Conference terri::cars_uk

    Could this be a problem with the inlet manifold gasket ???
    If air is getting into the system somewhere between the carb
    and the engine, you might experience this type of problem.

    It might even be that the hose connecting the manifold to
    the servo is leaking ... assuming the a Datsun Cherry has
    a servo for the brakes.

    You could always have a problem with the distributor. Perhaps
    the automatic advance isn't working properly.

  Mark

    The inlet manifold gasket sounds pretty good... I had a problem
    with the Exhaust manifold gasket breaking up. I'll stick that on
    the top of my list.
    
    I don't know much about cars, I just get the manual and follow the
    instructions... why the servo for the brakes ???
    
    I think the distributer is o.k.
    
    Ta,
    	Alan.
     

    The servo is usually tapped off the inlet manifold. If the
    pipe is leaking, it has the same effect as a leaking inlet
    manifold gasket ... air gets in.

  Mark

My metro does it to a small extent when the engine's cold and I'm using the
choke.  I thought it was just that the mixture wasn't right, so maybe your
carb needs adjusting?

Scott

    Fixed venturi carbs like webers, Ford etc as opposed to strombergs and
    solex and SUs usualy have some sort of accelerator pump to add extra
    fuel to the mixture when the throttle is floored. This pump is usualy
    a small part bolted to the main carb body and actuated by a lever
    and cam system from the main throttle spindle. This may or may not
    have a pump jet associated with it and built into the carb body. 
    
    What usualy happens is that the jet gets blocked or the cam needs
    adjusting.
    
    The best way to sort this is to by a Haynes manual and go through
    all the carb adjustments one by one.
    
    Hope this helps.....
    
    
    Simonf

Does this engine have a fixed or variable venturi carb??

If fixed venturi:

	Remove the air filter, peer into the choke tube while an accomplice
	smartly floors the the accelerator pedal (engine recently run but
	now switched off). You should see petrol issued from a delivery
	pipe somewhere in the choke tube - it may be difficult to see the
	delivery tube but you should certainly see/hear the petrol being
	squirted out. It is usually quite a reasonable quantity that is
	dumped down the choke tube if the accelerator padal is fully
	floored, also the delivery will continue for one or two seconds
	after the pedal actually hits he floor. There is not normally any
	adjustment - if it doesn't work the delivery tube may be blocked, or
	more likely the pump diaphram is shot.

If variable venturi:

	Check the slide damper has oil, remove the air filter and manally
	push the slide up - you should feel the damper resisting the movement.
	When you release the slide it should snap shut virtually undamped.

Have fun.

- John.

    ... also, some variable venturi carbs use diaphram dampers, rather
    then oil filled. Could be a broken diaphram ...

  Mark

Nobody's mentioned the fact that you can get the same kind of symptoms from a 
distributor fault - like damaged points, sticking advance weights, iffy 
condenser, worn cam lobes, broken or stretched springs, etc.

Dick

What is the correct sort of oil to put in the dashpot on an SU carb?
Haynes doesn't help: it says "fill with correct grade of oil..." but nowhere
does it say what the correct grade is!

I've always used ordinary engine oil, and it's seemed to work OK...

Scott

 I always beleived it to be more 3-in-1 type of oil that was supposed to be used
although never having used SUs I am not certain. It will be very useful to know
though, as the Sprint has SUs, 2 of them, sounds like fun to set up !!!!


		 Alan
		~~~~~~

    Light machine oil.....3 in 1
    
    Multigrade engine oil is too thick and will slow down throttle
    response.
    
    Simon
    

      Although not exactly the intended application, many people reckon ATF
    to be the best.
    

    I've been looking for a source of decent thin (like 10W) oil without
    all the anti-oxidants and detergents and froth killers that get put
    into a modern multigrade to use on my lathe headstock bearings. The
    lathe was built in 1952 and the manual refers to oils no longer
    made/sold/distributed. I contacted the a couple of makers of lubricants
    "recommended" in the manual and guess what they both said.....?
    
    "Use ATF fluid. Its a straight 10W oil and the only thing that is put
    in it is a dye to make ita nice pretty colour."
    
    So maybe the suggestion in -1 isn't so far off the mark after all.  

???

Scott

    I finally tracked it down to the hose between the manifold and servo
    for the brakes.
    
    Thanks for everyones help !
    
    Alan.
    

    See .1 :-) :-)


 Mark