an odd one

[worzel]

Hi all

Apologies for shoving this onto the forum but I've tried the correct owners' forum and they've not yet been able to figure it out.

Can anyone explain this-

I'm talking about a car running on twin 45 dellortos.

Air flow thru both is exactly the same ie correctly balanced.
Both carbs are jetted identically.
Compressions are all within 1lb of 170.
Valve clearances are to maker's spec
There are definitely no air leaks on the inlet side
Float levels are each to maker's spec.
No carb jets are loose.
Floats aren't punctured.

The problem- the rearmost carb requires that the slow running screws be turned out aprrox 3 full turns. The front carb however needs at least 1.5 turns more (this is using a colourtune to achieve the transition point from yellow to blue). I know some laugh at these devices but I've always had good results from them.

The odd thing is the car runs fine and has done for the last 7 years I've had it. The manual however suggests that starting from scratch one should close fully all 4 screws then turn out 3 full turns- then adjust to the desired emission level by simply turning each in/out quarter turn at a time.

I've not yet tried swapping the carbs round because I don't see any point at this stage.

Any ideas?

Regards

John

[tdafforn]

If it runs fine leave it!
Could it be that the air flow to the back carb is different to that to the front?
cheers
tim

[handi_andi]

Could be that the valve timing is slightly out, hence not all the inlet valves are open for the same amount of or timning of stroke. Hence different volumes of air getting sucked in.

Just a thought.

Andy

[twincamman]

Andy ---if it works well --accept it----zen ed

[wojeepster]

carbs aren't perfect, that is why they have a balance screw. let it be.

[reb53]

Sounds like a manufacturing difference .

How do the screws compare between front and rear?
One set may have slightly different diameters or tapers.

If they look the same the difference may be in the carb internals.
The production line only needs a slightly bigger or smaller drill installed and the result doesn't stop the carb working, just makes it a little different from the ones that were done that morning.

A bit unlikely I know, but a picture comes to mind of a hot Italian afternoon, Luigi's bored out of his brain, thinking of the weekend 'cos it is Friday........

Ralph.