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MG Midget and Sprite Technical - Midget 1275 engine troubles
| i have a 1275 midget that I have restored over the last two years. When I|
first bought it it seem to run fine and had no issues. However since putting
it back together this winter I am having problems with it. It started out
with a little miss but seem to slowly get worse. during the restoration I
replaced the points condensor cap and wires and have ststic timed it. The
next thind that came to mind was the gas that had been in the tank for two
which I drained and replaced with fresh fuel but still had no improvemnet. I
then changed the plugs out and found covered with black soot so I replaced
them as well. Still runs rough and sometimes starts hard. Tonight I went out
to change the fuel filter and it seem to run not bad however after about 10
minutes it started to sputter and stalled out and didn't want to restart,
however after a little coaxing did finally start bur ran horribly spitting
and backfiring until it finally quit. Now at the end of the day it will only
start if I give it fuel and will not stay running. It acts like it is
starving for fuel when it quits. To me that would only leave the
carburaters, that place where I don,t really want go or know what to look
for. Any suggestions or help would be appreciated.
Thanks Gerry Blank 74 Midget edmonton Alberta Canada
|What exactly did you take apart?|
|Brad (Sprite IV 1380)|
Did you take carbs off, if so did you change gaskets(carb to manifold) as this could be your problem,to find out try and get the car to tickover then grab the dashpots and try and move them back and forward,if the engine runs smoother at any time this could be the problem.
I presume you are running 1" 1/2 su's ?
|re-check the points gap|
you could be surprised...
Disconnect fuel line from carbs. Have suitable receptical available at line end.
Turn ignition on see if flow is constant. You may have a fuel pump issue.
Black plugs means mixture too strong so could be you have upset the tuning. Look on the archive for more details. Even a numpty like me can get the carbs sorted to run OK.
Otherwise, it must be ignition (again check archive on options). NB - weak/failing ignition items tend to give up more readily when they are hot in my experience.
|Im guessing a fuel pump issue also. and the loose manifold is always a possiablity....try spraying some WD40 or starter spray around the carbs and manifold while the engine is running ... if it speeds up, you got a leak...but the fly in the ontment is the plugs appear to be running rich...if you had an air leak you would be running lean an no sooty plugs|
Another guess...would be the dissy cap/rotor...it may have a fine crack and opening up when the engine warms up...and there is a rash of bad rotor bugs becoming almost as common as the condensers...yet the caps and rotors look perfectly good
If the car sat awhile Id pull the wires out of the cap and trim them back a bit...there maybe a bit of crossian on the little screw spike that holds the lead.
|Thanks to all for your respones. As for some answers to your questions. The engine was removed from the car but other than removing the carbs to clean and paint the block nothing was disturbed on the engine, all intake gaskets were replaced when the carbs were put back on. Last night I confirmed the points were properly set and for some unknowm reason I put the old cendenser back in as well I retightened all the intkake bolts. The car then started and seem to run pretty good but still had a slight miss. I will take it for a test drive tonight and check the fuel pump then see what happens.|
|why your out in the dark....find a place thats really dark so you cant see a hand in front of your face and pop the bonnet with the car running and look to see if you have a nice blue electrical light show...If so you will know what needs repaired and replaced|
| i took the car foe a test drive today and seem to run pretty good except one time while sitting at a light it started to sputter when idling but then smoothed right out when I pulled away and continued to run well. In the evening after dark I started it up and run horribly until I until I revved it a bit and then released the choke fully, it then seemed to idle quite nicely. I then turned out the lights and checked for sparks and noticed a very light sparking coming from aroung the porcelin on all for plugs, not a bright light show but a definite spark. These plugs were all replaced three days ago so it is hard to imagine all four being bad.To recap it seems to run fine when warm but doesn;t like to idle with the choke on even when it is cold. |
Any thoughts? Gerry
|what breed of plug did you fit?|
and what type of plug lead cap?
is it a bakelite (hard plastic) type or the rubber conforming type that slips over the sparkplug and grips quite tightly
If type a: get type b:
I find the conforming ones are less likely to get high voltage flashover than the hard plastic ones
but the sparking you saw might just mean there was hig atmospheric moisture content causing a runaway effect
There is NO definitive "this is wot done yer in mate" I'm afraid, just a series of maybes...
|I put NGK plugs in it the exact same plug that i took out and I have the rubber boot type wires that fit qiute tightly.|
|How's the earth strap?|
|Alex G Matla|
|Contrary to popular belief - not all Brits need a good belting before working when cold! If she doesn't NEED the choke to start, or she starts with it then runs well without it - don't bother using it!|
Tradition used to be - the only good use of the choke was to hang one's handbag on anyway :)
How's the weather in Edmonton? Or at least, what's the weather forecast for early May? I'm going to assume you're not under 6' of snow if you've been out driving though ...!
|It sounds to me like a partial blockage in one or both of the fuel jets. Blockages don't often occur in the jets of an SU carb because the needle tends to dislodge and break up any rubbish coming through. But occasionally a bit of crud gets through the little feed pipe but is too large to get flushed out through the jet. The needle can keep poking it back down the jet tube, clearing it for a bit but it then gets back into the jet where it impedes the fuel delivery again.|
Try removing the jets ( emulsifier tubes, I think they may be properly called). You can do this without removing the carbs. Take the air filters off to give you access. Remove the tiny cross- headed screw that connects the linkage leaver to the side of the jet. Don't disturb the nut around the jet which adjusts the height and also centres the jet and you shouldn't then need to readjust anything later.
Undo the compression nut on the other end of the feed tube at the bottom of the float bowl. Fuel will flow out of the carb, so be prepared to either just let it, or catch it in a small tin. The fuel rushing out will help flush any silt from the bottom of the float bowl. Take care not to loose the tiny washer and seal on the end of the tube. Lift the jet and tube away and clean it out and then rinse in petrol.
When you reassemble do NOT over-tighten the tube fitting at the bottom of the float bowl or it will deform the washers and it won't seal properly.
Of course.....it may be nothing to do with this!
|It might be a good idea to pollute your local area by spraying the carbs and linkages with aerosol Carburettor Cleaner spray, before stripping them down|
the spray looosens all sorts of "poo" and washes it all away
take the air filters off first so you can spray into the inlet tracts and watch the carbs change colour.
quite amazing if you have well dirtied up ones fitted
Spray down into the jets with the needles lifted and the cleaner will dissolve any deposits inside
carb cleaner is highly inflammable and needs treating with respect, but over the years it helped hundreds of motorists with seemingly irrepairable carb troubles to get back on the road
|Carb cleaner got my lawnmower going when nothing else would!|
|That does sound a bit less fiddly than my detailed explanation of cleaning the jet tubes! Must remember to buy some of that stuff for next time!|
it is damned good stuff
I would never HAVE a garage without at least one can of the stuff any more
You can run an engine on it even if the pump isnt working, a godsend if the tank is empty and you need to crank enough turns to get the pump reprimed
spray into the carb mouth (or injector airbox, plenum, etc) whilst cranking. If there is a back fire or flash its easier to let the button go than relying on splashed inside petrol flaming out
Not that we'd ever splash petrol down t'hole in a desperate attempt to breathe life into a reluctant engine
This thread was discussed between 16/04/2010 and 19/04/2010
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.