Ignition Amp wiring
Discussion
Evening all, hoping someone on here can give me a steer on the connections from the dizzy mounted amp to the coil on a rover v8?
Confession time, its not in a TVR, its not even a TVR engine...and the TVR I do own is a griff...but, it is a rover v8 in an MGB roadster and of a similar vintage to a wedge so thought this was a decent place to post a query.
A bit of context to the issue. The car sat in a dryish garage for a year having driven there under its own power. when I returned to collect it, it started and ran. over the next 500 yards things got progressively worse until it conked out and had to be recovered home.
Regarding fuel, I have swapped the fuel for fresh stuff, confirmed fuel pump is working, removed carb (weber 500) and cleaned with carb cleaners, reset floats, confirmed everything free, tipped out old fuel and reinstalled. Regarding electrics, I removed and cleaned plugs, checked cap and rotor and gave them a light rub with fine sandpaper, swapped coil, removed dizzy and turned manually to trigger spark on each plug in turn - all seems ok so assume dizzy pickup is OK.
I get an occasional backfire or pop back through the carb and have had one or two occasions where I thought it might run - few cylinders firing in succession on cranking, otherwise it is totally dead.
The one thing I can't check is the amp (aftermarket with the dizzy), but I have a spare lucas dizzy mounted unit I could swap in. due to space I can't connect the unit to the dizzy and I don't have the lead for the connection plug to the coil. I'm going to rig up some homemade wiring to see if this confirms the issue, but of the 3 pins coming from the amp, which one goes to positive and which to negative on the coil? the pins are on a bit of a limb out from the body of the amp, otherwise its a small box a little squarer than a credit card.
Thanks in advance, any guidance greatly received!
Chris
Confession time, its not in a TVR, its not even a TVR engine...and the TVR I do own is a griff...but, it is a rover v8 in an MGB roadster and of a similar vintage to a wedge so thought this was a decent place to post a query.
A bit of context to the issue. The car sat in a dryish garage for a year having driven there under its own power. when I returned to collect it, it started and ran. over the next 500 yards things got progressively worse until it conked out and had to be recovered home.
Regarding fuel, I have swapped the fuel for fresh stuff, confirmed fuel pump is working, removed carb (weber 500) and cleaned with carb cleaners, reset floats, confirmed everything free, tipped out old fuel and reinstalled. Regarding electrics, I removed and cleaned plugs, checked cap and rotor and gave them a light rub with fine sandpaper, swapped coil, removed dizzy and turned manually to trigger spark on each plug in turn - all seems ok so assume dizzy pickup is OK.
I get an occasional backfire or pop back through the carb and have had one or two occasions where I thought it might run - few cylinders firing in succession on cranking, otherwise it is totally dead.
The one thing I can't check is the amp (aftermarket with the dizzy), but I have a spare lucas dizzy mounted unit I could swap in. due to space I can't connect the unit to the dizzy and I don't have the lead for the connection plug to the coil. I'm going to rig up some homemade wiring to see if this confirms the issue, but of the 3 pins coming from the amp, which one goes to positive and which to negative on the coil? the pins are on a bit of a limb out from the body of the amp, otherwise its a small box a little squarer than a credit card.
Thanks in advance, any guidance greatly received!
Chris
There's a whole bunch of stuff here if you fancy some light reading.
http://www.mgb-stuff.org.uk/ignitiontext.htm#elect...
http://www.mgb-stuff.org.uk/ignitiontext.htm#elect...
I came across an MGR that had been stood and kept grinding to a stop as there was so much rust in the tank it kept blocking the fuel supply. If you want to check out the HT side of things, disconnect the king lead where it enters the distributor and tape the end connector 1cm from the chassis and crank the engine. A good coil and amp should generate enough HT to jump this wide gap.
adam quantrill said:
Actually don't leave it as wide as this, maybe 5mm max. I learned that if the HT is allowed to build up too high, the back EMF can kill the ignition amp.
Same applies to the king lead or spark plug leads going open circuit, so test these first with an ohmmeter/multimeter.
Was for many years something that never crossed my mind, it needed to and should have but didn'tSame applies to the king lead or spark plug leads going open circuit, so test these first with an ohmmeter/multimeter.
One of the better posts here in a long time yet will fade away
Deserves a sticky or topic of it's own
Sharing is caring
Happy Easter all, wee workshop update following HT test. The spark happily jumps a >5mm gap from king lead to radiator.
Fuel pump had a dodgy earth but thats been cleaned and it pumps fuel well to the carb.
In conclusion then, I have sparks (and presumably at approx the right time because the car did run for a bit) and I have fuel.
I've disconnected and blocked all vacuum ports ( servo etc).
Still nothing but the occasional backfire or pop back up the carb and very occasionally I get a few cylinders in a row - just enough to get my hopes up!
Fuel pump had a dodgy earth but thats been cleaned and it pumps fuel well to the carb.
In conclusion then, I have sparks (and presumably at approx the right time because the car did run for a bit) and I have fuel.
I've disconnected and blocked all vacuum ports ( servo etc).
Still nothing but the occasional backfire or pop back up the carb and very occasionally I get a few cylinders in a row - just enough to get my hopes up!
Could it be a blocked jet in the carb? Or stuck float, or blocked inline fuel filter? Are all the plugs wet after cranking so you know the carb is actually working? You could try dribbling a bit of neat fuel into the carb, with the air filter removed, while getting someone else to crank it.
Edited by KKson on Monday 5th April 12:07
I've got a couple of can of easy start on order so will give that a go. plug seems wet and on cranking I get a bit of a slow crank after a few revolutions as the fuel presumably sits there and causes a better seal. not sure the term for that? floats seemed free when I took the carb apart, although one bank of plugs was pretty back.
I know the fuel is old (about a year), but the car did run for a bit on it. I've also tried putting the fuel pump pickup in a fresh can of fuel, but no change
I know the fuel is old (about a year), but the car did run for a bit on it. I've also tried putting the fuel pump pickup in a fresh can of fuel, but no change
The carb is actually an edelbrock 1404 (weber 500). I've had it out and on the bench - one of the floats was bent and the valve sticking open flooding one bank, but I've sorted that I think. Gave it a good dose of carb cleaner. Can see the fuel from the accelerator pump being sprayed in and the plugs are wet...
Not done a specific compression check, but have turned it over with all the plugs out and it spun round quite happy, then when I put the plugs back in it struggled much more (just like it usually does when starting), so I think I have compression
Wondering if the leads and plugs are knackered? I've tested the king lead to get the spark to jump, but used another plug previously to test the dizzy. Seems odd that all magnicore leads or all plugs would expire at the same time though.
Only one way to find out I guess...
Also, is there a way to check is the main jets are blocked with the carb in situ?
Wondering if the leads and plugs are knackered? I've tested the king lead to get the spark to jump, but used another plug previously to test the dizzy. Seems odd that all magnicore leads or all plugs would expire at the same time though.
Only one way to find out I guess...
Also, is there a way to check is the main jets are blocked with the carb in situ?
Have you checked that the central carbon brush in the top of dissy cap is in good condition. The carbon can wear out or even the spring fail so it doesn't push the carbon contact on to the top of the rotor arm. Also I have had rotor arms distort with age and not pass the spark to the cylinders. I very much doubt the HT leads have all died at the same time. It's got to be something simple.
Carb wise I'm not familiar with the Edelbrock model. As recommended above though, take the air filter off and get someone to crank the engine while dripping fuel into the carb intake. Yes you need to be careful but it should fire up. If the engine stops when you stop dripping fuel in, then you know the carb is the issue.
Carb wise I'm not familiar with the Edelbrock model. As recommended above though, take the air filter off and get someone to crank the engine while dripping fuel into the carb intake. Yes you need to be careful but it should fire up. If the engine stops when you stop dripping fuel in, then you know the carb is the issue.
Edited by KKson on Tuesday 6th April 19:34
Check the leads with an ohmmeter/multimeter, 1.5k to 4.5k ohms usually depending on length.
check the plugs by connecting the lead and resting the metal against the block, you should see the spark in the gap.
THe rotor arms can also fail due to being new and poor quality, I had one go within a week with an arc through the plastic to the dizzy centre.
Those big carbs are prone to flooding if not set up right which will foul the plugs pretty quickly so bake them off in a low oven.
check the plugs by connecting the lead and resting the metal against the block, you should see the spark in the gap.
THe rotor arms can also fail due to being new and poor quality, I had one go within a week with an arc through the plastic to the dizzy centre.
Those big carbs are prone to flooding if not set up right which will foul the plugs pretty quickly so bake them off in a low oven.
Hi all, spending another few hours on the MG today. So far, taken carb off again, used air compressor to blow through everything, loaded with new clean fuel and reinstalled.
Leads have the resistance suggested, all tested with spark plug and can see the spark in all cases. all plugs tried and replaced and tried again.
Just done a compression test (cold unfortunately). cylinders 5&7 showing up lower than the others. the rest are all 125psi or thereabout, 5&7 are 100psi. Could this be the problem?
I've messed about with timing and fueling and no material change. The only thing I have noticed, after I crank it for about 10 cycles or so and the engine is struggling to turn as its getting flooded then I get a fire - i little effort that gives me hope.
I'm out of ideas now. I guess I have to choose between taking the heads off and seeing if there is a problem there or giving up and getting it off to a specialist with greater diagnostic abilities.
Leads have the resistance suggested, all tested with spark plug and can see the spark in all cases. all plugs tried and replaced and tried again.
Just done a compression test (cold unfortunately). cylinders 5&7 showing up lower than the others. the rest are all 125psi or thereabout, 5&7 are 100psi. Could this be the problem?
I've messed about with timing and fueling and no material change. The only thing I have noticed, after I crank it for about 10 cycles or so and the engine is struggling to turn as its getting flooded then I get a fire - i little effort that gives me hope.
I'm out of ideas now. I guess I have to choose between taking the heads off and seeing if there is a problem there or giving up and getting it off to a specialist with greater diagnostic abilities.
My ten penneth. I would have said that the compression is OK I think that is about what mine came out at when cold. There are a few factors that may well affect it like cam-type, whether throttle was open etc. Are you sure that the fuel pump is up to it?
When you say aftermarket ignition do you mean hall effect or similar as I had AccuSpark fail on a V6 however, read on below.
As you have timed the engine and have spark it is probably fuel related or air getting in from somewhere (failed gasket or hose). You also mention floats, is the distance set to the manual? and working correctly no pinholes and shut off as expected?
You also mention easy start I assume that you now have it. I would disconnect the pump feed to the carb and (block off to stop fuel going everywhere, easily forgotten), then as suggested previously squirt easy start directly into the carb whilst cranking (keeping your head well clear in case of spit back as no eyebrows is not a good look).
Other than that seems to me that you have covered most bases, other than swapping out the carb, which seems a bit of a waste as it was working early day's. One things for sure it will probably end up being a simple fix in the end.
When you say aftermarket ignition do you mean hall effect or similar as I had AccuSpark fail on a V6 however, read on below.
As you have timed the engine and have spark it is probably fuel related or air getting in from somewhere (failed gasket or hose). You also mention floats, is the distance set to the manual? and working correctly no pinholes and shut off as expected?
You also mention easy start I assume that you now have it. I would disconnect the pump feed to the carb and (block off to stop fuel going everywhere, easily forgotten), then as suggested previously squirt easy start directly into the carb whilst cranking (keeping your head well clear in case of spit back as no eyebrows is not a good look).
Other than that seems to me that you have covered most bases, other than swapping out the carb, which seems a bit of a waste as it was working early day's. One things for sure it will probably end up being a simple fix in the end.
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