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MG MGB Technical - MGB won't start
My neighbour has an MGB and asked me to have a loog of his car because he can't get it running. Starter turns engine over but doesn't seem to ignite.
I've pulled off the fuel line from carburettor and I had fuel flowind out. Fuel does have a very low pressure.. if I cover fuel line with my finger and turn ignition on then off then gently release my finger then the petrol sprays out for a second.
I think fuel looks good for me.
Next step was to check spark. Ignition lease are 1342 wich I think is correct.
Spark plug removed and checked for sparks. They all ok.
Next step was to remove air filters and spray some easy start while starting.
The car started and was running ON easy start as I was keep spraying it (5 to 10 seconds). Once I've stopped adding easy start the engine stool.
Then I've removed one spark plug again and tried to start with one plug undone looking for smells of petrol through the plug hole. No petrol there.
There is fresh petrol in the car by the way.
The car has twin su carbs.
Is it possible they have both failed/clogged in the same time?
Please, Can anyone recommend what to do next?
|What year is the car?|
Does it have the separate float chambers on the side of the carbs?
Had the owner been doing any work on the car before it failed, or did it just stop working?
|Dave O'Neill 2|
|Most likely, the carburetors have some foreign substance in them, probably old gas that's turned to jelly. RAY|
|Car was in the garage for years. Off the road no tax no mot.|
|As been said if it's been standing for a while fuel could be iffy. As Ray suggests make sure float chambers uncontaminated. Top up individual chambers with new fuel.|
Failing that it's back to basics: Make sure static ignition timing about right; points clean and gapped; substitute condensor if you've got a spare; make sure carb pistons both fall after a few secs with a click; make sure battery is earthing properly.
|P A Allen|
|New fuel in the tank is no guarantee that it has reached and is passing through the carbs.|
After cranking for a while with the choke out you should flood the engine, i.e. a removed plug should smell strongly of fuel if not be wet.
If no fuel smell then it looks like fuel isn't getting through the carbs. After being parked up for years the float valves could be stuck or blocked, or other gunge in them or the jet pipes (if HSs i.e. float chambers on the sides) as Ray suggests.
If HSs then it's very easy to remove the float chamber lids and see if there is any fuel in there. If not, no fuel is getting through the float valves for whatever reason. If so, then it's not getting up the jets.
With the lids replaced, the air cleaners removed, and the piston raised with a finger-tip, by blowing in the overflow you should be able to see fuel bubbling up from the jet.
HIFs (float chamber under the body of the carb) are trickier to deal with as really they need removing and inverting to remove the 'cover' and inspect the float valve and jet. After that you should really replace the O-ring that seals the cover. Again blowing in the overflow should push fuel up the jet, if there is any in the float chamber. If you can blow air through then there is no fuel in there. If you get no fuel and can't get air through then the jet is blocked.
|A couple of good guides to getting your car going - thanks to the mgaguru. |
|Something else you can check - make sure the caps (core plugs?) are still in the ends of the balance tube of the manifold, i.e. the cast pipe that runs across the manifold in line with the engine. Years ago I was just leaving work when the engine appeared to backfire and then cut dead on me. AA man could get it to run on easy start but not on it's own. I had a light bulb moment and checked the plug at the far end of the tube and found it was missing, so all the engine was doing was sucking air through the hole and not through the carbs. I then found the plug sitting on the bulkhead!|
It's pretty unlikely I know - but it has happened!
|Dave Smith GT|
|Was the choke pulled to start it?|
|Thanks for the replies.|
The carbs are the ones with the reservoirs underneath. Most probably they are clogged up somewhere or the float valve is stuck. Carburetors are simple devices not much can go wrong there.
Just one thing to ask. These HIFs do they have separate float valves or only one for the two?
The only thing I can't understand how come thet have failed in the same time.
I went over today to check it further but my neighboug has already phoned a classic car specialist and so he didn't wanted me to do anything.
I'll update once I find out what was wrong with it.
Dave Smith GT.. funny enough one of the plug was just about hand tight on this car as well.
|The carbs are fully independant.|
If the car wasn't used for years, then the concept of both carbs failing 'at the same time' doesn't really apply, one could have failed some time before the other.
Whilst the HS is incredibly simple, the HIF is more complex as it has additional passage ways and valves - particularly for cold-start enrichment - that can get blocked, that the HS doesn't.
Another demerit for the HIF is that you can't see the enrichment process, only the cam turning a spindle, you have to hope that is opening the valve. On the HS you can visibly see the main jet lowering and rising.
This thread was discussed between 08/06/2016 and 11/06/2016
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