MGB: Backfire on acceleration

Hi everyone !!

I got a timing light and went out to the garage to check the timing on the 79 and it was set at 20 degrees @ 1500RPM. I went ahead and backed it off to 10 degrees like the haynes says to. Well the engine sure does run cooler now (little below half way on the guage) But now I dont have any power and it backfires when I give it throttle. I'm wondering if I should advance the timing some more or what? (If I could only aford to take it to a MG garage, but then again, where is the fun in that?)

Thanks to all for being so patient with a dumb newbie.

Chris Chapman

Backfire on acceleration usually means a lean condition!! Oh, you are not a dumb newbie!! But I am sure Tom will be along soon so maybe a few more particulars such as stock cam?? Stock carb??

Engine and carb are all stock. Dizzy has been replaced with a points system and I'm not sure how I find out what it is without removing it from the engine.

Backfire is loud and sharp (good compression?) causes mucho black smoke to pop out (very embarasing for my little B. she thinks she is not supposed to pass gas)

Mine did that and I changed the condensor and she smartened right up!! But because you messed with more than that.........!! Anyway, condensors are cheap like dirt!! I actually switched to the Petronix system, and it works great!! I was a little leary about doing it, because a couple of people had said that the Lucas Sport Coil and the Petronix didn't work that great, but no probs!! Tom QWarren has run that set-up for 15 or 20,000 miles!!

From what I can gather she runs good other than that backfire. That leads me to think you have carbon buildup somewhere and when it's hot it ignites unburned gas as it enters the exhaust. Extra gas enters the engine faster than the engine can burn it upon initial acceleration and in your case something is igniting it as it is exhausted. Hot carbon is about the only thing that can do that. About the time she pops the engine has gained enough speed to burn all the gas that's coming in after that. I'd try a can of Sea Foam through the intake, that will get the carbon out. I think that will fix it.

john is it possible that the timing is to far retarded even though he set it to the specs

Not much chance of that. His temp is running exactly where it should be and the only things I've ever seen cause a bickfire in the exaust is carbon or a burned exhaust valve and it runs too good for it to be a valve. It's carbon, you can take that to the bank. Even a burned exhaust valve will seldom cause it.

Get a compression reading. If that is good, set the timing using the static method, use Sea Foam in your gas and see where you are then. A solid tune-up then and setting your carbs would be a good idea.

Well, lesson learned. After adjusting timing make sure you have all of your plug wires including the coil wire(my problem) firmly seated. Otherwise you can get missing and backfires !!

Good for you! It's the little stuff that gets you down.