Needles: A General Question

V

vin-kohler

Member
When I recently ordered a refurbish kit for my HS8 carbies I phoned Mark Gray about the applicable needle type. He recommended AAB. The istallation will take place once the days get warmer again.

Meanwhile I'm wondering: What are the crucial dimensions of the needle? Is it the diameter at the thick end or the degree of taper or the profile of the taper?

I understand that you occasionally abrade your needles for better performance. Which concept guides you?

Just a snoopy question - I know. Thank you all the same.

Vin
 
all of them :)

a minimal amount of petrol flows round the needle under low vacuum - the taper decides the richness at corresponding levels of vaccuum which is influenced by the throttle position and the vacuum into the cylinders.

Polishing shouldnt really be necessary - it will richen the mix at a given throttle opening...

Rich
 
Yes, Rich, I understand all that. But what I meant to ask is: How would you judge that you have the right needles?

Presuming your mixture is set properly for low power but you have pinking under heavy load. Would you consider to try a different type of needles or would you polish the slim end?

Is there anybody reading my thread who has experimented with that kind of tuning? I'm just curious about the procedure and the outcome.

Vin

(Edit) And a related question: Has anybody ever installed a cylinder head temperature gauge? Would be nice to have a life picture of the combustion condition.
 
Yes, Rich, I understand all that. But what I meant to ask is: How would you judge that you have the right needles?

Presuming your mixture is set properly for low power but you have pinking under heavy load. Would you consider to try a different type of needles or would you polish the slim end?

Is there anybody reading my thread who has experimented with that kind of tuning? I'm just curious about the procedure and the outcome.

Vin

(Edit) And a related question: Has anybody ever installed a cylinder head temperature gauge? Would be nice to have a life picture of the combustion condition.
Click to expand...
:) Now that's a more interesting question....

Pinking means it needs timing retarding or richening. I would and have tried different needles, but only on my v8.

I have a program (winsu - it's only about a tenner) It gives recommendations on the rich side for the v8 but that helps with setting a range at least. It doesnt have a 'model' of the 4 cylinder engine, but it does have the ability to tell you similar needles that are richer and leaner in specific sections of the needle.

So if you have AAB, It suggests AZ is the needle which is richer in the higher vacuum range. (whether that fits your carb or not i cant guarantee.)

The only ways to really find out are to get a rolling road tune, or fit a lambda sensor and gauge to the exhaust so you can measure unburnt fuel accurately. If you want a anecdotal test pull the choke out when its under load and see if richening the mix helps.

Hope that little lot is some help.

Rich
 
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