tickover slowing down

johng

CCCUK Member
I drove to the Nationals today, about an 80 mile trip in rather hot weather. The car went very well, engine temp and oil pressure remained stable throughout. However, about an hour into the journey the car started stalling when we came to a stop, because it was trying to tickover at about 400rpm. Prior to this journey it tickover was a nice stable 600 to 700rpm. Once we got to the show I screwed in the throttle stop until tickover speed was restored to 600 to 700rpm and it was fine for the journey home. The thing I don't understand is why did the tickover drop? It took a good couple of turns of the screw to get it back to normal. I did wonder if the distributor might have moved, but it felt tight.
 

Oneball

CCCUK Member
Could be the throttle screw wasn’t what was setting the idle speed. Cable snagged, choke, secondaries open
 

johng

CCCUK Member
If it was something that has now fixed itself, then presumably I'll have to wait for it to go wrong again before I can work out what it is. Engine certainly got warm enough to drop the choke fully today!
 

johng

CCCUK Member
Fuel evaporation?.. he says trying to sound like he knows what hes talking about.. which as usual, i dont.
Actually I don't think it was, because the car had no trouble restarting after it stalled. Didn't have any problem restarting after sitting around for a while at Stansted services either.
 

johng

CCCUK Member
The puzzle continues. I drove to the Essex area meeting last night (about a 30min drive) and all was well. However when I went to leave about 90mins later the car started up and was idling at around 2000 to 2500rpm. The choke was fully off, the secondaries were closed and the throttle mechanism was sitting on the throttle stop. Tried disconnecting and blocking some of the vacuum lines which made a small difference but not much. Finally just wound the throttle stop right out so I could drive home and tickover reduced to 1200rpm. Car drove home fine, about half way I noticed that tickover was down to 700rpm and when I got home it wouldn't tickover anymore as it was trying to run at 300 to 400rpm.
Anyone got any suggestions?
 

Oneball

CCCUK Member
Sound very much like either a vacuum leak or a sticking advance mechanism (less likely I think).

Have you got a PCV system? If you have I’d give it a thorough check especially the valve.

Check you’ve not got a failed inlet or carb gasket and all the nuts are done up.

And all vac lines.

What carb is it?
 

Oneball

CCCUK Member
For advance mech:

check the rotor arm is free to move on the shaft and that the springs and weights are still there.

suck the vac canister and make sure the mech moves

check the vac line is attached and no holes.
 

johng

CCCUK Member
Seems like Oneball got it right pretty much first time (no surprise there then). All four bolts holding the carb on were loose! With them tighten up, the throttle stop screw wound back in quite a long way and the idle mixture adjusted it's ticking over at 700rpm again. Just need a long journey now to see if the problem reappears. Not sure if I never did tighten up the carb bolts properly, or whether they've worked loose. I do have a thick gasket between carb and inlet manifold that I guess that could have "given" a bit.
 

Roscobbc

Moderator
I had some issues on the way to the Essex meeting last night as well. Temperature gauge was reading about 210 on the way there which even considering the temperature last night (about 23 degrees) was a little unusual for open road driving (heaving town traffic , yes) - some of the lads pointed-out a small amount of overflow for the radiator - nothing ususual, I'd checked the water level before setting out. Much the same on the return journey (obviously a lot cooler - but still 200 -210) - then there were a few spots of rain (or what I thought was rain......) - slowed to 55 -60 mph its normal crusie 'sweet spot' for engine temperature. Looked yet again at the temperature - this time off the clock!
The 'rain' was in fact rad boiling over. Didn't stop, slowed down, now in to urban light evening traffic. Couldn't see any split or leaking hoses, thermostat housing, water pump etc. After 15 minutes I released the rad cap which surpringly still held loads of pressure - the rad was 1/2 full. Clutch/viscous fan/water pump shaft had a noticeable greasy residue on the shaft and despite the engine being red-hot there was minimal resistance when trying to rotate the fan blades.....wrong!
Thinking about it the fan hasn't been 'spooling-up' on cold starts like normal. Anyway, trip to Europarts for some yellow Prestone coolant and then on to Customville for a new fan clutch.
 

johng

CCCUK Member
At least I'm not the only one with car problems then. Let's hope they are both an easy fix.
 

Forrest Gump

CCCUK regional rep
Seems like Oneball got it right pretty much first time (no surprise there then). All four bolts holding the carb on were loose! With them tighten up, the throttle stop screw wound back in quite a long way and the idle mixture adjusted it's ticking over at 700rpm again. Just need a long journey now to see if the problem reappears. Not sure if I never did tighten up the carb bolts properly, or whether they've worked loose. I do have a thick gasket between carb and inlet manifold that I guess that could have "given" a bit.
What I find curious is how suddenly the problem occurred. You would have thought that the idle would have gradually got faster over a period of time, as the carb became looser and the air leak worse??
Carb nuts should only be lightly nipped up of course John as there is a risk of bending the corners of the carb base plate.
 
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