Carburettors

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Stubaker58
Posts: 72
Joined: 28 Apr 2019 21:02
Location: Felixstowe, Suffolk

Carburettors

Post by Stubaker58 »

I’m looking for some help! I’m new to Morinis having bought my 1979 31/2 last year. It had been standing for some time, maybe twenty years, but is a low mileage example (23234Km). I’ve had to do various bits and pieces and it’s now road worthy and I’ve really enjoyed a couple of 50 mile rideouts.
The issue now is carburation. I’ve had both carbs apart, cleaned them up in a small ultrasonic bath and rebuilt them. I even got both slides the correct way round the second time! It’s an easy starter, no really, and idles at just below 2000rpm. I’ve had an initial go at balancing the carbs with a Carbtune and they seem ok. BUT at low revs and especially pulling away from rest it hesitates and needs a good blip, it certainly isn’t smooth. I’ve also noticed that when starting the enrichment lever on the left carb (front) has no effect, the right (rear) lever gives a big increase in revs. When cold there is also sometimes a puff of smoke from the front cylinder if the throttle is blipped. I haven’t changed the carb settings, when I cleaned the carbs there was some external corrosion on the emulsion tubes but the holes all cleaned up ok. The needles were shot so I replaced them (but not the jets, mistake?).
So what should I now be looking at? I don’t want the bike off the road for too long so I’d like to have the bits ready before I start.
Thanks.
George 350
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Joined: 16 Jun 2007 09:43
Location: Northampton

Re: Carburettors

Post by George 350 »

Worth removing the choke plunger and checking that the 'rubber' pad is still on the business end. Not unknown for these to go awol. The black circle on the end in the pic attached is the bit I'm referring to.
If it is still in place, is it still soft or set like rock? If not there, your bike will have the choke on all the time on that cylinder.
choke plunger.jpg
choke plunger.jpg (74.92 KiB) Viewed 11001 times
While you are dealing with the carbs, many people have found that a reduction in idle jet from a 50 to a 42 or 43 is beneficial in overcoming mid range flat spots.
Regards, George.
George
350 sport 1978, 350 Strada 1978
650 Norton 1967, 650 Kawasaki 1977 and 650 Enfield 2019
EVguru
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Re: Carburettors

Post by EVguru »

The enrichener has two actions as it's lifted.

First it uncovers then end of the starter jet to allow extra fuel to flow.

Secondly, it allows air to flow down the bypass passage, which is what gives you the fast idle.

I had been working on a bike where neither enrichener was giving the fast idle. It otherwise started very easily and I didn't investigate the lack of fast idle.
It's now occurred to me that perhaps the wrong enricheners had been fitted. The same style was used on several different carbs, the PHBH round slides as fitted to 500s for example and the lengths vary. If they're not opening up the bypass passage properly, then you wouldn't get the fast idle, or not a full one.

Off idle stumble is well know. Leaner idle jets as suggested, or a slide with a larger cut-away. The latter often works when a leaner jet hasn't.
Paul Compton
http://www.morini-mania.co.uk
http://www.youtube.com/user/EVguru
Stubaker58
Posts: 72
Joined: 28 Apr 2019 21:02
Location: Felixstowe, Suffolk

Re: Carburettors

Post by Stubaker58 »

Thanks guys.
I’ve got a couple of new Viton pads on their way to replace the old rubber ones in the enrichment tubes. I checked the left one and the pad was very deformed so I’ll change both as a start.
I’ll get a selection of jets, probably from KMT, once I see if the pads make any difference.
Thanks again
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Daddy Dom
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Location: Auckland, New Zealand

Re: Carburettors

Post by Daddy Dom »

I bought two new enrichers/choke plungers for mine. It changed the idle and low-rev running immediately, for the better.
I think it's a no-brainer.
DD
MRC 3082½
3potjohn
Posts: 1243
Joined: 02 Jun 2007 13:58
Location: Devon

Re: Carburettors

Post by 3potjohn »

I shall check mine as I have never replaced them. Bike running well however the rewear has less of a quickening effect when used in isolation. Certainly on my slide carbed Beemer, the choke pistons perish leading to poor running and sooty plugs. Are these the replacements from Eurocarb?
John
Stubaker58
Posts: 72
Joined: 28 Apr 2019 21:02
Location: Felixstowe, Suffolk

Re: Carburettors

Post by Stubaker58 »

Hi,
I’ve ordered my replacement viton pads from EBay seller dredgehead (554) at £5 delivered. I’ll let you know if the fit/work.
Regards
3potjohn
Posts: 1243
Joined: 02 Jun 2007 13:58
Location: Devon

Re: Carburettors

Post by 3potjohn »

I checked mine , both the tips and the o rings look fine. Eurocarb sell the entire choke (length is 34mm) for a bit over 16 quid + vodka and tonic. At least they are in stock for now but may disappear in the future which seems to be the way of things Morini.
I have seem similar on a trader’s stall for £40 each.
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Daddy Dom
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Location: Auckland, New Zealand

Re: Carburettors

Post by Daddy Dom »

3potjohn wrote:I shall check mine as I have never replaced them. Bike running well however the rewear has less of a quickening effect when used in isolation. Certainly on my slide carbed Beemer, the choke pistons perish leading to poor running and sooty plugs. Are these the replacements from Eurocarb?
John
Yes, the shorter of the two. I only got them because my choke levers broke but wow!!
MRC 3082½
Al Limite
Posts: 24
Joined: 27 Jan 2020 12:33
Location: Exeter, England

Re: Carburettors

Post by Al Limite »

Anyone contemplating the replacement of the enrichers/chokes check eurocarbs ebay site where they are on special offer at £11.95 each with free p&p. Ebay listing number 290761332749. Extremely fast delivery as well. I replaced both of mine during a carburettor rebuild and it has transformed starting and idling.
mbmm350s
Posts: 666
Joined: 22 Jun 2018 10:18
Location: Reading UK
Location: Berkshire UK

Re: Carburettors

Post by mbmm350s »

The enrichment circuit has many features of a carburettor. It has a jet 50 and combined atomizer notice the holes and narrowing of tube, a slide and a venturi all scaled to the requirements of the cold start stoichometric ratio. On some models one of the carburettors or sometimes both can vary the opening of the enrichener. Thus control the cold start idling speed
The carburettor and the enrichment circuit are in operation mutually exclusive therefore a fault in one will effect the operation of the other.
As many have stated the seal at the base of the enrichener slide must be good or the normal idle mixture will be too rich.
The slide must uncover the air port. This can be tested by gently operating the lever and the revs should increase and decrease with a cold engine.
As many have stated the seal must be good.
In extremely worn enrichment slides the air can bypass the main carburettor weakening the main idle mixture.
Now for the enrichener atomizer the question is where does the air to it come from. It comes from the vent just underneath the choke lever through a vertical drillway if this is blocked the circuit cannot work correctly. It is not an overflow as it is higher than the two other. On rare occasion fuel may be blown out of it due to backpressure
Much of the operation of the Dell Orto carburettors is described in technical literature which can be purchased from Eurocarb.
Mark
Stubaker58
Posts: 72
Joined: 28 Apr 2019 21:02
Location: Felixstowe, Suffolk

Re: Carburettors

Post by Stubaker58 »

Ok, fitted the two new rubber pads to the ends of the enrichment plungers. The old rubbers were crumbling and deformed. After a run out they seem to have made a considerable improvement, much smoother at lower revs. Now time to go over the mixture again as there’s a chance it’s not being enriched all the time.
Regards.
mbmm350s
Posts: 666
Joined: 22 Jun 2018 10:18
Location: Reading UK
Location: Berkshire UK

Re: Carburettors

Post by mbmm350s »

Hi,

Glad that the new enrichener seals improved things - many have found this to be the case.

The idle mixture screws, if the idle mixture circuit is working correctly they will adjust the warm engine speed (throttle stops set to give fast idle) between two points where it starts to stall
out = too much mixture and in = too little mixture) with the mid point spec at 1 and a half turns.
It is common to find the idle mixture screw has no effect, this indicates a fault, however the engine will run but getting a stable idle at 1300-1500rpm will be difficult.
If you find this it can be due to a leaky slide, leak in the inlet, blocked idle circuit, way too high float, or as once i found the wrong idle mixture screws fitted.

One point to note is that the idle mixture screw should have a tiny o-ring which may have been lost or is hiding in the bottom of the thread.
The needles were shot so I replaced them (but not the jets, mistake?).
By which you mean badly corroded , rather than worn. The atomizer ideally would be changed. If you mean worn then further investigation is needed.
Not all atomisers are readily available however most can be created from the available 260K by drilling the appropriate holes.
1979 31/2

Its helpful to know which model exactly A3 or K and which carbs VHBZ 25BS or VHBZ 25HS,
because the jets were changed for the K model. Also standard air box, open or sealed or aftermarket air filters.

The float heights should be set according to the Dell'Orto manual @ 24mm +/- 0.5mm to the base of the float.
The method shown in the blue book is confusing and imprecise in my opinion.
Float height
Float height
floatheight.png (140.83 KiB) Viewed 10717 times

Mark
JonD
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Location: Wantage

Re: Carburettors

Post by JonD »

After reading this thread I checked my choke rubber inserts, very deformed, possibly originals. Replaced with Eurocarb special offer chokes (34mm). What a difference, off idle stumble gone, idle very stable and better throttle response. Best value performance upgrade since getting a Carbtune for a very good price at an auto jumble. Will have to get the Carbtune out to reset the idle, now too fast.
mbmm350s
Posts: 666
Joined: 22 Jun 2018 10:18
Location: Reading UK
Location: Berkshire UK

Re: Carburettors

Post by mbmm350s »

Hi Jon

That's great. Many of us have been going on about these seals, there will be a run on them now!
Cheers
Mark
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