Carburettors

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3potjohn
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Re: Carburettors

Post by 3potjohn »

I had a go at converting some jets, in this case 264’s.I have very limited tools and not even a pillar drill. I acquired ten 0.8mm bits as I expected to break a few and as luck would have it a used 2.64 reamer appeared on eBay.
My next problem was how to set up the drill bit, so obtained a clone Dremel multichuck again on eBay which could go down to at least 0.8mm.
I then made up a small block of wood( yes wood again!) drilled to accept an atomiser, with numerous cross drillings of 0.8 mm at the various positions. This could have been inaccurate as had to rely on my trusty Aldi caliper but after measuring on each side got it pretty close. By inserting an atomiser then drilling through the guide holes it worked. Reamed out, then tested in my PHBH carbs. Absolutely no difference. Even the problem at progression with the existing correct jets was still there. Perhaps I could have inserted one or two of the drill bits to peg the atomiser in place but I only thought of that dodge now.
I could not guarantee that I could reproduce this a second time but it was the only method at my disposal.
John
EVguru
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Re: Carburettors

Post by EVguru »

3potjohn wrote: 28 Apr 2021 12:31Even the problem at progression with the existing correct jets was still there.
The needle is parallel until 1/4 throttle, so the main jet circuit has no effect until you reach that point.
The atomiser mostly affects mixture during acceleration.
Paul Compton
http://www.morini-mania.co.uk
http://www.youtube.com/user/EVguru
mbmm350s
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Joined: 22 Jun 2018 10:18
Location: Reading UK
Location: Berkshire UK

Re: Carburettors

Post by mbmm350s »

I wanted to update this thread for the benefit of other owners with similar problems. Knowledge and all that.
Thanks - feedback improves our knowledge.
Glad that improvements are being made since many parts may be worn and the permutations unless you return everything (exhausts, filters,ignition)
to stock are many.
I also noticed that if I cracked the throttle open hard while idling, the bike would stall. My conclusion is that the idle jet of 45 is now too small and I should go up to 46 or maybe 48 again, most likely the slides have had the biggest impact on reliability and actually I don't need such a small idle jet anymore.
This is a little worrying, normally a Morini is very responsive and only our mechanical sympathy stops it from revving hard and fast.

Too much fuel or too little fuel?. Too much un-atomised fuel can kill the flame. A gentle opening of the throttle is used to determine the idle jet size. If it stalls on return then may be the slides are a little low, the rev counters start at 500rpm and aren't very accurate is it really 1300rpm.
when mine reads 1250rpm the actual speed is 1000rpm ( I have the equipment to check and calibrate the electronic tachos) another read 1350 rpm for a required 1000rpm

The standard idle jet is 50. However many report this to be too large.
I run 48s in a VHBZ 25HS equipped sport with standard set up.
I do think a new 260K would be better than a worn out one.

You can convert a new 250K into the unobtainable and Moto Morini special 260BD by drilling 4 holes of 0.8mm
higher up the atomiser to weaken the mixture during mid range acceleration which is needed with the sport cam

A 260K has holes drilled counting from the bottom 2,4,2,0,0 if you have one to hand it is obvious.
To make a 260BD the drillings would go 2,4,2,4,0 a 2.60 reamer is needed to clean any burrs.
The selection of the 260BD was in part to help with the flat spot in the mid range
The mod can be reversed by filling with solder and reaming clean again.

Our friends in Italy do not think that the 260BD is the optimal solution and certainly not a panacea, later K, K1 and K2
and Dart K4/5 models had a different atomisers as changes to air filters and exhausts went on.

Cheers
Mark
simonnorthroad
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Re: Carburettors

Post by simonnorthroad »

I bought some NLM 'special cure' drilled atomisers for my girlfriend's 350, and all it did was move the flat-spot elsewhere (up, I think) in the rev-range!
mbmm350s
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Location: Berkshire UK

Re: Carburettors

Post by mbmm350s »

simonnorthroad wrote: 02 May 2021 08:56 I bought some NLM 'special cure' drilled atomisers for my girlfriend's 350, and all it did was move the flat-spot elsewhere (up, I think) in the rev-range!
Indeed Simon a familiar story , the 260 BD or any other weaker atomizer is just a final tweak often there are many other things to fix first.
Mark
MickeyMoto
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Re: Carburettors

Post by MickeyMoto »

There are too many variables. Modern fuel is one. Does it run better on supermarket fuel or Shell? How about 97 against 95? E5 or E10 (not that I've seen any yet!)?

Air temperature, pressure and moisture content are another.

Fuel tap flowing sufficient fuel? Tried with reserve open (on a full tank!).

Etc etc etc...

My Sport pulls ok from 2.5k, but in higher gears needs to be kicked down to get into the fun zone a bit quicker. Remember, it is only a 350 with minimal power. The top 1/3 of the rev range is where the Sport excels, but it should be able to potter in town. There may be a need to compromise, good town running, good open road running but a dance on the gear pedal to get from one to the other.

The other solution is to install a 501 engine. Pulls from 2k in top through to max...
3potjohn
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Re: Carburettors

Post by 3potjohn »

My Sport can potter along but open it up and away it goes ,very good response. Something to aspire too you might say.
John
mbmm350s
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Re: Carburettors

Post by mbmm350s »

Hi John,

The K motors of which I am sure yours is, add some more variables, improvements by the factory;
they have a different crankshaft, different carburettors of the VHBZ25HS type with different atomisers,
different exhausts etc. All of which make the K versions more tractable.

As Mike says there are so many variables and hence so many permutations.

In my experience over 40 years, for poor running, the chief culprits for standardish engines are
1. weak ignition system
2. Worn carburettors - slides, needles and atomisers and of course air leaks
3. Unsuitable exhausts

The type of fuel, air, the colour of my pants, etc don't make them un-rideable.
Mark
hendre
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Location: The Netherlands

Re: Carburettors

Post by hendre »

add "non-stock air filter systems" to the list... any Morini I have bought over the years was returned to the stock air filter box
3potjohn
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Joined: 02 Jun 2007 13:58
Location: Devon

Re: Carburettors

Post by 3potjohn »

Yes the K never misses a beat right through the range.It has stock air filters and Sito silencers of the black chrome variety. I am surprised how long these have lasted, but it won’t be long......
Was there a verdict on fuel height? I returned to this on my Coguaro. It originally had white floats but now black.Slightly heavier. I tried filling a removed bowl to within 5mm and then tried to quantitate that volume. Due to “less than ideal laboratory conditions “ the measuring cylinder recorded about 65 mL the first attempt. This doesn't take into account the displacement of fuel by the float mechanism and carb body.Measuring the true volume governed by the float gave nearer 38mL allowing for a dribble as the main jet was removed.Maybe too little. If only Archimedes had been a Morini rider.but that would have been ironic given his fate.
EVguru
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Re: Carburettors

Post by EVguru »

If you want to measure fuel height, modify a spare main jet holder to allow fitting a sight tube.
Paul Compton
http://www.morini-mania.co.uk
http://www.youtube.com/user/EVguru
mbmm350s
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Re: Carburettors

Post by mbmm350s »

Hi John,
As Paul says
The sight tube method is standard way on Mikunis etc and is often included in the overhaul kits, you could buy a Mikuni one and drill and tap M6?
a spare main jet holder to suit. However this will indicate only the difference if any between the cylinders. I am not aware of any published fuel levels for four stroke Dell Ortos. By the way carbs needs to have no more incline than about 30 degrees and should as far as possible be fitted vertically which is their natural position unless there are modifications particularly air filters.
For Scooter tuning PHBH clear plastic float chambers are also available try wasp performance or SIP-scooter
(also I find scooter shops most helpful in sourcing common parts)

To clear something up, for the standard setting of the floats black 16g versus black or white 10g
the fuel level is intended to be the same when the black floats of the first type are set to the correct height, other types are not adjustable.

Mark
3potjohn
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Re: Carburettors

Post by 3potjohn »

I have the original white floats on the shelf, so can go back to test again if needs be. Glass of Sangria in the afternoon sun has taken priority, in lieu of not going to Jerez.

John
morini_tom
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Re: Carburettors

Post by morini_tom »

Just to add my 2p worth to this thread, my 1982 sport has always (always is a loose term- I’ve had it barely a year) been a bit fluffy in the midrange. Starts and runs brilliantly everywhere but especially at low throttle openings in the 4-5000rpm range just doesn’t pull. Makes motorway cruising a bit tiresome.

The previous owner had seemingly replaced most carb parts but never fully rectified these slight fuelling gripes. I was going to make some 260BD atomisers to try and when I went searching for the donor atomisers what should appear but NOS 260BD… so I bought a pair, and they turned up today.

Removed the 260D atomisers from my carbs and fitted the BDs. Without rebalancing the carbs went for a ride and I would go as far as saying it feels like a different bike. No hesitation or stumbling, pulls cleanly through the Rev range.

Could of course be that the 260D atomisers I removed were worn but they look pretty new and suspect they got replaced when the previous owner did the needles.

Anyway, happy days.

I got the atomisers from TLM (guzzi dealer) in the Netherlands if anybody else needs some.

Tom


(For reference my bike has an S cam, not sure what pistons, standard intake and ignition and RMS 2:1. The issue was there with standard exhausts also but I did change to 115 main jets when I fitted the RMS)
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Paz2112
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Re: Carburettors

Post by Paz2112 »

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?
My Other Italian V-Twin is an Italian V-Twin
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