checked it out when I was doing the head gasket. I wish I could get all those little parts such as dist springs it's the little thigs that make all the difference.
Charles O'Brien

Ken. The important things have been said by others. Check for holes in the gas tank, lines, bad diaphram in the fuel pump and forwards to the carbs. (Dave DuBois has a good article on what you should expect from the fuel pump at www.custompistols.com/ under the MG, then "articles" section.)

After that, look to the ignition system. Paul Hunt, many years ago, mentioned the advantages of the stroboscopic timing light having the dial feature which allows you to check the amount of overall advance very easily. If you do not have one, set your engine to top dead center and make a second mark, using model aircraft paint, at 20 deg BTDC. This will, in most cases, allow you to see what you are actually advancing at most rpm ranges.

If the distributor is worn, John Twist, at University Motors Ltd, as an excellent reputation as a rebuilder. Les
Les Bengtson

This thread was discussed between 01/06/2005 and 04/06/2005

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