Hi, is this PHVA carburetor diagram correct?
If so, what would be the best position of the needle on stock A55 with Estoril Pipe:
(A) Leaner, (B) Lean, (C) Middle, (D) Rich or (E) Richer?
Being as every bike is a bit different , why not start in the middle and work out ?
What anyone tells you may or may not be ideal for your bike .
That diagram is correct, but no one has the answer to your question. You have to find out. I would suggest reading until it's totally obvious to you which setting on that needle is richer and which is leaner.
Get fresh plugs and check your work with frequent plug reads until you're confident that it's not gonna blow up and you're making the amount of power you were after.
The middle is what the emulsion tube was designed around. If the emulsion tube is stock for that carb then the middle setting will yield the correct air/fuel mixture at the throttle position range that the needle controls, 1/4 to 3/4 throttle I believe but check the carb spec for that.
> John Maxson Wrote:
> The middle is what the emulsion tube was designed around. If the
> emulsion tube is stock for that carb then the middle setting will yield
> the correct air/fuel mixture at the throttle position range that the
> needle controls, 1/4 to 3/4 throttle I believe but check the carb spec
> for that.
This is not correct. The interplay between seat and needle is exactly the thing you WANT to be changing here.
They wouldn't design and sell multiple needles each with 5 positions for the same emulsion tube if only one needle fit in only one position.
What John is implying is that ideally the factory should have sized the emulsion tube and needle to be tuned in the middle position, when the bike was new.
While this should be the case, even new they came differently.
There is no answer to the OP's question from a purely quantitative stance. Tuning the needle is simple enough to do, especially as in this case you really don't even have to take off the carb.
I have never seen any needle specs set at anything else besides middle and never had good results with anything but.. in all my tinkerings. Carbs are made to mix air and fuel at a 14:1 ratio.
Adjustments for altitude compensation could be why there are extra slots. 80's emission stds did away with the slots, I have put plastic washers under the clips of the single groove needles to get rid of lean stumble with good results.
I have carbs from the 80's and 90's that have select-able needle heights.
Also, I don't think a single carb I have is in the middle position. Carbs are not pre-tuned when you consider changes to exhausts and intakes, etc. Having a chambered exhaust vs. stock definitely changes the draw at throttle positions where the needle has the majority of the metering power.
Middle position if you have 13$ metal mesh filter or something similar and around 64 jet, if you’re dumb like many who don’t listen to my posts and still run stock plastic junk with foam inside air box only designed for stock pipe you are on your own!
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