mgb wont start? any ideas ???
Discussion
Hi guys, recently bought a mgb project but cant get the thing to start.
So far:
New fuel tank
New fuel lines and filter
Stripped down and rebuilt the su's today and they are all working ok now
checked timing
cleaned plugs
cleaned points and they are sparking when opened
fitted a replacement coil off another car
It has a spark at each plug lead, and fuel is getting through, but when I crank it with the plugs in, it doesnt fire just coughs every once in a while, then the plugs get wet.
It also cranks a bit slow, tried running a jump lead from the pos on the bat to the starter but makes no differance.
Has good compression and I can see the valves moving up and down with the rocker off.
Also tried adjusting timing slightly, abd checked firing order but no differance??
Any ideas much appreciated! thanks
So far:
New fuel tank
New fuel lines and filter
Stripped down and rebuilt the su's today and they are all working ok now
checked timing
cleaned plugs
cleaned points and they are sparking when opened
fitted a replacement coil off another car
It has a spark at each plug lead, and fuel is getting through, but when I crank it with the plugs in, it doesnt fire just coughs every once in a while, then the plugs get wet.
It also cranks a bit slow, tried running a jump lead from the pos on the bat to the starter but makes no differance.
Has good compression and I can see the valves moving up and down with the rocker off.
Also tried adjusting timing slightly, abd checked firing order but no differance??
Any ideas much appreciated! thanks
Got to be timing. Get No1 on compression - see if rockers 7&8 are rocking. Then poke a screwdriver down the plug 'ole and find a rough tdc. Make sure the points are just opening and the rotor is pointing at No1. Also check firing order 1-3-4-2
Petrol is new? Old petrol will go "off" after a few months.
Fit NEW plugs too.
Petrol is new? Old petrol will go "off" after a few months.
Fit NEW plugs too.
sounds like it could be fuel then - perhaps, others will know better
assuming you've used the Driver's Handbook (what?) to set up the tappets, points plugs, timing and carbs
I don't know if these might help you but perhaps worth a look for the principals
general adjustment, engine not running
http://www.youtube.com/user/Universitymotorsltd#p/...
general adjustment, engine running
http://www.youtube.com/user/Universitymotorsltd#p/...
how a SU works part one
http://www.youtube.com/user/Universitymotorsltd#p/...
how a SU works part two
http://www.youtube.com/user/Universitymotorsltd#p/...
matching pistons
http://www.youtube.com/user/Universitymotorsltd#p/...
I’d be derelict in my duty if I mention that carb setting and tuning along with much, much more information is available in the owners/Driver Handbooks - http://www.mgocshop.co.uk/catalog/Online_Catalogue...
ETA: be very careful about changing the condensor (like coil it rarely goes wrong) as modern ones can be rubbish same as rotor arms and points (recheck points gap)
go to http://www.distributordoctor.com/rotor_arms.html for reliable versions
assuming you've used the Driver's Handbook (what?) to set up the tappets, points plugs, timing and carbs
I don't know if these might help you but perhaps worth a look for the principals
general adjustment, engine not running
http://www.youtube.com/user/Universitymotorsltd#p/...
general adjustment, engine running
http://www.youtube.com/user/Universitymotorsltd#p/...
how a SU works part one
http://www.youtube.com/user/Universitymotorsltd#p/...
how a SU works part two
http://www.youtube.com/user/Universitymotorsltd#p/...
matching pistons
http://www.youtube.com/user/Universitymotorsltd#p/...
I’d be derelict in my duty if I mention that carb setting and tuning along with much, much more information is available in the owners/Driver Handbooks - http://www.mgocshop.co.uk/catalog/Online_Catalogue...
ETA: be very careful about changing the condensor (like coil it rarely goes wrong) as modern ones can be rubbish same as rotor arms and points (recheck points gap)
go to http://www.distributordoctor.com/rotor_arms.html for reliable versions
Edited by na on Thursday 8th March 20:00
thanks for the quick replies guys. I like to think I know what I am doing with the carbs. They are much the same as on my V8 bobtail so I;ve spent many an hour fiddling with su's lol.
Yep petrol is brand new, all new fuel lines throughout as the old ones where screwed (actually just rubber atm to get her running)
I will investigate the timing again tomorrow. Fuel and spark should do something. I mean it wouldnt even fire up on easystart which is affectuvely avgas????
I have heard of people talking about th compression ''blowning out'' a weak spark as you obviously cant tell if its sparking or not in the bore.
Ill start from fresh with the timing in the morning! After all you never know what muppet has been fiddling with the car previously when you buy a ''project''! :-)
Yep petrol is brand new, all new fuel lines throughout as the old ones where screwed (actually just rubber atm to get her running)
I will investigate the timing again tomorrow. Fuel and spark should do something. I mean it wouldnt even fire up on easystart which is affectuvely avgas????
I have heard of people talking about th compression ''blowning out'' a weak spark as you obviously cant tell if its sparking or not in the bore.
Ill start from fresh with the timing in the morning! After all you never know what muppet has been fiddling with the car previously when you buy a ''project''! :-)
Seems like you've had every option so far...
So for my three pennyworth, one of the previous posters said check the timing, take the valve cover off, turn the engine over by hand until the rockers on 4 (ie 7 & 8) are rocking and the piston of N0 1 is at or just before TDC. Turn over engine by hand with the ignition on and a spark plug in the lead and lying on the block so it'll earth. You should be able to check that the spark is near the correct timing, (what is it? 4 degrees BTC?)and firing on the fuel compresion stroke and before the exhaust stroke.
You have said theres a spark at each plug, so its not the insulating washer in the distributor (been there done that).
Have you got the plug leads on the correct order. The distributor rotates anticlockwise I think (A series does).
Failing that the starter is drawing too much current from a poor battery and there isn't enough at the plugs or the coil is breaking down, but check the obvious (ie the settings) before replacing items.
Can't believe its distributor or cap as you say you have a spark at all the plugs.
So for my three pennyworth, one of the previous posters said check the timing, take the valve cover off, turn the engine over by hand until the rockers on 4 (ie 7 & 8) are rocking and the piston of N0 1 is at or just before TDC. Turn over engine by hand with the ignition on and a spark plug in the lead and lying on the block so it'll earth. You should be able to check that the spark is near the correct timing, (what is it? 4 degrees BTC?)and firing on the fuel compresion stroke and before the exhaust stroke.
You have said theres a spark at each plug, so its not the insulating washer in the distributor (been there done that).
Have you got the plug leads on the correct order. The distributor rotates anticlockwise I think (A series does).
Failing that the starter is drawing too much current from a poor battery and there isn't enough at the plugs or the coil is breaking down, but check the obvious (ie the settings) before replacing items.
Can't believe its distributor or cap as you say you have a spark at all the plugs.
well there's only usually ignition or fuel so if you're sure the fuel is getting all the way there fully and properly then it's probably ignition (maybe?)
if you've put any new parts on like CB points, rotor, condenser then suspect these new parts
turning over slowly suggest possibly low battery(ies), poor battery connections or leads, poor connections or leads in the rest of ignition system in switches or wires, dissy cap, HT leads or EARTHS - check, clean, secure, protect all
you don't say which year so it could be twice the batteries twice the trouble with more leads and connection to be bad also later one has a starter relay?
ETA: you tried a lead from bat to starter did you also have a lead bat to engine for earth
if you've put any new parts on like CB points, rotor, condenser then suspect these new parts
turning over slowly suggest possibly low battery(ies), poor battery connections or leads, poor connections or leads in the rest of ignition system in switches or wires, dissy cap, HT leads or EARTHS - check, clean, secure, protect all
you don't say which year so it could be twice the batteries twice the trouble with more leads and connection to be bad also later one has a starter relay?
ETA: you tried a lead from bat to starter did you also have a lead bat to engine for earth
Edited by na on Thursday 8th March 22:50
john2443 said:
I don't know if B series are the same as A, but on As it's possible to get the timing 180 degrees out which means the piston is at TDC but on the wrong stroke, so make sure the spark is coming on compression not exhaust.
well done john2443, was waiting for someone to flag this up. OP do check this as it's easily done. also, you mentioned poor cranking, so do check your earthing straps well; particularly their condition. if poor earthing the old girl will really struggle to fire/fire properly. good luck One more thing to try:
I've noticed that my Amazon really does not like dirty or wet plugs... even if they're barely damp after repeated cranking of the engine; she will not start all.
Changed the carb over recently and had exactly the same symptoms as you OP, took the plugs out and cleaned them up, turned the engine over for a couple seconds on the starter to clear any excess mixture out of the bores, warmed the plugs up a bit with my trusty Zippo, screwed 'em back in and hey presto - the car started first turn of the key.
I've noticed that my Amazon really does not like dirty or wet plugs... even if they're barely damp after repeated cranking of the engine; she will not start all.
Changed the carb over recently and had exactly the same symptoms as you OP, took the plugs out and cleaned them up, turned the engine over for a couple seconds on the starter to clear any excess mixture out of the bores, warmed the plugs up a bit with my trusty Zippo, screwed 'em back in and hey presto - the car started first turn of the key.
Have you got transistorized ignition?
If not I would definitely fit this ASAP.
If there is one thing that has made modern engines more reliable it is the high output big spark every time approach.
If you have a six volt B then I would say there is every chance it is ignition failure.
If the car is not firing at all check for some smell of petrol from the exhaust. If there is none at all it could be a fuel problem.
But I think ignition will be the problem.
If not I would definitely fit this ASAP.
If there is one thing that has made modern engines more reliable it is the high output big spark every time approach.
If you have a six volt B then I would say there is every chance it is ignition failure.
If the car is not firing at all check for some smell of petrol from the exhaust. If there is none at all it could be a fuel problem.
But I think ignition will be the problem.
v8250 said:
john2443 said:
I don't know if B series are the same as A, but on As it's possible to get the timing 180 degrees out which means the piston is at TDC but on the wrong stroke, so make sure the spark is coming on compression not exhaust.
well done john2443, was waiting for someone to flag this up. OP do check this as it's easily done. also, you mentioned poor cranking, so do check your earthing straps well; particularly their condition. if poor earthing the old girl will really struggle to fire/fire properly. good luck 
to both of these.I was thinking earth straps where the OP said it turned over slowly.
john2443 said:
I don't know if B series are the same as A, but on As it's possible to get the timing 180 degrees out which means the piston is at TDC but on the wrong stroke, so make sure the spark is coming on compression not exhaust.
Think that was what I was trying to get over or one of then, hence checking spark against valve position!
Later MGB’s have a ballast resistor in the wiring loom; this can cause your symptoms. Take the tape off the wiring loom in engine bay and find the thick pink wire and remove it. Then take feed wire to coil and use a 12volt non ballast coil.
This was a common fault with later MGB’s, so might be worth checking
hope you get it sorted though
Martin
This was a common fault with later MGB’s, so might be worth checking
hope you get it sorted though
Martin
martin010161 said:
Later MGB’s have a ballast resistor in the wiring loom; this can cause your symptoms. Take the tape off the wiring loom in engine bay and find the thick pink wire and remove it. Then take feed wire to coil and use a 12volt non ballast coil. This was a common fault with later MGB’s, so might be worth checking hope you get it sorted though Martin
Martin, that's a knowledgable first post on PH. Welcome to PH 
Gassing Station | Classic Cars and Yesterday's Heroes | Top of Page | What's New | My Stuff