This week's strangeness: tickover dipping when braking

Doug

Doug

Member
Hi all

Today's question ...

Engine is 1725cc standard cast iron head, zenith carb- standard stuff.

When pulling up to a junction, the tickover dives, often to the point of cutting out.

I can't quite work out whether it's the brakes or just the fact that the van is being slowed (ie everything's being pulled forward). It definitely happens when I brake, but sometimes the tickover remains low when lofting off the pedal (I think).

Any thoughts what that might be? I wondered whether it was something to do with the brake servo, maybe letting too much air in or something and leaning out the engine. But the way it behaves it could be something else like (making stuff up here) a float chamber having all the fuel pushed up one end, or something .

Having found out that the air filter was completely blocked, I'm temporariliy running without one so I guess it's a bit more lean than usual. The result is a faster tickover generally (I had adjusted it before I realised the filter was blocked - it's now too fast, until I adjust it again), but when pulling up the cutting-out problem still happens even though it's coming from a higher tickover rate.

Any thoughts?
 
If it was OK before you removed the filter then don't touch anything until a new one is fitted or you'll just be chasing your tail. Do the revs drop as a result of dipping the clutch?
 
Thanks for responding, peoples -

It was doing the same thing before removing the filter, but not to the point where it was cutting out. It was on the verge though.
When dipping clutch: no difference in revs.
When stationery and applying brake: no difference in revs

It seems to be related to actually slowing down. Confusing!
 
Give the mixture screw a quarter of a turn anti-clockwise and see if that helps.
 
So. Tangentially this happened with my volvo v40 and garage tweaked ecu to no effect. It's a petrol but I end up taking apart the fall that added air / fuel. Complete mess inside. Cleaned and hey presto.

I'm no mechanic but hope it's a lead...
 
OnTheRoadAgain said:
So. Tangentially this happened with my volvo v40 and garage tweaked ecu to no effect. It's a petrol but I end up taking apart the fall that added air / fuel. Complete mess inside. Cleaned and hey presto.

I'm no mechanic but hope it's a lead...
Click to expand...
Hi - the "fall that added air" ? you lost me there ..
 
PaulJL said:
Its a stop start system.... Rootes must have used it years before modern cars had it fitted
Click to expand...
The stopping part : Yep, they have that nailed. No problem at all there.
The starting again: Less so. Not quite as good in this department.
 
ps. I think he's running lean - a little bit of choke diminshes the problem . so when the new air filter arrives I'll tweak the mixture as Panky suggests.
Dodgeram - I'm expecting to find all kinds of crap because he's mayonnaising the oil. Time for another new thread ..
 
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