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MG MGB Technical - '74 MGB sputtering constantly.....

I have a '74 MGB which sputters constantly while running, weak power while driving and will not hold idle and stall out. It smells like it is running rich. I've changed the plugs and wires. Any thoughts? Thank you. Austin.

How is the oil level in the carb dashpots?
David "btdt" Lieb
David Lieb

Low oil level in the carb dampers will only affect acceleration, not constant speed running. Could be absolutely anything - ignition, carbs or fuel supply. If the tach is fluttering it is ignition LT. If not that check fuel delivery which at the carbs should be at least one Imperial pint per minute and in practice closer to two, in a steady stream of pulses with minimal bubbles. If that's OK clip a timing light onto the coil lead and each plug lead in turn and watch the flashes. If one or more plug leads is erratic but the coil lead is regular (it will be four times more frequent than any coil lead remember) it is the distributor cap or rotor breaking down. If all of them are erratic but the tach is steady then probably the coil but could be the condenser. While the timing light is on 1 and 4 pooint it at the crank pulley and check the timing for value and wavering. If that's all OK I'd change the plugs, then do a full retune from scratch - valve clearances, ignition dwell and timing, then carbs.
Paul Hunt

I have to disagree with you there, Paul. If there is NO oil in there it WILL affect steady-state operation. Try it sometime.
David "I agree with the rest of it" Lieb
David Lieb

How, David, the piston is not moving? Oil only affects damping, which only happens when the piston wants to move upwards when the butterfly opens? Unless you are saying the piston is trying to flutter up and down all the time? It's not something I've noticed in 40 years with SUs, but stumbling on acceleration due to low oil is.
Paul Hunt

You say you changed the wires? Did you put the new wires in the right firing order? the order is 1-3-4-2.

Start with sparkplug 1, the one nearest to the waterpump. Then check the rotating direction of the rotor (there's an arrow on it or put the car in gear and push the car forward to turn the engine, and watch which way the rotor turns. In the direction of the rotor fit wire from plug 3, then plug 4 and lastly fit the one coming from plug 2.

My bet is that if you did know about the 1-3-4-2 order you fitted them the wrong way: clockwise or anti- clockwise. Don't ask how I now the symptoms.... (btdt?)
Willem van der Veer

I confess that it is not a problem you or I would tend to see, as we would not tend to try running our carbs with no oil. I agree that it should not affect idling, as there should not be any signal to the top of the dashpot (unless the butterflies are not closing properly), but there are pulses in the signal at steady state running and they could affect cruising.

I have not witnessed this situation myself, but I have had other people ask on other forums about similar symptoms and had them come back and relate that the dashpots were dry and that topping them up fixed them. Could easily have been a case of trying multiple things simultaneously and not really knowing what corrected the original problem. OTOH, there is absolutely no harm in topping up the dashpots and IMHO it should be done before trying your suggestions anyway.
David "yes, your suggestions are more likely to be his actual problem" Lieb
David Lieb

Thanks for the response, all. I woke up in the middle of the night thinking that the air filters may be dirty or clogged. Sure enough, since I store it in a garage separated from the house, it looks like a mouse crawled into one of the air filter housings and chewed holes in the air filter. That one carb was filled with crap. I pulled out everything I saw in the carb, put everything back together and the car started right up and runs fine. But, now the oil pressure is low (approx. 15 on idle, 30 at 2500 rpm) and white smoke is coming from the exhaust manifold area. During the winter a mouse got into the rear muffler and it was stuffed with crap. I replaced the muffler, tail pipe and connecting pipe to the rest of the exhaust right before these symptoms occurred. Could there be stuff up in the exhaust near the front? Could it catch on fire? How could all this affect oil pressure? Any additional thoughts would be appreciated.

White smoke "I surrender" signals from the mouse?

Seriously white smoke is usually water i.e. condensation in cold weather from a cold engine or a blown head gasket and coolant leaking into the cylinders otherwise.

Nothing to do with oil pressure which is going to be weak pump, leaking pump gasket, sticking releif valve, worn bearings, or simply an under-reading gauge which is thing that should be checked first.

BTW rotor direction is *anti*-clockwise.
Paul Hunt

The dashpots did have and always have had oil. I've owned 5 MGB's and am always religious about keeping the dashpots oiled. I'm just hoping I didn't get any of the air filter residue or anything up near the engine from the muffler before I replaced it. I don't know how that could happen, but something is definitely smoking out of the front exhaust area.
Any additional thoughts or recommendations would be appreciated.

Smoke just from the front of the exhaust system i.e. not from the tailpipe can be external oil e.g. from a leak or after work.
Paul Hunt don't think it might be residue from the air filter being chewed up and blown down the exhaust system and smoking? When I hit the gas in neutral I think there may be a bit of smoke coming out of the tailpipe as well. Could it catch on fire if that is what it is?

Mouse evil!
Mouse can and do go all the way up the exhaust and through open exhaust valves, and fill cylinders with dog food, nuts, mouse piss.
Also, if the carbs are off they can do the same through the inlets.
I've had it happen, on an MGB I had the carbs off for two weeks whilst waiting on parts. 5 lbs dog food in the inlet and cylinders, another ten blew out the exhaust after I fixed the engine.
A friend was a Triumph motorcycle mechanic and got a couple every spring where mouse had gone up the pipe and built nest inside a cylinder - extreme evil! Frequently meant new pistons, cylinders and sometimes heads.

If storing anywhere mouse might be, stuff oily rags in the exhaust and intake openings, DO NOT feed your dog in the garage where the car is!!!

The little buggers are evil, did I say? They will also eat your wires, brake hoses, rad hoses, upholstery, top, they LOVE modern HT plug wire insulation.
Buy cases of mouse deaders, cannon, laser ray screens, etc. Moth balls help, Tether your cats to the car and don't feed them.

The exhaust will usually clear up after blowing the garbage out, and while it could catch fire, it's very unlikely and well contained in any event (don't have the car backed in to the garage - it comes out like a flaming cannon). An advantage to straight through mufflers is that they are usually self cleaning; baffled ones can be irretrievably plugged.

Low oil pressure may be a result of fuel contamination due to driving with screwed up mouse killed carb, which might suck a whole lot of fuel in = extreme choke condition.

White smoke may be mouse piss soaked stuff in the exhaust, contaminated oil, etc.

Change oil & filter now.
It may clear up after 10 miles at speed, otherwise coolant leak as Paul suggests.

Death to mouse, and his friends chipmunk and squirrel!
(a damned red squirrel has filled one of my Magnettes with pine cone parts, and squirrel piss - and shredded upholstery!)

FR Millmore

Hey, don't forget their friends Rocky Raccoon!
I was one of the first to uncover this one:
David "the stench had to be experienced" Lieb
David Lieb

and thanks for the link to Thickos - my kinda guys!

FR Millmore

My scourge has been possums!

Nothing like a fearless rodent that will confront you, hissing and showing teeth, instead of running away like a mouse or squirrel. If he does go away, it will be a slow waddle, like he doesn't care a whit about you. Evil, stupid creatures. Right up there with roaches in my book.

*Blue* smoke when hitting the throttle after idling for a while is usually a sign of worn valve stems/seals or rings.

I don't think there is any chance of their being a fire inside the engine or exhaust, other than the usual 'fires' every time the plugs spark :o) Watch out for incandescent material being chucked out the back though as FRM says.

Other than that just run it, revving it, and see if it clears. If not watch the coolant and oil levels, coolant in particular would need to be checked when cold at about the same temperature of course.
Paul Hunt

Thank you for your comments FRM and Paul. You're right....mice are evil and I should have taken more precaution while storing it. I definitely will from now on! Oil and coolant levels are normal and I will change the oil and filter as suggested and check the results. I'm happy to hear that a fire in the exhaust is unlikely. I'll report back soon.
Thanks guys!

This thread was discussed between 18/07/2009 and 23/07/2009

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