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MG Midget and Sprite Technical - Engine tuning specialist required

The Frogeye is running very well, except for two issues. It rarely starts instantly unless weather is very warm (as it is now), and more importantly the fuel consumption is high. It struggles to get much over 30 mpg. Admittedly I mostly do short trips, but I was getting high 30s a couple of years back. My tuning skills are limited to plug testing and the time honoured process of setting the carb mixture. About 5 years ago I had a rolling road session, but the technician didn't do much other than to adjust the timing and verify that the mixture was OK. I have replaced the engine since then, but the spec is the same. I am reluctant to pay well over £200 for another session which might not tell me much.

I have been following AC Dodd on YouTube and he could I'm sure sort me out, but he did say he was heavily booked up. He would be ideal as he lives very near me, but I'm awaiting his reply. I can't find anyone else within striking distance of Salisbury who has the necessary skills. I don't mind driving for half a day if there is somebody.

It's a 998 with Kent 276 camshaft, HIF44, CAM4810 head with 1¼" inlets, 59D4 dizzy with Keith Calver Sports advance curve, Powerspark ignition.

The mixture is spot on according to plug colour, as is the ignition timing. But as I say I'm no expert.
Les Rose

Belay that, I have AC Dodd coming on 17th July.
Les Rose

Adrian Dodd has done a lot with my Sprite & midget group (formerly Kent Area Midget & Sprite Club).
We have had ‘audiences with’ at my house and tuning sessions at M.L.Motorsport of Higham. Several converted to his camshafts. He has machined engines, restored carburettors, re-curved dizzies &c.
Enjoy your time with him on 17th: and say “hello’ from me.
Alan Anstead

Les,

I had my Sprite rolling roaded at Peter Burgess's and once the new engine is finally settled in, I'll be going back.

Malc
Malc Gilliver

I'll look forward to seeing you on the tube when ACD uploads his "on the road tuning" video ;0)

A bit of advice before he turns up... check for air leaks, check your ignition lead resistance and check you have the correct plugs (BP5ES) and coil fitted e.g. primary resistance to match the dizzy (is it electronic with variable dwell etc.?)

Best of...
MGmike
M McAndrew

AC came today. He was here for over four hours which on a labour basis alone was good value. I could not believe the amount of kit he unpacked from his car and distributed around my garage. There will be a video, but briefly the main issues were the wrong coil, resistor plugs, and the carb not delivering enough fuel. He was very impressed by the breathing of my 998 engine, as indicated by the amount of fuel it was demanding. A couple of issues remain. The distributor advance curve needs to be adjusted, and he can do that for me later. Also the K&N filter was bunged up despite my attempts at cleaning with the correct products. The engine needs a lot more air flow than it was getting even with a clean K&N filter. AC said to fit the biggest filter I can get into the space available, and to forget the ram pipe. So guys, what do you recommend for my HIF44? I will have to run without one until I get it replaced.

The high fuel consumption seemed to be related to the carburettor piston damper, which was not rising fast enough. AC modified that with a file. But also I was not getting complete combustion because of weak ignition. On a test drive it goes like a banshee as soon as it hits 3500. I am looking forward to Sunday at Gurston Down.

Oh, nearly forgot, the slightly hesitant starting is because of a weak starter motor. A standard ungeared one is just not up to starting a high compression engine. So I am looking out for a geared one.
Les Rose

Brilliant, sounds like a worthwhile visit.
Pity he is so far away from Leyland!
Les Robinson

All sounds promising, I found the starter motor comment odd as I used a standard starter motor on my 1420cc A series without issues and it was a high compression engine. IIRC there can be problems with using the wrong pinion as there are 9 and 10 tooth variants. Can you post images of your carb and what ram pipe you have.

Sunday should be good at Gurston Down, I haven't been there in decades when I went to watch a mate do the hillclimb and I stood by the start line when Nick Mann did a run in his V8 twin turbo Morris Minor monster, one of the few cars I'd seen up to that point that looked really quick accelerating away from me, IIRC he didn't get the course record that day but did later in the year.
David Billington

Here is the setup that I had before today. I have no ram pipe or filter now.


Les Rose

I never had a problem when using a properly rebuilt standard M35 starter on race engines. I favoured the M35G version with a 9-tooth pinion.
Dave O'Neill 2

Another question. AC said that this hole should not be blocked. But all the HIF44 filters I can find do block this hole, as per the gasket shown. I am puzzled.





Les Rose

it is the Breather hole


Flip Brhl

I'm with Dave B on the starter motor question. IMO the standard unit is more than adequate in good condition, but they do get "tired" after 40 or 50 years service.
Sometimes they might need replacement brushes which is not difficult and the kit isn't expensive (Flip did exactly this a few years ago as I recall) but a strip down and thorough cleaning is a good start.
Don't apply any oil or grease to the spiral; it will cause the bendix to stick. A light spray of dry PTFE can be used if you want but oil will collect dust and cause trouble.
Greybeard

Les
This is a HIF44 gasket for the rear flange.

https://www.ebay.co.uk/itm/137516555527

I use a large round deep K&N filter and have a thin stub stack inside (ISTR about 15mm?)that just smooths the mouth of the carb.
richard b

Pencil lead, which is really graphite can be used to lubricate the bendix, as far as I know (just like using a semi-automatic rifle in hot climates where there is sand. . )

It's worth counting the teeth on the starter to ensure it has the correct number. The standard starter ought to start just about anything. The modern pre-engaged starters are better and arguably only essential when an oversize clutch plate might foul the gear on a bendix unit (it can smash the spiral gear inside when it does or simply jam and not release under any circumstances).

I have a gearless starter motor kicking around my garage if anyone wants it - free collection only. I haven't test to see if it works or not.
Daniel

AC said that the breather hole only needs to be left open when using a ram pipe, as I was until yesterday. I still don't understand why all the HIF44 baseplates block it. I have no filter at present, just the baseplate with stub stack, so the breather is blocked.

The car started instantly this morning, so I think the main cause of hesitancy was a poor spark.
Les Rose

Les,
Ventured into the garage and got a couple of pics of mine - bonnet safely catch caught me again ! Safety for bonnet not owner !

Filter is 65mm deep and the transfer hole is open - hope pic is clear enough.





richard b

Pic of the transfer hole.


richard b

Well having got the carb apart I thought I’d have a look inside !
The smaller hole doesn’t appear to go anywhere and the larger hole above actually seems to be the vent as far as I can make out.

Maybe changed as design developed ?

But what did surprise me was the lower say 20mm of the needle had a thinish layer of green verdigris sort of stuff on it which I cleaned off.
That part is always sitting in the fuel when stationary - modern fuel I guess !!!
richard b

MED very low "RAM" pipe. There is no interaction with the K & N filters. Problem is the price...


Flip Brhl

Les has a lathe!
David Billington

Indeed I do have a lathe, it's probably 100 years old and belonged to my dad. It wasn't new when he bought it. The stub stack on my backplate I made from resin, but a turned one would be neater. Flip's MED ones are like my resin one, with just two holes which I have always thought were for breathing. But those carbs are not HIF ones. I will have another look tomorrow when I have recovered from thrashing the car up Gurston Down.
Les Rose

I had another look at the carb, and that small hole is blind. I tested it by blowing into it and it does nothing. Very strange.
Les Rose

Here's my video of the Gurston event.

https://www.youtube.com/watch?v=gBsF7unxOC8&t=199s

The car took off like a scalded cat, but the gearing is wrong for the hill. It drops off the cam on the last corner. Explains why it had a 4.5 diff when I bought it.
Les Rose

Les, your Sprite sounds great and goes brilliantly, it looks pretty smart too.

I've seen plenty of videos of Gurston Down before but yours gives the best impression of the gradients - it's steeper than I thought. It's on my To Do list.

Just a thought on the camera position, yours gives a great view of the track but that's all. I have my camera attached to the passenger head rest stalk. The view ahead isn't as good as yours but it can see the rev. counter and I now have a GPS speedo on the transmission tunnel. My eyes are too rivetted to the road ahead to look at the dash during a run so the video is the closest thing I can get to data-logging without having an actual data logger.

Does AC's area of work extend as far as Shropshire?

Colin
C Mee

Colin, I have learned a lot about in-car video lately! I had the phone rigidly fixed to a silicone holder via an ally bracket screwed to the dash top, in an attempt to stop it from wobbling. But that caused vibration to be transmitted, which causes the rippling effect on the image. I tried to edit that out, with little success. Google's AI tells me that I need to insulate the phone from the body with a hefty suction cup on the windscreen. Not the standard spring loaded phone holder. I managed to damp out the wind noise with little bits of foam stuck to the silicone holder over the microphones. Next time I'll mount the camera on the rear deck, which should give better sound as well. Might even use a remote microphone. I have a year to work all this out before the next event at Gurston.

Yes it's a lot steeper than it looks from trackside. Even the final drag to the finish is steep enough to keep me in second for about half of it.

AC does occasional regional tours, but he is booked months ahead. He prefers to be contacted via Facebook messenger. I could not recommend him highly enough. He knows more about these engines than anyone else I have tried, and his charges are modest.
Les Rose

Les. I'm sure the suction cup would give a more stable image but I'm also sure it would not pass scrutineering as cameras must be rigidly mounted. You might be able to get it past a scrutineer if it is tethered.

Here's a photo of my set-up. The arm is intended for mounting on helmets to show the user's face while doing stupid things like bungie jumping. It's a fairly old basic GoPro and it's a bit awkward switching it on and off with gloves on when belted in; I'd really like one with a remote control. The tether is an old guitar string. I've never had any problems getting it through scrutineering.

When the camera was mounted directly on the head rest stalk it was fine with the roof down but with it up the light balance is wrong, showing the dashboard clearly but seriously over-exposing the view ahead. Yes, the camera shakes but it gives me what I want for reviewing runs.

Here are a couple of on-boards. One is my best run so far this year at Loton Park, the other isn't!

http://youtu.be/ZZX4-ZlFJOg

http://youtu.be/ShFU6069mhg

Colin



C Mee

Colin,

Odd you got a helmet mounted camera passed the scrutineer as a neighbour mentioned they wouldn't let a guy on a test day because of the camera on his helmet. I made a new 3D printed adaptor to fit a Garmin Catalyst camera to a mounting as the original had broken but the issue was brought up that suction mounting was not allowed, they had to be rigidly mounted, IIRC this adapter fitted a stem which connected to the rear view mirror.
David Billington

David, my camera's not helmet-mounted, I just re-purposed a helmet mount for the car using GoPro clamps etc.
C Mee

Colin,

Bit of a brain fart there as I appreciated that you didn't have it helmet mounted, it was someone else that was trying to use a helmet mounted camera at a track day and was told he couldn't, against the regs.
David Billington

AC Dodd's video is up now:

https://www.youtube.com/watch?v=tAKjwg1i34E
Les Rose

Thanks for the video, Les, I learnt a lot from it; it makes me realise how much I don't know.

Colin
C Mee

Me too Colin! What is a wide band?
Les Rose

Wide band lambda sensor? https://en.wikipedia.org/wiki/Oxygen_sensor#Wideband_zirconia_sensor
David Billington

Great video with some very interesting comments.
I have just replaced my H&H electronic ignition unit, my coil is standard RLB101 with 3 ohm primary residence, Colin was saying 1.5 ohm is better. H&H specify 1.1-3.0 ohm so 1.5 is within the range. My plugs always look a bit black so maybe 1.5 is better.
He also set the plug gap to standard 0.025”, I have just set mine to 0.030”.
Les Robinson

Just looking further into this and a 1.5 ohm coil needs a ballast resister, a non ballast coil equivalent is 3 ohm primary residence.
I think anyway!
Les Robinson

Right, I am now happy that my 3 ohm non ballast coil is correct.
Maybe my plugs look a bit black as mixture too rich.
Fantastic video though, just wish Colin was closer to me.
Les Robinson

Les, I think it's AC you need closer to you, not me.

My automotive engineering prowess is nowhere near as good as his - or yours for that matter.

Colin
C Mee

Yes meant AC, sorry Colin
Les Robinson

Les, you are correct, a 1.5 ohm coil needs a ballast resistor "if you are running points or a fixed dwell ignition model".

If you're running a variable dwell electronic ignition module you can (should) fit a 1.5 ohm coil to get the most bang.

Also, when running both of the above, the plug gap should be 25 thou. Only increase the gap when paired with a "high energy" ignition module and a 0.5 ohm coil.

Best of....
MGmike
M McAndrew

So my understanding is that the H&H ignition is fixed dwell therefore the standard 3ohm coil is correct - I think!
Plug gap, I have always used 0.025” and had slightly black plugs. Speaking to a few other people the gap should be 0.028-0.030” , in the video AC set the gap to 0.025”, but to be honest I’ve not got a clue.
Les Robinson

Les (Robinson)

My understanding is that your H&H ignition is a basic points replacement system that is intended for use with a 3ohm coil (or 1.5ohm with ballast). I'd stick with a 3 ohm coil. Plug gaps - maybe up to 28 thou rather than 30. You don't want to stress the coil too much (a larger gap would tend to).

Second opinion anyone?
Bill B

Interesting the H&H is fixed dwell when most modern units are variable but I guess if they are producing for "originality" fixed dwell makes sense and a 3 ohm coil is correct.

I still think 25 thou plug gap is what you need. 30 thou will work but likely to misfire earlier in their lifetime. Also, if there's any change (increase) in lead resistance, you'll see misfires appearing which TBF will give you early notice of an impending failure ;0)

Black plugs are usually related to running rich but can also be a symptom of incorrectly set ignition timing or advance curve. It sounds like you do need and tune up by someone who knows SU's.

It's a shame I have no plans to come visit my sister in Preston ;0)

Best of...
MGmike
M McAndrew

Interesting video.

Les, what was the air filter ACD recommended ?
Tim C

AC said to fit the biggest filter I could get in, and approved a RaMAir foam one. I only had to move one of the air horns slightly.

The reason I had a 3 ohm coil was that it was supplied by PowerSpark to "suit" their electronic ignition module. Having watched a lot of AC's videos I rang them to check and they insisted it was correct. They also said I could widen the plug gap. Hey ho.
Les Rose

Les,

Did they say if using their ignition module with a 1.4 ohm coil might damage it?
David Billington

No Dave, they just said it was the correct coil. They said the 1.4 ohm coil is for the high power module, and mine is the standard one. Seems a bit counter-intuitive to me, as the lower resistance should raise the power.
Les Rose

I was rather sceptical of his argument for fitting a 1.4Ω coil as ignitions are challenged to charge the coil at high RPM not at idle but I suppose it depends on the specifics of the PowerSpark module and how it does variable dwell. As you say PowerSpark specify a 3Ω coil so it should be good.
David Billington

Interestingly Aldon only seem to recommend their 1.5ohm coils for racing etc (3 ohm normally) with the original pertronix unit.

“4/6 Cylinder Fast Road/Race - 1.5ohm - Chrome Oil Filled - Ballasted N.B. These coils will overheat if NOT used for race/high speed/high rpm applications”

They also do a Pertronix 11 version and they recommend a ‘Flame thrower’ 0.6 ohm coil for that one !
richard b

Dave B,
If I understand things correctly (and it's been a looong time since I did any inductor theory) the amount of current drawn by the coil sets up a magnetic field which then collapses when the points open to induce a current in the secondary winding. Now, If the coil resistance is lowered, the current increases for any given supply voltage. However, if the time the current is allowed to flow is also reduced by varying the dwell, the mag field stays the same.

On a standard fixed dwell system the coil is sized to work when the time the points are closed is the shortest i.e high revs. Adding a ballast and reducing the coil resistance keeps the current in the system the same but if the ballast is by-passed (as it is when cranking), putting a higher voltage on the coil allows more current to flow giving a better spark.

Now, if you can "tune" the system to manage the induced mag field at all engine speeds and a fixed voltage, you can fit a coil of any resistance. A powerspark module does this by varying the dwell through the rev range and, as long as the module can handle the current flow, a lower coil resistance can be fitted. In the case of the standard powerspark module, it can handle a 1.4 coil as it needs to when starting a ballast system. So why not use that ability to your advantage and get a better spark when running which is what ACD recommends.

However, the risk is that the module is pushed to the limit of its current carrying abilities and shortens its life! It may also explains why a 0.5 coil is only recommended for fast road and race conditions where a module is only used for "short periods" and why its important to use heatsink paste when fitting a module to carry the heat away, more so with a 1.4 coil.

AFAIK AC only fits a 0.5 coil when a "high energy" module is fitted that is capable of carrying a higher current for longer. I think this is fitted as standard to a 65D dizzy and is available from Powerspark in a dizzy with a Mini advance curve.

I'm currently running a Powerspark and a 1.4 coil with ballast removed on a BGT and so far so good (famous last words lol)

HTH's.

Best of...
MGmike
M McAndrew

Richard b,
The Aldon system must be a fixed dwell unit and the Ignitor 11 is a variable dwell unit.

The Pertronix Ignitor III looks to be a whole new ball game!!

Best of...
MGmike
M McAndrew

Just read this thread for the first time and one thing I have found is with a pair of HS2s starting from cold is almost instantaneous, but with a HIF carb on the same engine it take a second or two of cranking before it fires. The HIF carbs have a completely different way of enriching the mixture for cold starting, so this may be the reason.

Also, all ignition systems, whether points or electronic are induction based, but during the 70s a different system called CDI (capacitive Discharge Ignition). Whatever happened to that?

Rob
MG Moneypit

CDI was very popular on motorbikes IIRC.
Dave O'Neill 2

Rob, you might want to read my other thread entitled "Fuel flow issue". Today the tank was full and the pump clicked twice, then the engine started instantly. Not even one revolution before it burst into life.
Les Rose

Les thats pretty well how my 1275 starts. A few clicks from the fuel pump. Wait a moment whilst that pressure build up manifests itself as fuel topping up any losses at the carb Then press 'start' and it fires up on the first compression stroke.
GuyW

Maybe whoever named it should have called it Active cv vs Passive cv.



anamnesis

But...as described in my other thread, when the tank is near empty the pump clicks for 5-10 secs. When it stops clicking and I pull the starter, the engine fires once, the bendix gear spins down, and I have to churn it over for up to 3 secs before it fires up. Once warmed up it restarts instantly. Next time the tank is low I'll record the process.
Les Rose

As the carbs have fuel in the float chambers, the pump isn't actually the issue taking three seconds to start- that tbh sounds more like your choke lever settings - confirmed by the fact it starts well when hot, and not needing choke.
Malc Gilliver

This thread was discussed between 22/06/2026 and 05/09/2026

MG Midget and Sprite Technical index

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