PHBN PHVA Carb Tuning - Needles & Atomisers, Main Jet

[fe53series3]

PHBN PHVA Carb Tuning - Needles & Atomisers

Some people choose a simple carb, that you don't spend time tuning..... because there are so few tuning options.

This is perfectly acceptable, if you just want your bike to be rideable.
But hang on......... you've just shelled out for a BBK... maybe even an expansion can and silencer.
Why would you go for a carb with few tuning options...... and accept just a basic state of tune?

We know with 100% certainty, that it helps if the simple carb is called a 'Race Carb'.
We also know that the true 'Race Carb' is the PHBN/VA, because it's tuning options allow adjustment down to the finest detail, across a massive spectrum of fuel delivery curves.

Some people choose the falsely named 'Race Carb' because it matches their aspirations, without the need for any tuning effort..... usually because they don't realise that tuning is not 'that' difficult.

So here we are gonna put that ghost to rest, and look at how we can arrive at a good basic tune, without worrying about getting performance absolutely perfect (like what you'd get with a so called 'Race Carb').

We'll then look at how we can home in on the perfect tune, to the smallest degree.

The video Tutorial:

Note:
It took around 5 attempts (it was not easy at all).
Please comment on whether the final attempt was understandable...... and whether you found it useful.

Also note: Main Jets, were not explained, neither the idle circuit.
These require further explanation.

Anyway.... here it is:

Note: I've just run it full screen, and the res holds up quite nice.

www.youtube.com/watch?v=BRN23fO9aKY

[fe53series3]

FYI

Tests should be done with a 'paint marked throttle grip' @ 50% open, and a new plug.
It allows you to still have fun on the bike whilst testing...... but never pass 50%.

This ensures that when you pull the plug, you will have a colour that represents your atomiser/needle combination.

Test results will be modified by the main jet size, so try to start with a mj as close to correct as possible.
However, once you understand your needles...... if a larger, or smaller mj is required...... you'll know which notch or needle to change to.

Due to PHBN's having a 'needle always in atomiser'..... the main jet can change.
Therefore, after acquiring the right needle....... Main Jet tests should be first carried out with marked throttle grip at 75%.
If colour is good, then test at WOT.

 




 

[fe53series3]

This is the 2nd in the series (of probably 3).

What I've done is presented a 'sea change' in thinking, that reflects the design nature of the Dellorto PH series.

Primarily you're going to have to ditch all the traditional carb tuning advice, that you've read....... because you must, if you are going to understand how to tune this carb.

Anybody who has read anything about carb tuning, will have learned that the main jet is established first, by testing at WOT.

First written decades ago.... this advice has been copied and pasted, and quoted (and requoted) without end.
I figured it was time that somebody pointed out that the emperor was wearing no clothes.

This video was way harder to make, than the first (needles), due to the need to switch the 'thinking on' to the realities of the carb design.

I didn't show mathematical evidence (for how much the needle blocks the atomiser at WOT) - my program provides all mathematical data, but...... it was all getting too complicated......... it's long enough as it is, at around 17 minutes.

Youtube suggests to me that some people don't watch my videos to the end (so I should shorten them)........ like as if I could give a toss.

I guess if I worked on this vid for a couple of days, I might shave a couple of minutes off it.
But hey..... if you want to understand how to tune a PHBN carb...... and literally understand why you are making the decisions...... I think this will provide you with what you need.

Having said that...
It's done now (TG)...... so I'm open to comments on whether it succeeds.

Here it is: