Delortto PHBH X needles

Check here for a list of various carb set-ups to help with jetting and all aspects of carb trickery!
Scooterdude
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Sun Apr 15, 2018 8:37 am

The general consensus is x7; x2; or x13 but has anyone had any success with say the x10 (same taper length of 20mm as an x7) but with a 1.4mm point as opposed to the 1.80 of the x7. Or the x11 (same taper length of 22mm as an x13) but again a 1.4 tip instead of the usual 1.8. So in effect everything should be about the same up until about half throttle then gradually richen up more before going onto the main jet.

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drunkmunkey6969
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Sun Apr 15, 2018 9:16 am

The X7, X13 & X2 needles are generally used in conjunction with AV264, 266 & 268 atomisers. It’s the relationship between those items (plus the other jets and the spec of your engine) which results in the correct air fuel mix. The atomisers have a specific height and internal diameter, and the needles have a specific length and taper. The ratio of the two combined, at different throttle positions and RPM ranges, gives the correct feed.

If you use a different range of needles, which you can do, then you need to look at different atomisers. So for example, you could use a fatter needle...this means it would sit tighter in the atomiser and allow less fuel mix through, so you’d have to use a larger atomiser to compensate...say a 270. And vice versa...you use a thinner needle, it will allow more fuel to pass between it and the atomiser, which may then be too rich...so you use a leaner/thinner 262 atomiser. The equation keeps going....taller AS atomisers run leaner at lower throttle position, so needs a needle with a richer taper. Shorter AV atomisers run richer so can use leaner needle tapers. But this is all relative to fuel demand from the engine, slide cutout height, needle clip position, pilot jet size, air and fuel screw position, main jet size, RPM range and throttle position.

The point being, you can’t just start swapping random needles around, hoping to drop lucky. Each component is part of an equation which effects other components...some massively, others hardly at all.

So the question is...if it ain’t broke, why try and fix it? AV264-268 work well with X7-X2 on our machines, when combined correctly with each other and the other associated/known jets/engine settings. Other combinations can be found....off the beaten path solutions...to do what? Achieve the same air/fuel ratio as the ones we already know about. The bottom line is, no matter what combination you use...you have to achieve a specific air/fuel ratio. So you can do it with the combinations commonly used, or with combinations not commonly used... but as long as the end ratio is the same, at all RPM and throttle positions, then that’s fine.


Scooterdude
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Sun Apr 15, 2018 11:37 am

Thanks Dan for a great explanation. Only reason im asking is no matter what combination of the above i try im still getting a rich half throttle leaning out to a digestive biscuit colour at three quarters.

Having said that and for reasons best known to myself i dont think ive tried x7 + 268 so will give it a shot later.

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coaster
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Sun Apr 15, 2018 12:19 pm

Scooterdude wrote:
Sun Apr 15, 2018 11:37 am
Thanks Dan for a great explanation. Only reason im asking is no matter what combination of the above i try im still getting a rich half throttle leaning out to a digestive biscuit colour at three quarters.

Having said that and for reasons best known to myself i dont think ive tried x7 + 268 so will give it a shot later.
Perfectly valid reason for exploring outside the box imho and is why strange combos are arrived at on the dyno. Thin washers under the needle clip, filed sections of needles, variable ignition curves, leaner/richer slides.....its black magic :?

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drunkmunkey6969
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Sun Apr 15, 2018 12:35 pm

Scooterdude wrote: Having said that and for reasons best known to myself i dont think ive tried x7 + 268 so will give it a shot later.

Before you do, what is your...

Cylinder kit
Crank
Carb
Exhaust

And what are your carb settings that gave best results to date:

Mix screw position
Pilot jet
Main jet
Atomiser
Needle
Clip position
Needle float valve

Also...

Are you using a fast flow tap, are you using an air filter, have you checked your flow rate.

What is your ign timing set at, what is your squish set at, do you know your compression ratio?

Paint the above picture, and I’ll see if I can make a suggestion to get you closer to a better result.

Scooterdude
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Sun Apr 15, 2018 4:51 pm

drunkmunkey6969 wrote:
Sun Apr 15, 2018 12:35 pm
Scooterdude wrote: Having said that and for reasons best known to myself i dont think ive tried x7 + 268 so will give it a shot later.

Before you do, what is your...

Cylinder kit
Crank
Carb
Exhaust

And what are your carb settings that gave best results to date:

Mix screw position
Pilot jet
Main jet
Atomiser
Needle
Clip position
Needle float valve

Also...

Are you using a fast flow tap, are you using an air filter, have you checked your flow rate.

What is your ign timing set at, what is your squish set at, do you know your compression ratio?

Paint the above picture, and I’ll see if I can make a suggestion to get you closer to a better result.
Hi Dan, its an RT 225 with full touring tune and reed valve all done by Mark Broadhurst and fitted with an NK road pipe. Timing set to 17 degrees, no fancy ignition curve boxes or anything.

Crank is 61/110 again rebuild by Mark.

Carb is a PHBH breathing through a remote filter.

OMG fast flow tap. All clear.

To date the best setting so far is: av266 atomiser, x13 needle top clip (go one position down and it splutters like mad).
40 slide, 58 pilot (55 seems to wooly) mixture screw 1.5 turns out.
Float valve is a 350.

But the strange thing is the main jet, now this is irrespective of weather the air filter is fitted or not, makes no difference: put the 135 in as the richest starting point as recommended and the engine wont splutter it just wants to rev....so i put a 140 in, same thing, so ok i put the biggest jet in ive got a 164 not the slightest bit of hesitation it just revs on through it ?
On the MB tech sheet it suggests an av264 atomiser, well i thought that was wrong but tried it none the less but without a main jet and the engine just revs through like it has a main jet??

Also this engine has the worst spit back ive ever seen on a Lambretta engine piston port or reed?

Scooterdude
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Sun Apr 15, 2018 5:16 pm

Ive tried the AV268/x7 combo this afternoon, needle top clip really rich at half throttle and doesn’t want to rev through it, feels awfull.

Scooterdude
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Sun Apr 15, 2018 5:48 pm

Sorry thats a PHBH 28 btw.

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drunkmunkey6969
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Sun Apr 15, 2018 7:50 pm

Ok a few things...

1) Do not ask me why, as I have absolutely no logical or factual reason as to why...but I always found 28mm PHBH a pain to setup. It sounds stupid, but it’s true...the were like an ‘oddity’ that I hated. 30mm is always a better option, IMHO.

2) Mark B did all the work, you’ve used his crib sheet, now you are struggling. Ring him for advice and jetting specifics.

3) The spitback behaviour and unusual non-response to main jet jet changes sounds unusual...there is likely something else afoot.

4) Check your atomisers are all definitely AV and not AS.

5) Off the cuff, if I were fitting ‘base settings’ as a starting point, I’d run 55p, AV266, X13 (2nd clip) and 132m. If it’s an air screw I’d have it 1.5 turns out, if it’s a fuel screw I’d have it 2.5 turns out. The float valve would be a 300 and slide a 40.

From there, it should be simple tweaks, with each step showing a corresponding response.



Scooterdude
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Sun Apr 15, 2018 8:06 pm

Cheers for that Dan, the carb was new about a year ago and i used it on another build and found if i over jetted it on the main jet the engine would splutter as you’d expect so now im wondering if there is a main jet passage within the carb body somewhere that has become blocked? Ive always asumed there wasn’t and it just fed straight up through the atomiser as you’d expect.

Regarding the carb do you think id see any real benefit to using a Delortto VHSH 30 flatslide or similar?

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