Rough running

[Robbie693]

Over the past few months my Plus 2 has gotten steadily rougher. It ticks over fine but opening the throttle slightly makes the engine vibrate as if there is a misfire. Also, when the engine gets hot (around the point when the fan cuts in) the exhaust starts to emit greyish/whiteish smoke (maybe with a hint of blue). No smoke when the engine is cold or until it gets hot.

I am also getting strong whiffs of petrol now and again (more than the usual smell from the boot - see my other post).

I took the plugs out and found them to be very black and soaked with petrol, even after it had been stood for a day and a half. I have leaned the mixture out a bit but it hasn't made much difference.

The oil is also very black but this is overdue for a change so probably normal...

I occured to me last night that maybe I have a loose jet or float valve. I've done nothing to the carbs since I bought the car 18 months ago and can't think of any other reason why it would suddenly start to run badly without interference by me..

Does this sound a plausible explanation and would it cause all the symptoms I have?

[carrierdave]

I would firstly rule out general engine wear and head gasket issues before you look at anything else.

Try and establish that all cylinders are up on compressor and that there is no undue pressure in the sump caused by a faulty head gasket.

Once you know the engine is all OK then have a look at the carbs and maybe fit them with new gaskets and float needles. Check the amount of float gap is correct.

good luck

[collins_dan]

I've had similar problems and am planning to check fuel pressure and possibly install an inline regulator. Dan 70 S4 SE

[ppnelan]

Do you have a fuel filter

Matthew

[Midlife]

I buggered about with mine for ages, it was running like a dog... and my plugs were black n orible looking, so I put new spark plugs in B7ES short tip not BP7ES, what a differance I couldnt believe it. I now know what fireing on 3 pots is like. Give new plugs a whirl.

[Robbie693]

Thanks all,

A compression test is something I want to get done but I haven't got a tester so I need to get the car to a garage.

The fuel smell is so strong it scares me so I'm avoiding driving it until I can find out the cause..

No fuel filter as far as I know - unless there is one in the pipe where it runs in the chassis. Doubtful though.

I put new plugs in when I found the others fuel soaked - no improvement. They are BP6ES, I would have thought if it was carbon fouling that was the problem there would have been an improvement temporarily until the new plugs sooted up?

[tdafforn]

had similar symptoms on my +2.
Ran well, then ran rough (like being on three cylinders), smell of petrol and fouled plugs.
replaced the plugs and all was well (for a while).
To trace the issue I
1) cleaned and rebuilt the webbers.
2) tuned them myself and then tuned them on a rolling road (worth the money)
This didn't fix it.
Tried a range of of different type plugs. Only difference, NGK plugs took longer to fowl.
Then thought about the overall state of the engine (67K miles, 30yo never rebuilt, lots of oil leaks , lots of crankcase pressure) and drew the conclusion that oil was leaking past the piston rings (had puffs of black smoke from the exhaust when driving) and/or guides.
Result decided to fix many birds with one stone and rebuilt the engine.
However I was able to keep the car running for 12 months and 8K miles before this drastic action by ensuring I only used it for longer runs (<20miles) then fowling was less of and issue.
Cheers
Tim

[Robbie693]

Well, in the absence of being able to do anything else for the time being I took the top off the carbs and had a look. I found the floats were set at about 18mm so I re-set them to 15mm.

Not made any difference to the rough running although it seems to pick up cleaner off idle.

However, I found a couple of things that may indicate the cause of the problem:

I have a bit of oil in the airbox. The breather doesn't seem to be blowing air out though.

Then I found a small amount of water sitting on the gearbox flange just below the head.

Head gasket?

Would this explain why the engine runs so hot (the fan cuts in everytime I am at a standstill) and the smoke from the exhaust when up to temperature?

[tdafforn]

could well be..
do you see bubbles in the radiator when the engine is running ?
Tim

[Robbie693]

Doh! Didn't look this time, but I seem to remember when I changed the coolant recently that there was. At the time I thought it was air in the system. I do seem to loose some coolant though, about a quarter of the overflow bottle every hundred miles or so.

[tdafforn]

Sounds rather like a head gasket!
Tim

[Robbie693]

Yeah, I feared so. Thanks Tim.

Assuming I'm going to do it myself, what should I look for when I have the head off as far a possible causes to make it fail?

[tdafforn]

Warping of the head is a popular cause..
You can check it with a straight edge and feeler gauges
Tim