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MG Midget and Sprite Technical - Cough, Splutter.

I have now had the carbs sorted. (I hope) There was loads of muck and stuff in them, apparently, the timing has been set, the tappets adjusted and the dash pots filled and it is now running sweeter on pick up - BUT there is now a problem when accelerating from a steady 30/40. If you floor the pedal it coughs and splutters and misses, more like an ignition problem.
It is a leaded head running unleaded petrol with valvemaster additive. It has points but soon to be replaced with electronic gizmo. Does the timing need to be changed at all for unleaded? The pancake air filters have lost their foam and are falling apart.
J Mee

iv got a 1977 1500 and it was running great. changed the airbox for twin pancake filters (100 worth not cheap crappy ones) and had nothing but trouble.coughing spluttering and basicly running crap even after its timing was done. after a week of this i changed the pancake filters back and put the airbox back on and its running fantastic again. might not work for you but gotta be worth a try.
roy j

Sounds like a possibility of 2 things.

Traditionally a weak mixture will cause spluttering and coughing and this needs checking,

however another cause of your problem JM can be that the oils in each dashpots are not balanced. Before filling with oil both carburettors should be emptied and then refilled with fresh oil that is exactly the same in each carb

Sounds like Roy needed a richer mixture with his new filters as well. :) have you still got them Roy?
Robert (Bob) Midget Turbo

Im thinking worn out dissy... to much play in the points plate.


Why? are you thinking that?
Bob Turbo Midget England

Hey bob,

Just my thinking... (and just a guess) that the vacume advance when fully and brutely activated is shoveing the points plate inside the dissy temporarly off center, if the little balls (cant remember if there are any) under the plate and/or the plate it self are worn then add in some shaft bearing wear ... Id think the breaker points plate would go out of round (for lack of a better term) for a brief moment causing a sorta short term misfire until the breaker point plate and worn shaft could re-agline itself after the vac advance went back to sleep, probably 1 good dissy rev for the re-aglinement. MMMMmmmm, More of a stall then a misfire that would have the appearance to be a cough/sputter

At a "constant" 30-40 mph J-mee would be in the 3rd gear range (well I would be) so the rpms would be rather low... guessing around 1500 to 1800, so there would be alot of avialible vac for the vacume advance to kick in right away and in a hard way, if you punched the gas pedal with some heavy boots, thus causing a worn dissy shaft along with a worn breaker points plate to move off center

If it where the dissy causing this then 2 cures, new dissy or a pertronix ignition chip to take the place of the points and condenser.

like I said, its just my guess as to why I think its the dissy.

but I was wrong way back in the fall of 1994 about how much suger to add to a gallon of lemon aide.. so Im probably due to be wrong agian at some point...LOL

Prop... disillision is really just another form of an illuision


Prop one problem at least, when you put your foot down at 30 MPH the advance does not "kick in" as you put it! it is already in, what actually happens is that the advance due to vacuum releases because the vacuum reduces so in your terminology it actually kicks out! and the dissy plate goes back to a neutral position
Robert (Bob) Midget Turbo


for some reason Id always thought of the vac advance working in the oppisite direction of what you stated. that the vac pushed the plate to advance, It certianly never occured to me that it actually worked in the reverse of what I was thinking.

on a fast 2nd round of thinking the new info certianly places a dead fly in my soup therory of a worn out dissy...

Ill have to kick that around the ol noodle for awhile

But I certianly like your thought on a weak mixture adjustment as a result.


yep bob iv still got them. iv put them in the pile of bits in my garage that iv wasted money on.i did put the car in the local garage to have the carbs tuned and balenced after i fitted them but to be honest i suspect they gave the job to the new kid as they did a crap some point il try them again and take it to a garage that nos classic cars for a tune.(im scared of carbs so dont touch them,lol)
roy j

a little more prop light of the new info

if the vac advance where not adjusted correctly... and I doulbt many are, cause no one knows the correct setting of that little adjustment wheel on the side that im aware of.

Plus if the dissy was worn as I was guessing couldnt there be a snap back of some sort when the plate was released due to the vac being applied from the carb releasing the plate to advance... sort of a momentary sticking situation in the plate / vac advance is what im mulling over in reflection

Im not sure that made any cognitive scence


Yes, the vacuum advances the timing (unless you have one of the 1500s with vacuum retard), BUT the vacuum is actually DROPPING when you step on the gas.

Also, that adjustment wheel doesn't "adjust the vacuum advance", it adjust the ignition timing. It is simply an easy way to micro-adjust.
David "go back to epoxying your truck frame" Lieb
David Lieb

LOL go for it Roy - you can always keep trying 'til you get it - it's not that bad - honest :)

I've invested in one of those electronic points replacements, will that make any difference? I'm not too clever at carbs and ignition. I can wield a spanner and do electrics but the workings of timing and fueling have always been a bit of a mystery to me!
J Mee

id certianly drop it in and see what happens. ehats the worse that could happen.. okay yeah a fire, but heck you got hot dogs and marshmellows right.

havent got my truck back yet... still looking for a ride to pick it up

rach i keep eyeing them up every time i open the bonnet (thats hood to all you lot that dont talk proper,lol),but to be honest the cars running so well just at the moment its a shame to poke sure thats gona change soon enough though.
roy j

I skimmed to the bottom, so apologies if this was mentioned above - the first thing I'd check in a case like this is the oil in the carb dampers. One of the functions of the dampers is to enrich the mixture on acceleration, and if you're getting (what could be) starvation on heavy demand, the enrichment function might not be up to scratch.

Only after checking damper oil would I even think of digging into the ignition.

Gryf Ketcherside

>>>>>>but to be honest the cars running so well just at the moment its a shame to poke about.<<<<<<<<

I belive thats whats known as "fixing what isnt broken"... if she is doing well, Id be 1/2 tempted to leave well enough alone till she broke or the snow and ice falls


This thread was discussed between 08/06/2010 and 10/06/2010

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