Carburettors

The 3 1/2 forum
lemans
Posts: 44
Joined: 01 Oct 2017 18:52
Location: Heino

Re: Carburettors

Post by lemans »

morini_tom, I would love to buy a set of 260BD, could you point me in the right direction of a URL for the page that they are on?

https://shop.tlm.nl/nl/verstuiver-260-b ... moto-guzzi
morini_tom
Posts: 819
Joined: 05 May 2006 13:47
Location: Northampton

Re: Carburettors

Post by morini_tom »

Paz2112, yes the link as in lemans' post above is correct and where I got mine from.

Looks like they are only listing 1 in stock now though, although still useful to have something to copy. But these being stocked by a guzzi specialist got me thinking maybe some Guzzis run them, and so I just did a bit of searching and lo and behold, Stein Dinse are also listing them (and annoyingly at half the price I just paid!)

https://www.stein-dinse.biz/product_inf ... _id=215439
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Paz2112
Posts: 126
Joined: 07 May 2015 12:32
Location: Northern Ireland
Location: Northern Ireland

Re: Carburettors

Post by Paz2112 »

morini_tom wrote: 19 Jul 2021 22:44 Paz2112, yes the link as in lemans' post above is correct and where I got mine from.

Looks like they are only listing 1 in stock now though, although still useful to have something to copy. But these being stocked by a guzzi specialist got me thinking maybe some Guzzis run them, and so I just did a bit of searching and lo and behold, Stein Dinse are also listing them (and annoyingly at half the price I just paid!)

https://www.stein-dinse.biz/product_inf ... _id=215439
Thank you, I ordered immediately. These have been impossible for me to find and I had given up. The link worked, with postage and taxes the two 260BD Atomisers cost me 30 Euro.
My Other Italian V-Twin is an Italian V-Twin
dave3840
Posts: 6
Joined: 04 Jun 2022 21:50
Location: Oldham, Lancashire,

Re: Carburettors

Post by dave3840 »

Hiya fellas,
I'm experiencing many of the troubles many other riders are and read the possible solutions with great interest. My main problem at the moment is that the bike refuses to tick over, well I say refuses, it will tickover but at near maximum revs, it does settle after a while and I'm working my way through it, very slowly (Slowly because I have Parkinsons) Just a couple of questions

If ,like mine, the slides are worn, then won't the carburettor bodies have equal wear making slide replacement a fruitless endeavour ?
Has anyone got a solution for the carb rubber manifold mounts ?
Has anyone tried the PWK carbs they're ever so cheap, I have heard that they can be very good though/ If so what about choke jet and needle sizes.


thanks ,in anticipation guys, hope to meet up with some of you when the weather changes, assuming I get the 3 1/2 running something like !!!
Steve Brown
Posts: 1285
Joined: 12 Nov 2007 23:44
Location: Leicestershire

Re: Carburettors

Post by Steve Brown »

Hi Dave and welcome to the club and forum. Can I ask a few questions about the easiest mistakes or faults?
First to come to me is are the slides in the right way round? i.e. cutaway facing the outside.
Then are the vacuum connection ports connected (or blanked off)? They need to be one or the other and not open to atmosphere.
Are the throttle cables adjusted correctly with a 1/2 mm of slack and not trapped, keeping a slide open?
Not tried those carbs you mention, sorry.
Not sure what you mean about a solution for the rubber mounts-are yours cracked or perished?

Those are the first places to look, hope it's an easy fix!
All donations to the rest home for old Camels, Leicestershire.
dave3840
Posts: 6
Joined: 04 Jun 2022 21:50
Location: Oldham, Lancashire,

Re: Carburettors

Post by dave3840 »

Hi Steve thanks for responding,

I hadn't realised that the slides were handed, though I'm pretty certain that I haven't swapped them as I would only work on one at a time, I will check on this asap, what would be the symptoms ?

The vacuum ports are blocked off.

I have fitted new Venhill cables, they did need adjustment to ensure it's not idling on the slides.

The rubber manifolds appear to not be cracked but it seems difficult to tighten the clamps without some distortion of the rubber which I think may be causing a leak, I have discovered one clamp was worn and not tightening up properly and I have just replaced it.

Just out of interest,I have also fitted a Sachse ignition system to the bike. Which is a 1975/1977 reg Strada 2 x wire/ drum
3potjohn
Posts: 1109
Joined: 02 Jun 2007 13:58
Location: Devon

Re: Carburettors

Post by 3potjohn »

This may help, if it has not already been suggested.
https://m.youtube.com/watch?v=oKBdvmGYWQM

I have had problems with chokes not sealing well in the off position once, which made for an increasingly rich mixture.
Good luck sorting the high RPM thing. I assume the slides are not hanging on the cables?
John
Steve Brown
Posts: 1285
Joined: 12 Nov 2007 23:44
Location: Leicestershire

Re: Carburettors

Post by Steve Brown »

dave3840 wrote: 30 Nov 2022 22:20 Hi Steve thanks for responding,

I hadn't realised that the slides were handed, though I'm pretty certain that I haven't swapped them as I would only work on one at a time, I will check on this asap, what would be the symptoms ?

The vacuum ports are blocked off.

I have fitted new Venhill cables, they did need adjustment to ensure it's not idling on the slides.

The rubber manifolds appear to not be cracked but it seems difficult to tighten the clamps without some distortion of the rubber which I think may be causing a leak, I have discovered one clamp was worn and not tightening up properly and I have just replaced it.

Just out of interest,I have also fitted a Sachse ignition system to the bike. Which is a 1975/1977 reg Strada 2 x wire/ drum
The slides are not handed but best to keep them in the carb they came from.
What I was thinking was that they or one of them, may be in back to front? It can be done without too much effort and that does result in very high RPM idle.
All donations to the rest home for old Camels, Leicestershire.
dave3840
Posts: 6
Joined: 04 Jun 2022 21:50
Location: Oldham, Lancashire,

Re: Carburettors

Post by dave3840 »

Thanks John, there is freeplay in the cables, I am thinking maybe I have put the slides in about face, Ill check this out in the morning, and hopefully correct my cock up.
dave3840
Posts: 6
Joined: 04 Jun 2022 21:50
Location: Oldham, Lancashire,

Re: Carburettors

Post by dave3840 »

Thanks very much Steve,
your diagnosis was absolutely spot on. I HAD replaced the back to front (what a plonker) things are much better now, I need to balance the carbs properly as on a brief test today it wasn't running the cleanest but thanks to you I am on the right road. What is your opinion regarding worn slides, would the carb body not be worn also ? Thank you very much, once again. Safe riding.
Steve Brown
Posts: 1285
Joined: 12 Nov 2007 23:44
Location: Leicestershire

Re: Carburettors

Post by Steve Brown »

Ahh that's good then! Don't worry-you're not the first to do this and definitely won't be the last either. Worse still I might even have done it myself. Possibly. Allegedly etc
Ref general slide/bore wear. I used to be a bit too worried about this and changed a pair or two of the original flat slide type carb for later round types etc. Then as was pointed out by Paul Compton (the club guru) it wasn't as critical as we might think. Being a flat slide they are drawn by the engine vacuum inwards against their mating/sealing face so any gap is reduced then and as long as they are not mismatched in wear pattern then not a lot will leak by the slide. This theory is also helped by the return springs-the top of the slide is angled where the spring engages it, and that also holds the slide against that face of the body.
Once I found out where to buy replacement jets and which ones were actually giving trouble, I haven't had to retire a single one of the old VHB type carbs.
The usual culprits carb wise are- idle jets being a little over size for modern fuel, needle jets and needles being worn oval and sneakiest of all the choke plunger rubbers ageing and going hard or sometimes disintegrating. Either way they then don't seal and allow random globules of fuel to get by and really mess things up.
Then the biggest carburation problem of all turns out to be ageing electronic ignitions! :roll: That's a whole other topic!

Oh yes-round slide carbs are more sensitive to bore/slide wear, I think. But even they still cover a huge mileage as long as they are protected by a filter. All learned either from this club or the hard/expensive way of buying lots of these bikes and thinking I could sell them at a profit! I'm now retired but still optimistic that this time next year I'll be a millionaire. (In Turkish Lire seems favourite)
All donations to the rest home for old Camels, Leicestershire.
3potjohn
Posts: 1109
Joined: 02 Jun 2007 13:58
Location: Devon

Re: Carburettors

Post by 3potjohn »

Isn’t that a relief! I can beat this...as I once installed second gear backwards, it lasted six years.
I rebuilt my carbs completely back in 2008. Since then I have not had recourse to really touch them but when I did look at the slides this year, whilst renewing the perished rubber cable covers they had started to wear. I did try different pilot jets back in the day and tried 43 and 45, settled on the 45. The entire choke mech can be got from Eurocarb if needed. They are the 34mm variety, number 8294. But of course yours may be OK.
Good tuning.
John
dave3840
Posts: 6
Joined: 04 Jun 2022 21:50
Location: Oldham, Lancashire,

Re: Carburettors

Post by dave3840 »

Big Thanks To Steve and John, It seems I have a lot to learn, but for now I'll just try to ride it, when the bitter cold weather allows
mbmm350s
Posts: 573
Joined: 22 Jun 2018 10:18
Location: Reading UK
Location: Berkshire UK

Re: Carburettors

Post by mbmm350s »

I like easy fixes!

Many years ago i took apart a 350 and everything was back to front or upside down, like the rocker trunnions, the pushrods were swapped, the single disk was on the right. I asked the owner if the speedo worked - he admitted that it never did.
Ref general slide/bore wear. I used to be a bit too worried about this and changed a pair or two of the original flat slide type carb for later round types etc. Then as was pointed out by Paul Compton (the club guru) it wasn't as critical as we might think. Being a flat slide they are drawn by the engine vacuum inwards against their mating/sealing face so any gap is reduced then and as long as they are not mismatched in wear pattern then not a lot will leak by the slide. This theory is also helped by the return springs-the top of the slide is angled where the spring engages it, and that also holds the slide against that face of the body
This is quite correct when it comes to air leaks.
However the atomiser jet diameter is 2.60mm and the needle 2.45mm, meaning there is only 0.075mm clearance between needle and atomiser wall.
If there is more than 0.075mm wear on the slide face combined with wear on the carb body, obvious where the anodising has been completely removed. On a flat surface you can easily slip a feeler gauge under the edges of the slide where the wear occurs first. When the wear is this much case the needle will be in contact with the atomiser wall, causing problem with fuelling and further wear of the needle and atomiser.
In addition the small bush in the top of the slide, below where the needle is secured this can be worn so much that the needle is very sloppy.
Given that quality slides are available from Eurocarb its probably not worth the effort of trying to rectify the problem.

A very badly worn slide or loose needle can be one of the numerous causes of a flat spot in acceleration.

So how worn is worn? If the slide has lost all its grey anodizing except maybe a small section of the venturi, or is badly scored then i would think about replacement.

Cheers
Mark
70sbikes
Posts: 78
Joined: 13 Nov 2014 11:44
Location: Melbourne Australia

Re: Carburettors

Post by 70sbikes »

Mikuni VM28's work pretty well. I did this to see if (a) it could be done, and (b) if it would be an improvement. Ticks for both.

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