Effect of carb needles?

[Silverspur]

Just completed the Moto Pistón on the Strada. She went well with a couple of reservations. The first is a hesitation to pick up again at mid-high throttle after the throttle is rolled off. The plugs look very black but I did ride through the centre of London on my way back from the ferry so that may have sooted them. Anyway, I stripped the carbs and all is normal except E24 needles are fitted instead of E17s. Would anyone know what effect that would have on the carburation, weaker or richer?

Second problem was a jerkiness when pulling away. I had rebuilt the clutch before I went and it seemed OK, so I pulled off the rear wheel to check the cush rubbers. They seem fine but I have no idea what a knackered set look like...so I ordered some new ones. The other reason to check the rear wheel was to try to find what was causing the rear brake to 'pulse' which wasn't much of a problem when moving but caused embarrassing jerks when coming to a halt. However the drum does not seem to be oval but, here again, I don't know how much out of round a drum would need to be to have that effect, and it is difficult (for me) to measure to fractions of a mm over such a width.

Also, while stripping the rear brake the felt washer between bearing and brake plate was missing and M'dina don't have spares. Do I need it? Should I fabricate one?

Thanks in advance,

[Steve Brown]

The felt washer isn't too critical especially if you have sealed wheel bearings fitted and the hub bearings have not been over greased.

As for the needle question, I'm going through the same experiments with my Camel at the moment. I found a chart giving the needle dimensions by googling Dellorto 'E' needle charts. The differences can be quite small but still have a significant effect. Obviously the originals are mostly worn or damaged by now too. That can have a big effect as well. The needles in my Camel are corroded and were covered in a laquer/or stain that I just couldn't wash off. I ordered new ones from Dellorto UK on Thursday and they are here today!

[3potjohn]

Let us know what the sizes of the pilot jets and atomisers are. Are the jets loose?Are they clean? any corrosion?
Possibility of sinking floats or other cause of over rich mixture. Are the choke mechanisms Ok ?
Are the O rings OK when you have the floatbowls off.Also are the slides the correct way round way round?
I have had exactly this on a beemer and it was due to choke piston leaks, but that was on Bing carbs of course.
Good luck John

[Silverspur]

Atomisers are 260, idle jets 50.

I checked the float heights (OK) and valves, no grooves.

All the O-rings look fine and the starter mechanisms seems to be working properly.

But I'm still confused about the needles. Does a higher number mean fatter needles/weaker mixture or thinner needles/richer mixture? Anyone know?

[AntietamClassicCycle]

The number doesn't seem to correspond to any dimension. Here's the chart:

[Silverspur]

Thanks Charlie. It would appear that the only difference between the recommended E17s and my E24s is the latter has a 1.5mm longer taper. Otherwise they are the same. So that means it shouldn't affect the mixture, right?

[72degrees]

"Needle Characteristics
◦Thinner needles are overall richer, and thicker needles are overall leaner.
◦Needles with longer tapers are "earlier" because they begin to meter the air fuel mix at a lower throttle position, and they tend to be richer overall.
◦Needles with a shorter taper are "later" because they begin to meter the air fuel mix at a higher throttle position, and they tend to be leaner overall.
◦Needles with shallow tapers and fat tips are leaner, while needles with pronounced tapers and small tips are richer.

As stated previously, a good place to start is with the needle clips. Raising the needle by putting the clip in a lower notch will richen the midrange mix, and lowering the needle by putting the clip on higher notches will lean it out. If you find the bike responds poorly on all notches or only runs okay on one of the very outside notches, you should look into getting a different needle. "

From a Scooter tuning website, so more aimed at 2Ts with PHBG Dellortos, but the principles are the same.

Which goes on to state "Needle selection is somewhat of an art..."

So an E24 has a longer taper than an E17 so is a bit richer - at least in the throttle range where the needle/atomiser relationship is important.

Are the needles in a 'standard' clip position?

[mbmm350s]

Hi
The taper is longer but the needle is the same length so for a given throttle opening that is in the regime where the mixture is controlled by the taper the mixture will be richer. Its almost the same as raising the E17 needle.
If the needle and atomizer are in good condition you can restore to similar to e17 by dropping the needle. I would be surprised if it made any difference.
Please specify atomizer exactly it should be 260K for Strada cam and 260BD for sport cam. That's for A engines. Later K engines have different settings I would expect a 260D. I assume it's not a K2.
Please say whether the Airbox and exhaust are standard.
General consensus is that 50 pilot on vhb and vhbz carbs is too large. It is easy to determine this if when opening the throttle gently the engine is fluffy or sounds dull it's too big. Most are running 48 or 45. Also another indicator is the idle mixture screw is ineffective or is nearly screwed in. But please make sure as another poster says to check the chokes are sealing and the float heights.
Also check the condition of the slides if there is a noticeable step in the engine face the the needle doesn't run centrally in the atomizer and wear occurs. An almost unrideable Strada which I rode recently was found to be due to a a seriously worn needle. The needle was loose in the slide.
Also make sure the throttle opening is synchronised.
Often these mid range flat spots turn out to be ignition related with a weak ignition being the most likely cause.
Mark

[72degrees]

Hi

If the needle and atomizer are in good condition you can restore to similar to e17 by dropping the needle. I would be surprised if it made any difference.

Mark

Assuming the needle clips aren't already in the top groove Hence my question.

I've found my very non-standard 375 (L5 cam) to be fairly sensitive to needle height - but then that's running PHBH28s.

I completely agree with all your other suggestions, though in my experience, if the spark is significantly weak WFO (often selected when hill climbing) performance may also suffer.

[Silverspur]

Thanks everybody. Enough to think about and some obvious steps to take. At least I now know which way to go! Thanks again.