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MG Midget and Sprite Technical - Fuel vapourization?
|Started using the Sprite in anger for work this week and have encountered an issue with miss firing. After a long climb up a steep hill the car splutters and loses power, this happens just as the hill is flattening out. I can keep the car moving slowly and after about 20 seconds starts to pick up and then runs fine again. The copper fuel pipe runs vertically between the engine mount and carbs and feels warm from heat from exhaust. Could this be fuel vapourization? I have standard fan and SUs.|
|Don't drive up Mucklows!|
Or Waterfall Lane
No really, (mine goes up there easily), I don't know about vaporising for this problem.
More likely the pump isn't providing enough fuel on demand to keep the floats floating so the fuel level gets too low to reach the jet. Then the car really does just run on fumes
How old is the pump? Can you check the flow by disconnecting the carb suppply and running it into a catch jar
Engine off, cold. We do not want the West Midlands Fire Service to have to make a visit...
I hope someone can tell you how quickly a pint should fill the jar, 'fraid I can't remember.
(Looked at the picture, nice looking car)
|Bill, the hill in question is Portway Hill near Dudley Golf Club do you know it? The pump is new electronic one from Leacy MG, the instructions did say to fit a restrictor before the carbs (small bore plastic tube supplied with pump) thought this could maybe the issue, purpose of tube to limit flow when idling etc. I have just got the car on the road after a six year on off reshell so afew teething problems :)|
|That hill up from Whiteheath*, yup I used to work round the corner. Used to get chips from the Whiteheath chippy before the yellow chips shop opened nearer to Blackheath|
Many years ago :)
Try without the restrictor for a day or so and see if she'll fly up there without
Maybe reduce the size of the restrictor if that helps, perhaps slit the reducer length wise to retain some "smallness"
I have a Leacy electronic pump (round and fits within the midget's original bracket?) but there was no extra restrictor in mine
Must be a reason for it
*if it loses it there, I suppose you haven't tried Mucklows yet
|Another suppliers' bodge to get round flogging non-standard parts I suspect. The CORRECT specification fuel pump (3 to 4 psi) will deliver sufficient pressure for WOT under load, yet not so much that it overcomes the float chamber valve at tickover. Keep the car as the factory designed it and you won't have a problem.|
|yellow chips! now I feel peckish. I think I'll try without the restrictor at the weekend, also Mucklows now the challenge has been laid down, could always nip to 'Our Plaice' at the bottom of Gorsty Hill. Sounds like an idea for a tv show touring Black Country hills and chip shops :)|
|If you are using a AUF 214 SU fuel pump (OEM for the Midget), it will supply 1.1 pint per minute at 2.7PSI. Someone is blowing smoke saying that a restrictor between the pump and the carburetors. The float and needle valve will control the amount of fuel being delivered, based on the demand from the engine.|
As for fuel vaporization in the line up to the carburetor, that is highly unlikely as the fuel is being delivered under pressure. This is the main reason for having the pump mounted in the back of the car. Cheers - Dave
Is the car getting hot on these hills? It could be that on a long climb the valves are heating up and just binding a bit. You may have got the valve clearances a bit on the tight side.
|When I rebuilt my Sprite I bought an electronic version of the original AUF 214 pump. At least that's what the ebay seller advertised it as. All was fine until, on holiday in the Cotswolds I tackled "Fish hill" near Broadway and experienced the problem mentioned by Andy. I posted on here and was given lots of good advice as to what it might be. I eventually did a flow test and found that the delivery of fuel, although pathetic, was enough to keep the car going in most cruising situations, but not WOT for any length of time. I bought a Quinton Hazel electronic pump and have had no problems since. I've even been back up Fish hill and the car flies up it.|
So, I think Andy's problem could well be pump related.
|I agree with David, my money (if I was spending this year!) is on the restriction.|
My pump, which I think is similar has no restriction and no problems up those hills.
|Removed the restrictor from the fuel line and cruised up Portway Hill at a steady 30mph without any problem! I did compare flow into a jar with and without restrictor and as you would expect the restrictor slowed it down but IT have to say only slightly. But as they say just is enough. I'll monitor it over the next few days.|
Next hill MUCKLOWS :)
|I got to try without the restictor for a day and see what happens|
|Prop and the Blackhole Midget|
This thread was discussed between 19/07/2012 and 21/07/2012
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.