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MG Midget and Sprite Technical - Max Advance

Although I am thinking of changing my name to Max Advance, this thread is actually about the old perennial of ignition timing. I have just bought a new fangled 123 distributor and was wondering whether to install it with a maximum advance of 30 degrees or 33 degrees. 33 seems a bit high or am I wrong. Spec = MG Metro head, ported, Hif44, LCB, 1.5 rockers. I know this kind of question have been asked before but I'd like to ask it again.
Chris H (1970 Midget 1275)

Whoops - I just found Eddy Veugers earlier thread on this subject. Still, if anyone has anything to add I'd be grateful. Chris
Chris H (1970 Midget 1275)

Depends in part on what static setting you use.

IIRC the std dissy has 13 deg advance on the bob-weights; this translates to 26 crank advance. Then add in 7 static and you have 33 deg total.

What CR are you running?

A
Anthony Cutler

Anthony

I have no idea what the compression ratio is with the new head (should have measured it before fitting)
Chris H (1970 Midget 1275)

Max advance as a name....HHhmmmm

Sort of like "Max headroom" from the early 80's

Prop...I want my MTV...Prop
Prop***The End in 2012

In asbsence of CR info, you should start with low adv and increase - checking for pinking / detonation as you gradually advance the ign, and moving back to last good setting.

Start with say 28 max (5 static and 11/12 dissy that is 24/26 crank degrees) to start. Choose a slighly lower rate of advance to begin with.

Best done on a RR.

A
Anthony Cutler

Chris,

The best way to set up your ignition timing to get the most out of it is on a Rolling Road.

In an ideal world, the RR operater would have a 'knock' sensor which he will attach to the block whilst running the engine, run the car up so it is developing full power and then 'swing' the distributor to gain your maximum power output whilst observing for 'knock' (pinking).

All this will be done on a hot (temp) engine running at circa 6000rpm, so not many RR operators are willing to do this......

Good luck.

Mark.
Mark T. Boldry

Hi Chris,

Glad you found my thread! I have made a study out of it, also on ported and manifold vacuum.

I had the dizzy out 5 or 6 times until I was happy with the setting. I settled for nr. 5 curve. 30 max is enough, I wouldn't go higher, especially on a 1275 (mine is 1430 and bigger engines can handle more advanced ignition). It started knocking on nr 7, so I went back two steps to be on the safe side. It is running like a dream now, excellent pickup, driveability and smooth idle.
Tonight I'll start experimenting with the vacuum. The vacuum is just for fuel economy anyway, so I'll hook it up to the manifold. If it screws with my idle I'll change to ported vacuum (ported vacuum gives no advance at idle when the butterfly valve on the carb is shut).

Fitting it is really one of the easiest jobs I've ever done!
If your midget is RHD than you'll need angled HT leads though!

Good luck!

Eddy
Eddy Veuger

Hi
I have followed ignition timing threads before and the practice of running the most advance before detonation worries me still. I must be getting old but I was taught years ago to set ign timing on a roller the idea is to get to a point of max horsepower at a given rpm them pull the timing back till the power just starts to drop off then just creep it back up to get max HP. Repeat this at several different rev spots and use the results to build that magic detonation free dizzy. Using the max advance method as suggested elsewhere promotes early big end failure and the risk of detonation when being worked real hard. I'm for 30 max for a 1275 with a suitable curve to suit the particular engine. Tell me if i'm wrong though.
G J Rayner

Hi GJ

I used to set my ign by ear so that it never went into pinking (most likley with std dissy at around 2 - 3K), starting from retarded setting.

Unless you have access to RR (as everyone in thread recommends, and I as i have done many times to find least advance for best torque), this is a reasonable way to go - assuming you have a sensitive ear to catch feint pinking noise.

A
Anthony Cutler


Chris--I have the same setup you do except-- standard 1.3 rockers, and standard but ported head, with CR of around 9.8 or 10.0. I use 92 octane fuel, 180 degree thermostat. I'm running the most aggressive curve available on the 123 dissy. (I think it's no. 8? with max advance, I think 32?). However, it may be too much. On long climbs (freeway, 70 mph or so) I start to lose a little power and the engine temp goes up 20 degrees or so. But I couldn't hear any pinging. (But you can't hear much anyhow for all the wind noise). I think I may be into borderline detonation. Also, I may be running a little too much initial advance. After setting the idle advance at the recommended 10 degrees, I twisted the dissy just a little more because it sounded and idled better.

Recently, I lost some power after a long high speed run and discovered that the No. 3 spark plug insulator nose had partially crumbled. Which could be a sign of detonation. On the other hand, I had taken those plugs in and out so many times (checking plug color) that maybe the ceramic had been weakened on that plug.

I've since put new plugs in (BP6ES). I'm going to start over from "zero" and back the curve selection down one notch. (I think I will keep that little bit of extra advance at idle and choose the "30 degree total" curve). Will let you know how it goes. Car runs wonderfully in all other circumstances (newly rebuilt engine).

Cheers!
JM Morris


Update: 123 Dissy has been set to curve 7 (which is most aggressive curve with total 30 degree advance). I decided to set it according to the instructions (gives 10 degrees advance at idle of 800 rpm). Runs great. But one problem--checked the plugs again and the nose ceramic is bone white. Plugs are apparently too hot. Gonna now move to BP7ES, one range colder.

Will update next next weekend.
JM Morris

Update: Changed over to BP7ES plugs and that's still too hot!! Having to order BP8ES plugs. They're not an in stock item locally. Won't be in til Tuesday.
JM Morris

Or is it running too lean? Got a Colour Tune?
David "the glass has to be leaking" Lieb
David Lieb

Agreed - probably rich or retarded, i.e. static setting not right. easy to Richen one flat and take a look at plugs. Normally - white electrode and black surround on body.

A
Anthony Cutler

Mine's a 1330, 276 cam with a played about with Hif44 and we reckon about 11:1 compression (I'm using BP7ES plugs).
Had mine on the rolling road today as the 123 was set at number 1 (I think) and the carb had completely the wrong needle fitted. It was running so lean that it wouldn't go above 70mph.
first run in a sorry state gave us 70(56)bhp @4300 rpm, which clearly wasn't right.
We ended up setting the advance at 27 degrees (7 degrees at idle 900rpm) Changing the needle to a BBW and ended the morning with 102(81)bhp @5882 rpm.
Not the worst £100 I've ever spent.
I was expecting (based on nothing whatsoever) about 90 bhp.
More importantly is feels good all the way up to 6000rpm.
I can't for the life of me remember what setting we ended up with on the 123. Toby will remember though.
G Lazarus

Im glad that worked out for you then Gary, I'll just watch at the next track day then!

he he
Bill sdgpm


Hmmmm...

That'll be why I couldnt catch you at Marham then Gary!
Bob T

JM
Please richen it up and/or check your fuel supply (volume and pressure)before you melt the thing. Your problem looks like a fuel starvation thing from here
When the mixture is correct-- after a full throttle run your plugs should a light brownish/varnished timber sort of colour on the centre insulator and charcoal grey on the outside ring but dry If the grey is at all damp and canbe rubbed off onto your finger it is too rich and on the other hand if it is light grey or lighter and the centre is light or whiteish it is too lean. The heat range of the plug wil NOT change the mixture.
Hope this helps Willy
WilliamRevit


Yes--I've come to the same conclusion--way too lean. Currently running a BFM needle. (Maybe that's why I've got basically no power beyond 5000 rpm?) Now going to move to the BDL needle. Fuel pressure regulator is set at
1 1/2 pounds. Is this enough?
When I bought the carb from APT, it came with the BFM. I asked for "the next stage richer" and they sent the BDL. We'll see what happens. If I still get white nose insulators, I'm going to start filing on the BDL needle.
Yes--I have a ColourTune. But I'm not sure I can accurately read it, except at idle. I'm somewhat fearful of "putting the pressure to it" with higher rpm, and at any rate, I can't read it out on the highway under load.

You guys in England are lucky. It seems there are lots of rolling roads available there. We have nothing available around here. And even if we did, nobody here is going to have a selection of SU needles to try.

I've been looking for months for a good analog A/F ratio meter. Something I can read while driving the car. Everything I've seen available requires welding a bung in my header, and is digital only.

Open to all suggestions.

Thanks loads!!
JM Morris

JM

Given that you have the same set up as me (more or less) then I can't understand why you are not using a BDL needle in the first place. I set my car up as if it was an MG Metro (as it had a Metro head and metro HIF carb) and MG Metros were fitted with a BDL needle. I compared the BDL and BFM needles using WinSU and BDL is consistently richer than BFM (i.e. it is consistently thinner than the BFM needle). I think you may find a big difference now.
Chris H (1970 Midget 1275)

yup all needles for the MG Metro start with BDL except later (maybe fuel economy or emmisions concious) BFY

I dont know how BFY differs but expect its less rich, anyone able to confirm?

That (BDL) is the factory setting and ought to be basic kit
Bill sdgpm

Mine ran like a pig on BDL, we eventually settled on the BBW for mine, but I wouldn't mind getting Mr Burgess to have a go with his emery cloth on that one.
G Lazarus

I know you don't like speaking to me Gary but there is no reason why your engine should have run as badly as that with a BDL needle. The BDL is probably not perfect but it should not have been that bad. Are you sure there was not another reason for the total lack of power before the RR session?
Robert (Bob) Midget Turbo

I suspect what Bob isnt saying is we need to have an idea what curve the dizzy is set to now, too

As Bob says BDL ought not be very far out because it's where the factory setting started

But I have seen a lot of HIFs that didnt live up to their "star billing", I think that Geoff has one* on his shelf in the garage, which when in my car hit a virtual brick wall at 3,200 and I never did get to the bottom of it. Could easily have been an advance issue, but I just fitted another one instead which whizzes up to speed

*I'm not sure where that one finished up...
Bill sdgpm

Not really Bob,

The first run was 70 (56)bhp
the second run was 97 (78) bhp and all we did was change the needle, but I can't remember what to.
the last run was with the changed profile on the 123, the timing done and the BBW needle which gave 102 (81)bhp.
Toby may be able to tell you more as I was in the car with my foot to the floor so might have missed/forgotten something.

What do you feel would have been the cause of such poor performance?
G Lazarus

The Hif was Alex Wainwright's very played about with one, but if it was a bad one, why did get such a marked increase in power when only the needle was changed?
G Lazarus

Just for information - a BFY needle is virtually identical to a BDL except it is slightly leaner at the bottom end/low revs. BBW is richer than BDL from about half way along its length and the difference gets bigger as you proceed down the needle to become VERY rich at full power.
Chris H (1970 Midget 1275)

But my compression is about 11:1 (we think)
G Lazarus


Chris H: The carb may have come from the factory with the BFM needle installed. And me--I didn't have a clue as to where to start on needles. Now I'm starting to get a better picture from you guys.

Frankly, the car has run great and is getting excellent gas mileage. If I were to drive it normally or baby it, the BFM needle would probably "get by". But i just can't keep my foot out of it.

How about the fuel pressure regulator? Is 1 1/2 pounds enough? And then of course, there's the question of whether or not the regulator is accurate, and whether or not the fuel pump is keeping up at higher, extended revs. (The regulator came from BV or Moss).

What plug gap is everyone running? I've got the Lucas sport coil so I've opened the gap up to .035.

Thanks, fellas!
JM Morris

With the 123/Mini, tou can probably open the gap even a little more. The problem with running more gap on a Lucas dissy is that the spark finds alternate paths to ground in the distributor cap, but the Bosch cap on the 123 might be better at resisting that.

1 1/2psi is not really the question. The question is whether the regulator you are using is capable of flowing enough volume to supply the engine at the higher revs. The Bentley manual indicates that the pump should be able to push 67 US Pints per hour, so about a pint per minute. Since you desire to wring rather more power from the lump than the factory did, I would kinda want to see a bit more ambition than that from your current configuration.

The SU carbs tend to be unable to resist more then 2psi or so at the inlet needle (I would try opening it up to 3psi and seeing whether you get any flooding at an idle).

You might also want to open the regulator up (if possible) and look for any sign of deterioration of any rubber bits in there. Some regulators do not seem to be able to handle modern fuel additives very well/long.
David "you might want to try a different fuel pump" Lieb
David Lieb


Update: Changed to the BDL needle. Plug ceramics have gone from brilliant bone white to slight greyish tinge on white. Still too lean. Guess I'm ready to go to the BBW needle.

What's the best source of SU needles here in the states?

Thanks!
JM Morris

Joe Curto?
Trevor Jessie

http://www.joecurto.com/
Trevor Jessie

Hi guys
Just one little thing-- The plug colouring suggested earlier is for full throttle runs only and will be at an air/fuel ratio of somewhere between 13 and 12.5 to 1 .
If you are checking plugs for less than full throttle (for example-cruising)they will be lighter coloured as the cruising mixture will be leaner, probably about 15 to 1. or even leaner. For anything other than testing for mixture at full throttle a gas analyser is the way to go for acurate measurements Good Luck Willy.
WilliamRevit

Have you tried WinSU: http://www.winsu.co.uk/
It's a pretty cool program, I used with my mini and it got the needle choice bang on and was only a couple bhp out on the power estimate. Only catch is it's free to try but it only recommends needles if you pay £10.
Grant S

This thread was discussed between 28/01/2009 and 02/03/2009

MG Midget and Sprite Technical index

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