Derbi Variant PHBG 17,5 AD #2585

Mike Mayer /

Hi guys,

I am using a Dellorto PHBG 17,5 AD #2585 clamp-typ carb on my DERBI Variant Start5, with 65cc Gilardoni and FASMEM exhaust.

Out of the box it comes with AN262 atomizer and W6 needle, 55 idle jet and 82 main jet.

Have swapped it to correct 2-stroke AU262 atomizer and W7 needle, 42 idle jet and 65 main jet.

Problem is that it still runs boggy, too rich (for my understanding) and fires after 1/2 throttle....

Main jet used from 75-95 without significant results, now with 65 better.

Question:

I am still to rich with the 42 idle jet?

Idle jet on PHBGs tend to influence all the throttle way from 1/8-8/8 including WOT.

Somebody uses this same carb and can give me a jetting advice?

Thanx for any advice (edited)

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Re: Derbi Variant PHBG 17,5 AD #2585

man that seems really low, are you sure its not an ignition problem?

i usually run 19s and 21's and they jet in the 80's for a main. the au atomizer will open up flow so you'll run a smaller main but 65 seems real small.

i dunno though, PHBGs don't make no goddamn sense. every time i build with one its a guess-and-check crap shoot.

Re: Derbi Variant PHBG 17,5 AD #2585

Mike Mayer /

> Graham Motzing Wrote:

> -------------------------------------------------------

> man that seems really low, are you sure its not an ignition problem?

>

> i usually run 19s and 21's and they jet in the 80's for a main. the au

> atomizer will open up flow so you'll run a smaller main but 65 seems

> real small.

>

> i dunno though, PHBGs don't make no goddamn sense. every time i build

> with one its a guess-and-check crap shoot.

Yes, 65 main jet. I also think it’s too small. But using the 42 idle jet until now, bigger then 65 main jet impossible to ride

With idle jet do you use?

Will check ignition, although moped on sidestand does not miss fire (edited)

Re: Derbi Variant PHBG 17,5 AD #2585

Overpriced Parts /

You got to knock out the 4 stroke bushing in your carb and press in a 2 stroke one, Just changing to a 2 stroke atomizer is not enough

Re: Derbi Variant PHBG 17,5 AD #2585

Mike Mayer /

> Ken Roff Wrote:

> -------------------------------------------------------

> You got to knock out the 4 stroke bushing in your carb and press in a 2

> stroke one, Just changing to a 2 stroke atomizer is not enough

I also have changed the 4 stroke bushing to the 2 stroke AU bushing

Re: Derbi Variant PHBG 17,5 AD #2585

Get a Mikuni VM20 and hold on to your nuts when you open it up.

Re: Derbi Variant PHBG 17,5 AD #2585

your choke might be stuck open, enrichening everyhing, thats a super thick choke cable. , 65 main does seem small. needle can be dropped as well.

Re: Derbi Variant PHBG 17,5 AD #2585

Mike Mayer /

Hi guys,

after two days of trying anything nothing went better. All jets, idle and main I have tried, the engine still was impossible to jet properly.

Still bogging and missfireing.

Today morning, it was cold outside by 18° y decide to try a new NGK B8HS plug after I suspected it could probably be an ignition issue.

Wow!! Now it works...! But this would mean trying to jet the engine I have “killed” 2 news NGK B8HS and this was the cause engine was missfired and imposs to jet.

Ok, the third, new, NGK B8HS out and a new B9HS in. No missfireing!

Still good with 80 main jet! Needle W7 (2 notch) and 42 idle jet.

So I think the problem was all the time 2 plugs I had ruined by not being the proper ones.....

Now I can start to carburate properly ..... I hope so!

Thanks for all and still interested in any advices for the Gilardoni 65cc (edited)

Re: Derbi Variant PHBG 17,5 AD #2585

Mike Mayer /

Using now 78 main jet and W7 needle.

Any advice for the idle jet? It is now 42. The PHBG 17,5 AD came with a 55 idle jet, which I think is too big. (edited)

Re: Derbi Variant PHBG 17,5 AD #2585

> Mike Mayer Wrote:

> -------------------------------------------------------

> Using now 78 main jet and W7 needle.

>

> Any advice for the idle jet? It is now 42. The PHBG 17,5 AD came with a

> 55 idle jet, which I think is too big.

on similar Derbi builds I've used 36-42 pilot jets, so you're probably pretty close.

I've had so many NGKs come bad straight out of the box that I no longer buy them. I switched to champion plugs exclusively.

Re: Derbi Variant PHBG 17,5 AD #2585

> Dave & Bummerzz Wrote:

> -------------------------------------------------------

> I've had so many NGKs come bad straight out of the box that I no longer

> buy them. I switched to champion plugs exclusively.

Sorry about your 'luck' .

In all my years , I don't recall every having a bad NGK out of the box . That's a lot of plugs .

And , just as an opposition , Champion plugs would be the absolute last resort for me . I've had way too many of them be bad . Not necessarily right out of the box .

Re: Derbi Variant PHBG 17,5 AD #2585

Mike Mayer /

As we are now at the plugs,

which termical grade should I use for the Gilardoni 65cc?

NGK B9HS ok, or better B10HS?

It’s summer and hot.....( 25°-32°C)

Re: Derbi Variant PHBG 17,5 AD #2585

Do your self a big favor and bin the PHBG, you going to be fucking around for weeks on end, spending a load of dosh on jets etc. at rip of prices.

Get your self a Mikuni. full stop, better still get your sel a Mikuni clone for penny's on the dollar man. you can get a whole set of idle jets for penny's on ebay.

I spent ££££££££££££££££ on phbg carbs and wasted so many summers on them.

not no more.

Re: Derbi Variant PHBG 17,5 AD #2585

You should be around a 92 main(if you have no air leaks), 42-45 idle(I like 45 for when you're coasting down long hills) and a W9 or W16 needle. Your lean in the mid-range with the W7 needle that's why I bogs until you past half throttle then runs good on top end. The W7 is too far and has it lean.

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