MG MGB and MGB GT Tech Talk
as posted earlier my 78mgb was running rough,have zenith carb,installed manual choke.set timing,new plugs,filter.seems to idle allright but when i go to drive it,it seems to have no power,plenty of oil in the dash pot.what could be causing this?thanks
Easy check for a plugged converter or internally failed muffler. Just go buy a vacuum gauge and run the line into the cabin so you can read the thing while under different loads. Most of the gauges have color coded segments that relate to different problems. You will know in a moment if the exhaust tract is at fault.
They are not expensive and a decent gauge will out last you and your dog and it will be of help in many other ways during it's tenure in your tool box.
Jack
While it may be all of the above, it also may be the rubber diaphragm in the Zenith. Have you checked it or replaced it recently? If it has a pin hole or slit in it the symptoms will be exactly as described. If you recently replaced it, did you make sure and put the tabs on the diaphragm back in the correct slots? The tabs make sure you have the piston oriented properly.
replaced the diaphram,i think it is a timing issue because when i try to set it up on it's timing i have to put it all the way retarded to get ten degrees from tdc.this is with the vacume advance plugged.car starts and idles @about 1000rpm's.could it be the points?i have them gapped @15.checked for vacume leakes.i'm going to replace cap,wires and rotor.i'm going to replace the dizzy over the winter.thanks for all replies
It could be a bad condenser. Even new ones can be bad. Otherwise its possible that your plug gap is off. If its set properly on one lobe, it may be off on another from a slighly bent shaft. I see that all the time, even on new distributors. If you can put a dwell meter on the car while its running, you can check the average gap (dwell) and increase/decrease it as needed.
I see you stated new 'filter' - long shot but if you did not put the air filter back on the car the ZS carb would produce this scenario. Ask me how I Know - I spent a full weekend test driving with no power under acceleration. Turns out that without the air filter on the carb the mix is all messed up and the car will run like a sick dog :)
HTH, John