Side Draft Carburettors for a Geminin

Engine related articles specific to induction (carby, EFI etc.)
tobytj
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Side Draft Carburettors for a Geminin

Post by tobytj »

I though I would throw up a bit of basic information about the side draft carby application for a Gemini. Specifically some information to Gemini enthusiasts looking to use the following variants of twin throat side draft:

- Weber DCOE
- Dellorto DHLA
- Mikuni-Solex PHH

These carburettors all share the same bolt patterns for manifold connection and air cleaner connection – but the other parts (jets, etc) don’t interchange

References:

I will draw heavily from references to the book.

Hammill. Des, How to Build and Power Tune Weber & Dellorto DCOE, DCO/SP &DHLA Carburettors; Velcoe Publishing.

Strongle recommend this book to enthusiasts.

Also useful sites:

www.dellorto.uk.co Dellorto and Weber information
http://www.rmcarburetors.net/index.htm Mikuni – Solex
http://www.redlineweber.com/html/Tech/T ... ntents.htm tech info on DCOE

http://www.wolfcreekracing.com crazy yanks into Mikuni - Solex

Whats the difference? - Weber, Dellorto, Mikuni?

Weber DCOE

Image

Image of Weber DCOE courtesy of www.dellorto.uk.co

The original Weber DCO carburettors appeared in the 1950’s as specialist racing carburettors for Aston Martins, Ferrari , Jaguar, etc . They were individually sand cast and expensive. (You can still get parts for them!!). In the 1960s, die casting technology made Webers more affordable and the DCOE series was born.

The most common DCOE are 40mm and 45mm, but 42mm and 48mm are around. There is also the DCO/SP in 48, 50 and 55mm (that I know little about). Here is a link to an exploded diagram for a DCOE.
http://www.dellorto.co.uk/editor/upload ... OEdiag.pdf

and a parts list

http://www.dellorto.co.uk/merchandise/products.asp?
CategoryID=3&PartsectionID=57

Dellorto DHLA

Image

DHLA 45 in a single sidedraft application on a 4Z engine with a Lynx manifold

Dellorto did not start making 40 and 45 DHLA’s till the late 60’s. They tried to improve on the Weber design – and I think they did this in little ways (diaphragm fuel accelerator pump, plastic floats, etc) but for all practical purposes they both work well and are easy to maintain and tune. Dellorto stopped making DHLA carbies in the 80’s but the parts are still available.

http://www.dellorto.co.uk/editor/upload ... ladiag.pdf

and a calibrated parts list for all Dellorto

http://www.dellorto.co.uk/merchandise/p ... ectionID=9

Solex and Mikuni- Solex PHH.

Image
A pair of Mikuni – Solex PHH 40 S5’s

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The S4 version of the Mikuni – Solex PHH 40. The only real difference from S5 is the top cover plate.

Image

The business end of a Mikuni – Solex PHH 40 S5. Note the typical manifold bolt pattern shared by all these carbies. You can see the diaphragm accelerator pump system that is identical to the Dellorto.

Solex is a French company who had their own version of the weber style side draft . In the early 70’s they sold the licence to make them to Mikuni, who improved on the design. The problem with these carbies is there are so many variants and they are difficult to get parts for as Mikuni don’t support them anymore. Stay clear of the European Solex stuff.
The more common ones in Australia are 40mm come from Japanesse model Toyota Celica 2T-G and 18R-G engines. Commonly known as the S4 or S5, also known an PHH44 for the 44mm version. The link below will take you to a site that identifies different types

http://www.wolfcreekracing.com/carbid.html

http://www.rmcarburetors.net/index.htm

The distributor in the USA claims to have every part for a PHH available and the Aussie distributor has a bit. Looks like the range of tuning parts is restricted compared to DCOE and DHLA. Here is a link to the parts list and exploded diagram:

http://www.wolfcreekracing.com/Mikuni1.html

You can pick them up pretty cheap compared to a Weber or Dellorto. The Mikunl - Solex PHH uses a Dellorto style fuel pump arrangement and externally they look similar. The set up with the chokes and small venturi seems to be the main difference with PHH. The weber cold-start mechanisms are notorious for failing and running rich (they can be blanked off) the DHLA and PHH use totally different cold start systems.

In future posts I plan to look at the selecton of the carby (the better models) and some tuning info.
tobytj
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Post by tobytj »

Carburettor Selection

The following are some of the considerations when selecting and purchasing sidedraft(s)

Quality

The Mikuni – Solex is a well built carburettor but the Italian versions of the Weber and Dellorto are superbly engineered. For example the Mikuni – Solex butterfly shafts are bushed and subject to wear while the Weber and Dellorto shafts have proper sealed bearings that can be replaced in the unlikely event they wear out. Be careful of ebay adds for new DCOE’s – they maybe Chinese variants (they might be OK but the Italian stuff is tried and proven).

Don’t pay big dollars for chinese copies or Mikuni – Solex. They are not in the same league.

Chokes and jets

Check the choke size that is fitted to the carby. If you look down the airfilter end of the throat the size in mm should be stamped on the edge of the choke. The seller should tell you what jets are fitted. Factor in the cost of changing chokes and jets to take you to your starting jetting configuration (more on that later)

Damage

All side draft are prone to damage at the flange where they bolt to the manifold incorrectly attached (i.e. without soft mounts and thackery washers/rubber grommets) or if they have been in an accident or mishandled. In addition there are specific issues to watch out for with Dellortos.

- Float support pillars – one of the float support pillars cast into the top cover of a Dellorto (float chamber cover) has a split leg that grips the fulcrum pin for the float. They are easily broken and if broken the carby won’t work properly. Suggest you remove the top cover and check this if buying any Dellorto. I bought one with the top of the leg broken off but fortunately it was still usable as the break was below the pin

- Late model 40mm Dellorto idle screws. Some 40mm DHLA use a fine thread idle adjustment screw recessed in a tower casting. Fine threads in cast aluminium combined with a recess that traps moisture and dirt is a dumb idea. They can seize terminally. If buying one of these check that the idle adjustment screw moves freely. If stuck it may loosen with wd 40 and a little mild heat (let the seller attempt this). If you strip the screw head your bu##ered.

Image

Picture of a Dellorto 45 that has an unenclosed idle adjustment screws common to all DHLA 45s and many DHLA 40s this type of idle screw gives no trouble. If you have a tower type idel screw seal it with silicon after tuning to keep the crap out.

Some are worth more than others

Some Weber and Dellorto 40mm variants were modified for emission control reasons. The non emission control DCOE and DHLA models are known as “universal performance” models. For motor sport applications the emission model should be avoided. These emission models should be fine for street application but I would not buy one by choice – and you should pay less for them. On ebay a lot of ex Alfa Dellorto DHLA 40s come up for sale – they are probably emission models.

- Dellorto DHLA 40 “universal performance” have no suffix letter after “DHLA40” on the model ID and have three or 4 small (1mm) progression holes as well as the DHLA40E (4 large progression holes) and DHLA40C (six progression holes). The FGHL&N models are emission carbys

- Weber – the DCOE 11 and DCOE 2 models are the ones to have.

- For Weber and Dellorto 40s the emission models can be spotted by a large number (5) of large diameter progression holes, idle screws in towers, vacuum take off on one carby, small or no float chamber vent

Image

Photo of a DCOE2 “universal performance” – the brass screw nearest the idle adjustment screw gives access to the progression holes – or just open the butterfly and bit and look down the throat. (the other larger brass screw holds the pump jet in place).

As far as I know, Mikuni – Solex had the emission control stuff bolted on and are not modified internally for emission??

Image

Close up of the Solex – note that the progression hole cover is sealed on these side drafts.
tobytj
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Post by tobytj »

First question is - single or twin side drafts?

Image
Photo courtesy of MTCX_coupe76. Gemini single and twin side draft manifolds. Pretty sure the twin is only available second hand, not sure about. LYNX is the common brand but I have one that is unknown brand also

Side drafts were designed for race applications to provide one throttle per cylinder and maximise flow efficiency, thereby maximising HP. The single side draft, feeding two cylinders instead of one is a bit of a compromise, but on a road car it’s a good one.

- Stock engine = Marginal, a Weber 32/36 might be a better option. There will be an improvement with side drafts but you won’t get your money’s worth.

- Single side draft - Mild to moderate street engine, good low range acceleration, good cruising torque, coupled with a mild cam (70/30), extractors and bit of head work/early head. Will run strong to around 5500 rpm and the power then flattens dramatically.

- Twin side drafts – Moderate street engine to hot race motor, still strong in the bottom end but able to develop full power over 7000 rpm depending on tuning.

The advantages of a single side draft are that it will still give you a big boost over a stock set up, doesn’t have synchronisation issues, more fuel efficient and cheaper (you only need one set of everything). Also I am told you can use the standard master cylinder set up?? (not sure about that!) – you definitely need a remote (TX, diesel or other brand) for twins. Not sure about twins clearing the dissy on a 4Z ?? looks like it should.

What choke?

For single side draft, in a mild state of tune 34mm or 36mm (it’s a toss up), possibly 38 for moderate tune or 2000cc. If you are needing 40mm chokes in a single side draft for a heavily modified engine then twins is probably what you need. If you a have a DCOE or DHLA 40mm carby - go for 34mm choke as a 36 mm choke will not flow as well as it will in a 45mm carby.

Image
Weber 40DCOE choke (top left) and auxiliary venturi (bottom left) with a Mikuni-Solex PHH 40 choke, auxiliary venturi and sleeve right. (Dellorto 40 and 45s similar to Weber). The PHH 40 set up with a separated auxiliary have been known to vibrate loose and if you tighten the holding screw too tight- fracture

For twins - Hammil’s book says “In most instances, unless your engine really is a heavily modified unit, the 40’s with 34mm chokes will prove to be the best choice, especially for a street car”. He goes to say that smaller chokes can often result in better acceleration. The Mikuni-Solex came out commonly in 28mm, 30mm and 32mm chokes and a lot of people run 32mm – so if you have them, use them.

For well modified engines Hammil’s tables work out as 34mm for 1600cc, 36 for 1800cc, 38 for 2000cc and 40mm for 2400-2600 as a starting set up. For high mod engines only track testing or dyno will identify the optimum.

E tubes

The following is mostly about Dellorto and Weber as there isn’t a lot of choice n Mikuni-Solex and the PHH uses a slightly different system.

Fuel does not flow directly through the idle, progression or main jets systems. Fuel is mixed with air first to form an emulsion of air and fuel. The emulsion is further mixed once it is discharged to the manifold so it is at optimum fuel air mix during combustion.

Image

Idle and main jet set ups for (L to R) Dellorto, Weber and Mikuni - Solex
The function of the e tube is to control the mix of fuel with air to form an emulsion particularly during acceleration. If the E tubes are wrong the engine won’t accelerate cleanly.


According to Hammill, There are heaps of Weber E tubes but the common DCOE ones (lean to rich) F11,F15,F16,F2, F8, and F7.

Image

Weber set up showing E tube holder, air correction jet, E tube and main jet (top) idle jet holder and idle jet

Dellorto - For non emission control (lean to Rich) 7772.10, 7772.8, 7772.2, 7772.1, 7772.14, 7772.5, 7772.7 and 7772.6. The emission control e tubes are 7772.8 through to 7772.16 (so some overlap)

Image

Dellorto set up showing E tube holder/air correction jet, E tube, main jet (top) idle jet holder/ idle air jet and idle jet

For twin carburettor set up (recommended starting point)

- Weber, 1600cc – F16 , 1800-2200cc – F2,

- Dellorto 1600cc to 2000cc - 7772.10 or 7772.8, the next step up being 7772.2, 7772.1 and 7772.14. For highly modified racing engines 7772.5, 7772.7 and 7772.6

For single side drafts a richer E tube is required to so that enough fuel is available to two cylinders (rather than one) during acceleration. For Dellorto 7772.6 and Weber F2

Image

The Mikuni – Solex system is a little different but the same principle. The large brass cylinder is the jet block assemble and the emulsion is mixed inside it. Air enters the air correction jet and is dispersed through a “bleed pipe” (read E tube), fuel enters through the main jet at the bottom. In a weber or Dellorto, the emulsion mixing occurs in the cavity around the E tube. In a Mikuni – Solex the mixing occures in the jet block which is a tight screw fit into the body of the carburettor.
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Post by tobytj »

Jets

Idle jets


Idle or progression jets should be no richer than is necessary for off idle progression. On all side drafts the idle jet system feeds an air and fuel mix to the idle mixture adjusting screw and the progression holes that flow as the butterfly starts to open and before the main jets kick in.

The mix is controlled by either the size of the jet or the size of the air bleed. On a weber and a Mikuni-Solex the air bleed is drilled into the jet but on a Dellorto the air bleed is in the idle jet holder.

Weber – the idle jets are identified by two codes – a number and an F code suffix depicting the air bleed size. For example 45F2 and 45F8 both have the same opening for the fuel (.45mm) but the F8 is a richer jet because it has a smaller air bleed hole. The bleed suffixes from lean to rich are:

F3, F1, F7, F5, F4, F2, F13, F11, F8, F9, F12 and F6 but Hammill suggests narrowing the choice down to F2, F11, F8, F9 and F6 for performance engines.

Image

Weber idle jet holder and jet. Note the air bleed hole drilled in the jet (F8 size bleed)

Weber jet sizes for the fuel go up in 5’s – 40, 45, 50, 55, etc

Dellorto – idle jet holders (air bleeds) from lean to rich

7850.10, 7850.5, 7850.9, 7850.4, 7850.1, 7850.3, 7850.6, 7850.7, 7850.2 and 7850.8

Image
Dellorto idle holder and idle jet.

Dellorto jet sizes go up in increments of 1, - 60, 61, 62, 63, etc. Expect to make changes in size jumps of 2 to 3.

Twin Carby suggested starting idle jet sizes are 1600cc – 45, 1800 – 50, 2000cc – 55, 2600cc-60. For Weber it is suggested you start with an F2 and go for the same fuel hole size but richer F number if it stumbles in the progression stage. I that does not fix it go up a fuel hole size (sounds expensive!).

For twin Dellorto suggest you try what ever idle holder came with the carby and bump the jet size up or down in increments of 2.

For emission control Dellorto Twins you may need to start with a 60 because the air bleed is pre drilled in the body and it is big (lean). The holders are special to emission control carbies and don’t interchange with non emission control. These carbies tune best to 1750-2000 engines.

For single side drafts you need a rich air bleed (F9 or 7850.2) and about a 58-60 for 1600cc (that’s a bit of guess) up to a 64-66 for 2000cc (that’s what mine are).
tobytj
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Post by tobytj »

Stop Press! - Mikuni Data

http://www.mikunipower.com/PHH01.htm

I finally entered the right search engine word combination and struck gold with a site from which you can download the original Mikuni PHH service manual.

http://www.mikunipower.com/PHHCarbs/PHHcatalog28.jpg

Also on the site is the full parts catalogue and for Mikuni – Solex PHH 40 and 44 noting that they may no longer be available.

http://www.mikunipower.com/PHHCarbs/PHHcatalog28.jpg

This site is the complete Standard jetting chart for all PHH original applications.

From this the potential Gemini starting idle jet sizes for PHH are

- Twin PHH40 with 32 chokes - 57.5 for almost all applications in
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Post by tobytj »

Main Jet System

Auxiliary Venturi


The auxiliary venturi provides the “sucking power” that draws the air/fuel emulsion into the throat of the carburetor. It’s like when drinking a milkshake.

Image

The last part of a milkshake is the froth which is an emulsion of milk and air – just like the emulsion of fuel and air in a carburetor main jet mixing chamber. You get more froth if you –a, suck harder or b, use a large straw.

Image

The amount of “suck” that the auxiliary venturi exerts depends on it’s size and the velocity of air flowing past it. The air velocity depends on the, engine capacity, choke size, state of engine tune/modification. The amount of fuel passed also depends on the size of the opening between the auxiliary venturi and main jet chamber.

For twin carbys, - for All weber, a size 4.0 for up to 1600cc, size 4.5 for up to 2000cc and a size 5 for 2500cc ish. For Dellorto – a 7848.1 for 40mm is the most common and a 8011.1 for 45mm. But try the one you have first. You should use the smallest one that works (for weber). If the top end performance suddenly flattens off -.try a bigger size.

For a single, carby use at least a 4.5 in the weber. The power will flatten off noticeably in a single at high revs regardless.

Main Jets.

We are in to huge opinion country now. A little theory on the main jet circuit might help you appreciate why main jets can vary and their interaction with E tubes and air correction jets.

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The diagram (copy from Mikuni Service manual) is a typical fuel demand curve. The engine needs a bit richer mix for low speed loads and high speeds. The main jet system is designed to vary the fuel mix at different stages to match the profile of the engines fuel demand. The main jet, E tube and air correction jet work together to do this in a well tuned engine

Image

This is a representation of the main jet system at idle, moderate throttle and open throttle. (yeah it ain’t the best drawing). At idle, nothing is happening, the chamber fuel level is the same as the bowl which is controlled by the float level.

As the throttle starts to open fuel is drawn to the top of the chamber and mixes with air entering through the air correction jet via holes in the E tube that are above the fuel level in the chamber. The wider the throttle opens the more fuel is passed and, if the main jet is sized correctly the fuel chamber level drops.

At full throttle the chamber is under full vacuum and fuel and air mix as soon as fuel enters the chamber. Fuel is entering at the fastest rate possible for the main jet size and all E tube holes are in play.

The E tube design controls the relative richness of the emulsion by the position of the holes and the thickening of the tube at varied heights which dictates the level of volume of fuel (and height) at a particular point in the cycle. As the “suck” increases, more fuel is drawn through the main jet but the level drops and more tube holes came into play to balance the mix – and all this without a computer!

If the main jet is too small, the level of fuel in the chamber drops too quickly, too much air enters and the mix is too lean – engine stumbles at 1800-2500 rpm. If the main jet is too big the level of fuel remains too high for too long, not enough air mixes in the emulsion and the engine is too rich – engine heavy and sluggish.

So, the amount of “suck” exerted on the main jet chamber by the auxiliary venturi influences jet size. High performance engines with good flow rates “suck” harder and need bigger jets to keep up. Lots of thing affect engine flow rate (and auxiliary venturi efficiency) so jetting for mains is not an exact science.

For single carby applications the rule of thumb is a bit easier – for 34 chokes-155 main jet, for 36 chokes -160 main jets, for 38 chokes – 165-170 main jets. All singles move a lot of air past the auxiliary venturi and have more consistent performance -so this guidance I have found to be pretty good.

For twins carbys in a modified engine 1600cc/34 chokes -135 main jet, 1800cc/34 chokes – 140 main jet; 2000cc/ 36 chokes – 145 main jets, but drop 5 in size for mild tune engine and perhaps another 5 in size for smaller chokes. It is a bit of trial and error with mains.

Air correction

From our little diagram above, at full throttle, the fuel jet is flowing as fast as it can but because air flows better than fuel, if unchecked, the volume will keep increasing and too much air will be in the emulsion and the engine will run lean at high revs. The air correction jet limits the amount of air flow through the E tube at high revs. Start with 160’s for twins and 180 for single. Go up is 15-20 steps if the high revs stumble and see if it helps.
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Post by tobytj »

Correction to the very last sentence in the post above. If the engine is running too lean at high revs but is otherwise good at mid throtttle, go down a size in the air corrector(15 -20). if it is boggy and too rich at the hight end go UP a size to lean the mix.
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Post by tobytj »

Trumpets and Ram Tubes

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Above selection of trumpets for 40mm side drafts. The centre trumpet is specifically for a 40mm DCOE which are designed such that the trumpet secures the auxiliary venturi and choke in place. The 40mm DCOE unlike the 45 DCOE, DHLA and Mikuni Solex, does not have screws retaining the auxillary venturi and choke. I have seen 40 DCOEs with bolt up type trumpets and the auxillary venturi shimmed – but it isn’t right.


Trumpets are recommended for all side drafts to improve performance – in two ways potentially

1. Reduce turbulence – the majority of air entering the throat of the carby comes from the edges not the centre. Trumpets reduce edge turbulence and improve flow.

2. Ram Tube affect. At the moment that the valve or port first starts to open, a pressure wave starts to travel back and forth through the inlet tract, changing from plus pressure to minus pressure, or effective suction. If the wave front is caught at the right moment, it can be used to help ram mixture into the engine, thus inducing a form of mild supercharging. Reference http://www.bgideas.demon.co.uk/tmanual/Tm_Ch2.pdf

Trumpet Selection

Trumpets come in all sizes but are selected often to optimise the ram tube affect at a desired rev range. Long trumpets for mid level response. Short trumpets for high speed response.

First you need to calculate the ideal “ram length” which is the distance from the inlet valve to the end of the trumpet. You can calculate approximate correct ram length using the formula below, where L = length.

5791 x T
---------- = L in mms
N

Where T = Total intake valve duration in degrees
N = The estimated RPM at which max. power is required, minus five hundred

Gemini twin manifolds are pretty long becasue of their "s" shape to clear the shoker towers, about 350mm from the valve to the outer edge of the carby before add ing the length of the trumpet. By my calcs trumpets ranging in length from 80mm to 20mm will maximise the ram effect between 4200 and 5500 rpm depending on cam duration.

I am not sure if this works for single carbies – but I guess it should.
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Post by tobytj »

Update on some jet sizes for a single 45 DHLA with a 34mm choke. Testing has shown that the starting sizes recommended above are bit rich for a mild to moderate 2000cc engine. 148mains and 60-62 idles a better starting point
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Post by F3ARED »

Moved to technical ;)
Previously GeminiCoupe/GeminiRollingShell/SCAR3D/Jonnoisac#nt

78 TD Gemini Sedan - R.I.P
81 TE Gemini Sedan
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Post by tobytj »

Difficult To Remove bits

I had read about the following procedures but had not ever used them until I bought a Weber DCOE 45 that obviously had not been apart for a long time - if ever. Both the choke and auxiliary venturi were nice and stuck due to residue build up and a minor amount of corrosion.

For choke and venturi removal make sure the locking screws on the side of the body are removed (early 40 DCOE of course do not have these).

Before beginning soak the parts with WD40 and let sit for at least 10 minutes

Auxiliary Venturi

This is pretty simple. Use a thin wooden dowel as a drift and attack the venturi from the butterfly side. The drift was to be thin enought to squeeze through the open butterfly and sit ont he bridge of the venturi.

Make sure you rest the drift on the bridge section of the venturi (one on a Dellorto, two on a Weber) and not the centre tube. The dowel might splinter but that’s OK. I also use tooth brush handle as a drift – use wood or plastic which is softer than aluminium.

Stuck Chokes

Image

These can be really tight and a home-made puller is the best tool.

The business end of the puller is a slotted piece of 5mm steel (that started life as the backet for arm rest of cheap computer chair). The end piece has to be custom shaped for the carby so it is just wide enough to engage the rim of the choke.

Image

In the photo I am obviously holding the choke the wrong way round (tool resting on the aircleaner side of the choke not the butterfly side) but you get the idea.

The end piece is slotted so that it can slip through the choke from the air cleaner side.

Image

The other end is obvious. With the choke end of the device in position gently tighten the nut to withdraw the choke. My manual advises placing cardboard under the edges of the puller to protect the soft aluminium of the choke. Certainly round off the edges of the tool and apply some masking tape perhaps.

Image
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Post by tobytj »

Weber Cold Start Enriching System Problems

This is a procedure that DCOE users should consider during a rebuild.

Side draft carburettors use an enriching system to provide and additional richer fuel air mix to the engine when cold. The Mikuni-Solex and Dellorto systems work fine but the Weber systems are problematic according to tech references (Hammill).

The enriching circuit in the Weber DCOE is like a mini main jet circuit with flow controlled by piston shaped control valves to a passageway that opens into the engine side of the butterflys. Dellorto and Mikuni-Solex use a different system.

There are two separate problems that can occur with 40 and 45 DCOE.

- Fuel leaking through the control valves and into the throttle body

- Fuel splashing out of the enriching mechanism activator (which is vented) during hard driving.

The first problem, extra fuel entering the throttle body, can make it almost impossible to get a good tune at idle and low speed particularly if it is only happening to one choke of four.

The enrichment mechanisms for side drafts are seldom used. The fix to this problem is to tap a 6mm x 1.00 grub screw into the passageway in the throttle body. The grub screw should be recessed and not obstruct the throttle body.

Image

The tap will work easily into the aluminium. Suggest you insert a rod or a straw into the passage first to guage the angle of the tap.
If using a short grub screw it is suggested restrict the tap depth so that the screw bites firmly not the aluminium where the tap ends. With the longer grub screws this isn’t an issue as the screw will bottom out in the passage.

Image

You do not want this screw coming out and getting into the engine so use a good dose of thread lock and slightly peen the end of the thread (carefully). The enriching mechanism internals should be left in place.

SuperCheap sell little packet of assorted grub screws or you can get them from most parts shops. The carburettor is not permanently damaged by this mod and the fuel enrichment system can be reinstated by removing the grub screws.

This mod is recommended as a precaution for any DCOE where the fuel enrichment mechanism is not being used.

For the second problem of fuel splashing out can be remedied by removing the fuel enrichment activator mechanism and replacing it with a blanking plate the same size.
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Post by tobytj »

Air filter clearance - single sidedraft. I can confirm that a standard 80mm K&N styles oval pancake filter will not clear the shock tower. You need to use 65mm wide filter.

The 80mm Tantilisingly close and woudl look awesome however...
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Post by tobytj »

A small update on idle jet selection on a Weber for a single 45 DCOE application.

The DCOE idle jets have come in different air bleed sizes for a given fuel hole size. A 50F2 has a larger bleed that a 50F9 and the air bleed on a 50F6 and the smaller the air bleed the richer the jet. But it is not quite as simple as going up a grade in jet richness in steps. Tuning manuals don't explain this well.

You have to get
both
the air bleed size and the fuel jet size right. F9 or abouts seems to work for a single DCOE on a G180. If you go for a large bleed hole like an F2 and the right size fuel hole (say 55) the car will accellerate well but the idle will be all over the shop and require lots of idle screw turn out and still be rough. Similarly if the the air bleed is too small (F6) you can get good idle on less than a turn out of the idle screw but have a boggy and flooded progression in either 50 of 55 fuel hole sizes.

My advice would be if you can get a DCOE to idle around well 1.25 turns out on the idle screw I would not wander too far from that air bleed size to go richer or leaner before jumping a fule hole size.
tobytj
Long Term Member
Posts: 1881
Joined: Tue Apr 10, 2007 3:46 pm
Location: Brisbane

Re: Side Draft Carburettors for a Geminin

Post by tobytj »

Some more DCOE servicing info.

Believe it or not, the photo below is of the same Weber DCOE part.

Image

This is the leather washer that seals spindle bearing on a DCOE and stop water and dirt getting into the bearing and also air from being drawn into the throttle body via the spindle shaft.

This is the bearing that the leather washer covers. If the leather washer is as worn out as the one above then the bearing can be dirty , rusty and seized up – and this one was dry and a little stiff and binding.

Image

The bearing can be cleaned with wd40 and cotton bud or rag in-situ if it is not rusted. Then regreased. Avoid removing the spindle unless the bearings are cactus.

The leather washer is nothing special so you can buy it or make your own.

Photo below is the retained and spring that hold the leather in place. The retainer gets a bit mashed when it is removed but the new ones are cheap or it can be straightened.

Image

It is only the Weber that has this maintenance issue. A Dellorto DHLA has sealed spindle bearing.

When removing the 11mm nuts from the spindle to access the bearings, support the spindle shaft with a pair of ling nosed pliers over the butterfly with a piece of aluminium strip from a coke can to protect the butterfly from the steel jaws of the pliers
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