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V50II carb settings - or possible upgrade?

Discussion in 'Small Block' started by Steamchick, Sep 7, 2021.

  1. Steamchick

    Steamchick Just got it firing!

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    Hi all... I'm new to this chat-line so forgive me for having "zero" background. - My assumptions are all probably off-target?
    Also, I couldn't find a "Model specific" V50II sub-site...? - Any suggestions?

    I have owned a V50II for 23 years... used small-time for commuting and local trips... but until 2018 the commuting etc. was mostly 3 miles town/dual carriage-way, then a 3 mile blast at up to legal speeds (honestly, your honour...). But traffic had been getting very thick so in the last few years I had been spending more and more time trying to keep the idle working usefully, and minimising "pops" on over-run.

    So retirement came, and I'm down to a couple of hundred miles a year (local town work mostly) - and have finally reached a fairly usable tick-over!

    But the bike has always had a huge flat-spot below 2500rpm... where opening the throttle too much ay low revs (1500rpm~2500rpm) it makes a hell of a lot of intake noise with very little increase of performance.

    Now I worked in engine design on cars back in the late 1980s~90s. I've been around engines and bikes for over 50 years, but am always willing to learn - especially about carbs - as I have never had to do much real carb tuning. (mostly "stock bikes and a lot of use", rather than "a lot of tuning and rarely used").

    During recent pandemic restrictions I spent a bit of time studying the mixtures I get - because the bike doesn't suit the congested city driving I do mostly... which seldom gets to the 30mph limit, and when it does the speed cameras are everywhere!!! So this riding is a common thing for me now, so instead of blasting around at 1/2 throttle and up I am tootling along at barely a crack of throttle. Something the Original designers (nor I) ever envisaged for this bike.

    The idle - being set, working and stable, and showing a good burn with the optimate (glass spark=plug), just doesn't like the throttle being open slightly. The mixture goes exceedingly rich until about 1/4 throttle - which I understand is the slide cut-away ratio along with the pick-up orifice just up-stream of the slide.

    The bike has VHB carbs.

    From 1/4 throttle upwards everything is fine, and in tune. Carbs have been cleaned, (Ultrasonic and chemical) and I am now sure all passages are as "originally intended".

    I suspect the rich mixture - just off idle before the slide opens 1/4 or more - is a "fuel boost" to prevent the engine dying when pulling away moderately (The new experience for me..). I had learned (20-odd years ago) to feather the throttle to get past the flat-spot, but now, with heavier town traffic, I am riding more and more at low speeds just using that part of the throttle constantly, rather than driving through it to a place where the carb is OK....

    What are the "simplest" and "Best" solutions to my dilema? - I'm sure I'm not the first to need improvement of the factory tuning for low-speed urban use?

    I see I can buy some 26mm PHBL carbs on e&@y for just over £50 each... Dell-Orto copies of for 125cc 4-stroke singles.... but will they be better for the "town" riding I now find myself doing more and more? The cost of buying lots of jets and slides from Dell-Orto suppliers for my carbs is seriously worth more than the expected improvement, which is probably something that is cast/drilled into the main body anyway...?

    ebay.co.uk/itm/124813341223?3D%

    I have found the bike to be "more reliable" than bikes I had in earlier life... But mostly because I needed reliability above performance for the commute to work. Guzzis are somehow endearing - with their quirks of the heavy throttle springs (Italian law = quick close), Italian law quick release side-stands, coupled braking, Italian police riding position and all the other things the press find to be "not Japanese" (I.E. Easy and finely tuned) ... But "That's why I like it!" - But now I need a town "crawler" so I can be smoother and easier (like I had with the many Japanese machines) without constantly de-clutching, revving - and now I have to clean the plugs often from the soot caused just off idle! - I'm just not riding on open roads every journey to burn away all the soot from the plugs.

    Cheers!

    Steamchick
     
  2. john zibell

    john zibell Moderator Staff Member GT di Razza Pura

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    You may benefit using needles with less taper. Less taper should lean out the low end a bit. Do a search on Dellorto tuning and you should find examples of needle shapes.
     
  3. Adamigo

    Adamigo Just got it firing!

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    Hi, you seem to have a lot of background, so I don't want to sound silly, but: ignition advance under 2500 is static, and then jumps from 7? to 20 or 30-plus degrees, to rise then smoothly with revs from there on. So, your impression of reach mixture could also be a poor combustion and you can't do much about it. Apart from going one gear down? I got V50II but haven't ridden it for years now, but used to commute on it and that switch of advance point is best noticeable when you gradually slow down, then, reaching mentioned 2500rpm, you feel like throttle closed itself entirely, such is a loss of power just because of massively retarded spark at that point. V50 IIIs, the ones with mechanical points or motoplat ignition, were told to get rid of that whim. I just got used to it:) MkIIIs also had VHB 26 instead of 24, and you will even find VHB28 factory fitted to late V35s, so there is a space for some fiddling. You can also try to go down on idle jet size, possibly more choke on cold start will be required, but then , as we know, up to 1/4 throttle if not further, an idle jet plays a big part in carburation. Enjoy your problem!
     
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  4. V700Steve

    V700Steve GT Reference GT di Razza Pura

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    What we had in USA for the III is PHBH 28 with an accelerator pump, similar pump in the VHB here, With the pump there's no bog or flat spot.
    I had a very good DelOrto supplier from PA here called Herdan, If you can't find anything over there in UK.
     
    Last edited: Sep 8, 2021
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  5. Steamchick

    Steamchick Just got it firing!

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    Thanks guys, First, it certainly is not needle. I tried altering that and it affects other things, but not the zone just after "lift-off" from idle. And reading all the carb advice in books (including the Del Orto stuff - but mostly related to later carbvs and not the VHB set-up from 40 years back!), they all aexplain it is the slide profile that sets the mixture at the point where I have the dead spot.
    Notwithstanidng, as the idle has been a constant pain (VERY susceptible to weather, temperature of engine, etc.) I have now made a couple of idle jets that are smaller than factory standard (No 40 jets). The No 40 jets "as factory" are somewhere a trad larger than 0.45mm diameter... I suspect 0.47mm? But haven't found tables of bore to fuel jet number.. So I started with a "silly small size = 0.30mm jet. Basically, this will not pass enough fuel at idle for the engine to run... It tries, but just won't. (Yes, I have compensated by re-setting idle air-screw). But I have opened these out to 0.35mm and I have a satisfactory Idle. - This must be the minimum fuel jet size needed for the enging to cope with friction, oil pump and alternator loading, and the general engine loading of valve springs, pumping losses, etc.
    Now these jets show rich - but less rich than the 40s - when I check on the colour-tune. For riding, I could possible say there is an improvement, but then in some traffic, there isn't enough improvement. I simply have to attack the slides and convert them from "40s" (4mm difference from upstream to downstream size) to 45s, then 50s, etc. to see what is best.
    There can be a number of reasons for this tuning "glitch". The Factory tuning (according to press reports from late 70s) tell the tales of needing a bike tuned for the Rome Police, who whizz around Rome, dodging in and out of traffic and need ecomony, yet fast response to accelerate as needed. I think (assume? Guess?) that the transition from idle to 1/2 throttle or more causes a slight "fuel pump" as the slide transits the first 1/6th of travel because it is set so rich as standard. This will "rich boost" will help alleviate any hesitation and means that when the revs are up (over 3000rpm) it does have a very good throttle response.
    But we are in different times with different fuels.
    Despite being able to buy Esso "SUPER" 99 octane ("Super" means a cost penalty of £1.50 per itre... or $5.76/Short (US) gallon?), without the thermal effects of the density of lead additives the modern fuels don't do as well in this high compression engine. (Until 5 or 6 years ago I could still get some leaded "4-star" 99-Octane which was a whole better riding experience than unleaded!). I also use a valve lubricant, which will have a micro-effect (0.6%) on reducing the fuels performance. But the worst of Modern Riding is the proliferation of speed cameras, traffic, traffic lights, traffic congestion, slow drivers, more traffic... etc. All this means I spend a lot of time tootling along at somewhere between 10~25mph and don't reach 30mph as often as I should prefer... The consequence is that I either run just off idle thottle at 2500~3000rpm and have no hesitation issues, or change up a gear to run around 2000 rpm and have almost no acceleration and black sooty plugs within 3 miles or so! - Not the planned riding usage of Messrs Guzzi when tuning for the dashing Rome Police!
    So if anyone has needed to do such tuning and has a different slide setting that works, that will give me more knowledge than I currently have. Otherwise, I'll just change my slides in small steps... - or sell it and buy a small Honda... (= defeat!).
    Cheers!
     
  6. V700Steve

    V700Steve GT Reference GT di Razza Pura

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    My suggestions if your carb settings do not show any difference then the timing is off or advance is stuck or compression is down. Timing mark should be 10* on the square punch mark on flywheel for idle. Make sure it advances when you give it fuel. If you been riding it for 23yrs things change like pitting on valve seats, ring wear, etc. I would do a compression check & leak down test 1st before proceeding with carb changes.
    I've been doing V50's since 1980 and never had to put a leaner slide in them. Your bike should still use somewhat close to original settings unless modified. The most I had to do for open intake & exhaust was go up a couple numbers on pilot jet, main jet, and one notch on needle.
     
  7. huub

    huub Just got it firing!

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    on the V50-1 ( with VHB 26 carbs ) modifying the slides was a standard job, especially if you had changed the air filter arrangement to a more open filter.
    with stock slides they would run way too rich off idle

    i run mikuni VM carbs on my lario , but that is mainly because of the size.
    ( stock lario carbs are too small)
    the VM fitted straight into the lario.
    even the air filter fits.
     
  8. Steamchick

    Steamchick Just got it firing!

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    Thanks Steve,
    But I have checked compression, valve clearances, timing, advance/retard, etc. and all the colour-tune and riding issues fall down to the change of use to congested town use - that I didn't do a loy of previously - where I am just feathering between idle (closed throttle) and "just off closed". - Which is where the engine does NOT pick-up cleanly, and the Colour-tune says it goes "massively rich". All the books say "it is the slides". I'll develop it myself, as MG tuned it differently (for fast "get-up and go"!) according to all the press stuff from way back when. Funny, talking to a couple of guys who had these way back, they all seem to remember this characteristic, but like me for 20 years, it didn't bother them as they were jusy accelerating rapidly through that point with lots of revs. But now my local traffic simply crawls around at 20mph, gentle speeding up and slowing down. So the Advance-retard syndrome mentioned by Adamigo is very pertinant, as this is all running below 2500rpm. But ignition is something that doesn't make the plugs so sooty! (Although I believe the old adage, "if you think it is carburation, it is probably an ignition issue, and vise-versa!"). I am using the standard air-filter (new within a few hundred miles) and carburation is blob-on everywhere else in the range. Curious, how stockists do list no 50 and 60 slides... as well as my 40s? - but at £50 each! = more than new Chinese carbs?
    Thanks all,
    Ken
     
  9. V700Steve

    V700Steve GT Reference GT di Razza Pura

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    OK, looks like you have it sorted what you need to do in the off idle w/slide cutaway. Machine shop can cut them easy and more precise than sanding them down.
     
  10. Paul Brice

    Paul Brice Just got it firing!

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    " But ignition is something that doesn't make the plugs so sooty! "

    My LHS sooty plug problem is pure ignition unit.. Anything that starts misfiring the spark plug(s) when you start loading the engine (in my case the Electronic Ignition unit) absolutely does that. My other engine had similar problem a while back with original points set up & running it with open front timing cover in dark garage showed where that spark was going wrong !
     
  11. Steamchick

    Steamchick Just got it firing!

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    Hi paul Brice... I had a misfire problem for a couple of weeks - chased everything (different bit each day) until I replaced the plug cap - and found the fault! Meanwhile, due to sometimes prolonged running as a single (more than a second or 2) it wore the rings to a 40 thou gap! - fuel wash and the nicasil bores I guess? So I had to replace the rings as well... fix it quick or knacker the engine!
    Change the spark-plugs and plug caps (side for side will do?) and see if that changes the misfire (to the other cylinder?) . Easy quick and cheap to fix.
    Ken C
     
  12. Steamchick

    Steamchick Just got it firing!

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    I'll try one in my milling machine - 0.5 mm at a time, then do the second one to suit...
    Thanks,
    Ken
     
  13. V700Steve

    V700Steve GT Reference GT di Razza Pura

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    Just had a pair of 50 slides in my hands the other day, in VHB30's on a 73 V7 Sport. Put 40's in it and all stock stuff.
     
  14. Steamchick

    Steamchick Just got it firing!

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    Hi gents. So I milled 0.5mm off my slides (filter side), so now they are "45's"... Checked with Colour-tune plug - after resetting tick-over - and still lots of yellow flame as soon as the slides are lifted... But (may be a false improvement?) the tick-over is now better than I can remember for a while, as it is pretty consistent. But I haven't taken it on the road yet to see what it does with a warm, hot and very hot engine. And I want to get in the town-traffic to try it for the "desirable smoother ability to crawl" at between 5 and 25mph at low revs... I doubt I am there yet, but may be a small step in the right direction?
    Huub, your comment is the best so far - as it suggests I'm doing the right thing... Do you have any idea how far people modified slides on the V50 1? I am basically clueless, and following only what I have learned from reading Dell Orto amd Amal blurb on how carbs work. But if someone has made some improvement somehow, then that will be very useful so I know "when to stop" machining my parts...
    I am concerned that getting the "town crawl" right may screw-up the "open road fun" element of riding.
    I am half-way to thinking "Don't knacker what you have, buy some cheap Chinese carbs and knacker those instead". We'll see...
    Thanks for your support, all,
    Ken
     
  15. Planter

    Planter Just got it firing!

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    Hi
    In case of help :
    I run a V50 III. 55k miles. Carbs are PHBH 28.
    Using pod (pancake) filters in place of the original air filter. This required a re-jetting mains to 134 (118).
    Idling jet is 42 (50) and Throttle valve is 40 (50) (numbers in brackets are numbers stated in hand book).
    Carbs balanced against each other.
    Starts and idles easily and pulls cleanly through the rev range.

    Not that related, but found that in replacing the air filter an plumbing in the crankcase breather it was important to have a one way valve in the line to give smooth idle.
    Simon
     
  16. Steamchick

    Steamchick Just got it firing!

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    Hi Simon, Thanks for your tale. Interesting how you have used a 16% smaller idle jet, 42 from 50, but 20% "richer" slides, 40 from 50 - probably necessary to compensate for the smaller Idle jet? In my case, the bike is so rich in the "slide affected" region, that I am gradually opening it to permit more air to improve constant slow traffic running.
    Crankcase breathers feeding into intakes take a bit of tuning - I worked on a complex one on an engine at work that had 3 phases: for high vacuum (slow running), low vacuum (Highway and acceleration) and over-run (Max vacuum when you want to stop blow-by gases from being sucked through the carbs). You could try finding one on a car in a scrap-yard and modify that to fit?
    K
     
  17. Paul Brice

    Paul Brice Just got it firing!

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    Not sure I understood where/why you want to connect the breather return into vacuum side of intakes ?

    The original Mk3 V50 simply separated out the oil mist (& returned it to bottom of the sum) & fed the blow-by to the inlet side of the carbs along with the inlet air coming in through the air filter. Most air pod conversions just put an oil mist separator into the blow-by flow; return the separated oil (same pipe as OEM) into sump; and let the separated blow-by flow out to atmosphere through a small filter or bit of pipe.
     
  18. Steamchick

    Steamchick Just got it firing!

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    Hi Paul:
    To reduce emissions from the breather, it is modern practice to take these throigh the engine and burn any hydrocarbons... The huge amount of air for normal running versus the blow-by gas volume means you only need a small hole (maybe 1mm?) from the intake to the breather to take in adequate blow-by gas to keep crankcase pressure from becoming a nuisance (leakage). Simon said he had introduced a non-return valve. "that'll do".
    Ken
     

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