3 1/2 sport carbs

[StevenCroft]

Ive been given the run around, the VHBZ 25 on my 3 1/2 sport needed refurbishing. The parts worn out are the needles and atomisers 260BD, resulting a loss of top end power. Dellorto are no longer able to supply the atomiser and the UK marque specialist led me to believe the same ?. Italian parts specialist Moto Mecca also searched their suppliers without any success. Can anyone out there tell me if they are having similar problems.

[3potjohn]

What about 260D's? Do Eurocarb not have any.Someone with more knowledge than me should be able to clarify.

[hendre]

still available at TLM (Netherlands)
https://www.tlm.nl/magazijn/webshop/los ... ails/13914
there is only 2 left...

[EVguru]

The 'K' atomiser (which is available) can have extra holes added to turn it into a D or BD and NLM can do that.

I have a drawing somewhere of where the extra holes go.

[Harry]

Contact Eurocarb (Contact Developments) 0118 943 1180 they are the Dellorto concessionaires and will advise you on options regarding your emulsion tube. I do not have a lot of faith in NLM when they told me that the air in England is different to the air in Italy! They will also send you if you ask a parts list for the VHB carb.

[EVguru]

Contact Eurocarb (Contact Developments) 0118 943 1180 they are the Dellorto concessionaires and will advise you on options regarding your emulsion tube. I do not have a lot of faith in NLM when they told me that the air in England is different to the air in Italy! They will also send you if you ask a parts list for the VHB carb.

Since the climate is different, the 'air' will be different!

Eurocarb have already been mentioned and are out of stock of D and BD atomisers.

I've put a sketch up on my webspace http://www.compton.vispa.com/Morini%20atomisers.jpg

[Harry]

How? Chemical composition of air is regarded as uniform unless you live in Bophal. Air density changes with pressure and for 'ordinary' bikes like Morinis it will not make a lot of difference unless like you, change your jets having taken pressure readings on a daily basis. In the dim and distant past I did use to change my caburettor settings, but that was on pukka grand prix bikes and was usually for the meeting.

[72degrees]

I do find that even a 'sports' 125 two-stroke is sensitive to the difference between hot dry air and cool moist air. Better cylinder filling with the latter I think. Not as important as jetting for"The Mountain" but noticeable. Perhaps not an issue on cooking four strokes.

[StevenCroft]

Thanks Guys, im trying out new PHBL 26 carbs as advised by Dellorto, their physically bigger and required some g modification to the fittings. Im still not happy and tempted to fit cone filters, but NLM are horrified at the thought of removing the airbox why ?. Rob at Dellorto has already been very helpfull giving advise as to jetting and needle settings.

[Harry]

I run K & N's round filters and have never had any problems except rain at first dripping off the tank which drains into the float bowl. Solved that problem by inserting drain holes at the bottom side of the filter just before the 'bell mouth' and even in torrential rain no problems with water ingress. I did make up covers standing proud of the filter and covering the top but found the holes work just as well. NLM argue that it weakens the mixture on the back cylinder, but if you take all the trunking off the back carb, the bike will not run above about 30mph owning to the ram effect on the float and 8 stroking (rich mixture). Have a look at the racing Morgans with the front facing carbs and you will see covers over the carbs. With the K & N's fitted they have the same affect.
The 350 racer I once had ran with K & N's had no ill affects.

[Harry]

PS: The 26 mm PHBH carbs fit with no modifications. The 350 racer had 28mm PHBH carbs. PHBH are a much better carb with the round slides.

[EVguru]

There have been people who have made 'pod' filters directly fitted to the carbs work properly, but others who have not. Putting the standard airbox back on just seems to help in many cases.

There are two problems. One is that often the carbs are being run without the additional support they used to gain from the intake rubber, so you can end up with fuel foaming or float problems. The second problem is that you may have carbs seeing a different air pressure. Of course quite often pod filters are associated with 2:1 exhausts and some of these just seem to make the engine impossible to jet so it runs without any flat spots, so that may be part of the problem.

Ram charging should make a carb run lean unless the float bowl sees the same pressure as the intake. That's why 'suck through' setups were much more popular on supercharged engines. Early petrol turbochargers were Diesel engine derived and lacked propper oil seals on the bearings and would loose their oil if subjected to the vacuum created by a shut throttle upstream.

[hendre]

Thanks Guys, im trying out new PHBL 26 carbs as advised by Dellorto, their physically bigger and required some g modification to the fittings. Im still not happy and tempted to fit cone filters, but NLM are horrified at the thought of removing the airbox why ?. Rob at Dellorto has already been very helpfull giving advise as to jetting and needle settings.

I swapped my VHB for PHBL without any modification to the fittings, perfect fit...

[Harry]

Not quite sure what EVGURU is talking about. Surely if you have no flat spots in your carburetion, means that it is sorted so perhaps everyone should fit 2-1 exhaust systems? I have removed the cross over pipe in the exhaust, which does make tuning easier. Having run Morinis both with 2-2 and 2-1 exhausts systems and with K&N type filters and with the standard system, I have been able to jet and tune the carburetors with no problems. I have had hiccups on both sets ups when coming off idle onto progression but never flat spots up the rev range other than from over extended cam timings.
Regarding turbosupercharging, these compressors were first applied to petrol aero engine during the First World War, having been designed in the late 1800's and were only subsequently developed for marine diesel engines 4 stroke in the 1920’s and then marine 2 stroke engines after the Second World War. Mercedes Benz used supercharging on their SSK cars in the 1920’s, which blew into the carburetor, overcoming rich mixture by pressurizing the whole of the carburetor not just the inlet tract to overcome the rich mixture. They were able to engage and disengage the supercharger with a dog clutch from the throttle pedal, whereas Bentley’s ran with superchargers always engaged between carburetor and engine; WO Bentley did not approve of his engines being supercharged!
The seals on turbochargers depend upon on size. Large marine turbochargers are usually fitted with labyrinth seals on both turbine and compressor sides. When the throttles are shut too quickly the excess air usually blows back through the air intake with alarming noises with banging and high pitched screaming, cadets and junior engineers on their first trips would shit themselves on first experiencing this phenomenon. Who ever was on the controls would set the poor lad up by having him(or her) stand by the inlet to one of the turbochargers which were rated up to 3500kw as an initiation. On smaller turbochargers the units were developed in unison with petrol engines and despite the use of labyrinth seals no oil was sucked out of the compressor side. This was so before the development of pressure bypass valves better known as waste gates then the crankcase oil system would be pressurized with consequent results. The usual method of sealing the turbine and compressors sides these days is with piston ring type seals. As turbo chargers are only fitted to engines with injection systems on cars for everyday use, then the throttles are often fitted with bypass valves to stop excessive vacuum in the induction tract, so that the spool does not slow down reducing turbo lag. It also stops the relief valves blowing off which, if you go cruising round town in a Subaru at night thrills the knob heads looking on and makes you look like an even bigger one.
Regarding support, I have had no support on my every day 500 for 14 years with no problems; it is the fuel in the float that foams. You will find that a lot of carbs are rubber mounted to stop foaming, remote floats on Amal GP carbs fitted to Manx, G50 et al are all rubber mounted.
The corrugated and restrictive intake system on the Morini is fine for every day use, especially if you modify the air box relevant to 500 and 350, but for volumetric efficiency it has got to be suspect. Also for ease of maintenance, if you do it yourself, many seem to be lacking in this ability today, K&N types are easier to clean and a damn sight cheaper and easier to remove than the filters fitted to the Morinis. Incidentally I used to clean these filters with Jizer then under the tap to rinse out and dry in the sun or blow off with air and refit.

[stillooking]

It's good to read the thoughts & experience from more knowledgeable posters on this subject; I must admit from my own v.limited knowledge (& experience) the air filter assy. looks to be good in thought but practicalities are not so good. I'd very much like to get rid of the OE assy, it really is quite annoying trying to service it, plus I doubt my bike has an 'leak free' filter hose & housing as well. I've always held back from modifying as I tend to think the designer knows best, usually (sort of!) plus I've read previous reports from various sources saying leave it as is etc..

What I want is to retain the same engine characteristics, same or improved MPG (not less), same speed/performance, improve serviceability and not have to spend £30(nearly) on air filter elements