Datsun Roadster Forum-311s.org

Hi guys,

Does anyone here run 40DCOE Webers on their roadster?

I have them on my modified H20, and while they perform really well for the most part, there is a persistant stumble/hesitation when accellerating - most prominent when depressing the accel pedal quickly at anything below 3000rpm.

I've been fiddling around to try and get rid of this stumble for ages now with no luck - I've tried different idle jets, different pump jets, fiddled with float levels, and have just installed a closed off pump exhaust to increase the duration of the pump shot, but still no luck.

What combination of jets do you run in your webers?

Any ideas what it might be?

Mike

I hate webers, a friend of mine has one on his Austin Healy, and they are a pain. That said, I bet you have a wrong jet still, remember you have pump jets, air jets, fuel jets, imultion tubes, and some others that I can't think of. I would try different pump jets to solve your issue, if you have access to some, I would try the next sizes larger and smaller.

Just my $.02

Will

My understanding is that the transition porting on the DCOE is less than optimal. Jetting can ease it some, but the Dellorto and Mikuni Solex carbs are generally regarded as having better transition porting. The strength of the DCOEs (and the DCOMs - a newer improved version with an actual accelerator pump like the Mikuni has) is that they have TONS of support for parts and such. The Dellortos have fair support and the Mikunis are about unsupported by comparison.

All that rambling having been said, here are some sites that may help:

http://hometown.aol.com/DVAndrews/index.htm

http://www.teglerizer.com/dcoe/tweakingdcoes.htm

http://home.att.net/~jason510/weber.htm

http://teglerizer.com/dcoe/

The third one (Jason510) is specific to making Webers work on a Datsun and he explains how he eliminated the transition issue. There are other sites that refute what he has posted, but if it works for him, more power to him! (Pun intended!!)

Hope that at least a little of this helps...

Thanks Sid,

Would you believe I have already seen all of the pages you listed, and know them quite well, some I've read MANY times (as I said I've been trying to fix this for ages!!).

I actually have some late model 44PHH Mikuni's (I'm told they are the NISMO version) which I'd like to install, but need to find some throttle levers to go on the rear of the carbs (the U20 setup has the levers on the front - my setup needs them on the rear). In the meantime however, I'm so close with the Webers, I'd still like to try and get them right!

Any other suggestions?

Cheers
Mike

Mike,

The U20 linkage pulls from the rear iirc. Been a while since I looked at it. Is your linkage set up for a center pull, or divorced pulls? send me a pic at spl310@hotmail.com. I have some linkage bits here - we may be able to work something out!

Just looked at this photo of a U20 setup...

http://members.oztralia.com/~mikew/images/seats2_04.jpg

We were both right/wrong.

On a solexed U20, the levers are on the rear of the front carb, and on the front of the rear carb. I need to have the levers on the rear of both carbs (I think this is what you called divorced pull?).

Anyway, they are the levers I don't have .

My car is in the workshop at the moment so I won't be able to get you photos until the weekend.

[speaking of the workshop, that reminds me - I need to start a new thread about my clock! And another about axle tramp!]

Mike

OK, now I understand. The U20 has a center pull setup - that is that the linkage is between the carbs and uses a single connecting rod to move the plates as they are interconnected. Many other Datsun setups have divorced pulls as I call them. That is the linkage lever is on the same side of each carb. This is what the stock 1600 SU setup is like. I have some of those linkages, but don't recall if they went on the front or rear of the carbs as installed in the car. I will try to look today. If you have the center pull setup and the stuff I have fits what you need, we can work out a trade...

This may be obvious but I'll say it anyways...check the sync between the carbs and also between the venturis (shafts twisted). My dellortos on my Cortina would do the same thing for the longest time. I finally narrowed to a twisted shaft on the front carb.

Hey Sid,

Here are some photos (took me a while to get them up here - have been very busy last few weeks!).

These are of the currently installed Webers, notice the levers are at the rear on both carbs.

http://mike.dsrcvic.com/pics/IMGP6268.JPG
http://mike.dsrcvic.com/pics/IMGP6272.JPG

These photos are of one of my solexes, notice the levers are on the front (it's the same on both carbs).

http://mike.dsrcvic.com/pics/IMGP6280.JPG
http://mike.dsrcvic.com/pics/IMGP6281.JPG

In order to fit the Solexes on my manifold, I need the two pieces (throttle stop and throttle lever) to go on the rear of each carb. Let me know if you've got them, and hopefully we can work something out.

Cheers!

Mike

Mike,

Sorry, but the ones that I have are the same as you have on your Solex carbs. I do have a couple of suggestions for you though. Weber linkage parts are CHEAP!! You can get another pair of linkages and make them work on the Solex carbs. As I recall, the weber throttle shaft is smaller than the Solex, so you would just need to file the holes bigger.

The next option is a little more elegant. Gerardo Magana has reproduced the OEM Mikuni carb linkage pieces for the U20. Get a set of those, bolt them on and then the mods to your manifold linkage is easy. You would simply remove the end throttle linkage arm from the cross shaft on the manifold and only use the forward link. That would give you the center pull type linkage and it should work fine.


The costs should be comparable either way that you go.

BTW, for some reason, the only way I could see the photos was to save them to my PC and then view them. I could not view them in the browser. Very odd...

I don't think it's as simple as that is it? The throttle stop and idle screw setup is different on the solex.

Also, I don't want to use the centre setup unless I have no other choice, as my manifold is a custom jobbie, and I'm not sure that the carb spacing is right for that setup (the manifold is off an L16, cut, shortened and welded, and welded to H20 manifold flanges).

Anyone know of a supplier that sells these parts (throttle stop & throttle lever)?

Mike,

The nice thing about the center pull linkage is that it is made such that it will allow differences in carb spacings. I believe that the stuff that Gerardo sells would work fine. As far as OEM Mikuni pieces, I don't know of a vendor off hand.