Weber 40 DCOE Idle Jet query

[4129R]

I am re-jetting a pair of 2nd hand 40 DCOEs, and I have a query about the brass carrier for the idle jets.

I am fitting 45F8 jets in place of the existing 45F6 jets, but the carriers they came in differ from the normal carriers I am used to.

The carriers in these 40DCOEs have 4 much larger holes above the bottom thread, and instead of a second thread higher up, they have an O ring.

I presume these carriers are carb specific, so I should re-fit the existing carriers, even though they have 4 much larger jets in them?

My second query is about the brass butterflies which open and close with the throttle.

I was told to check there was no daylight around them when closed, and to loosen the 2 screws to adjust them if there were daylight. No matter what position I move them to, there is still daylight at one side. Should I replace just the brass butterfly for new, or are they matched to the aluminium carb casing in the factory, and are not replaceable? 

[jbcollier]

DCOM carbs were Weber trying to make their side drafts emissions compliant.  You need to use the holders that came with your carb.  The holes you are worried about are just unmetered passages.

Regarding the throttle butterflies, have you backed off the throttle stop screw?

[4129R]

DCOM carbs were Weber trying to make their side drafts emissions compliant.  You need to use the holders that came with your carb.  The holes you are worried about are just unmetered passages.

Regarding the throttle butterflies, have you backed off the throttle stop screw?

Thanks for that, you confirm what I thought about the idle jets

All throttle stop screws removed.  If the swivel pivot goes from 9 o'clock to 3 o'clock viewed from the engine side, both butterflies have light at 3 o'clock. I have removed both butterflies, cleaned them with wire wool, cleaned the carbs with wire wool to remove any corrosion or dirt, but still no difference.

[Kendo]

Is there any wear in the throttle shafts or bushings? Can the butterflies be installed upside down or backwards? Or are they symmetrical in both axes?

I assume both butterflies show the same daylight? Could that be another emissions “feature”?

[jbcollier]

Butterflies have beveled edges so there are only two different orientations possible.  If one side shows only a very slight amount of light, that should be fine.  Very, very difficult to machine things perfectly so both would seal completely.  Even a few thou off would result in what you are experiencing.  No play in the shafts/bearings?  Adjust the butterflies as best as possible and you're good.

[4129R]

Is there any wear in the throttle shafts or bushings? Can the butterflies be installed upside down or backwards? Or are they symmetrical in both axes?

I assume both butterflies show the same daylight? Could that be another emissions “feature”?

No play in the shaft.

The butterflies can only fit one way around, and they are marked on one side 79'30 for the angle.

Both show the same amount of daylight.

I have ordered 4 new ones for 79'30 from the Weber main agent. If they don't improve the darkness, then I know it is as good as can be.

[4129R]

Butterflies have beveled edges so there are only two different orientations possible.  If one side shows only a very slight amount of light, that should be fine.  Very, very difficult to machine things perfectly so both would seal completely.  Even a few thou off would result in what you are experiencing.  No play in the shafts/bearings?  Adjust the butterflies as best as possible and you're good.

I had bought 7 pairs second hand, and all the others show no daylight. This is the only pair with the O ring on the idle jet. They have no country of manufacture cast in. Usually Italy or Spain.

[jbcollier]

Now I'm getting confused.  If you have DCOMs then you have to use the idle jet holders with the o-rings.

[4129R]

Now I'm getting confused.  If you have DCOMs then you have to use the idle jet holders with the o-rings.

I have, thank you. I assumed the holders were carb specific.

Can you tell me what the difference is between the DCOE and the DCOM, apart from the idle jet holders?

Ah, I found the difference:-


Weber OEs and OM differences
"I've been digging out jets and chokes from the DCOEs that I got for use in my DCOMs. I thought I'd share some of what I'm finding now that I have both side by side.

The jets, chokes, tubes and gaskets are all interchangeable. However the carriers are different. The OMs on the right in the pic show an O ring for the idle jet carrier and the OE has two sets of threads. For the main assembly the carrier itself is the air corrector and would have to be drilled out to be able to use air correctors from the OE style.

On the pic of the bottom of the carbs you can see the big difference in the OM has a mechanical accelerator pump and the OE has jets for this circuit. I also noticed that the OM has a lock down for the venturies where the OE uses the air horns to lock it all in place.

The top view shows a lot of changes. The OM fuel inlet is on the top and has a filter on the banjo bolt. OE is on the side and has a separate top mount for the filter all by itself. The OM also has both metered and direct vacuum ports and no accelerator jets."

[jbcollier]

The DCOM needs the o-ringed idle jet holders or it will have a vacuum leak and run like crap. Myself, I would not fit DCOM carbs.

[4129R]

I bought 4 new butterflies from Webcon, the UK main agent for Weber, and they won't even fit in the 40 DCOE bodies.

I compared them with the ones showing daylight, and there is no visual difference. The size difference must be 1 or 2 thou.

I cleaned up the carb bodies to remove discolouration, and they still don't fit.

Back to the drawing board ................