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MG Midget and Sprite Technical - Back from the dead

I am helping a friend get a 1967 sprite back on the road after sitting for over five years. The biggest obstacle was convincing him that the car needed a 12 volt. battery instead of the six volt that he and two previous mechanics thought was correct. I am able to get it started but it wants run very fast over 2,000 rpm.. I also have fuel leaks out the throat of the carbs and some around the bowl covers. I suspect the after market electric fuel pump, with no markings, is putting out too much pressure, so i just fill the bowls and disconnect the pump. I have disconnected the throttle linkage and if I manually hold down the throttles, with idle screws backed out, I can get the speed down to 12-1500+ rpm. But if I take the pressure off the speed runs back up. If I look into the carbs. the discs seem to be shutting. The discs do have the pop off valves. My air flow meter shows the same from one carb. to the other.
I would just like to get the idle down so I can do further checks ie. timing,mixture etc.
Should I try retarding the timing to get the speed down? Or am just dealing with a large vacuum leak.
B Stone

Thanks for all the great input in sorting this out.
B Stone

“Should I try retarding the timing to get the speed down? Or am just dealing with a large vacuum leak.”

I don’t know.
Dave O'Neill 2

Hi B Stone, welcome.

"I suspect the after market electric fuel pump, with no markings, is putting out too much pressure" - you could start with eliminating this concern by disconnecting the fuel line before the carbs, switching ignition on for 10 seconds and measuring how much fuel comes out.

Sorry to hear about the previous mechanics(?) thinking the Sprite (Spridget) is a MGB, this can happen when no research or reading is done on a subject that isn't known about, we all learn for a first time.

The very first thing you should get your friend to do is buy a reprinted copy of the relevant Driver's Handbook (midget version will be the same in all but name) as this will tell all the other things he won't know about his car including how to operate and drive it and all the service and maintenance checks and how to do them and the factory settings of when the car was new (see photo below).

It is not the factory (or Bentley) type workshop manual it is for the driver/owner - but it has lots of relevant information (including replacement 12v bulbs).

The relevant Driver's Handbook may also highlight other non-standard or non-origin parts or components on the car which may or may not be helping the car. Some changes and variances on a car of this age are to be accepted, some are good others are not. Some modern made parts and components are good others are really piss-poor in construction and function and these can cause rather than help solve problems.

Perhaps a (not too big, one per post) photo of the engine bay might help as another starting point here.

Cheers.



Nigel Atkins

'Thanks for all the great input in sorting this out.'
Hi "B"--You have to be a little patient as we are spread out all over the clock---

The flooding out the mouth of the carbs and at the float bowls,could be the pump as you say but most likely rubbish from old fuel in the needle and seats in the float bowls--a bit of a clean out could be all that's needed there
Soumds like a bit of a linkage problem if the speed comes back up when you release the throttle but really it could be one of several things
Just have a little check and make sure the choke returns back properly on the bottom of the carbs after pushing the choke in
also if you're turning the pump off the fuel level might be getting low enough to make it run lean which can cause erratic idle speeds
Interesting your airflows are equal though
Does it have any vac hoses on the manifold going to anything like a brake booster or vac gauge that might be leaking
It also could have been like it when it was parked years ago
Something else to check is the distributor the advance system could be seized or semi seized from sitting or the advance springs may have rusted away, wouldn't be the first that's happened to--To check, remove the dist . cap and twist the top shaft (rotor button)to see if it's still spring loaded and moves and returns
If it's gone sticky it may well have advanced up when you started it up and stayed advanced causing your issue

willy
William Revit

Finally able to get back to my friends Sprite. I purchased the correct pressure Faucet pump. The previous mechanic mounted the pump on the drivers side inner fender.So I mounted the new pump in the same location. Is this too high for the pump to work properly? I know normally they are mounted near the tank. I went back to a base line on the carbs. of raise the jets fully up and then down two full turns,disconnected connecting bar and turned the idle screws in 1.5 turns. used some choke to get it started. It wants to hunt and run rough at low speed and also randomly race (3,000 rpm +) I guess. Kinda unnerving when that happens.Too erratic to get an air balance reading. Could flucuating fuel delivery cause these symptons ?Notice back carb. piston seems to run higher than front and occasionally a back fire from the back carb. Tried adjusting mixture a couple of flats each way and idle screws, not much change. The tank is new and I tried blowing through the hose. Thinking it might be some blockage. Maybe I need to use an air hose. Seems like it's going from lean, to rich.
B Stone

Thought we'd lost you-!
Welcome back
On the fuel pump mounting , yes "most" pumps are designed to be pushers not suckers so need mounting down near the tank
It will probably still work up front but not ideal
It sounds like a linkage problem with the carbs if one piston rises and the other doesn't BUT earlier there was equal air flow on the carbs so that's a bit strange
The front carb piston could well be stuck/sticking
I'd pull both dashpots off and give the pistons and covers a good cleanup with some carby cleaner or something
While you've got the pistons out is a good time to check the throttle linkage and make sure both butterflies are going right back at idle and that they both open exactly equally as you open the throttle
No sandpaper or course abrasive pads to be used cleaning the pistons/housings be gentle on them so that they retain their size and finish, and some light oil on the piston guide shaft on assy and in the damper tube
I tend to leave the piston outer and housing dry, some people oil them--at least if it's dry they don't tend to get gunked up
As far as the ign timing goes if you put a timing light on it, that should tell you if it's out, but I can't see that being the cause, even if it's miles out the idle won't go that high, rough maybe but not 2500rpm

willy
William Revit

Manifold air leak, possibly in the front carb?
GuyW

A vac. leak is a definite possibility as Guy says , manifold gasket or a perished vac. hose etc. Does it happen to have a power booster on the brakes
If you get a piece of garden hose ,one end to your ear and have a listen around with the other end near the manifold, carbs, hoses etc ,,with a leak big enough to do that you should easily hear it
Does it have one of those larger pcv valves poking up out of the inlet manifold, if it has it may have a hole in the diaphram, clamping the rubber hose would check that
willy
William Revit

Or get a volatile spray like carb cleaner and with the engine running, spray the jet onto potential leak areas - the revs will rise if there is a leak at that spot as the fluid cuts out the excess air supply and replaces it with the flammable fluid. But use it sparingly.
GuyW

This thread was discussed between 12/04/2019 and 30/06/2019

MG Midget and Sprite Technical index

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