Car now rebuilt. Car wont idle when you brake ?

[xchipx]

Well have just stripped and rebuilt/refurbed the carb.

The car actually starts in the cold, and idles now :D

However, the idle is very very lumpy (without the choke on ) at any temperature.
If the car is rolling, and you put the clutch down, or put it in neutral - and at the same time you are slowing down by braking, it makes the engine cut out.

If the car is stationary, at idle, pressing the brake DOES NOT make the idle change.

So in my theory it is something to do with gravity. There are no probs under throttle at all, only idle ( or cruising with a trailing throttle )

Could it be when braking while moving that the fuel is moving about in the ( carb, fuel lines, pump, fuel tank ) that is starving the engine or making it overfuel ?

The carb was fitted with a new float valve, and the original float appeared to move alright.

Thanks again
Mark

edit (yes i know, the title is meant to be carb, not car :P )

[Fishey]

Quite possibly the one way valve on the back of the inlet manifold, i had exactly the same problem and that is what it was!

[Sparkie]

have you actually tried winding the idle mixture screw out - what effect does it have?

[bye_all_c_ya]

replace the vacuum hose from the brake servo to the rear manifold id put my money on that hose ;)

[Alex]

Sounds like an air leak.

[xchipx]

Tried playing with mixture screw today, wound fully in or all the way out, not the slightest bit of difference ?!?!

[xchipx]

replace the vacuum hose from the brake servo to the rear manifold id put my money on that hose ;)

If its the one i'm thinking, its quite a thick hose, right ?

[xchipx]

I dont think its the hose leading to brake servo.....

Pressing the brake when not moving does NOT make the car cut out.

Pulling the handbrake when rolling, DOES make the car cut out .

Seems like something to do with gravity ??? Its nothing major, but it is starting to piss me off. Help appreciated...


Fuel pump? Pressure regulator ? Filter ?

[Alex]

Take the idfle jet out and clean it. Then squirt WD40/carb cleaner (with straw attached) where you removed the jet from for about 10 seconds. :)

[xchipx]

I totally striped and rebuilt the carb from scratch with the proper webcon kit tho.

However, on the articles section it says there is a rubber seal on the idle jet? My jet has no seal that i can see of ??!

Would this really cause the idle to spaz out when i brake ?

[Shane P]

I totally striped and rebuilt the carb from scratch with the proper webcon kit tho.

However, on the articles section it says there is a rubber seal on the idle jet? My jet has no seal that i can see of ??!

Would this really cause the idle to spaz out when i brake ?

You need to have that O ring in place

As far as i am aware, the only way your brakes can affect your idle is if you have a faulty one-way valve on the back of the inlet manifold

[xchipx]

But the handbrake isn't even connected to the servo unit because its cable/drum, and the idle prob only happens when moving :laugh:


Where is the O ring you mention ? I can not find a diagram of one anywhere

[Alex]

Carbs always tend to get bits of swarf in them when they've been rebuilt, you certainly need the O-ring around the idle jet. If you haven't got one try some PTFE tape around the thread..... :)

[xchipx]

Note : the idle prob was there before i dismantled the carb #

Thanks for that, so its actually the screw in thread that is where it needs a seal?
I will go have a look.

There was defo no seal on mine

[xchipx]

Thanks mate, have just put a seal on it - no difference sadly.

Is the little bit inside the idle jet supposed to move around?

[xchipx]

:eek::laugh: The mix at idle is around 1.8λ so thats 25:1 AFR ( this might not be entirely accurate )
That is perfectly stoich for methanol :eek:

There must be an air leak ! ( Providing the gauge was accurate )