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MG MGB Technical - su pump ticking rate

I've just got my garage find moving and done a couple of runs round the block in it to check the brakes. I notice that the SU pump is ticking rather rapidly. Several times per second at times (seems to be when I accelerate). When stationary there are hardly any ticks. I'm sure that the engine isn't drinking fuel (i'm on '12 flats down' setting at the moment) and I can see no evidence of the carbs overflowing. I'm not familiar with the operation of SU pumps (although I had one on my '71 Sprite previously). Is there a diaphram that may be perferated in there somewhere. The pump looks to have been a recent addition and there are two or three old pumps in the boot so looks like the PO may have had some problems!
Steve Church

I just had a thought. I emptied the tank of old fuel (could be 15 years old!) and put one gallon into an empty tank. Could I be sucking in air? How close to the bottom of the tank is the fuel outlet? I'll put some more in tomorrow as I need to set up the carbs ready for the MOT on Thursday.
Steve Church

My guess is that you are low on gas. Put some more fuel in the tank and I'll bet that the problem goes away. RAY
rjm RAY

Steve-
Check the fuel line that connects the fuel tank to the fuel pump. If there's a hole in it, then the fuel pump is sucking air and will cycle rapidly just as you describe.
Stephen Strange

What does it do with the ignition on and the engine stopped, that is the real test. It shouldn't click more than once every 30 secs, if it does, either a carb is overflowing or one of the non-return valves in the pump isn't sealing, on a friends car it turned out to be a kinked hose. If it is sucking in air it normally chatters ten to the dozen, less so if it is just a pin-hole or loose clamp on the tank side of the pump, which probably won't leak fuel. Check delivery by removing a feed pipe from a carb (note that if the ignition has only just been turned off you should get a spurt), direct it onto a container and turn on the ignition. The pump should deliver a minimum of 1 Imperial pint per minute, and in practice closer to 2, with negligible bubbles. Bubbles show it is sucking in air.
PaulH Solihull

Paul - "The pump should deliver a minimum of 1 Imperial pint per minute, and in practice closer to 2, with negligible bubbles."

It should be 2 imperial pints per minute per specs and in actual tests, it will put out 3 pints per minute. Cheers - Dave
David DuBois

Depends on the pump, the earlier HP is 1 pint in 1 min 5 secs and so is obviously more than enough for the MGB i.e. emptying a full tank in less than an hour and a half.
PaulH Solihull

I've put in another gallon so now have two in the tank (I can't fill it up by driving to the petrol station as its not MOT'd or taxed). Went around the block again and I still have a high rate of ticking which seems to be dependant on revs/load. Back in the garage at idle is a slow rate but when I pick up the revs I get maybe one or two ticks per second at around 2000 rpm. With the engine off I get one maybe ever 30 seconds or more. I set up the carbs tonight and had to back off several flats from the 'twelve flats down' position but did get to the point where the mixture was too weak (revs dropped when I lifted the pistons). I can't see any obvious leaks. Tomorrow I shall do a flow test and look for bubbles. My main concern is to get it ready for it's MOT on Thursday. The limited time I've had it on the road (private of course) I am quite pleased at how it runs.
Steve Church

Doesn't sound much of a problem then, especially if you have the choke still partially open. The faster you use fuel, which happens at higher revs, wider throttle openings or when the choke is out, the pump *will* tick more frequently. It delivers a constant amount of fuel for each tick, so to feed a higher demand it has to tick more frequently.
PaulH Solihull

You might find that the pump is simply worn out. The pump which was on my MGB originally (a strange Australian thing) was fine around town and on the East German Autobahn, where only 62.5 MPH was allowed. When I got to the West German Autobahn and gave it some welly, the car would start to hesitate at 85 MPH or so, when the pump couldn't keep up. I'd wait and see but keep a spare in the boot... Mike
Mike

Mike ,
There are actually two in the boot. Old ones that the PO had obviously had trouble with. The one fitted looks newish (the PO laid the car up in 1995). Are there any rubber bits inside that may have perished in that time?
Steve Church

Steve. After that length of time then it is more than probable that the diaphragm has dried up and deteriorated along with the valve seals and gaskets. You would be well served by getting an overhaul kit and bringing the pump back up to specs.

Tony
Tony Oliver

Or send it to Peter Cole pcoleuk@gmail.com and let him work his magic on it. Cheers - Dave
David DuBois

Tony,
yes that seems a good idea. However after having a quick look this morning at fuel pumps on ebay it looks like my pump may be a QH part (i.e not S.U)(it has a blue end cover). I'm not sure if spares kits are available.
Steve Church

Steve, if that is the case, dig one of the old pumps out of the boot and do as Dave suggests. You won't regret it.

Tony
Tony Oliver

After you remove the pump, remove the plastic end cap and
check the points mechanism. If the points mechanism is black
and sooty, then the pump diaphragm has developed a leak
and the diaphragm must be replaced. "The Complete MGB"
Bentley manual documents how to do this.

However, I more greatly suspect that one of the plastic reed
valves in the pump has a hairline crack and so some of the fuel
is swishing back & forth in the pump IN-OUT chamber. If so,
then it's best to change both of them while you are there.
They are fairly inexpensive and easy and straight-forward to
remove, inspect and replace - if you can find the parts.
Daniel Wong

Until the delivery rate is measured, and found to be inadequate, there is not much point in doing anything as far as a repair is concerned. If the clicks are more than 30 secs apart as Steve says then there is nothing wrong with the valves.
PaulH Solihull

I've checked out one of the spare SU pumps I have and cleaned up the contacts. It ticks away nicely and gets loaded down when I block off the ports. I may replace my existing one with this. Question. Can the pump be installed with the ports oriented any way? A picture would be good.(Existing pump has a hard connection to the tank so that port is fixed). Also my existing pump appears to be made by Hardi, a German manufacturer. I know nothing of these. Anyone come across them before. I installed a fuel filter in the engine bay tonight and noted that the pump pulses fuel through it about once every 1 1/2 seconds when the choke is in and engine is at tick over.
Steve Church

Steve, the outlet union on the SU pump should be marked as such and also usually has instructions that it should be at the top when mounted. It is not critical but my experience on the test bench is if the outlet is not at the top the fuel pump is not quite as efficient. They will run upside down but very poorly.

Cheers
Tony
Tony Oliver

I'll second Tony's advice. Besides being inefficient, a pump that is not oriented with the outlet port at the top can trap air inside, adding to the inefficiency.

The German Hardi pumps is a very good pump, but when they die, just toss them as parts are not available to repair them. Cheers - Dave
David DuBois

This thread was discussed between 17/10/2010 and 29/10/2010

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