Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - EDIS Megajolt Rubber Bumper

Hi Everyone,

Im currently installing a EDIS Megajolt system on my 79B. Im wondering if I can pick anyones brains in the forum who has been there done that. Im curious to know where you mounted your VR sensor and if you have any pictures or can give me some advice as to what you used. I have a few other questions as well.



Have a look on this site, there's some pictures and lots of nice information to read.


Here is an update... I got her to start! Very cool seeing it all come together finally.

I was aware about that link in the past, I had some more detailed questions that I ended up sorting out on my own.

The problem was trying to realize a diagram from the megajolt website. I had already mounted the trigger wheels to the crank pulley with the missing tooth being at the TDC marking so I had to have the VR sensor mounted at a specific exact point in order to have the Ford EDIS unit run the MGB on its own in limp home mode, with out the Megajolt unit.

I had orignally had the VR sensor at 90 degrees after top dead center instead of before top dead center... (This has to do with my trigger wheel mounting point already being set) Long story short I found a bolt just to the left of the crank shaft that I could run a simple L bracket off of. It ended up being very very easy considering the tight tolerances and was 90 degrees before top dead center.

That proved to be very successful in getting the car to start and run in limp home mode (@ 10 BTDC)

Next up I have to clean up all the wiring, make my bracket for the VR sensor permanent, or use as a template and have my friend who has the machines at work etc to make a nice looking bracket. Then fit the Megajolt unit and go from there.

Im very very pleased... I had a big problem after fitting new twin SU's to my 79B. I couldnt get the static timing set on my distributor and was tuning the carbs from scratch which was proving to be next to impossible with the timing not being set or wear in the distributor etc in making it impossible to get some baseline settings... Not sure of the exact reason.

Now with a known solid baseline I am going to setup the SUs, then get the Megajolt box hooked up to a laptop and start realizing what has been a fun interesting technical journey into the megajolt world. I dont think its going to be the last of my head scratching but please if anyone is having trouble keep me in mind, maybe I can help.

I hope to post some videos and take some pictures as well.

Hi Mr. JRB- You're one of the few out there I am aware of really doing the Ford EDIS. Are you going 2.2 MS or what? Who did your trigger, and is it in front or behind the pulley? How did you attach it? Yes, a picture would be worth a thousand words. I could use 4-6 of those custom sensor mounts if you're going that way. What gap your plugs, Champion 9-Y's?, with those 60k volt coils? Tell me about your SU woes, I've a bit of experience with them. I'm if you wanna connect
vem myers

Hi Vem,

Im using the latest megajolt unit, not the megasquirt.

I ended up not being able to get her started this weekend... I had my new iPhone ready to take some lovely HD footage. I was excited to put it up on youtube but thats going to have to wait till another day. This weekend was absolutely brutal weather wise here in NY. But I did give it a shot on Sunday.

I was getting some backfiring from the carbs originally when I had her running. So I planned this weekend to verify with a timing light that I was running at 10 BTDC. This is all dependant on my VR sensor location which should be spot on.

With the backfiring I should be attributing it to timing, too rich, and valve adjustment correct?

Its just been a real pain with my SU"s. Ive installed HS6's on my TR7 and havent had problems. I just want to be able to get the engine started again so I can verify my timing then trace everything else down... I guess I can crank her over tonight and verify timing while cranking if anything... The SU's on the TR7 was such an improvement... I had zeniths, then dual downdraft carbs that proved such a hassle to get tuned properly... Then the HS6's which were smooth sailing.

I am not at the point of gaping my plugs any larger yet. But I cannot wait.

In regards to the trigger wheel, I bought one that didnt have a lot of mounting options... I originally purchased one with various ways it could be fitted but for the life of me I cannot find what I did with it. The trigger wheel is actually smaller in diameter than the pulley which made the tolerance for the VR sensor very close... It is mounted on the outside so I do not have to buy or have a new pulley bolt machined. Would be a lot easier to have a larger wheel. My father works at a company that has a large shop attached and he was able to call in a favor and have it mounted with set screws which were drilled and tapped... The problem with the later model pulleys is the rubber. I had to mount it to the outer part of the pulley but should have been mounted to the inner part. Its something I will sort out after everything is setup.


Hi MR JRB- I'm surprised to hear the 1.5 su seem to be vexing you. These jewels are usually very reliable when the spindle isn't leaking and supply enough to fully power most iterations of the 1800 up to around 2 litres. Peter Burgess notes the 1.75 SU on the 18 V provide marginal improvements only at high RPM. Having referenced that however, I have a brand new 1.75 " Magnaflow manifold and a fully rebuilt set of 1.75 " HIF by you-know-who, if you want to go that way. I'm seriously considering just having the existing pully notched, or perhaps Hans Pedereson's spiffy new HB product cut via cnc. I hear your point about the split HB on the MGB but wonder, really, if timing is significantly affected. I mean, isn't it possible the very stiff rubber just "dithers" the timing marks while dampening the vibration? I dunno, does anyone out there...Steve, Chris, Peter, have insight? Cheers, Vic
vem myers

Ok here is the update.

Long story short... I pulled the plugs and they were wet. I bought some NOS champion plugs, the plastic box containing the hight output plugs looks like its been on the shelf a while but the plugs are great.

I tried cranking with the EDIS to no avail. So I switched back to the distributor and she started up. She also ran a lot better than the last time I cranked her with the distributor connected. So Im pleasantly suprised and happy.

Im going to do the EDIS system as a hobby when I have the time etc... For right now I will be setting up the HS4's... Then I will get back to the EDIS and update this thread when I know the carbs are where I want them.

I checked the timing of the distributor and its running at 15 BTDC. What timing is everyone using? I know stock is 10 BTDC but I remember people were running a lot more advance. Its a 1979 B with the lucas electronic distributor and the HS4 carbs...

Timing is another movable feast. For high-compression engines the criteria will probably be how much advance you can run without pinking at any combination of throttle opening, revs and load, which is quite likely to be less than the original book value, definitely on the lower octane fuel. For low compression the book value is probably OK, on those you can sometimes keep on advancing without pinking until it stalls the starter.
PaulH Solihull

Hi JRB- A few thots: The EDIS by Matt is a simple spiffy add for the MGB, but time intensive, and apparently a smidge quirky on map out. One sage, prolly Paul, noted that a GB 123/pertronix with tight bushings is going to approximate the performance of an EDIS setup without the EDIS setup. On my SC car, I had Jeff S recurve the dizzy with a Pertronix and the marks under light are dead steady. Isn't a 1979 MGB with HS4 a retrofit? If it has the federal cam and the Onerous dizzy, 15 degrees sounds pretty high...8-10 degrees sounds closer to right. You can't do much with the fed flat cam and D-45 tied up with the smog salad for performance. If somehow, you can duck the smog requirements in your state, a 1962 cam, hardened lifters and a D-25 with vac curved by Jeff could really brighten up your ride. In my really skewed opinion, best bolt on after that is a Burgess head, then next rung up would be an early Moss supercharger. Cheers, Vic
vem myers

Some more ramblings then. I am trying Ray W's ( the golden SC RB MGB in America Somoa) and others suggestion of running 87 octane fuel for slower, smoother, more complete burning. Previoulsy, and since 1971, I have never put less than 91 octane in any of the B's. In the 77 MGB car--Burgess FRBV head, P285, Pertronix, peco, Harlan Rollers-- I've been diluting a mix from pure 91 to 89/91 to 89/87 to straight 87 last tank. With the above specs I was at 18 degress initial, but have taken it down to 10* last week to eliminate pinking. Side benie is the 285 now idles at 600 rpm smooth as silk, no lope whatsoever. Again Mr. JRB, the HS SU weren't stock on the 79 New York ( or anywhere else in the USA) MGB, and it probably has the old flat fed cam and de-curved 45-D dizzy known as the "Opus" or "Onerous" depending on who's talking. If so, retaining that cam and curve will ensure anemic performance regardless of the HS upgrade from the Zenith Stromberg ( which isn't a really bad carb after all). Take a look at John Twist's U-tube on MGB cam profiles. The fed cam looks like a sad impersonator compared to the 62 spec MGB cam, which is still a great all around performance cam. Good luck on the EDIS when you get back to it. I could still use those mounts for the pickup if you have extra. Cheers, Vic
vem myers

Ok back again... I have the b idling on the edis. Balanced the carbs. Checked the timing that's supposed to be 10 btdc. It's reading 5 btdc. Solid as a rock too I might add. No varying at all. I originally had someone check the timing and they read the timing marks wrong. I put my gunson color tune spark plug on and it was reading blue at idle but backfiring out the carbs which seems like it being at 5 btdc. I'm going to wire the mega jolt to the edis and factor in the 5 degree difference. Load up a map and have a go. Tune the carbs and see where I'm at.

Ok, I am sitting on the edge of my new Fiero speaker seats. Matt has some good maps as I recall. Are you using an AFR?

vem myers

AFR? Awesome beer cooler by the way. No Coronas for me unless Im at the proper venue...

Im glad someone else is excited along with me. I get a kick out of seeing it run on the edis. I have a busy schedule this week and wont be able to get to it till this weekend.

I should be able to take some video.

I have the edis being powered by a separate 12V source.

Im going to have to tidy up the wiring and mount everything etc and wire its power supply up to the car.

I also do not have a suitable laptop. I am going to load up a map into the megajolt for starters and see how she runs. Need to go over the brakes and fit a new clutch slave cylinder before I borrow a pc laptop and do some runs...

JRB- Christmas Kudos on your stick, grit and success. I share your kicks at distance. I've had 3 @ MegaSquirt 2.2 in the bin for 2 years, trigger wheels hanging, etc., for a while. You however, have put it all together and made it happen. Love to see the vid on u-tube or as an upload. Serious congrates and a very Merry Christmas to you.
vem myers


I put a supercharger in a RB B a few years ago and installed a MJolt system to produce a customised advance curve. The VR sensor was mounted through the front of the gearbox bell housing with the flywheel drilled, tapped and low profile screws set into a circular pattern. Worked fantastically well.

Chis Betson(MGA engine builder in Southend Essex)came up with the idea when we installed a SC in a MG Special I had built. Chris is the guy to talk to:
J Harle

Very cool Chris. Ive seen that on other cars. How many teeth are there on that? 60-2? Any pictures?


This thread was discussed between 13/10/2011 and 09/01/2012

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.