New MGB engine only firing on 2 cylinders
Discussion
Hi Guys,
I wonder if anyone might be able to help.
New stage 2 engine with crossflow head and twin 45 webers. New 123-ignition dizzy.
It's only firing on cylinders 1 & 2.
It's sparking and fuel is getting to all cylinders. Compression is good.
Timed to TDC. Checked and double checked firing order - 1-3-4-2. Pretty sure dizzy is set up correctly - although a little unsure which hole on the dizzy the LED shines through - I've set aligned it to directly under rotor at TDC (pointing to lead 1).
Any thoughts any idea on what to check next?
I wonder if anyone might be able to help.
New stage 2 engine with crossflow head and twin 45 webers. New 123-ignition dizzy.
It's only firing on cylinders 1 & 2.
It's sparking and fuel is getting to all cylinders. Compression is good.
Timed to TDC. Checked and double checked firing order - 1-3-4-2. Pretty sure dizzy is set up correctly - although a little unsure which hole on the dizzy the LED shines through - I've set aligned it to directly under rotor at TDC (pointing to lead 1).
Any thoughts any idea on what to check next?
The light can shine through any hole on the dizzy but if you are near the mark you could always turn it by hand while it's running until you get an evenish tickover then set it up at 10 deg btdc (or whatever they recommend) with a strobe. Starting with simple stuff, make sure the plugs aren't wet, are the carbs balanced, are all the jets clean, are all the valve clearances correct? The go on to the more complicated things that you would normally look for.
Edited by jagracer on Friday 22 April 16:49
Sebring67 said:
Any thoughts any idea on what to check next?
http://www.mgocspares.co.uk/acatalog/MGOC_SPARES_M...Sorry...
barefoot said:
It says in his post "compression is good" 1st reply asks if he has checked his compression do people actually read the posts? 
LOL - its a forum - people don't always pick stuff up first time - get over it.Valve timing worth a check? If the inlet valves aren't behaving correctly could be fuel isn't getting into cylinders. Would still have good compression.
Other common factor is the rear carb. Fuel might be reaching the carb but is it reaching the cylinders?
I apologise for missing the compression check part of your post OP.
Obviously the guy above who lambasted me for my carelessness helped enormously with his post and described exactly the problem, oh wait he didn't he just came on to b
h.
The reason I mentioned compression check is I have known gaskets to go between 2 and 3 and 3 and 4 cylinders before, giving precisely your problem.
However if compression check is good then lets look elsewhere.
You say it's only running on 2 cylinders, what precisely is it doing? I ask as Bs don't like to start on 2 cylinders so you must be working hard to get it running at all, is it running rough like a lawnmower and when you pull the plug leads off cylinder 3 and 4 no change, but when you pull 1 or 2 off it dies? Will it rev up and start to pull cleanly?
Pull the spark plugs out after running it for a minute and look at them all, what colour are they? If 3 and 4 are bone dry then it suggests that the carb isn't actually supplying fuel, I'd expect them to be wet. If they are wet it suggests they aren't firing or are firing at the wrong time. I assume you have swapped the leads on 3 and 4.
Get a rough idea of where the dizzy is now and with the engine running and the clamp screw loose gently (and carefully, you don't want a belt off a ht lead) rotate the dizzy clockwise and anticlockwise. The engine will either die or pick up.
Failing all that I'd be tempted to throw a standard dizzy back in and rule out the 123 being faulty.
The above looks a massive list of checks but will in reality take around 15 mins.
Obviously the guy above who lambasted me for my carelessness helped enormously with his post and described exactly the problem, oh wait he didn't he just came on to b
h.The reason I mentioned compression check is I have known gaskets to go between 2 and 3 and 3 and 4 cylinders before, giving precisely your problem.
However if compression check is good then lets look elsewhere.
You say it's only running on 2 cylinders, what precisely is it doing? I ask as Bs don't like to start on 2 cylinders so you must be working hard to get it running at all, is it running rough like a lawnmower and when you pull the plug leads off cylinder 3 and 4 no change, but when you pull 1 or 2 off it dies? Will it rev up and start to pull cleanly?
Pull the spark plugs out after running it for a minute and look at them all, what colour are they? If 3 and 4 are bone dry then it suggests that the carb isn't actually supplying fuel, I'd expect them to be wet. If they are wet it suggests they aren't firing or are firing at the wrong time. I assume you have swapped the leads on 3 and 4.
Get a rough idea of where the dizzy is now and with the engine running and the clamp screw loose gently (and carefully, you don't want a belt off a ht lead) rotate the dizzy clockwise and anticlockwise. The engine will either die or pick up.
Failing all that I'd be tempted to throw a standard dizzy back in and rule out the 123 being faulty.
The above looks a massive list of checks but will in reality take around 15 mins.
wildoliver said:
I apologise for missing the compression check part of your post OP.
Obviously the guy above who lambasted me for my carelessness helped enormously with his post and described exactly the problem, oh wait he didn't he just came on to bh.
The reason I mentioned compression check is I have known gaskets to go between 2 and 3 and 3 and 4 cylinders before, giving precisely your problem.
Get a rough idea of where the dizzy is now and with the engine running and the clamp screw loose gently (and carefully, you don't want a belt off a ht lead) rotate the dizzy clockwise and anticlockwise. The engine will either die or pick up.
Failing all that I'd be tempted to throw a standard dizzy back in and rule out the 123 being faulty.
The above looks a massive list of checks but will in reality take around 15 mins.
Didn't you read my first post, I've covered that Obviously the guy above who lambasted me for my carelessness helped enormously with his post and described exactly the problem, oh wait he didn't he just came on to b
h.The reason I mentioned compression check is I have known gaskets to go between 2 and 3 and 3 and 4 cylinders before, giving precisely your problem.
Get a rough idea of where the dizzy is now and with the engine running and the clamp screw loose gently (and carefully, you don't want a belt off a ht lead) rotate the dizzy clockwise and anticlockwise. The engine will either die or pick up.
Failing all that I'd be tempted to throw a standard dizzy back in and rule out the 123 being faulty.
The above looks a massive list of checks but will in reality take around 15 mins.
Seriously though, the 123 dizzys are a pretty good bit of kit and he does say there is a spark so I would doubt it's that unless it's not fitted properly. I bet it's more to do with incorrect HT lead placing or the plugs are wet, Webers can flood an engine very easily.
Podie said:
Having been out with a few MGB owners last week, and one running on 2 cylinders, the issue was a pattern part rotor arm....
As above, they are a good distributor, cap and rotor are Bosch.One other thing OP, make sure you haven't timed it 180 deg out although I doubt it'd run at all like that.
Edited by jagracer on Saturday 23 April 09:39
barefoot said:
Wildoliver I did not come on to bh but surely if you are going to take the time to post a reply it is worth taking the time to read the post it was not a long one, your reply was as useless as mine! Anyway bh over meant no harm 
Well as far as I can see your contribution to this post has been the sum total of sod all. h but surely if you are going to take the time to post a reply it is worth taking the time to read the post it was not a long one, your reply was as useless as mine! Anyway bh over meant no harm Edited by barefoot on Saturday 23 April 11:48
I may not have actually helped the guy but have at least tried. I apologise I missed a bit of the original post however I do know B series engines inside out and the fault being shown screams either plug leads the wrong way round or loss of compression across 2 cylinders that have a tendency to go between for some reason.
Even if I had seen his comment I would still have questioned if they had really been checked properly as a lot of people will assume compression is good as it's a new engine.
The reason I asked precisely what was happening is all too often in these threads an OP wants some advice on a problem that sounds quirky, about 20 posts in it turns out that the original problem has been badly described and running on 2 cylinders actually means it sounds a bit rough or there's a bloody big hole in the block which they thought was meant to be there. If we start at a known point and move logically on from that point then the guy can get some good advice and actually solve the problem with our help. Start from the middle and we will just chase around in circles.
So to the OP.
How have you identified the actual problem.
Has the compression actually been checked.
Are the tappets set up correctly.
Has the engine ever run in any configuration (eg on different carbs, original dizzy etc.)
Is the 123 new, has it ever run on another car.
Are you getting spark to all 4 plugs? Not just check one and assume all work.
Are the plugs wet/dry/clean/dirty.
Now i feel bad. I just thought it was the typical PH banter i see thrown about on here so much.
I don't think you should stop supplying sebring67 with help just because of a couple of tossers such as my self. Also, if you could help me on my post regarding the CB conversion that would be great
I don't think you should stop supplying sebring67 with help just because of a couple of tossers such as my self. Also, if you could help me on my post regarding the CB conversion that would be great
Wildoliver
And I owe you a bit of an apology I was a bit OTT with my 1st post but I am a very keen MG nut my 1st ever car was a MGB GT in 1973 and have had several since in the last 5 years alone I have owned and restored these:
And the one I have just completed
Not a BGT but was a great car
Latest project
And my pride and joy that I will keep
Sorry for taking the topic off on a tangent just wanted to try and show I am an MG/classic car fan not a troll on here!
And I owe you a bit of an apology I was a bit OTT with my 1st post but I am a very keen MG nut my 1st ever car was a MGB GT in 1973 and have had several since in the last 5 years alone I have owned and restored these:
And the one I have just completed
Not a BGT but was a great car
Latest project
And my pride and joy that I will keep
Sorry for taking the topic off on a tangent just wanted to try and show I am an MG/classic car fan not a troll on here!
Edited by barefoot on Monday 25th April 10:26
Back on topic:
If the old, breaker type distributor is available it should be a relatively quick job to refit it and try starting there - that will at least eliminate one problem. Also, have all 4 plugs been checked for a spark? One advantage of a contact breaker ignition system is that you can set up static timing using a test lamp.
Are the tappet clearancer OK? I know that you have compression but if the clearances are wrong then it may affect the timing and amount of fuel/air in there. I got caught like that once after replacing a rocker shaft on a Mini engine - I dropped the new one on without resetting the clearances and it would not run.
If the old, breaker type distributor is available it should be a relatively quick job to refit it and try starting there - that will at least eliminate one problem. Also, have all 4 plugs been checked for a spark? One advantage of a contact breaker ignition system is that you can set up static timing using a test lamp.
Are the tappet clearancer OK? I know that you have compression but if the clearances are wrong then it may affect the timing and amount of fuel/air in there. I got caught like that once after replacing a rocker shaft on a Mini engine - I dropped the new one on without resetting the clearances and it would not run.
Edited by Richard Moss on Thursday 5th May 07:13
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