Revs drop on inclines

mornin all.
I have a question that I hope someone can shed light on. My series 3 petrol station wagon is running well at the moment, touch wood. However, there is one little thing that I can't seem to solve. It's tick over speed is probably a little higher than it should be because if I set it to what it should be, it will stall when stationary on hills. If I'm in stop start traffic and I have to stop on a steepish incline, the revs drop quite noticeably when I take my foot off the accelerator and apply the handbrake. Driving up hills is no problem, well, relative to a series anyway, it's only when I have to stop. Any thoughts?

Col

Adjust the idle setting? What kind of carburettor is fitted? Sounds like it's set slightly too low.

It's the original zenith. If I set the idle so that it ticks over ok on hills, it is too fast when idling on the flat. I have never been able to get it to maintain a steady tick over for very long anyway, the carb has been serviced and I've spent ages mucking about with the mixture screw and the slow running throttle screw. I can get it ticking over nicely on my drive but after I've been driving it for a few miles the tick over speed changes. Therefore I set it so that it ticks over at about 800-850 rpm but when I stop on a steepish hill the revs drop to about 500 or it stalls if I don't tickle the accelerator pedal with my foot. Fuel is still being pumped to the carb so I reckon something is going on inside the carb. It's not a big issue for me but as I have fixed the major issues, my attention is now focused on the little things especially now I taught myself how to ignore all the weird noise it makes.
Col

Check for crud in the tank / blocked fuel lines / blocked fuel vent / fuel filter(s) etc to make sure fuel comes out of the tank "with ease"

Check fuel pump - ideally measure the pressure...

...then look at the carb.

(Sorry but I'm a firm believer in checking the basic stuff before pulling the more complicated bits to pieces - it could very well be the carb what with all that ethanol chucked into "petrol" these days but I reckon that checking the other bits first is wise)

Thanks for the advice Stretch. Mine has two tanks, the main one at the rear and another under the driver seat with a switch-over valve fitted to the seat box. There is fuel in the front tank although I don't use it because there is some crud in there. There fuel lines all seem OK and the fuel filter is new. How would I measure the fuel pump pressure?

Col

Colthebrummie said:

Thanks for the advice Stretch. Mine has two tanks, the main one at the rear and another under the driver seat with a switch-over valve fitted to the seat box. There is fuel in the front tank although I don't use it because there is some crud in there. There fuel lines all seem OK and the fuel filter is new. How would I measure the fuel pump pressure?

Col

Click to expand...

You'd have to stick in a temporary "T" piece and between the pump and the carb and connect a fairly low pressure gauge to the new junction.
I've just had a quick look through my series 2 green book but as usual I can't even find a specification. But at a guess you'd expect to see about 4 PSI to about 10 PSI if all was well.

If you were able to do this then you could drive along with your gauge and see if a nose up attitude caused a drop in fuel pressure on the gauge. In the event that the measured pressure (what ever that is - so long as it seems "reasonable") stays constant then you can be sure that the the stuff before the gauge is gonna be alright.

Mmm, that's well worth thinking about. I have considered rigging up a temporary electric fuel pump to see if that cancels out the low revs on hill issue. I suppose I could just Jack the front end right up and see if the pump struggles to keep the filter full.

Col

Yeah you could try that - in my experience doing things like that usually result in accidents though - if you do please film it and post up the carnage on the toob!

Wot cud possibly go wrong?

Col

If dual tanks possible for change over valve to be allowing air to be sucked in instead of fuel , could also be a perforated pick up pipe in rear tank . does it happen when tank full?

Colthebrummie said:

Wot cud possibly go wrong?

Col

Click to expand...

to fix the incline problem i did this

Rev's dropping when hand brake applied is often because of movement of engine/gearbox on their mounts affecting the length of the throttle linkage.

tottot said:

Rev's dropping when hand brake applied is often because of movement of engine/gearbox on their mounts affecting the length of the throttle linkage.

Click to expand...

Really? I'll have to look into that, the mounts are all 40 years old so they are probably not as good as they could be.

Col

Blackburn said:

If dual tanks possible for change over valve to be allowing air to be sucked in instead of fuel , could also be a perforated pick up pipe in rear tank . does it happen when tank full?

Click to expand...

It's rare that the tank is full. There is always some fuel in front tank even though I don't use it. Rear tanks is about half full at the moment, next time I fill up I try parking on a hill and see if it still happens. To be honest though, with it being a petrol, I wouldn't have thought air in the fuel would be much of a problem, the fuel filter is always nearly full.

Col

Some later models had a short rod with bushes each end that went from somewhere on the gearbox to the chassis leg to limit movement If I remember right.

tottot said:

Some later models had a short rod with bushes each end that went from somewhere on the gearbox to the chassis leg to limit movement If I remember right.

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I've not got that on mine.

Col

You need to look at the fuel level in the float chamber.

wammers said:

You need to look at the fuel level in the float chamber.

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Yes, that is my suspicion too. Although when I serviced the carb, I checked the float height and it was at the correct level.

Col

is it a weber 34