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MG MGA - Getting the right Engine tone

I was just wondering if any of you can give me an insight about what I am experiencing.

I have tuned the carburetors several times with the method described in the SU Carb tuning manual, with (what I think is) success.

The car runs fine, and has good power but at idle (around 800-1000rpm), the note is not as regular as in modern cars today. It seem like the 'sound of the explosions is grouped in threes'(like "pop pop poptoro pop pop", rather than "pop pop pop pop pop". Difficult to explain what I mean...

My question is weather this is normal for an MGA, and cars with mechanical distributor, and if it is a sign of the points/distributor/cap being worn.
Since the engine runs good I guess the static and dynamic timing are correct, but I never check it.

I was wondering if changing the distributor cap and points many and improvement to the steadiness of the engine.
Obviously at higher rpm this can't be noticed.
I also realise this could come from the mechanical carburetor which is less precise than modern injection systems.
Probably nothing to worry about...?
Gonzalo Ramos

I wouldn't worry much. If it really irritates you then the fully electronic 123-ignition promises "spark-balancing" to even out the misses you get with a conventional systems.
http://www.123ignition.nl/brand/MG.html
Willem vd Veer

Is the car running a little rich. Sometimes when you tune the car if its a little rcih it can sort of gallop in sound rather than be a smooth even tone. This can also happen when you over rich the mixture with the choke.
DJ Lake

I was once told by an old BMC engine tuner from the 60s that a correctly tuned B-Series engine does not idle that smoothly, but sounds something akin to what I think you are describing. Mine does the same although not sure about the poptoro bit!

Steve
Steve Gyles

I have owned six MGA's, currently two (which have been comprehensively restored) . None of them have idled very evenly, ie not as well as MGB's (dare I say it!), despite repeated tuning etc by experts.
Barry Bahnisch

I hate to be different, but my completely bog-standard 1500 (apart from K&N filters and 25D4 distributor) runs as sweet as a nut at tickover and everything above! Distributor is a 25d4 with conventional points, ignition timing is 32 degrees full advance @3000rpm (with vacuum disconnected during timing), plugs are NGK B6ES. The carbs have been overhauled and are fitted with Grose jets in the float chambers. Carb dampers are the correct non-vented cap type (the standard carbs fitted on my car have the internal vent port) and the dashpots filled with genuine SU damper oil. Carbs have been balanced using a gunson Carbalancer and mixture is set so that when the pistons are lifted at tickover, a momentary increase in revs is just perceptable. Valve clearances are set to 17thou hot.
I have heard plenty of other MGAs that run rough on tickover (never heard a Twin Cam with a nice tickover yet!), they all sound to me like they are running too rich, but as I say, mine is a pleasure to listen to at tickover and performs very well with the "taps open"!
Lindsay Sampford

Dont wish to sound envious of your sweet tick-over Lindsay but the next time I see your car with the bonnet open I may accidently snip one of your plug leads!

Its for your own good!

Only then will you be able to join the rest of us in the "Lumpy-Idle MGA Society"

Colyn
Colyn Firth

Colyn, I shall certainly end up with egg on my face if it's running like crap the next time I see you! You might not have to snip anything, are you doing The Southern Tour or am I safe 'till next year?
Lindsay Sampford

Southern Tour? I hope your passports are current up there in the north. You will need them to come down to 'our' part of the country.

Lindsay, my engine sort of burbles at idle. There is no variation in the RPM. I guess it boils down to description. Put mine alongside yours and they will probably sound the same, but I would say burble and you would say smooth.

Steve
Steve Gyles

Gonzalo,
The Brits seem to have hijacked your thread!..:)
Is it possible your car has a "fast street cam" upgrade? If so, due to valve opening, more overlap on a performance cam, it may be a little "lumpy" at idle. This is not necessarily a bad thing.

GTF
G T Foster

Are you doing The Southern Tour Steve? http://www.mgcc.co.uk/mgaregistereventscbl.html be nice to see you. How's your application for "Southern Citizenship" coming along?!
Lindsay Sampford

Sorry about my "smooth idle envy syndrome" taking over your thread Gonzalo although it does seem to be very similar to your condition. Its just that Lyndsay's "sweet-idle" just got the better of me for a moment there!

My MGA is fitted with an MGB 3 bearing engine which is mildly tuned and has an uprated cam installed.
This is most likely the reason for my lumpy tickover and I have had to increase the idle speed a couple of hundred rpm to help offset this.

I have owned 2 MGAs before this one, both of them in standard tune and I recall that both had pretty uneven tickovers. I have also noticed that on all three cars, the tickover speed tends to reduce as the engine temperature increases.
So if I were you Gonzalo, I wouldnt worry about it too much.

Yes, Lyndsay, we are booked into the Southern Tour, you may not be able to see me though.

I will be wearing a "Ghillie suit" Cammo outfit and I will be invisible in my hide in the hotel grounds with my insulated wire cutters in hand.
Just patiently waiting to snip the odd HT lead on any "Smooth-idling" MGA that drives by!

So beware of the militant branch of the Lumpy Idlers Liberation Organisation, more commonly known as LILO.

Colyn
Colyn Firth

I think I know where this lumpy tickover thing comes from. Walk round the pits on a race day and you will hear lumpy running at "tickover" (usually about 1500 rpm on a racer!) all over the place. Chug-chug-snort cough-splat-rort-bang-chug... they go, until...the leather-clad driver drops into the seat, plants his right foot on the pedal and, as the rev counter hits about 4,000, transformation! Suddenly it all pulls together and sounds like some kind of raging beast waiting to do battle! If they just went from a smooth tickover and climbed steadily up the revs where would the drama be?
So, are some folk deliberately making their cars run rough at tickover?
True, an engine with a particularly bumpy cam and high compression is not going to sound it's best at tickover, but a perfectly standard MGA (apart from the Twin Cam!) at tickover should, as Steve says, burble.
Lindsay Sampford

This is my 1500 a while back. Really a pretty smooth idle.

http://www.youtube.com/watch?v=0YjWWhZpDA0

Jim
Jim Ferguson

Yep, sounds just right Jim.
Lindsay Sampford

Gonzalo, are you still out there? You've gone "quiet". Is your car still missing at tickover or have you found it? Listen to Jim's car on the YouTube link above, that's what a standard 1500 should sound like, I can't remember whether you have a 1500 or a 1600 but they should sound about the same. You could try letting it idle for about 10 minutes, stop it and then take the plugs out to see if there are any clues there i.e. sooting or different colours on the noses.
Lindsay Sampford

I've gone quiet cos I haven't really had time to mess around with it yet.
In fact I am getting married, so I have some 'STUFF' to do, that is less interesting that working on my car, but I have to do it.

Jim, indeed you car does sound VERY smooth at idle.
I will have to post a video of mine too to see what you guys think.
In fact I was planning to meet with Terry (another fellow MGA owner from around Miami) to compare the engine sounds.

I find that the sound at the engine compartment on mine is relatively smooth but the sound it mainly a 'Tappet' sound. However the sound at the exhaust is a bit more splashy/irregular. Understand what I mean?

I have a normal compression 1600, so I guess I can tune it to run very smooth...

I will also try to take the plugs out after the next drive to see what they tell me.
Gonzalo Ramos

I just saw GTF's post.

How can I tell what kind of CAM is installed in my car?
The rebuild history of my engine is unknown.
Gonzalo Ramos

They do make a lot of tappet noise with 17 thou clearance, that is normal. The MG ZA Magnette (same engine but probably different cam) called for 15 thou valve clearance, and that was noisy enough! But you definitely should have an even sound at the exhaust not 1-2-3 mis-one.
Lindsay Sampford

When I completely restored my MGA Roadster, finished 12 years ago, I correctly set the carbs and all settings, timing, etc. and haven't touched it since. No need since it runs sweet and strong, smooth and straight. Stock 1500, stock cam, stock distributor, stock ignition, stock everything. If it ain't broke don't fix it. Do it right, spend the time and $ the first time and forget it. My .02 and I'm sticking to it!
BRIAN WARMUTH

My MGA 1500 is very stock and at idle produces what I would call a "throaty 4-cylinder rumble" through a very cheap aftermarket muffler (I think the brand was called "Thrush") but no uneven popping noises. I have always thought this was normal!
Tom Heath

Hi Gonzalo,
See this article on working out what cam timing you have.
http://cranecams.com/?show=article&id=3
Regards
Mike
Mike Ellsmore

Gonzalo,
I hope you are going to post some photo's of you and your bride driving off from the wedding using wedding cars tunbridge wells in a red MGA!
Congratulations, and all the best of luck!
Phillip
Phillip Hughes

Well, just got back as a married man!
I would have used the MGA to drive of but I got married in Spain an the MGA is in Miami.
Oh well, ... : (
I would have done it in my dad's Panther Lima that he just bought... but thats a different beast altogether.
Finally just drove off in a modern Mercedes!

No that I am back I will get stuck into the original topic of this thread...
Gonzalo Ramos

Gonzalo

Congratulations. Best wishes to you both.

Steve
Steve Gyles

This thread was discussed between 13/08/2010 and 31/08/2010

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