Delorto VHB 30 mystery...HELP

[spmoto]

A few months ago I was at my friends local all brands cycle service shop and a customers T3 was in the yard. I casually mentioned that I'd be interested in a clean example like it and if he ever heard of one to let me know. Not to long after I had a bike listed on Craigslist and my mechanic friend called to say that he had a T3 he'd trade with me. I went to see the bike (posted pictures here a while back) which hadn't run for a while but looked pretty good with low miles. We tentatively made a deal and he set about going through the bike refreshing all the fluids, cleaning up the brakes and rebuilding the carbs. I went to pick it up and it ran ok but not as it should but I agreed that I could sort out the rest.
The bike has K&N's, some unknown exhaust and the rest is pretty much stock including points etc. So, I began to dig in first double checking the timing and carb sync. , all ok so far. Then I popped the tops off the carbs to check the needle setting and I couldn't understand what I saw. It's been aa while since I've been inside a VHB but I knew it wasn't right but to be sure I pulled up Greg Benders rebuild pictorial on This Old Tractor and my hunch was confirmed. (See the attached pictures, the third image is how the needle should be retained) The needles had C-clips installed in the second notch and were sitting on top of the slides with the proper clip sort of holding them in place. So the needles were effectively raised the equivalent of at least 4 or 5 notches. How did/does it even run like this. I tried installing them properly, rotating through all three notches with no success. It will start and idle fine but once "on the needle" it pops and farts.
So, what to do? I'm stumped. Oh, I went further and pulled the carbs apart. Everything is clean and clear and the jets are all stock sizes: 50 pilots, 130 mains, V9 needles and 40 slides.
Any and all suggestions will be appreciated.

[Two Checks]

Too small main. Go to 140-145. You didn't mention the atomizers. Should be 265 Iirc.

[spmoto]

Two Checks,
265 atomizer. I just got a shipment of jets from MG and bumping up the mains was going to be my next step, but I wanted to see what others had to say. I've read here so many times that everything from off idle to to almost full throttle is strictly the needle and that the main doesn't come into play until WFO. I've always scratched my head at this as it seems there must be some synchronicity among the circuits.

[Tom H]

The Delorto tuning guide explains alot. This is just one of the pages. Scroll to the bottom for back forward and index.

http://www.ducatimeccanica.com/dellorto_guide/dellorto_2.html

There is a easier to use version of this but I can't find my bookmark for it.

Tom

[moto-uno]

  A couple of other things ( if the 265 atomizer is correct ) , there's also an air passage that feeds air into the atomizers , make sure it's clean .
Another point is (if they are similar to mine) these came with a type of accelerator assembly (spring and piston) at the bottom of the atomizer that
is frequently jammed or the spring is broken (or missing) that can lead to poor off idle throttle response .   Peter

[moto]

Raising the needle that high would have richened the mixture around quarter throttle. If it runs that way this means that the mixture was too weak without the needle raised that high. A likely cause of that I think would be wear in the throttle body or on the throttle slide. I do notice the throttle slide looks not too good in the pictures. Other air leaks should be suspected.

You shouldn't need to increase the main jet size, for the reason you gave.

Moto

[moto]

  . I just got a shipment of jets from MG ....

If all your jets are new, this strongly suggests your slide and or your throttle body are worn out. Sorry not to have said this previously.

[Two Checks]

130 mains are way too lean even with stock filter and pipes. And oxygenated fuel doesn't help.
Four bikes with 130s wouldn't run properly. A switch to 142s cured all four.


Unless you are at high altitude but then the 50 pilots would be too rich.

[moto]

130 mains are way too lean even with stock filter and pipes. And oxygenated fuel doesn't help.
Four bikes with 130s wouldn't run properly. A switch to 142s cured all four.

Unless you are at high altitude but then the 50 pilots would be too rich.

With stock filter and pipes, the factory spec is 120 main jets.

I have pod filters and the Valtek mufflers, with a crossover, on my T3. It ran 125 main jets when I bought it. Trying to correct a stumble off idle, I changed to 140's and found them too rich. I solved the off-idle problem by adjusting the throttle cut-away and going to 130 mains, which work well. I live at 800 feet above sea level. (The OP's problem does not appear to be the one I had.)

The OP's problem is not the main jet size, and attempting to solve it with extra large mains won't help with what's going on with the raised needle.

Moto

[SED]

I've had some success with stumbling off idle on the LMIII and popping through the carb on the bacon slicer, so here are a couple of things to try.  FYI - I have no experience with VHBs.

Check or replace the condenser and coils.  Check that the spark plug gap is correct.  A weak ignition loves a rich mixture. I've had popping disappear when a coil was replaced and again when a magneto was rebuilt.

Make sure the cable pull is balanced.  One slide lifting before the other can cause popping.

Confirm the float level is correct.

Check that the slide cutaway is correct.  Not sure how this works with the flat-side VHB, but the measurement should be 1mm = 10 on the slide number, so a 50 slide has 5mm of cutaway.  More cutaway means a leaner mix on transition from idle, but in my experience - cutaway should remain stock.  In other words, if the cutaway seems too lean, but the measurement is correct, the real problem is elsewhere.

Check that the needles and atomizers are correct.  The needle code should be stamped below the notches.  Dellorto needles are usually 2.50 mm diameter at the top but they make some with larger (leaner) and smaller (richer) diameters.  The similarity in size also means that a PHBH needle can be dropped into a VHB slide - so check the prefix.

VHB needles come in a variety of diameters (A in the picture) and this diameter (along with atomizer diameter) has a big impact on mixture as the slide lifts.  The taper doesn't have much effect until about 1/4 throttle.  However, a taper (C in the picture) that is too short can also cause popping.




(wrapping tape around the twist grip and marking 1/4, 1/2, 3/4 and full throttle is a great way to determine whether the popping is more likely idle jet or atomizer/needle sizes)

Check that the idle jet is correct.  The idle jet and mixture screw control the mixture with the slide closed, but as soon as the slide starts to lift the transfer port is exposed and the size of the idle jet determines how much fuel flows through the transfer port.  In other words, all the fuel that comes out the transfer port has to first flow through the idle jet.  If the jet is too small it will lean out too much as the slide lifts.  You can see if this is true by getting the bike to idle slowly then screwing in the slide stop screw on one side.  The engine should increase RPM smoothly. Try a richer idle jet if it starts to stumble.  (my LMIII needs richer idle jet on one side because of a worn intake guide - only took a few years to figure this out!  )

I'm still not completely happy with the slicer's carburation, but my experiments indicate that popping is a balance between idle jet size, atomizer size, needle diameter and length of taper.

This picture is a good visual of the relationships.  The only thing to add is that "needle jet" (atomizer) also includes the needle (top) diameter, and that "jet needle" refers to taper shape and length. Also, main jet size seems to have influence down to low throttle openings if other settings are lean.




Hope this helps.  Let us know how it goes!

[spmoto]

Thanks Peter and Moto. I did check the accelerator pump and all is well, springs are fine little ball rattles freely and everything is clean. Air way to atomizer clear as well.
I bumped the pilot from 50 to 54 and main from 130(stock according to my manual) to 140 and after initial try with the needle in the middle notch I raised the needle. And, I was able to use the proper clip. It actually runs pretty good though, having read what moto said about worn slides / tb's, there may be something there. Does it make sense that a bike w/ 15,000 miles would be worn that badly? Maybe it's 115,000 mi. Hmmm.
What's the chances of finding a good pair of VHB's? Any way to confirm the ware question?

Thanks again guys!

[spmoto]

Many thanks SED also! All good info.

[SED]

I've replaced PHF and PHBH slides with new and they made a difference even in the old bodies.  The round slides are hard chromed and you can see the wear.  I'd think 15,000 miles would be too few miles to wear out the bodies completely even without airfilters.

You might call Herdan for replacement slides - they have tons of stuff (website shows only a fraction).
https://herdan.com/

[spmoto]

Thanks SED! Wow, Herdan, I haven't thought of them for decades. They used to be the Morini importers. I wonder if Hermie is still involved?

[SED]

Talked to Hermie last week - still makes me laugh.

[acogoff]

     I would suggest making sure the double intake gaskets are not sucking in unmetered air.

[Kiwi_Roy]

In the first picture isn't the needle way too high?
I think the clip is supposed to br in the slot below
But it looks like the wrong clip anyway, should be "L" shaped.

[Chuck in Indiana]

SED said..

A weak ignition loves a rich mixture.

No truer words were ever spoken. I've mentioned before that most carburation problems are generally ignition. 

[Two Checks]

Quote from: moto on Today at 01:41:44 PM

With stock filter and pipes, the factory spec is 120 main jets.

I have pod filters and the Valtek mufflers, with a crossover, on my T3. It ran 125 main jets when I bought it. Trying to correct a stumble off idle, I changed to 140's and found them too rich. I solved the off-idle problem by adjusting the throttle cut-away and going to 130 mains, which work well. I live at 800 feet above sea level. (The OP's problem does not appear to be the one I had.)

The OP's problem is not the main jet size, and attempting to solve it with extra large mains won't help with what's going on with the raised needle.

Moto

Changing the main won't fix an off idle stumble. The pilot is too lean.

And a 140 jet fixed his problem.

[moto]

Ah, I am in the the presence of a main-or-pilot-jet tuner.

The stumble is generally the fault of the cutaway if the idle is otherwise properly adjusted. Reasons why a too-rich mixture might seem appropriate have already been mentioned.

It might be better in the long run to find and correct the underlying problem. A stock 120 main jet is specified in the factory manual (T-3 Additions, p. 90), in Haynes (p. 82), and in the Chilton Motorcycle Repair manual of 1976 (p. 1394). A 130 works fine with my more-open setup, described earlier.

Close study of the Dellorto tuning manual reveals all.

Moto

[tetarabra]

Needles much to high ?

C needle clips are for PHF or PHM.

L clips are for VHB .Slots on the top of the slides are used to lock clips in height.

[Two Checks]

So if a 120 or 130 main works properly...why don't they?
A friend bought a G5 from the owner of a local Guzzi dealer. It had 120s in it and pinged like a coffee can full of rocks. Fatter jets fixed it.
My Cal III had 130s. You couldnt open the throttle all the way. The engine would die out. Bigger jets fixed it.
Two other Guzzis-an 850T and SP II- same thing. And they all run smoothly with good plug color and 40+ mpg.
BTW...those size jets are called "Euro spec".
Can't argue with success.
I would say in your case you have slides that have been changed from factory.

[moto]

So if a 120 or 130 main works properly...why don't they?
A friend bought a G5 from the owner of a local Guzzi dealer. It had 120s in it and pinged like a coffee can full of rocks. Fatter jets fixed it.
My Cal III had 130s. You couldnt open the throttle all the way. The engine would die out. Bigger jets fixed it.
Two other Guzzis-an 850T and SP II- same thing. And they all run smoothly with good plug color and 40+ mpg.
BTW...those size jets are called "Euro spec".
Can't argue with success.
I would say in your case you have slides that have been changed from factory.

Where to begin?

Guzzi knew how to jet its stock bikes. The T3's left the factory with 120's, and this was before the January 1, 1978, EPA regulations, so there were no separate US/Euro specifications. The T4's continued the same. The G5 had 130's when it came with VHB's, and 112's when it was later fitted with PHF's. Cal III's had 130's (with PHF's). The 850T's were 142's (VHB), and the SP II's were 125's (PHF). All those bikes would take full throttle and not ping (when in tune and using proper fuel) when they left the factory, or they wouldn't have left it. (Dave Richardson, in Guzziology, notes that EPA had no emissions specification for full-thottle operation.)

It would surprise you, I guess, to learn that the Lemans III, with the same 36mm PHF's in both cases, had 120 jets in U.S. spec, and smaller 115 jets in European spec. Guzziology offers an explanation for this (version 5.1, p. 7-21, Un-Americanizing your carburetors/Carb basics).

Pinging is usually the result of too-advanced ignition timing or too-low-octane fuel. Going rich can suppress pinging by cooling the charge, which accounts for your "successes" when you have substituted larger main jets. However, throttle response is worse with too-rich jets and mileage may also suffer. (My T3 gets 50+ mph on the highway, by the way.) You can even wash oil from the cylinders, at least in principle.

Look, I don't care much about your bikes. I tried to steer the OP away from just going up in main jet sizes because his reported problem was not near full throttle. Instead, he had problems near 1/4 throttle as I understand it. He'll get a better-running bike if he applies the proper tuning principles, instead of reflexively plugging in bigger main jets.

Your comments make it clear that you should study up on how to tune motorcycles. Good luck.

By the way, I do have modified slides, but these don't affect full throttle operation. I modified them in 2008 according to a suggestion from Pete Roper, using a file to reduce the cutaway by a small amount. I did this after experiments with the pilot jet, needle position, and even the main jet proved little help in curing an off-idle stumble. Pete's clear understanding of carburetor principles led him to recommend this approach (though not necessarily by using a file), and my own careful reading of the Dellorto manual led me to understand he was correct. The small change worked perfectly.

Moto

P.S. to spmoto (the OP, if still reading this thread  ): On opening up Guzziology to check the date that EPA regulations became effective, I was struck once more by just how great a reference it is. Besides recommending the Dellorto tuning guide, I give my strongest recommendation to reading the Carburetors chapter of Guzziology. The book is more than worth its cost. You will be interested to read the author's comments about the durability of VHB carburetors and the possibility of improving their sealing without buying new slides or bodies.

M.

[moto-uno]

 ^ +1  :)
A couple more points ( I don't believe I've seen this mentioned ) , but have you tried spraying WD-40 around the intakes ? great check for air leaks.
And if the throttle slides are that worn , I've removed the air filters and simply pressed against the slide(s) with a screwdriver to see if there's a change in the idling .
Peter

[Two Checks]

You don't care about my bikes because they fly in the face of your narrative. And so does the OPs.
If an engine runs well except when WFO its lean on the main.
Especially when it pings under load at WFO and all else is set to factory specs. Its odd so many Guzzis are rejected from factory specs because they run like crap. EPA specs are lean for emission purposes.
BTW if as you said 850Ts are jetted that way from the factory, why aren't G5s with the same carbs?
I've jetted carbs on race cars, race fuel and alcohol. I think based on experience I can tune carbs.


I'm done here, the OPs bike runs well now and I'm glad for him and hope he enjoys his bike.

[moto]

...BTW if as you said 850Ts are jetted that way from the factory, why aren't G5s with the same carbs?

There are reasons. If you took your own question seriously, instead of posing it as a rhetorical one, you could learn a lot by looking for its answer.

But your very use of it as a rhetorical question confirms your lack of basic knowledge. There is no point in discussing this with you, though I tried. I've suggested things you might still profit from reading.

As I said before, good luck.

Moto