Wildly fluctuating tick over

Speedfreak

Active Member
Had this issue for a little while, and recently it’s got worse. I have wildly fluctuating tickover, the revs will go from being far too high (as I turn up the idle speed) to virtually stalling. When I’m driving along if I pull up quickly at a roundabout or set of traffic lights it just wants to stall. I can sit there with the engine ticking over and every 10 or 20 seconds possibly longer the revs will pick up and drop all on their own. I overhauled the carburettor with the usual bits and pieces, ( it was doing this before the overhaul )and the mixture has been set correctly and tested. I appreciate there could be various reasons for this, but what are the most likely causes and where am I best to start? 2000 SC. Thanks, Steve.
 
It's possible the carb has greater problems that a rebuild kit will fix. In particular, a badly worn throttle shaft & bushings is going to make it impossible to set a reliable idle between the air leak & the butterfly ending up in slightly different positions every time you move the pedal.

Yours
Vern
 
It's possible the carb has greater problems that a rebuild kit will fix. In particular, a badly worn throttle shaft & bushings is going to make it impossible to set a reliable idle between the air leak & the butterfly ending up in slightly different positions every time you move the pedal.

Yours
Vern
Would that actually cause it to fluctuate all on its own, because I can be 10 feet away from the car however,it’s like there was a ghost in the machine?
 
or incorrectly adjusted float levels...or sticky needle and seat. See if it still does it with the reserve tap on. if it doesn't then look at the fuel pump/filter. If you take the bell off and pull the choke on all the way you should be able to see the fuel level in the jet. it should be just below the top. If its hunting like an old bus its probably a manifold leak. If its completely random its back to needle and seat adjustment. Also check the float isn't full of petrol...if it was and you've drained it then you will need to adjust the needle height to compensate for the extra flotation. my thinking is the float sounds like its too high.

A drop of engine or gearbox oil on the spindle will tell you if air is leaking in there. The engine will even out till the oil is sucked in...Same goes for the gasket around the manifold top closer panel.
 
An easy test for spindle and bush wear: have the car sit at idle, spray starter fluid on the areas where the spindle enters. The carb body, if you have a change in engine speed you have wear and leaking going on.
 
Just a quick update, we’ve done a smoke test, and it looks like the suspicions you guys had were correct that the throttle spindle has wear in it, looks like we found the problem, now need to find a solution to fix it. As you guys suggested, I sprayed some carburettor cleaner where the spindle goes through, and the revs rise as predicted.
 
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Absolutely! Bad bushings and worn spindles can have you pulling your hair out!
Hi,Is replacing worn spindles, and probably just as importantly bad bushings a DIY job? Is it likely to be a question that both are worn, it looks to me as though the repair kits only offer the spindle, not the bushes?
 
If you have HIF6 carbs you can just replace the bushes at home along with a new spindle. You’ll be amazed how worn the old ones are when you remove them!

with HIF carbs replace the spindles, bushes and spindle seals to ensure all is good again.
 
If you have HIF6 carbs you can just replace the bushes at home along with a new spindle. You’ll be amazed how worn the old ones are when you remove them!

with HIF carbs replace the spindles, bushes and spindle seals to ensure all is good again.
Mine would seem to be HS6 the type that has a separate float chamber. Well at least that’s what the Haynes manual tells me. I’m a 2000 SC
 
Mine would seem to be HS6 the type that has a separate float chamber. Well at least that’s what the Haynes manual tells me. I’m a 2000 SC
Damn, ok. You’ll need to have new bushes fitted and reamed then. Burlen do it amongst other specialists. Unless you have access to a mill and some machining skills yourself.

I will say this; it’ll transform performance and fuel economy when done. Well worth the down time and extra effort.
 
Got the old carburettor off, I’ll make some phone calls tomorrow to find out where to send it. In the meantime I’ve had a carburettor on my garage shelf since 1992. I thought to myself, what have I got to lose. I took it to pieces, I cleaned it, I put it back together, and I fitted it to the car. It started first time! Running considerably better than the old carb , and it keeps me on the road while get in the other one sorted. Thank you to everyone for all the help
 
So it’s helped the varying idle?
Yes it has, however I still have a delay in the car settling to idol. But when it does it stays there. When I spray starter fluid over this carburettor however the revs do not rise or fall as they did with the old one, however I do wonder if I might have a tired distributor?
Since fitting the “on the shelf for 30 years“ distributor, I’ve covered 165 miles, so there can’t be too much wrong with it I’ll get my original in for a rebuild next week.
 
I have had the Issue of slow or no return to idle caused by weak bob weight springs in the dizzy in the past.
my distributor is quite old and has been on the car for many years and many miles, so while I’m spending the money on the carburettor, I might as well go the whole hog and sort out the dizzy as well.
 
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