V50-III, adventures in jetting with a question.

[not-fishing]

I've been working out the jetting of the little V50 I picked up a few months ago.  She was horribly boggy 1/4-3/4 throttle.

Stock is 118 mains, 48 pilots and needle on 2nd notch I think - never can remember on the needle

Mine has K & N's now and I'm running 125 mains, 54 pilots and needle on the 2nd notch.

My 29 mpg fuel consumption tells me I need to Lean-R-Out so I'll make the change to 122 mains, 50 pilots and leave the needle alone. a ride will tell me if I need to change it

My source for the jets only has 118, 122, 125's in the mains and 48, 50, 52 and 54 pilots so my choices are limited. 

I do know Dell'Orto does sell the jets in single digit increments so my question is:

Without a Dyno how can you really tell if a 123 vs a 122 main is better jetting?

Many decades ago when I Cafe'd out my 400F I had a guy Dyno tune the bike after I'd installed pod air filters, exhaust and electronic ignition.  I believe it will be a heck of a lot more expensive now.

[kevdog3019]

Yeah... well, you're doing it the right way; trial and error (if you can't dyno it $$) .  The idle jets should be pretty obvious by how it idles.  THey don't make a difference after idle.  Something near stock should be fine there since you're not pulling in a lot more air than the box at idle.  50's should do it I'm guessing.  122 seems a logical place to go from 125.  I'd think you're close with that.  If just off, 120 should be the answer.  Run it and check behavior and plug chops. 125's are a big change.  You're other question about knowing difinitively.  Well... you won't know until you try everything around it and you may have to be VERY sensitive to feel it.  Mine made a pretty obvious difference (to me) and I still don't know if it's the end-all because I stopped there so far, but the plugs look grand and it runs super, so I'm happy. 

[Chuck in Indiana]

THey don't make a difference after idle.

Oh, yeah.. they do. Up to around 3K rpm or so..
1/4 to 3/4 you're talking about the slide, cutaway, needle jet, and needle/needle position.
I posted a thing from Delorto one time, I'll see if I can find it.
Probably tomorrow. I need ice cream. 

[kevdog3019]

Oh, yeah.. they do. Up to around 3K rpm or so..
1/4 to 3/4 you're talking about the slide, cutaway, needle jet, and needle/needle position.
I posted a thing from Delorto one time, I'll see if I can find it.
Probably tomorrow. I need ice cream. 

Ok... officially they do make some difference, but I'd say if you're good around idle and the transition off idle is good, that is fine.  If you're running stock slide/atomizer I would only look to the main jet and needle instead of scratching your head.  You're only talking pods vs. filter so it's not a big deal.  I think I kept what my set-up was and raised the needle a notch if memory serves me right.  If it's fine up top and down below and there's weirdness in the middle, play with the needle height.You can choke the bike while riding to get a sense for what that does.  If it runs healthier, raise the needle, if it bogs, lower it (Im talking mid-range).  I'm just going on personal experience and lots of others have their own conclusions.  Thee's more than one way to skin a cat but I like starting with the basics and what's there.  Do one thing at a time so you know what that one thing did.  If you do two adjustments you may never know which did what.  Keep it simple.

[agoldfish]

The slide makes more difference than you think at smaller throttle openings. A 50 slide has a 5mm cutout in it. 40 is richer, 60 leaner. So if its boogy (rich boggy is when it will be reluctant/slow to rev and lean boggy it makes that deep drone through the intake and is .. relucant to rev) at smaller throttle openings playing with the slide can help ALOT.

I have a V50 Monza with foam pods and the Lafra Comp pipes. 52 Pilot, Needle on the lowest/richest slot and 125 mains. Runs VERY well but is a lazy up to 4K, from there on it goes better than you'd think. Otherwise stock carb parts. I have a little fiddling left to do but i am generally happy with it.

I have spent the last 12 years fiddling with PHBH carbs as i have been running them on my tuned Vespas that long, so have a huge box of bits to play with.

I made a little chart, to show what has an affect where from 0-100% throttle. mark you gas grip and go from there.

https://www.flickr.com/photos/chris900ssie/25842059043/in/dateposted-public/

Chris

[Chuck in Indiana]

Very nice explanation, Chris..

[Chuck in Indiana]

I think this picture is a good resource..
carb_jet_circuits by Charles Stottlemyer, on Flickr

[not-fishing]

The slide makes more difference than you think at smaller throttle openings. A 50 slide has a 5mm cutout in it. 40 is richer, 60 leaner. So if its boogy (rich boggy is when it will be reluctant/slow to rev and lean boggy it makes that deep drone through the intake and is .. relucant to rev) at smaller throttle openings playing with the slide can help ALOT.

I have a V50 Monza with foam pods and the Lafra Comp pipes. 52 Pilot, Needle on the lowest/richest slot and 125 mains. Runs VERY well but is a lazy up to 4K, from there on it goes better than you'd think. Otherwise stock carb parts. I have a little fiddling left to do but i am generally happy with it.

Thanks Chris & Chuck

I couldn't leave the V50 alone last night so I changed the pilots to the 50's that I had, the mains to 122's and left the needle in the 2nd notch (from the top).  The boy did his "seat of the pant's" evaluation so that told me he couldn't feel the difference so I figure I'm headed in the right direction. 

I might fuss with the needle after I ride it but more than likely I need to wait until I get the optic trigger to make sure I have a good spark.

Thanks I'm going to print out you're spreadsheet along with the color chart for the V50's maintenance book.

One thing that my son comments on is the slippery seat under hard braking.  I don't have much problem but I sit way back on the raised portion.

Rear-sets would be nice but I'm not sure I want to pay the $500 or so for them.  Unlike many other's I like where my Griso's footpegs are located.  The Griso's pegs remind me of Hunt-seat.

Mark

[agoldfish]

The main jet really does only come into play at 3/4 throttle and above. You can even leave it out and the bike will be ridable to after 1/2 throttle.

Idle jet is of very little consequence once you have it close. 50-54 will see you right. The mixer screw gives you the fine adjustment. More than 3 1/2 turns out, go up a jet size. 1/2 a turn out go down one. 1 1/2 turns is ideal but not critical.

the Area where you use the throttle the most 1/4 - 3/4 is all about the slide, needle and emulsion tube. The stock Monza needle position is 3rd from the top, so try the lowest clip setting for sure.

;)

Chris

[Chuck in Indiana]

The main jet really does only come into play at 3/4 throttle and above. You can even leave it out and the bike will be ridable to after 1/2 throttle.

Idle jet is of very little consequence once you have it close. 50-54 will see you right. The mixer screw gives you the fine adjustment. More than 3 1/2 turns out, go up a jet size. 1/2 a turn out go down one. 1 1/2 turns is ideal but not critical.

the Area where you use the throttle the most 1/4 - 3/4 is all about the slide, needle and emulsion tube. The stock Monza needle position is 3rd from the top, so try the lowest clip setting for sure.

;)

Chris

I hear what you are saying, but the picture that I posted from Delorto says otherwise. They are all interrelated. Admittedly, the idle jet is most important for idle and the main is all important for WOT.

The main jet really does only come into play at 3/4 throttle and above. You can even leave it out and the bike will be ridable to after 1/2 throttle.

There's a difference between rideable and correct.
I'm not trying to pick a fight here, and what you say is mostly correct, as far as I know, but if someone is trying to tune their Delorto, the above graph is instructive. There are subtle interactions between the idle jet and main jet even at 30% throttle opening.

[tpeever]

The main jet really does only come into play at 3/4 throttle and above. You can even leave it out and the bike will be ridable to after 1/2 throttle.

Idle jet is of very little consequence once you have it close. 50-54 will see you right. The mixer screw gives you the fine adjustment. More than 3 1/2 turns out, go up a jet size. 1/2 a turn out go down one. 1 1/2 turns is ideal but not critical.

the Area where you use the throttle the most 1/4 - 3/4 is all about the slide, needle and emulsion tube. The stock Monza needle position is 3rd from the top, so try the lowest clip setting for sure.

;)

Chris

I vote for needle position as well. If you are at position 2 now (from the top I presume?) and it feels rich, and stock is 3, is it possible that needle and needle jet are worn or are you using new parts? I have heard a few people talk about bad aftermarket carb parts (like jet sizes being way off etc.) but can't remember if that was Del Orto or Amals.

[agoldfish]

I'm not trying to pick a fight here, and what you say is mostly correct, as far as I know, but if someone is trying to tune their Delorto, the above graph is instructive. There are subtle interactions between the idle jet and main jet even at 30% throttle opening.

Chuck, i am not spoiling for a  rumble either!  ;)

I just wanted it to be clear that upping a main jet is far from enough when tuning. Its role is in the PHBHs and the Mikunis 38s (on Ducatis 2v machines  - of which i have had plenty) is not minimal but only really critical for WoT. Lets be honest, once past 1/2 throttle next stop is WoT. I used my Vespa for 3 weeks WITHOUT a main jet to commute on, it would bog an die at 3/4+ but was otherwise fine. Give it a try!

The emulsion tubes do go oval, the needles seem to suffer somewhat less with high Kms. Worth replacing if you are ordering parts as they arent expensive, really. But if it runs fine why bother. I'll dig out my chart of PHBH needle profiles, if you are a carb nerd like me it is quite interesting.

Slide for VERY the transfer from idle to 1/4 and needle and emulsion tube up to 3/4. Try the needle at the two extremes, might help you get a feel for whats going on.

As an aside, when playing with PHBHs on the Vespa i had a 30, a 28 and a RARE 26mm. The bike is tuned from its original 4bhp to give about 20 and it will out drag my MONZA mostly on the back wheel. Anyway, the 30mm carb required the smallest or leanest jets to get the best out of it and the 26mm the richest. A gas speed thing no doubt. The 28mm giving the best combo of bottom end torque and top end rush. 30mm gave the most top end but was flat down low, the 26 the Yang to the 30mm Ying.

Chris

[kevdog3019]

I think this picture is a good resource..
carb_jet_circuits by Charles Stottlemyer, on Flickr

I'm still looking for the fine print that states "Your real problem is likely electrical". ;)

[Chuck in Indiana]

I'm still looking for the fine print that states "Your real problem is likely electrical". ;)