Morris Minor Owners Club

1962, 948cc unleaded head.

I have just replaced the fuel pump (MMOC Recon) as the old one had been exhibiting intermittent faults after decades of service.

The new pump seemed to improve just about everything.

I also cleaned the carb.

I checked and set the fuel mixture using the advice in Haynes-".......dashpot, if engine increases a lot it's too rich, engine decreases, too weak, if engine note increases slightly, then it's correct."

On a test drive I found the engine pulled nicely up the steep incline that is my avenue, whereas it used to struggle a bit before the replacement fuel pump.

Still on test and she seemed to be running brilliantly, lots of grunt and lively acceleration.

I then decided to go on the A55 dual carriageway to check all was okay at speeds.

As SOON as the speedometer passed 50 mph there was a definite, slow and a backfire.
I limped off the A55, and kept speed to 30 mph..............only to experience a series of small backfires, coughs, wheezes and sneezes and a refusal to run as smoothly and elegantly as she had when first starting out.

Fuel tank is full. As is radiator. Well serviced. Plugs, air filter all relatively new. New cylinder head gasket 2 years ago.

I thought about possible over-heating but she had been ticking over for a good 20 minutes static on the drive just one hour before the test with none of the symptoms experienced at 50 mph.

ANY leads gratefully received.

Test the fuel pump! Pump a couple of pints up into a can and tell us how long it takes..... Was the pump chattering away 19 to the dozen?? There's no such thing as an 'MMOC recon' - although an MMOC member may have reconditioned a pump of course - but to what standard??

I called the MMOC parts chap but as he was just about to go on holiday for 3 weeks, he referred me to Brian Wood
at the Bournemouth branch as Brian Wood refurbishes all the fuel pumps for MMOC I was informed.

The replacement pump is refurbished/recon and carries a 6 months guarantee.

I don't think the replacement fuel pump is the problem as these symptoms were beginning to show when the orig fuel pump was in place.

I am thinking that it might be blocked fuel line due to dirt from the tank-most of the sediment lies on the bottom but when the extra fuel needed (over 50mph) is called for the pump works faster and stronger bringing up sediment.
This will show up in the filter within a few days I would think.

Another thought is the exhaust pipe. Recently a friend had a problem with (Fiesta) engine falling away uphill, on level ground it ran perfectly.

After a few days of tests, noticed a wisp of smoke from the back box and upon examination the back box was filled with what looked like scores of jigsaw pieces. The box had corroded from the inside and blocked tail pipe when jigsaw pieces fell to the back of the back box when going uphill.

I am back on tomorrow, so will check these things out and, just to be sure, will test the fuel pump rate.

When you cleaned the carb did you clear the silt out of the float chamber AND the pipe that leads to the jet?

Hi

Yes, both of these cleaned and checked.

A dirty carb would be liable to cause problems at all speeds, whereas this problem kicks in at 50mph plus.

I will check the exhaust later today, and inspect the fuel filter on the pump.
If these provide no clues, I will do a compression test and install new plugs.

I would take it out and as soon as it falters,switch off to stop the pump and have a look in the carb bowl,see if its full,sounds like starvation to me,caused by a sticky needle valve in the top of the bowl.Once you slow down the bowl fills up and is ok for a while. Worth at try.

Many thanks indeed-I will put this at the top of the check list.

A dirty carb would be liable to cause problems at all speeds

If the feed to the jet is silted up it will only flow enough petrol for a certain speed.
Roy's fix should work, rev the engine and momentarily put your hand over the carb inlet, that should induce a lot of extra flow and pull the silt out.

Many thanks,
I have a list of things to go for now.
I was hoping to start today but a slight emergency has arisen.
I will be starting tomorrow.