Morris Minor Owners Club

It was a new pump, and forgot to mention that the coil was also changed, so it wasn't the coil.

If you haven't already checked, you might find the ht leads are breaking down at some point. What about the cap having a hairline crack and arcing across?---or even plugs.

The leads & plugs were changed for new ones and it was a complete electronic dizzy so there was a change of cap. The back firing stopped when the dizzy was fitted. I'm just flummoxed over why the 'stuttering' problem would only appear when going over 50mph

Well maybe not appropriate here but I had a problem once when accelerating or at least calling for more power, the car would hesitate and faulter, it was a long while before it was traced to a broken wire to the fuel pump, not visible as the outer casing of the wire was intact but inside was broken and barely making contact, I presumed when more current was asked of it the wire couldn't cope. Although this was not on a minor, you might need to consider these obscure things! Good luck.

the only thing i can think of lou is i wonder if the vacuume / advance unit is not working , that is a old dizzy but the electrics inside are new did the new plugs help

Sounds like it's starving for fuel when the demand is up. You need to flow test the new fuel pump. Also possible that the pump is OK but there is a restriction in the fuel line between the tank and the pump.

Carb piston rising and falling easily? Ignition timing set to, not quite pinking? Is it a NEW dizzy???? And put the old coil back on!

Can I get a few things straight here, is it only doing this when the engine has been running for a while and only when you go over 50 ish miles an hour after a few minutes. If the above is true can you check the fuel pipe under the car to see if it has been squashed with a jack or axle stand (it would restrict fuel flow at higher speed only). A fuel flow test as suggested earlier would confirm but you need to flow at least two pints. The only other thing I can think of is a build up of heat under the bonnet causing vapour lock (I think you mentioned that), with the addition of more ethanol in the fuel these days it is becoming more of a problem. If bar seal has been used in the past to seal a water leak I have known it to collect at the rear of the engine water jacket causing a large hot spot. As the water is unable to pass through that part of the engine no matter how good your cooling system is it will put a lot of heat under the bonnet. Only way to find out though is remove the head and investigate, a last resort I think.

Fit a NEW electronic Accuspark Louise, for all it costs, to eliminate any more problems there. And time it to 'not quite pinking. No more worries there!

OK, this is off-the-wall / out-of-the-box, BUT....

Check the prop shaft. I recently had what I, and three other Minor experts, all diagnosed as a misfire at about 40mph. After changing everything (ignition, fuel, head, even the damn engine) the problem was still there. Eventually traced to a worn UJ, not making any of the usual noises or displaying any other symptoms typical of that fault, and even feeling OK to initial inspection.

One of my other threads on "not the average misfire" was resolved by a change of air filter - it looked OK, but clearly wasn't.

So, two things that you could check. As regards possible fuel starvation, have you tried a different fuel cap in case the vent is blocked.

We covered the cap idea extensively a year ago!

amgrave wrote:Can I get a few things straight here, is it only doing this when the engine has been running for a while and only when you go over 50 ish miles an hour after a few minutes. If the above is true can you check the fuel pipe under the car to see if it has been squashed with a jack or axle stand (it would restrict fuel flow at higher speed only).

That's exactly the problem amgrave - I'll take a look underneath at the weekend as I'm thinking that there could well be some sort of 'blockage' which is restricting the fuel flow. Thanks to everyone else for their advice. I've changed the fuel cap and tried 4 different coils (2 new and 2 'old'), the air filter is nearly new, the carb has been tuned and the timing is OK. It's running really well at the moment apart from the spluttering & kangarooing when I go over around 50/55mph so I don't think there's a problem with the dizzy.

Is there enough oil in the carburettor dashpot? Wrong needle? Or needle out of true alignment?

the oil in the dashpot was topped up

Too much oil is bad.... Only needs 2 tsp...engine oil.
Louise - I dunno why you put yourself through this every year. Just buy a brand new electronic dizzy, and a new 'points' SU fuel pump, and then there is really only the overall engine condition (so set gaps and run comp test) and possibly the fuel pipe (buy a new one - not expensive) and all should be well for many years to come !

Lou a last resort as you seem to have tried everything, can I assume the rotor arm is of the type without a rivet as the ones with rivets have been know to cause problems similar to yours just a thought in case as even the new electronic dizzys don't always have the better type of rotor arm.

the rotor in that dizzy is a red one with no rivit

I know people don't like threads were the OP doesn't say if a problem was fixed, so thought it was time for an update. To recap, my traveller started 'stuttering' when driving at around 55mph. It would sometimes come to a stop but usually slowing down solved the problem. Various items such as electronic ignition, coil & fuel pump were fitted and the carb was cleaned and set correctly. Thanks to everyone who offered suggestions in the past but we didn't actually get to finding what the problem was. The traveller spent the winter in the garage and had little use due to me having a knee injury (caused by fitting a new interior!) which required surgery. Anyway, to cut a long story short, he's got a new MOT and this morning I took him for a 60 mile drive. As previously, he was running really well until I hit 55/60mph and he started 'stuttering' again. He didn't cut out but I pulled into a layby for 10 minutes and he ran fine again after that, although I stuck to no more than 50mph.

In view of all the previous suggestions I think it does seem to be a fuel starvation problem. The pump is new and the fuel flow has been tested and was OK. I filled up the tank about 10 miles in to the journey and noticed that the fuel filler pipe seemed a little loose, in that it moved a bit when filling, but the clips that are holding the rubber pipe at both ends seem tight. Just a thought, but could there be a problem with the filler pipe which is causing a vacuum/fuel flow restriction when the pump is pulling more fuel through at higher speed? I had a look at the fuel pipe under the car and couldn't see any problem (although it wasn't the easiest of jobs with dodgy knees!) Any suggestions appreciated as I'm wary about risking it on another trip to the National (approx. 150 miles) bearing in mind it's broken down on route to the last two.

Well -the vacuum in tank is easy to test - just take the cap off and listen for any air intake noise....and try a short run without the cap fitted to see if that solves it. Could the carb just be set too weak? You would need to pop out a plug after a run and look at the colour - should be 'digestive biscuit' colour. Also check the plugs don't have an 'R' (=resistive) in the code.

Thanks Roy. I took the cap off previously and didn't hear any air intake noise but can try taking it for a run without the cap on, although I have to go quite a way out of London to find a road I can do over 50mph on. The plugs are NGK9's I think, fitted by Dale Brignall on the way back from last year's National. I'm pretty sure that the carb is set right as a chap at the National spent a lot of time cleaning it and setting it up so it ran perfectly (for a donation to charity).