dellorto phbg question

Alan Jackson /

I have a phbg 21mm on a 73cc reed kit

im far too rich at 1/8 to half throttle even with needle on top notch and a 30 pilot jet

someone has fitted a w16 needle which could be the problem - im about to change it to a W7, and the atomiser is a 262 AU.

I noticed the W16 needle is the same diameter as the W7 for the top half of its length and its only the taper that goes thinner hence richer.

my question is, at 1/8th throttle am I actually on the taper? ie is that metering my fuel at such a small throttle opening? or is it down to the atomiser which need changing for a smaller one.

I suppose I can wait till the W7 needle arrives but I could also order a smaller atomiser.

last question, is there much difference in atomisers should I go one size down to a 260 or will that not make much difference.

I can get the bike running fine at wot its just 4 stroking like mad on part throttle.

cheers

Re: dellorto phbg question

Dirty30 Dillon /

Slide cutaway tunes 1/8-/14 throttle.

Re: dellorto phbg question

Alan Jackson /

is a 40 slide

if im over rich do I need smaller cutaway? and is that a smaller number?

haven't looked at slides yet.

Re: dellorto phbg question

Overpriced Parts /

> Dirty30 Dillon Wrote:

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

> Slide cutaway tunes 1/8-/14 throttle.

I’m sure you mean1/4 throttle not 14 but needle and slide both work at 1/4 throttle (as well as pilot jet and main for they don’t shut off) so get a w7 needle and a 30-40 slides

I use a w7 and a #30 or 40 size slides as well as 262 or 264 atomizer whatever works) on polini reed kit so it may work for you on 74cc Gila kit or whatever your running

Re: dellorto phbg question

I was having the same issues with the same carb. i enden up with the 262 atomizer, w7 needle and #50 slide, 40 pilot, 96 main on a 74cc gila kit. Not that yours will tune in exactly the same but you have an idea. Then again iam still tunning and new to this so take it with a grain of salt.

Also check your timing i was having problems with my idle being rich and fouling the plug. it turned out my spark wasnt hot enough.

Re: dellorto phbg question

Alan Jackson /

im running at 0.8mm btdc

if I go #50 slide wont that make it even richer?

ill try the thicker needle W7- ive just bought a pack of needles so can play around.

I had read on a wiki on here if it was too rich even with a small 30 pilot then the atomiser is too big.

with someone fitting a thin (race?) needle to my carb that could be the issue.

Re: dellorto phbg question

relax, you'll see vast low end improvement once u change too the fatter needle. that being said i hate waiting for stuff in the mail, biy wait....if the atomizier if its the four stoke one... oh oh order a two stroke one now..., look up the difference.

Re: dellorto phbg question

todd amundson /

You sound very lean down there

Re: dellorto phbg question

The higher the slide number the steeper the cut away. Higher number slide = leaner mix

Re: dellorto phbg question

Michael Forrest /

even when the beginning of the taper is lower than the top of the narrow part of the atomizer there is fuel flow thru that small area between the needle and the atomizer. I think the atomizer diameter is usually about .15mm bigger than the fat part of the needle.

Re: dellorto phbg question

Alan Jackson /

wow fitted a big fat one 2nd notch from top - W11, I think, and what a difference!!!

its a 4 geared moped and it nearly power wheelies

instead of having to whack the throttle wide open all the time there is instant power

on part throttle and low revs .

its still not perfect and it seems to have weakened my main (1.8mm tip of needle) but at least I know I will be able to get it near enough by juggling needles main and pilot jets

I got loads of jets and needles and hopefully I wont have to buy slides or atomisers

mine is deffo the 2 stroke AU atomiser.

I know this because I wasted almost a full day trying to dial it in with a reedless top end kit and couldn't get anywhere near.

#it had a 4 stroke atomiser

luckily I had a 19mm phbg that had a 262 AU fitted so swapped it over

the bike gets to 50mph real quick but i cant gear it up anymore so need a larger rim on the rear wheel

wonder what 1inch bigger will give me in top speed?

edit 18 inch rim as opposed to 17 inch will only give me 2 or 3 mph according to gearing commander.com.

don't sound right to me (edited)

Re: dellorto phbg question

Alan Jackson /

> Michael Forrest Wrote:

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

> even when the beginning of the taper is lower than the top of the narrow

> part of the atomizer there is fuel flow thru that small area between the

> needle and the atomizer. I think the atomizer diameter is usually about

> .15mm bigger than the fat part of the needle.

i understand that but the needles are the same diameter above the taper 2.5MM

( actually measure 2.48mm) so you wouldn't think theyd make any difference when needle is below start of taper.

but it has.

Re: dellorto phbg question

Michael Forrest /

well it depends on the inner diameter of the atomizer.

yours is 2.62 and your two needles are 2.5 which gives a normal clearance.

I'd try a W12 which has a taper angle of 2 degrees. the W7 has 3.5 degrees and the w16 has 3.9. Large angles mean it gets rich quick when opening the throttle.

http://www.dragonfly75.com/moto/jettingDellorto.html

Needle taper change requires a main jet change also. Forget what you were told that main jets have all the control at full throttle. It just isn't true. You'll need a bigger main jet. (edited)

Re: dellorto phbg question

Alan Jackson /

ta for that.

(btw I never did get round to making a pipe to your excel spreadsheets a few yrs back

still got them so who knows one day, first I need to get a tacho sorted so I know whats happening now)

Re: dellorto phbg question

Michael Forrest /

When you get ready to make the pipe let me know so I can set you up with the latest version of software.

Re: dellorto phbg question

Alan Jackson /

I found that with the bike ran better on half throttle with a 106 main jet. just on the verge of 4 stroking at wot.

as I reduced the size of the main jet I could open the throttle more and more until ive got a 96 in now and it runs the same on just over half as it does on wot.

but no better? why is that?

i'm gonna keep trying going smaller with the man jet but am scared of going too weak and meltdown.

think ill do a plug chop first with this jet.

the bike runs brilliant low revs as long as I don't open the throttle too much then as the revs rise I can give it more and more throttle.

Re: dellorto phbg question

Michael Forrest /

what you just described sounds like a lean condition, not being able to crack the throttle open quickly

Re: dellorto phbg question

Alan Jackson /

I have only tried the one needle, the big thick W11

ill try the W7 and see what difference that makes

Re: dellorto phbg question

Michael Forrest /

he W11 has a taper a little bit more than 2 degrees

Re: dellorto phbg question

It sounds lean but that is an awfully big jet on that setup. I would expect that to run 88-90, maybe you are chasing an air leak? Exhaust leak some folks over look, those get worser at high speed.

Re: dellorto phbg question

Alan Jackson /

to be fair the header to silencer joint was leaking a tad. I sort of fixed it 80% but now have totally fixed it

I have yet to test for jetting as its in bits awaiting higher primary gearing plus clutch drum.

it is a 21mm and its a copy - not the real phbg

parts wont arrive till midweek so it will be a while before I can add anything further

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