Am I missing something obvious?

[Jimmy F]

So, my Morris isn't too healthy. She'll sit and idle perfectly but if given revs for a few minutes splitters and dies.

 

Tanks were recently resealed and we have no problems there. Fuel pump is an electric one and all lines have been replaced within the last month. I have, this morning, replaced the spark plugs and distributer cap, along with the leads (fitted spade ends) and anew rotor arm.

 

Still got the same problem. She's not dropping any liquids either.

 

Any ideas?

[radiomike7]

When it splitters and dies, have you still got sparks? If not, the most likely culprits are the condenser or coil, both can break down when hot.

[Gordon_M]

Condenser. Even brand new condensers tend to be a bit iffy these days.

 

 

Still got the WW2 condenser you took off last time you changed it? try that one, they really made condensers back then

[arcot1751]

You say the tanks were " resealed" could some of the old sealer have broken down (ethanol in fuel) and blocked a jet ? Are the float levels correct ? When it dies have you checked for fuel actually in the float bowl ? I agree condensers and coils can cause the same problem but often something recently done has a knock on effect so may be fuel related

[Jimmy F]

I didn't get a chance to do anything with the carb as we had a leak in the water tank in the loft and my other half insisted that was more important! Haha.

 

I shall check the needle and such at my next opportunity, but not sure if it may be worth replacing the cool anyways. I believe they're the same as the ones on a Morris minor??

[ted angus]

I had exactly those symptoms and it turned out to be the rotor arm- it was a brand new LUCAS product, I fitted another one same problem- put the old original one in I retrieved from the dustbin and its been good ever since-

 

when you open the carb in addition to checking needle function etc check that the float has not become pourous

good luck

TED

[Tony B]

Banging an old drum. An electronic ignition unit such as Frank Jolleys save a lot of headaches, and you can still go back to flash bang ignition if you want to.

[Jimmy F]

My original rotor arm was really pitted, so had to replace, but that is definitely something to consider.

 

Really think it may be to do with the ignition? She's firing fine and idles fine.

[Pete Ashby]

The other thing to consider which is ignition related is the mechanical advance on distributor, i'm not familiar with the 4 cylinder Morris engine is it vacuum or counter weight operated?, either way check the operation usual suspects for vacuum systems are a perished or detached pipe, or less common a perished diaphragm. The counter weight system suffers from either stuck weights on the pivot pins or broken springs. Try the easy stuff first before taking the base plate out to look at the weights.

 

Pete

[fv1609]

My original rotor arm was really pitted

Jimmy do you literally mean pitted or was it rough & slightly bumpy?

 

If it was pitted it means there is metal loss from the rotor arm to the brass pillars that go to each plug lead. This suggests you have a positive spark at the plugs rather than a negative one. The spark prefers to jump from the hot central electrode to the relatively cooler side contact. The spark is more reluctant to jump from the colder side contact to the centre electrode & requires 30% more HT voltage to achieve this.

 

The cause of a positive spark would be if the leads to the coil SW & CB have been reversed.

 

If you are going to Evesham I have range of test equipment so that I can measure HT, test coils, capacitors, rotor arms (if fitted on the distributor shaft), sparking plugs & insulation etc. This can be done without the vehicle.

[GeePig]

If we are talking simple, then you could try a syringe and timing light.

 

Fill the syringe with a little fuel and, with the air filter off and the engine in splutter mode, spray a bit of fuel down the carb to see if it continues to splutter or picks up. That should tell you if it is fuel starvation. No peeping down the carb to watch where the fuel goes, mind, you don't want to lose your eyebrows...

 

Second, when you use a timing light it doesn't just show the timing, it shows whether the ignition is still firing. When you rev the engine you should see the timing change in a smooth manner. If the flash disappears then the problem is in the distributor/coil/leads area, if the timing changes unexpectedly then the problem might be the mechanical or vacuum timing mechanisms.

 

I always remember that the problem is probably not what we think it is, because if it were then we would have fixed it already. :-D

 

trevor

[Tony B]

A cheap spark gap that fits between the plug and lead is ideal for showing if there is a spark.

[GeePig]

A cheap spark gap that fits between the plug and lead is ideal for showing if there is a spark.

 

I have not seen one of those, what are they like? Do they just go between the lead and the plug?

 

Wifey tends to steer me away from the tool sections when we go shopping...

 

trevor

[Hair Bear]

Is the tank vent clear? If the vent was blocked the tank may have vented through pin holes you have now sealed up!

Just a thought...

[jenkinov]

If you have tested the spark and its strong I would suspect fuel starvation ...an area worth investigating is the fuel pump the diaphram occasionally fail becoming porous ..often running ok on idle but failing when put under load...

 

Jenkinov

[fv1609]

A cheap spark gap that fits between the plug and lead is ideal for showing if there is a spark.

The problem with those neon test gadgets is that they only tell you HT is getting to the lead. If it flashes it is taken to mean that a spark is being produced.

 

But this is not necessarily so because if you have a cracked insulator the HT can be leaking to earth. Thereby completing a circuit to light the neon without there being any spark.

 

It would also flash misleadingly if the insulator was sooted you could get spurious sparking across this without a proper spark at the gap yet the neon would be flashing away making you believe that the sparking plug was performing correctly.

[R Cubed]

Had a similar problem after fitting new plugs leads and rotor arm on our Sierra, turned out to be the new NGK plugs which I had fitted, there was a fault with them and gave a very naff spark, fitted the old Motorcraft plugs back in and got a nice fat blue spark again.

 

In a separate incident a friend of mine had re built a Triumph 5SW and he could only get 10 miles or so before it would start missing or if stoped would not start again, he also had a NGK plug in it, after I told him of my problems he changed it to a Champion and has not had a problem since.

 

Check the plugs.

[gas 44]

The problem with those neon test gadgets is that they only tell you HT is getting to the lead. If it flashes it is taken to mean that a spark is being produced.

 

But this is not necessarily so because if you have a cracked insulator the HT can be leaking to earth. Thereby completing a circuit to light the neon without there being any spark.

 

It would also flash misleadingly if the insulator was sooted you could get spurious sparking across this without a proper spark at the gap yet the neon would be flashing away making you believe that the sparking plug was performing correctly.

 

I think Tony meant that it shows HT from the distibutor, they are just a quick (and fairly good test for that) I'm not sure anyone has good enough eyes to see what goes on inside the head.....have they

[Tony B]

The local Lidil was doing fibre cams for about £60 a few weeks back! :-D Missed them unfortunatley.

[fv1609]

I'm not sure anyone has good enough eyes to see what goes on inside the head.....have they

Quite

 

The next stage would be to remove the plug & earth the thread & see if a spark is produced across the gap. This would establish that the HT was not being lost by some internal plug fault.

 

But of course the plug gap is quite small & a reduced HT might still produce a spark in air but not under compression. As a guide to the adequacy of the HT then the plug lead connector should be held against an earth point & one would hope to see a spark jump a cm or so.

[LarryH57]

If the MV idles well but does not drive, it could be a problem with the carb. With mine the float had a crack in it and swelled up and then the replacement part I bought turned out to be too big (it was built in Taiwan), so also failed to work properly on the move, but was OK when the vehicle was stationary. I also found the rubber O ring seal between the upper and lower parts had swelled so did not fit allowing the carb to flood.