Mixture screw issues.....

[Leigh5T]

I'll try to cut a long story short...
I had issues with my carb during idle and cruise conditions, hesitating and lumpy.
I Plummed in my Lc-1 & Db to find it was VERY lean at idle (Like 18:1afr) and leaner during overrun (20+ afr).
Tried Adjusting mixture but the screw did noting.
Removed the carb to Find the mixture screw had snapped.
Sorted that, built it back up with a rebuild kit and roughly set the mixture and idle.
Ran it up till warm and set the mixture and idle till it was ticking over at 900rpm with about 14.5:1 afr.

In order to get to that mixture at idle the mixture screw is all the way out!
To the point where i can move it side to side slightly on its threads!

Other than that it idle's great! better than it ever has before.

I take it this is not normal? any ideas? Cheers in advance guys.

[Adey aka Ewok]

I'd be looking for a leak around the manifold bud

[Leigh5T]

Ok i'll have a look for a leak later.

Took the 5 out for a drive see what afr's look like.

Idle is just under 15afr at 1k rpm
drops to around 13 under light acceleration
cruising at 14.5
when at about 2k rpm in third with almost no accelation it rises up to 16!
WOT it's at 14! and starts pinking!! backed off !

I am very new to this so bare with me. I know all them figures are very lean!
Idle's ok but the mixture screw is a bit concerning.

It's alot more driveable around town now though and idle's great.
Obviously avoiding boost until sorted.

[Leigh5T]

Drove the 5 to work today and it idle's fine at just under 15 afr (still with mixture screw almost hanging out) but when throttle opens very slightly it leans to 16!

Slightly more throttle and it drops to 12-13

Not tried on boost as i think the pressure is set too high.
There was a bleed valve on when i got it and don't know for definate what it's set at. The previous owner said 14psi but who knows. Will get a gauge asap.

Could the afr problem be the acc pump setting? (Like a fool i didn't check this when rebuilt the carb)

Also shall i bin the bleed valve?

[Markey Mark (BD)]

Whats the carb spec mate?

This will give us abit of a clue as to whats wrong

[Leigh5T]

Whats the carb spec mate?

This will give us abit of a clue as to whats wrong

Well, Like a dick i didn't check when i rebuilt it.
Think the best thing to do is whip it back off again and check then it'll give me a good place to start from.

Will i be ok to strip it back down and rebuild using the same gaskets?

[Kris M]

If / when you strip it down again, dont just take for gospel whats stamped on the jets, get some micro drill bits in there untill you find one that fits. They may have been drilled out before you see

[Leigh5T]

If / when you strip it down again, dont just take for gospel whats stamped on the jets, get some micro drill bits in there untill you find one that fits. They may have been drilled out before you see

Top tip!

[Leigh5T]

Right ive just had the carb off again to check the jets.

1.2mm main
1.25 air corrector.

Reset the accelerator pump with the 5mm drill bit.

Changed plugs whilst i was at it.

Still no difference!!

When revving gently up to about 2k the afr creeps up to 17!
slight hesitation and holding back during this too.

will boost be a factor this low down in the revs?

[Leigh5T]

Also whilst i have the carb elbow off ive just noticed that fuel is coming from here when revving is this normal?



Its like fuel is escaping around the acc pump instead of going through it?
You can see the fuel in the pic around the air corrector.

[michael tierney]

that little gasket(flat red rubber ring) is tricky and will leak if the old one is'nt fully removed.also make sure the gaskit between the body and base lines up properly(hole-wise) and that ur idle jet is clean.check that ur exhaust is'nt blowing or leaking near ur sensor because it will cause ur readings to be high on the air side!

[Leigh5T]

that little gasket(flat red rubber ring) is tricky and will leak if the old one is'nt fully removed.also make sure the gaskit between the body and base lines up properly(hole-wise) and that ur idle jet is clean.check that ur exhaust is'nt blowing or leaking near ur sensor because it will cause ur readings to be high on the air side!

Ive managed to stop the fuel leaking by putting an o ring around the acc pump jet (if thats what its called?) instead of that flat red one.

still doing the same thing.

Checked for leaks and cant find any. but it is running poorly during that low rev range which makes me think its more to do with the carb.

Seems like there either isnt enough fuel or too much air down low in the rev range.

[michael tierney]

pipes and one-way valves,manifolds loose.from the way ur describing it, it sounds as if somethings getting worse!

[Leigh5T]

Ok well ive not checked valves or pipes.
I have just tried covering the top of the carb up a bit whilst its running and i can get it to richen up.
suppose it would be worth changing the manifold gasket anyway?

[TrixNFlix]

Is it not going to be easier in the long run for you to pressurise the boost circuit and find the leak that way?

[Leigh5T]

Is it not going to be easier in the long run for you to pressurise the boost circuit and find the leak that way?

Im ignoring the boost circuit at the min cos ive not got the carb elbow attached.
having the same prob weather its attached or not.
Im only checking it whilst stationary at the min obviously.

[TrixNFlix]

Ok well why don't you just put the elbow on and pressurise from there, at least then you'll know whether the manifolds blowing before you change it, and then you've checked all the vac pipes for future reference.

[Leigh5T]

Ok well why don't you just put the elbow on and pressurise from there, at least then you'll know whether the manifolds blowing before you change it, and then you've checked all the vac pipes for future reference.

Right ok cheers i'll have to bodge something together to pressurise the system.
Haven't got any kind of pump with me at the mo so it'll prob be 2morro now anyway.

Any ideas what else i can check for now?

[TrixNFlix]

You could do all the things you said like change the manifold gaskets, wip the
carb off, take it apart again and rebuild it again checking all the seals are there, replace all vac pipes, etc etc but all this might not be needed. If I could only bodge something up to pressurise the system tomorrow, today I would try and tighten up the manifold nuts, change vac pipe from top of inlet to aei unit and check both valves on Back of inlet manifold are screwed in properly and not leaking. Hope this helps abit.

[xchipx]

Sorry to bump an old thread..

The symptoms are exactly the same oh how my car was running.
Did you get to the bottom of this in the end?