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MG Midget and Sprite Technical - Carb Balancing

I have a simple but effective carb balancing manometer. Even though using this as per on line and manual instructions I have never been fully happy with the results. Either tickover was a bit lumpy or throttle response was a little lazy. After examining the the carb set up I noted there are two clips on the shaft which joins the throttles and these have a prong that fits into slots in the leavers on the butterfly spindles. As the shaft is rotated by the accelerator cable the prongs turn the throttle leavers. The slots are wider than the prongs so the the throttle springs can pull the butterflies down without being hindered by the clips on the connecting shaft.

I was loosening the clips, balancing each carb and then retightening the clips. This was fine providing both of the prongs on the clips were in alignment within the slots. If they were not one throttle would open a little more than the other when accelerating.

I have now balanced each carb, with the clips loosened i.e. for tickover, and then wedged the accelerator open slightly and reset the balance, locking the clips to the spindle.

This appears to have produced a nice, 700rpm tick over - consistently! and a snappy throttle response.

Jan T
J Targosz

Well done.

But you'd have got there a lot sooner if you'd have read the Driver's Handbook relevant to your model - other paper printed and electronic publications are available.

Extracts below from my stock.




Nigel Atkins

You tell him Nigel, by crikey, it's in the book--lol
But even by setting it up with the correct clearances with feeler gauges, if you have a suckermeter it pays to double check at light throttle as Jan has now done with his throttle wedged on a bit
The lower the speed after both throttles have just come off their stops the better for this, it's that initial little balance just after cracking the throttles that makes all the difference --
normal tuning stuff
willy
William Revit

Well I did put >>other paper printed and electronic publications are available<<.

TBH sometimes I found using the feeler blade sometimes worked and other times it didn't so I set the gap using an individual wire feeler gauge until I dropped it in the engine bay and it disappeared forever (how?). Then I went on to just using my wonky eyes. As is known I'm not the best at setting the carbs, luckily if they're clean, lubricated and not too worn there does seem to be a reasonable amount of tolerance.

I referred to the Driver's Handbook as some people don't know of its existence and just how much is in it, on the car and servicing but you do have to read it and refer to it when required. As has ben discovered a few times even long term owns can benefit from reading the Driver's Handbook (but male ego can sometimes get in the way).

And anyway my commission from sales has dropped a lot recently.


Nigel Atkins

I do agree Nigel-the handbook was printed for a reason, but sadly most of them don't get used much.
William Revit

Willy,
are you alright? You do realise you're agreeing with me, sit down and rest and it'll probably pass, if not possibly best to seek medical advice.
Nigel Atkins

Much to Nigel's horror and disgust, I like the driver's handbook and refer to it often. Its so nice to have a compact book where all, or at least most, of the contents is useful information. One becomes so weary of modern car handbooks that are so packed out with unnecessary drivel like how to open the glovebox and not to drink the windscreen washer fluid, but have little or no useful factual data.
GuyW

I agree Guy. I find the handbook a useful tool and quite often refer to it. I guess people of a certain age are used to cars needing checks etc on a regular basis whereas moderns hardly need touching at all. The manuals for these are more to protect the maker from an injury claim!
Bob Beaumont

I well remember the Handbook for the 1999 Mk2 MX-5 and at least a third of it was safety warnings like don't put your head under a wheel and let someone drive over it, your head not the wheel, but the the Miata was popular in America where they litigated against their own stupidity.

Now they seem so complicated even if you know what is meant there's confusion. Mind you I still find the good book's description of setting the carbs a bit confusing, perhaps I should put my head under a wheel and see if that helps.
Nigel Atkins

Nigel--You know i agree with most of what you post here,
----speaking of the Mazda handbook, back in the early days the Mazda handbook used to be in both Japanese and English--The bulk of it was Japanese with little translated fillins
I can remember a guy come in one day with his Mazda van and complained that the wheelnuts were too tight and he couldn't get a wheel off, bit weird as we were a bit pedantic about wheelnut tensions during predeliveries---He'd read the hand book and followed the instructions for jacking etc and found the wheelnut wrench(under the hatch for the engine bay-?) but couldn't budge them--They have LH threaded nuts on the LH side which caught him out---He had noticed an asterix in the instructions but couldn't find a reference to it and wanted to know what it was for-----Well, i decided to run through the handbook with him so he'd know--
Went through jacking, he was ok with that then the wheel wrench,ok then it said undo the nuts with the asterix quite prominent---looked and looked,nothing, then found on the bottom of a page 5 pages on which were mostly in Japanese, it said in quite small writing -NOTE-LH wheels have LH threaded wheel studs
stupid handbook---I know it got lost in the translation process but it sure tricked this fella
William Revit

--" not to drink the windscreen washer fluid -".

Is that really in a modern handbook Guy? I won't be surprised if you say yes. 😅
anamnesis

I don't own a drivers handbook but do have an original workshop manual. Unfortunately this is for 948 and 1098 cars and mine is a 1275. I considered buying the correct one for my car but decided against it after looking up ignition timing in the edition I have. Maybe a 1275 is different to earlier models but the info was useless to me. A picture shows the pulley, viewed from the front, aligned with the TDC pointer. The front crossmember on my car totally obscures the front of the pulley and the only way I can set TDC is to crawl under the car and look at the pulley from the rear. This requires a white stripe to be painted on the back of the pulley. To make matters worse the manual says turn the engine over with a spanner on the front nut. The crossmember also prevents this and because the front of the car is raised the only way to turn the engine is to take out the plugs, lift one rear wheel and rotate this. If the 1275 manual shows how to easilly set the timing can someone please let me know and I will look out for one at the NEC in November.

Jan T
J Targosz

Jan, the manual doesn't tell you but the solution is to fabricate a pointer on the top of the chaincase and re-mark a tdc notch on the pulley.
GuyW

Jan, I found I could turn it over by taking the plugs out and pulling on the fan belt.
Jon
Jonathan Severn

If you print off a 360 degree scale you can set idle and full advance too.

f pollock

or rocking the car in top gear with the brakes off (on a level surface of course!)
Bob Beaumont

This thread was discussed between 03/09/2022 and 06/09/2022

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