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MG Midget and Sprite Technical - That was FUN! - But why wasn't it faster?

Just come home after our first competitive hill climb at Loton Park. Dry for practice but damp, then wet for timed runs - made for a very exciting second run! One or two hairy slides but no trips onto the grass and everthing came home the same shape that it was this morning - apart from our faces which came home with big grins on!

The scrutineers only picked me up for not having yellow tape on my earth lead and didn't even notice the diameter of the rollbar tube!

In the course of the day we discovered that there is a leak in the clutch system, which made gear changes tricky till I scrounged some fluid for the last runs. Hoping a new hose will solve that one.

The bigger problem was a reluctance to pull properly at full throttle in the hill - on some runs it just wouldn't give anywhere near full revs, even when dropped a gear (all done in 2nd and 3rd). Worst on my final run but as I ran to the line on the level it seemed to clear and pick up properly. This has never happened when revving with no load on the engine or when on the flat and didn't happen on the downhill section of the course - absolutely no problem on the way home! Could this be a wrong/insufficient oil in the dashpot problem or sticky carburettor pistons?

Could it be a fuel delivery problem - the fuel pump's where it belongs by the back axle and is not very old. After the car has been standing a while it takes longer for the pump to stop ticking than my Morris Minor, (though it does have two float chambers to fill) There is an inline fuel filter adjacent to the pump. The tank was full at the start of the day (will go for part full next time to reduce weight!)

There was no spluttering, just a reluctance to rev.

The car is a 1275 Sprite MkIV bored +30 on standard SUs and air filters.

Got home hours ago but still buzzing!!

Colin
Colin Mee

May seem a bit obvious, but have you checked that the butterflies open up fully to the horizontal when the pedal is to the floor?
Guy Weller

Thanks Guy - haven't had time to investigate properly yet but that will be high on the list.

Happy to accept comments about the obvious - I'm great at overlooking it!

I'd rather spend time fixing something obvious that I've overlooked than mis-diagnosing and spending money replacing a part that wasn't faulty in the first place, which is my usual practice!
Colin Mee

Hi Colin, Im very envious I bought my midget with the
intension of doing some local hill climbs(wiscombe)
but god interveened now I cant get a liscence.
Very similar 1275 +30 on su's at present.
Have offered to son and future son inlaw but no takers. If you get to Wiscombe drop me a e mail
Regards Pete
P C Knightley

Methinks it was fuel starvation. Tested the petrol pump today - less than 3/4pt delivered in a minute. The pump was chattering away merrily all the time so I don't think it was having any problem pulling fuel through from the tank.

I trawled the BBS archive last night and I've decided I need one of the Facet pumps - but which one to go for? My workshop manual says that an SU AUF305 should deliver 2pts/min and I've been advised that I need 3PSI.

The Facet 'Road' says it's for engines up to 1600cc and delivers 1.6pts/min @ 2.5 - 3PSI.

The 'Fast Road' one is for 'up to 2000cc or smaller tuned engines' delivering 2.4pts/min @ 4 - 4.5PSI.

And then there's the barrel shaped Interrupter type - but that looks a bit OTT delivery 4.6pts @ 6.5PSI+.

The engine hasn't had any uprating since I got it but I plan to make some changes to find a bit more power so I'm minded to go for the 'Fast Road' pump with a pressure regulator.

My car is still positive earth but the pumps are all negative - I presume I can get away with isolating it on rubber bobbins and wiring accordingly. Plus I'll probably wire it through a separate fuse with a switch on or under the dash.

Or are there some other options I should consider? Any suggestions gratefully received.

Colin
Colin Mee

I have got the barrel interrupter version.(silver top) super reliable and has been on the car for years without a bit of bother. Its feeding twin HS2's now without any pressure restrictor. Mine is positive earth wired as you have suggested. The advantage of this pump is it has the capacity to take an engine upgrade should you go for a more spirited fuelling system. In my case it used to feed a 45DCOE weber back in the days when I sprinted the car.
Bob Beaumont

Colin, there are many facet pumps to choose from, see this page:
http://www.fuelpumpsonline.co.uk/facet-fuel-pumps-8-c.asp
Trouble is, a lot of suppliers only stock one or two and will push you to what they have in stock. Personally I would *not* bother with a pressure regulator, it's just something else to fiddle with and go wrong or leak or cause problems. Just peruse the specs carefully and choose what's right for you. Find a place that will order it in for you if not in stock. The SUs should be able to cope with up to 4 psi, if not then the float chamber valves need looking at. Having said that, the cube road model should be OK for you.
http://www.jjcraceandrally.com/race/fuel-pumps/facet-solid-state-electronic-fuel-pump
David Smith

Bob, David Thanks for the comments - all very useful.

I was looking at pumps on the JJC site earlier - I've had a few bits from them recently. I've also seen them on the shelves at Demon Tweeks and they're only half an hour away so I might just take a run up there soon as I prefer to see things in the flesh before buying whenever possible.
Colin Mee

Colin, I've got the cheapest square Facet one and it has been fine for the last 7 years. I use a Filter King filter and regulator and works fine (though very noisily!) with 100+ bhp.

One of the problems I had was fuel pick up and needed at least 3/4 of a tank as I think the internal pipe in the tank was broken. Only showed up on full bore runs up steep hills like Loton. Hopefully the pump will sort it though.

Good luck next time!

John Payne

Have you checked the fuel filter as well? And the air filters can pull the RPM down under load if they are clogged.

Cube pump should be fine, it was perfect on my MG Metro even for mild competition.
Max max-at-midgetmax-dot-com

Colin,
an SU pump that "chatters away merrily all the time" could indicate a leak in the upstream bit of flexible hose. It wouldn't necessarily show as a leak out of fuel, but can allow the pump to suck in air into the inflowing fuel when it is operating. This would reduce the volume of fuel arriving at the carbs. A more powerful Facet pump may overcome this but may in the process be masking the underlying problem.
Guy W

Hi,
I had a Facet cube type fitted when mine threw a wobbly on a Rolling road session.
It's performed without fault for the last 5 years or so on a fast road engine with no regulator.
1275 +30
Piper 270 cam
MG Metro head
Maniflow exhaust and manifold
HIF44 with K&N filter.
Puts out 93BHP at the flywheel so if you are looking to do some additional mods the cube type should be fine.

Thanks
Mark
Mark Whitmore

Thanks for all the advice. I had a good run out today and tried hard to replicate the problem - not a stutter, it ran perfectly!

Guy - The air leak is certainly a possibility - it always takes a while to prime the float chambers but before last weekend's outing I had been fiddling with the pump to mount it more securely. The hoses and clips are all new but I could have loosened one of the connections by accident.

Max - the fuel filter is also quite new and looks OK but the air filters are definitely past their best but a pair of new filters arrived yesterday so they should eliminate that as a cause.

Mark - Thanks for the reassurance about the Facet pump - there's one on order along with a Filter King pressure regulator and new braided fuel hoses for the engine bay arrived with air filters so I am hoping the stuttering will be a thing of the past once everything is in place. I'm assuming I'll need to make a mounting plate or bracket for the Facet pump - does it have to sit upright?

Following discussions in another thread, I'm thinking of putting the panel light switch elsewhere and using the panel light switch for the fuel pump.
Colin Mee

Colin, the pump was fitted in the same position using the original pump mounting points (possibly one new hole was drilled).
The pump was mounted using rubber bobbins to cut down on noise/vibration. I will take a pic later on when I get chance.

Thanks
Mark
Mark Whitmore

>>>>>>I'm thinking of putting the panel light switch elsewhere and using the panel light switch for the fuel pump.

Don't do it!!!!

1. Race tracks of the world are littered with people who have ground to a halt, having forgotten to switch on their fuel pumps!

2. Something else to go wrong, another lot of wiring to break down, another switch to fail

3. safety. You don't want to have to switch off the pump separately to the ignition. If you then wire the pump switch through the ignition, why put the extra switch in?
Max max-at-midgetmax-dot-com

Hi, pic of the pump as promised.

Mark

Mark Whitmore

And one of the rubber mountings

Mark

Mark Whitmore

That was even more fun! Two days of brilliant sunshine at Loton Park, a six second PB and First in my (Beginners) class on handicap!

Thanks for all the advice: The Facet pump seems to have sorted the fuel supply problem. Still not happy with the clutch (lengthy threads elsewhere) but getting there, new master cylinder on its way. I have found that if I keep off the clutch except when I'm using it (if that makes sense) it works fine. If I keep my foot on it for any length of time it will balk.

By the last run I had a much better feel for what was happening in the corners, on the brakes etc. Not impressed by the comentator's suggestions that there would be no chrome left on my doorhandles by the end of the day! Definitely some work to do on the rear end!

Very shaky but here's some video of practice on Saturday: http://www.youtube.com/watch?v=zE0oJooEbto&feature=youtu.be

Many Thanks to everyone who offered advice.

Colin
Colin Mee

This thread was discussed between 13/04/2013 and 09/06/2013

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