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MG MGB Technical - Hard Starting

Hi all, just finished going through the archives and have some ideas but hope that the combined expertise on this sight might help. My 1974 MGB GT with stock configuration is back on the road after a 3 year rebuild. Initially it ran great and started easily although the fuel gauge no longer works. I noticed that the fuel tank was leaking so I purchased a new tank (correct vented tank for the 74) and a new sending unit. Since replacing the tank I have had an annoying problem, it starts beautifully on a little choke when cold and runs great with no miss and plenty of power BUT if I stop for a few minutes or even an hour and try to restart the car it cranks and cranks and if I press the gas pedal to the floor it will start but there is a smell of gas and it will run really poorly until I blip the throttle a few times and then it runs great again. I have pulled plugs and distributor cap and all is well although the points may need replacement.

Any ideas what else I should look at ( also the gas gauge still doesn't register but heat gauge works fine so it probably isn't the voltage stabilizer...just another thing to check out.)

Thanks
Brian
Brian Smith

You may want to check the float height in the carbs. Sounds like the fuel is bubbling out of the jet and down the carb throats from heat expansion. Do you have the heatshield installed for the carbs?
John H

John, the heatshield is in place. Strange thing is that nothing has changed other than what I have indicated above, it just started doing it. Could a condensor cause this problem and if so wouldn't it also affect the fast running?

Brian
Brian Smith

The condensor is a possability but normally it would not want to run at high rpm as you mentioned. The fact that you need to hold the pedal to the floor to get it to start would indicate flooding. Next time with the engine hot turn on the key but don't try to start it. Listen for the clicking of the fuel pump, if you get a couple slow clicks and it stops, the carbs are likley fine. If you get several fast clicks when first turned on or it continues to click, you are losing fuel somewhere. A slow click once in a while is also normal.The ignition system could be the cause as items like ignition coils like to die when hot but normally would not operate again until it cooled down.
John H

OK, replaced points, rotor, condensor and plugs, pulled air cleaners (stock) and checked carbs. So far the hard starting is still in evidence. The fuel pump ticks a few times when starting it first thing in the morning and with choke it fires right up, it is only when the car has been run and I have stopped and then come out to start it again that the problem has started. The fuel pump is not ticking when I turn the ignition on so I assume that the floats are full and I haven't seen any evidence of the fuel overflowing into the carbs.

This happened suddenly so it has to be something simple and may be a carb float but before pulling the carbs I was hoping that someone had another idea???

Thanks
Brian
Brian Smith

Have you done the first test for a non-starter which is clipping a timing light onto the coil lead and each plug lead and watched for flashing while cranking? Whilst on 1 or 4 point it at the crank pulley and check the timing.

Could be hot failure of the coil, although an hour should eliminate that and any other heat-soak effect, except possibly sticking advance in the distributor. Nevertheless it is now time to go back to first principles and check the basics, and in fact this should have been done before you started spending money. Much better to find a loose wire first, than spend a shed-load of money and *then* find the loose wire ...
Paul Hunt 2

Paul

I agree but the problem is that it fires up and runs beautifully from cold. It is only after driving the car and stopping that it is really hard to start, requiring that I pump the gas pedal. It will then sputter and pop before clearing itself and then away it goes. This is a problem that just started. I drove this car daily for 6 years and then after retirement pulled it off the road and rebuilt it totally. Once back on the road it ran fine until a couple weeks ago.
Brian Smith

Well, on the one hand I can only repeat that eventually one puts logic aside and goes back to first pronciples when all else fails, and on the other hand what have you got to lose?
Paul Hunt 2

Strange world isn't it. I have just caught the same problem, but after my trouble with the carbs earlier on (solved by Paul) I am still carefully looking at the carbies. I have been through all of the above and even used two different distributors with no luck. I am now thinking of new carbies.

I have just acquired a new coil which I will fit when I have found my oil filter which kindly fell off yesterday when I was doing 60mph. Very scary.

I am reading this thread with great interest.

Tony
Tony Oliver

Thanks all, as of today the problem appears to be solved. We had a run today and everything went well until I tried to start the car to head home and it really didn't want to start. Finally got it going and drove home and figured that I better get into it. So I checked the compression and it was good across the board. Then pulled the carbs and took both of them apart and cleaned them up, floats (HIF) were good and they were clean inside but the needles have the viton tips but theu too looked good. Got everything back togather and tried to start it again and it just wouldn't start but a strong smell of gas. I took the recirculating hoses off and cranked it again and the front carb had gas poring out. At this point we took the fuel line off the front carb and blew out the line (in the carb) with compressed air and whatever was blocking the carb cleared and it now starts and runs just like its old self. Always something new and different but glad to be back up and running again. It is hard to have everyone looking at you when the car won't start.

Brian
Brian Smith

This thread was discussed between 09/04/2008 and 20/04/2008

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.