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MG MGB Technical - Powerspark 25D distributor

After much deliberation about which replacement for my distributor I have settled on the Powerspark 25d electronic and fitted it yesterday. All I can say is what a difference it has made. I decided to go for electronic ignition and replace the dizzy at the same time as there was a lot of play in my old one. It was easy to fit and has made the car run a lot smoother, and started better from cold this morning also. Another problem I have always had was with the car running on and it appears to have stopped that as well. The other strange thing is that I have read that electronic ignition doesn't work with an RVI rev counter but in my case it has made it work better - it used to only just into life occasionally but appears to be working OK now!?! Some people have questioned the reliability of electronic ignition units so I am just going to keep the entire old dizzy assembly in the boot in case of emergency as swapping it out won't be too much of a big deal if it fails.
Paul.
P.S. the cost of a 25D dizzy, new silicone HT leads, 4xNGK spark plugs and a length of vac pipe was less than £79 including delivery via simonbbc online ebay shop.
Paul1970

Paul,
welcome to the world of electronic ignition and replacing the rest of the worn dissy and no more fiddling with those nasty points all the time

you're more likely to need a spare HT lead set than fully dissy in the boot if you've got those red HT lead set, personally I'd look at changing them at some stage for quality leads to use the extra performance you now have, from 'performance' - http://www.performanceleads.co.uk/

you may also be able to gap the plugs wider to take advantage of the fatter spark giving even more performance improvement
Nigel Atkins

Thanks, I will bear it in mind about the HT leads, though I must admit they actually look like they are good quality. (They are already made up, not like the ones in the bundle deals from Accuspark). My plugs are gapped at 0.025" what would you think the gap could be increased to??
Regards
Paul.
Paul1970

"no more fiddling with those nasty points all the time"

I rarely have to adjust mine from one replacement interval to the next, and they go quite a bit longer than the recommended replacement interval before making a noticeable difference to anything. But there we are.

It's the sum of the air gaps in the HT circuit that determines the peak HT voltage, and the plug gap is the biggest of those. The HT will keep rising until it does jump the largest gap, then it stabilises. If you increase the gap too much you can cause other HT components to break down. 25 thou was the recommended gap for the 25D4, 35 thou for the 45D4. The increase *may* have been because the 45D4 can better stand the higher voltage, maybe not.
Paul Hunt

PaulH,
you're obviously not doing much mileage if you don't need to adjust the nasty CB points for wear

you have to check them about 300 miles or a couple of weeks after fitting in case they've adjusted themselves and check them at services and perhaps lubricating

for the spark plug gap bear in mind PaulH now has a new electronic system rather than an old worn dissy with those nasty CB points and has new rotor, cap and HT leads and has reported an improvement in starting and running so a try at increased plug gap is worth a try

I have the fully electronic 123 dissy with high quality (but not over expensive) HT lead set and have been running a wider gap on the spark plugs since the 123 installation without any problems (I'll add that I know of as I've no calibrated electronic equipment to confirm this)

Nigel Atkins

"you're obviously not doing much mileage if you don't need to adjust the nasty CB points for wear"

As I said I rarely have to adjust them FROM ONE REPLACEMENT INTERVAL TO THE NEXT, that's 10,000 to 15,000 miles. That's using dwell to check them, which is preferable to feeler gauges and gap as it is 'dynamic' and 'non-invasive'. I've never had a problem with points in nearly 50 years.
Paul Hunt

it all depends on how long it takes to do 10-15,000 miles, annual for some (very few I admit) or ten years or more for others

it's easier to fiddle about with points on a B than a midget but anyway I prefer the various electronic ignitions that I've had on classics over the last 20 years and not had to adjust at all in over 200,000 miles
Nigel Atkins

"it's easier to fiddle about with points on a B than a Midget"

The Midget must be horrendous then, the RHD B is bad enough. I take the distributor out to change the points, and set them up on the bench. The V8 has a hex shaft sticking out the side of the distributor so you can set the gap using dwell with the engine running. Ironic, really, as the distributor is about the easiest thing to access on that engine.
Paul Hunt

not horrendous but not much fun or room to get at or see them particularly as a roadside repair when a new set freshly fitted only weeks before decide to close themselves up - and this was many year before the rubbish built points of recently

taking the dissy out means more work and mess and more potential for difficulties, mistakes and errors

I'm quite happy to be at home or at a pub than messing with fiddly points at the roadside with rainwater irrigating my nether regions or as part of a service

but as always each to their own
Nigel Atkins

Paul, all V8 powered GM cars of the '60s used the same points. Nothing like standardization. It made it quite easy to reach the distributors mounted at the rear of the engines as was used in Chevrolets. I have a flexible handled hex wrench especially designed for this application. It must be close to two feet long. Too bad Lucas didn't copy the design. Adjusting the points would have been much easier. RAY
rjm RAY

I first started driving and maintaining cars in the late 50s, and owned various motors from this era since and can honestly say that the thing that needed servicing the most was the points. When I bought my MGB 7 years ago the first thing I changed was to fit an electronic ignition, I chose to fit the Petronix system because it cannot be seen so still looks original. It has worked faultlessly since. No mechanical points for me thank you.
Trevor Harvey

rjm RAY, California, USA

I grew up with the GM ford distributors changing out points.

When I dragged my first MG back... the mechanics asked me where I got the sewing machine parts..
Refering to the distributor....I always chuckle a little when I see a lucas one as they are tiny.

Ive run electronic ignition in my MGA for 15 years....
The same one all this time. Never had an issue.
I should send the distributor out for rebuild as it was old when I put the petronix kit in.

I bet the the springs are worn and the curve tired...
anyway Its got an early B motor but still pulls well!

If you like points ...thats fine but it does seem to me one of the best cheap improvements and steady firing is due to electronic ignition!:-)
Steven Devine

Steven, when I installed a Moss supercharger system, on my '67 B back in '02, the big hurdle was the ignition system. Moss suggested a distributor, which they carried in stock, for the application. I purchased it and quickly found that it was a piece of junk with no country of origin listed on the box or the distributor itself. The shaft bushings quickly wore out and a pertronix unit unit failed due to the poor machining of the distributor. After a lot of research, I located a company in TN that produces GM HEI ignition systems for just about everything. All of their components are made in house to the highest standards. Their MGB distributor is based on an '80 Jeep four cylinder HEI system with the coil in cap design. The module is custom made and increases dwell time and the coil puts out 50,000 volts! It's the size of a V8 distributor, but puts out incredible power and fires the .055" sparkplug gap recommended by the manufacturer. Besides replacing the cap and rotor every couple of years, maintenance is nonexistent. RAY
rjm RAY

Wow....I would love to have a supercharger for an upgrade...Ha ha! Dyou have a picture od your distributor on the engine? That really must be something to look at. Did they upgrade an "Iron duke" 4 cylinder jeep distributor?
Steven Devine

"GM HEI ignition systems"

This was the system used in the North American 45DM4 distributor. However any trigger and electronics is only as good as the mechanicals. It's variable dwell which *reduces* dwell i.e. coil energising time at anything other than peak rpm, which reduces coil temperature. Coil voltage is limited by plug gap. It may well put out 50kV on test, but it shouldn't get anywhere near that in use.
Paul Hunt

Paul, Davis Unified Ignitions designs and makes all of their components. Even though their system is based on the GM HEI system, it is a far superior item that has delivered amazing performance in the ten years that it's been installed on my car. Steven, I'd have to dig through my archives to find a picture right now, but you could go to their website to get an idea of what it looks like, sans the supercharger of course. The Jeep engine was produced by AMC, at the time. However, I owned a seventeen foot boat, for many years, that had a 120 HP iron duke engine as the power plant, coupled to a Mercruiser sterndrive that was modified to get me into water so shallow that the local residents claimed that they had never seen a power boat that far inland before. I do miss that boat. RAY
rjm RAY

Paul1970,
Hi just read your thread on the Powerspark 25D dizzy, I've gone down the same route, how did you initially set up your timing, was it with a strobe at tick-over, or at 3000 rpm with an advance strobe light. If so what values did you use?

Thanks
Elliot
Elliot Smith

This thread was discussed between 01/04/2014 and 23/04/2014

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