Poor idle...again

[Lukey]

In the past weeks my idle has become very bad again, the symptoms are it idles very poorly sounds like it's running on 3 cylinders, then 4 and then 3 again. This is accompanied by mayo building up in the rocker cover and when pulling up to a junction and dipping the clutch abruptly it will cut out. When idling the idle slowly gets more and more choppy over a period of a minute until you give it a bit of a rev then it settles back and starts the cycle again. There is absolutely no loss of power at all.

I was certain that my head gasket was weeping, I don't appear to be loosing any water and there's no bubbles in the radiator.

I took a compression test first and then a reading with a vacuum gauge.

Cylinder 1: 162
Cylinder 2: 166
Cylinder 3: 162
Cylinder 4: 166, apparently. I'm going to check my compression tester tomorrow. They seem quite high.

Vac was reading 1.1 2/3 inHg at idle snapping the throttle it rose to 0.3 then to zero when throttle released. It took a few seconds to rise back up to 1.1 2/3. Needle was stable throughout the readings.

That led me to believe I had an intake leak, car didn't respond to using propane around the manifold. I then took it off to inspect the gaskets they were all fine.

I then took the head off to inspect the head gasket, again fine. Inspected the head and the valves, I found that exhaust valve no 1 has recessed in to the head, Is this the cause of all my problems?

Normal Valve



Bad Valve





Mayo



Gasket



The gaskets at the carb end were OK too.

[mogbob]

Lukey
Your compression figures look good and you seem to have eliminated
a head gasket failure as an explanation for the mayonnaise.
It could be a combination of the recent cold weather and mainly short journeys where the engine doesn't get up to a good working temperature
regularly.Clean up the mayonnaise and give it a good run every now and then.
How long has the head ( unleaded presumably ? ) been running on unleaded petrol( mileage ) ? With or without an additive ?
It could be carbon build up on the other valves , giving the impression that
one is at fault, i.e not seating properly.
Whilst the head is off the car it would be a good idea to look at the valve seats, without the valves in situ.Are they all similar ? Having gone this far now, how about doing a decoke to get the valves seating properly ?

This misfire symtoms at idle points to an electrical cause.The "dipping of the clutch abruptly / cutting out " smacks of loose/ broken leads.
The connection makes and breaks with movement.
Go though the battery terminals connections, engine earth. low tension leads and the plug leads.As the plugs are out I assume that you are happy with those and that the gap is correct.
Maybe the engine mountings are " pass their sell by date " allowing the engine to move excessively.

My thoughts to be going on with, for what they are worth.

Bob

[bmcecosse]

There was obviously no need to remove the head! The exhaust valve is fine - don't worry about it - and your compressions were excellent. Looks like the engine was running a bit 'rich' - hence it wouldn't idle cleanly for any length of time. New spark plugs would likely be a good idea (what plugs were in it ?) - and set the mixture properly when it's all back together. Mayo is simply due to short runs/cold running engine. Try a hotter thermostat (88 degrees) and make sure the engine breathers are clear. And if it falters when clutch is in - probably caused by clutch drag - so make sure there is sufficient 'free play' in the clutch movement, and just raise the idle speed slightly to compensate.
It will be fine !

[Dean]

Would it be worth checking that pipe that goes from the carb to the dizzy and making sure it's giving proper vacuum?

[Lukey]

Everything noted, I'll look at what you all suggested tomorrow. With the mayo I was pretty convinced that it was weeping because I am cleaning the rocker cover out every week and going for long drives 45 mins+. My oil must be contaminated some how? I'll change it again.

I checked the HT leads when this first started happening, no cracks and they all read about 8 ohm through my multimeter.

Every ancillary on the car has been rebuilt or reconditioned within the last 2000m they all work as they should. It was running very rich to my surprise when I pulled the plugs out. I think I didn't adjust the mixture after I discovered a fuel leak from the bottom of the float chamber. Hasn't been like that for long.

I'm not really sure how to check push rods for wear, might as well seeing as they're out. What am I looking for?

[bmcecosse]

Never ever known them to wear! Only check would be for straightness - roll them on a block of steel. Cam followers can certainly wear - pull them out and inspect the underside for any pitting or crazing. But they would not affect idling - it's just been too rich.

[Kevin]

Every ancillary on the car has been rebuilt or reconditioned within the last 2000m they all work as they should.

Hi Lukey when I read this I just wondered what you had done to the carb because if you have wear in the spindle and bushes it can give idle probelms and just replacing the spindle is often not good enough as the bushes often become oval and need replacing, I have just had this done recently.

[bmcecosse]

Worn spindle /bushes can cause weak mix at idling, which if overcorrected can then lead to rich running - since the spindle leak becomes insignificant when the throttle is open, but the jet has been screwed down to correct the leak at idle. However - it's not usually a huge problem unless the carb has been run with a very heavy return spring - and/or has done huge mileage.

[Lukey]

Hiya, I sent the carb off for a rebuild in the end. The gaskets arrived today, so we shall see. If this dosn't work I'll just take it as an omen to put the 1300 in.

[bmcecosse]

Where did you 'send it off for rebuild ' ? Not normally an economic proposition!

[Lukey]

A local engineering company that specialises in Land rovers. What size torx nut do I need to remove the con rod bolts on a 1275?

[Matt]

Its a 12 pointed 1/2" hex socket/spanner

[bmcecosse]

" A local engineering company that specialises in Land rovers. " Bon chance !! Do they know anything about SU carbs ??

[Lukey]

Yes they're fantastic, it's run by two brothers one of which is a mechanical engineer. Living in rural Wales we need alot of agricultural machinery taken care of they basically specialise in taking care of. Not really an engineering company, they just do loads of fab work.