450 Desmo Dellorto PHF32 Jetting

[ChrisS]

Hi All,

Recently purchased a 74 450, it has a PHF32 on it and soots the plug deluxe.

It’s only got 5000 original kms on it and compression is good, no oil at all on the plug and would only idle with choke out.

Pulled the carb apart had it professionally cleaned and reassemble.

That got it idling without the choke but plug still looks rich as, and is not happy on steady state running, it’s fine when you crack the throttle, it starts second kick every time.

Has any one have a suggested place to start on jets, slides, needle positions etc,

Cheers

[Ventodue]

Hi Chris and welcome to the Forum.

As I''m sure you know the PHF32 wasn't fitted originally to the 450 Desmo. Your nearest 'best reference' is the 350 Vento. Try:

Idle jet: 50 or 55.

Atomiser: 265AB

Slide: 50/3

Needle: K3, middle slot.

Main: 135 or 140.

HTH

Craig

[graeme]

Try the same as a Darmah 32 Dell’Orto settings off the web.
But with 262 instead of 265 atomiser

This worked for me on ‘74 Desmo and Scrambler

Graeme

[graeme]

Australian 95 fuel
Don’t know where you are ???

Graeme

[double diamond]

What spark plug are you running?

Matt

[ChrisS]

Cheers Everyone and thanks for the welcome

Answers to a few Q’s raised

NGK Iridium BR7, thought it might give a better spark than a standard plug

Yep live in west oz, it’s done it with all fuels however presently running it on 98

Yes on the non original although it looks like it’s been on for many years, half tempted to put a Mikuni or original carb on

All help on this is really appreciated

Regards,
CHRIS

[graeme]

Hello Chris

98 does tend to make carb engines run rich.
95 is a bit better suited to older engines unless you have higher compression

Run too rich and you run the risk of washing oil from the cylinder. Especially with 98 octane.
I know, I nipped two pistons using 98.

Graeme

[double diamond]

If you haven't already,you might try disabling the accelerator pump. This doesn't really sound like the source of your problem, but it would eliminate the pump as a source of your issues and it's simple enough to do. Depending on what accelerator pump ramp you slide has, the effect of the pump only complicates figuring out the settings of the other circuits.

If it runs poorly at steady state but good when you crack the throttle, it sounds like it's lean. Then the accelerator pump richens the mix when you twist the throttle, which activates the accelerator pump. Check for air leaks at the manifold/head junction and the carb/manifold. Non-standard carb conversions present a number of opportunities for air leaks between the carb and head.

Matt

[graeme]

Yes I agree about removing the pump.