Recently the engine is sort of misfiring or not running clear on a celleration above 40 mph. I will check the distributor cap and rotor when it has cooled down.
And starting from cold was difficult, with a ton of white smoke rising from near the carbs (the bonnet was open) at one moment. It eventually started, with tons ofvsimilar white smoke from the tail pipes. It then decided that tickover was to be 1750rpm instead of 750. It remained at 1750 during slow driving at at the end of the half hour incl some motorway at 65 mph.
The high idle/tickover was new today, but the hesitent performance has been going on for a while.
The fuel is fresh and the King filter is clean.
Is your brake fluid reservoir still full? Radiator level OK.
Gerard
Yes, thank you, but I don´t see the connection to my engine issues…?
Peder,
The clouds of white smoke are typical of a problem in the vacuum side of the brake servo system. The servo can fail such that there is a vacuum leak, which makes the idle go up, and this leak pulls brake fluid into the intake, which causes the car to lay down a (massive) white smoke shield.
It’s really quite impressive.
Try clamping off the vacuum feed line to the brake system, if the idle goes down then you’ve got a problem in the brake vacuum (usually the servo).
It could be a head gasket leak, but there the idle doesn’t usually go up.
Probably referring to the possibility that the vacuum booster is leaking brake fluid into the vacuum side and this is being sucked into the intake causing the white smoke. Also, a vacuum leak at the booster could be the source of you high idle. You could clamp off the vacuum line to the booster as a test to see if there is any difference.
Also, IIRC, automatic transmissions that have a failed diaphragm in the vacuum modulator can draw transmission fluid up into the inlet manifold causing a similar smokescreen. The BW12 in our XJ6 has just this setup. Can’t speak for earlier series transmissions. Paul
1 Like
Thanks to all. I have learnt something new, BUT, here is what happened this morning, 10 mins ago.
It started as always on the 3rd attempt. Ran at about 1000rpm with the hisser/AED, producinga lot of white exhaust, but far less than yesterday, and only through the tail pipes (unlike yesterday).
After a few mins I stopped the hisser by pulling the wire. Back on and it settled without the hisser and now runs normally.
While at 1100 I clamped the vacuum hose, both by the intake manifold, and by the brake booster, but this did not change the idle at all…
Just went out to check on her. Running very smoothly at 700 with minimal white exhaust fumes.
Time for a coffee…!
Update:
Just drove the car for 15 mins, directly from 15 min start and warmup, as per above. The engine now runs strong and perfect. The hesitation/”misfiring” and weak feeling has disappeared! Very strange.
I felt that the idling had crept back up,to 1750 as I had to brake to drive at low speed in the village. And when stopping for an errand confirmed this.
2 mis later it would not start. 4th attempt, with pedal half down, it did start. Again up to 1750. Drove back home and opened the bonnet by my garage. Tried to bring the idle down by squeezing the vacuum hoses with a large plumberĹ› wrench, but this made no difference.
So what is going on…?
Might add that yesterday, before starting, I added some Redline SI-1, which is supposed to clear the carbs etc. I do this to my cars 2-3 times a year. I added the equivalent for 40 L as
I thought the tank was full (which they usually are), but saw that it was just 1/4 full. The petrol was not old. The brake booster is perhaps 5 yrs old.
Might this overdose have caused the massive white smoke (must have come from the AED)?
But I then switched to the other tank which was full, as I drove off last night, with the usual poor, hesitating performance on accelleration beyond 40mph.
Peder, when you are under way you can turn off the hisser by quickly turning the ignition off and back on, once you are happy that the engine has sufficient heat in it.
i think you will find that is your problem!
I once added a VERY small amount of kerosine to the 91 petrol, on a WW2 GMC truck designed to run 65 octane fuel…the amount of white smoke was unbelievable
fill one tank up, and see if that fixes it
Fir Robin:
But I did that prior to taking off. It idled well at 700 for 15 min before I left, and behaved well for the first 10 min of driving. It then decided to increase the idle to 1750 while driving…
For Tony:
So the white smoke came from the overdose. Fine, and that then cleared the carbs so that it now runs clean and smooth all the way…Great.
But why does the idle go to 1750 after driving for a while?
Would the hisser have come back in action? There was too much noise to distinguish when I opened the bonnet at home to try to squeeze the vacuum tubes. Next time, if it happens again, I will pull the wire to the hisser and see if idle falls back to 750
You never did mention if any of the levels were low? My hisser never idles that fast so a vacuum leak is indeed suspect. My hisser idle is around 1000. Extra oil, diesel or even an additive could indeed cause smoking. Watch some of the videos of being added to a vacuum line on a vehicle:
Look around the three minute mark on this video and you will see some smoke.
This Seafoam can be added to the crankcase, the gas tank, air intakes and your bath water - It’s great stuff!!
Put a manual electric switch override onto the hisser - you will thank me later.
Gerard
would certainly have a manual switch on my hisser to be sure
have experienced “variable idle” on my 420G
-
reason number 1;.some fault in the return spring situation, such as detached or broken spring, OR loose return spring bracket on throttle shaft of at least 1 carb, OR for some reason, 1 carb piston is staying up higher (remove plenum and look up carb throats),
OR binding in the accelerator/throttle parts, which are complicated, especially if they have been worked upon, its not easy to put everything back together for ideal motion -
never totally sorted why the original engine idled high sometimes,( now has a later engine with different throttle & choke setup)
Reminds me of being young and stupid and dosing my Dolomite Sprint with Redex. Filled our yard and neighbours’ with white smoke. Paul
Just thought of this as I was blasting down the highway at 80MPH today. Have you checked the carb pistons to make sure that they move freely up and down and that all the carbs are full to the overflow hole with 20 weight oil? You might have some sticking and the bells are not moving correctly… Do the test where you lift each carbs pistons to make sure the idle changes as described in the service manuals
Gerard