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 Weber 28/36DCD, don't get me started

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T O P I C    R E V I E W
mellePosted - 06 May 2019 : 13:03:14
Weber 28/36DCDs have a reputation for being difficult cold starters. I've been experimenting with different starting fuel and air jets since I swapped the Solex 32TDID on my 96 for a DCD, but I still couldn't get it to cold start without a lot of cranking and a liberal dose of brake cleaner. Until I re-read John Passini's brilliant Weber book.

Here's the trick: don't follow Saab's cold start instruction.




Follow Passini's instructions instead (see p.94 of 'Weber Carburettors Tuning Tips and Techniques').

quote:
To obtain the maximum force from the air blast through the numerous bleeds, the throttle should be kept closed. If the accelerator is jiggled, the depression in the starting duct will be reduced and at the same time the accelerator pump will be injecting liquid fuel. Either use the starting device or jiggle the pedal not both.


Mine starts on the switch every time now, gotta love a free upgrade!

www.saabv4.com
10   L A T E S T    R E P L I E S    (Newest First)
mellePosted - 14 May 2019 : 11:48:59
The DCD does have fast idle!

As for air leaks: I've rebuilt a few DCDs and DGAVs and I've found the DCD certainly is the better built carb, it seems to be made out of a tougher alloy. Of course 40-year old DCD spindles will have more wear than those on a brand new DGV. It makes sense to upgrade the spindle bushings on a new DGV with roller bearings to help minimise wear; unfortunately this is not possible on DCDs.

www.saabv4.com
pchristyPosted - 14 May 2019 : 09:01:03
The mixture enrichment system on a DCD is very powerful! If you pull it all the way on, you WILL flood the engine! I always found that around 25 - 30% was plenty. Also, it doesn't have a "fast idle", so the engine tends to die very quickly unless you crack the throttle open a bit.

Actually, as soon as the engine has caught, you can usually push the enrichment control fully home. It might pay to let it warm up for a minute or so before driving off, as otherwise it might cough a bit when the throttle is opened.

I preferred to forget the enrichment, and just pump the throttle a bit to prime the engine. I only used the enrichment when it was *really* cold!

I've now fitted a DGV, which has a more conventional setup, though again, you can push the choke in pretty soon after its started. (I got fed up with the air leaks on the DCD!)

--
Pete

--
Pete
"Duct tape is like the Force: It has a light side and a dark side, and it binds the Universe together!"
mellePosted - 13 May 2019 : 11:49:56
The DCD has a cold start enrichment system, which functions as a "carb within a carb", as Passini puts it. Your DGV has a traditional choke-flaps-and-an-extra-squirt-of-juice system.

www.saabv4.com
andydeans3Posted - 12 May 2019 : 22:52:17
Melle

What's the difference between them?

Andy

1978 LHD SAAB 96
1978 MGB Roadster
2008 LHD "Classic" Renault Twingo
1991 Nissan Figaro
mellePosted - 12 May 2019 : 18:44:10
Andy, yours is a DGV, which has a completely different cold start system.

www.saabv4.com
andydeans3Posted - 11 May 2019 : 20:08:42
Melle.
I have a thread running about cold starting with my Twin choke Weber DCD.
From one day to the next, no problem.
Full choke, one pump of the accelerator, away she goes.

However, leave it a few days, and can be difficult.

Case in point tonight. Preparing to go to Alford tomorrow.

Car has not run for a couple of days. Choke, pump, wind and wind, nowt! Another pump, wind a bit, and she catches, splutters a bit, then goes.

If I leave it a week, it's more difficult. Sometimes have to jump a spare battery on it, as the main battery starts to flag with all the starting motor winding.
In this case I usually squirt some Cold Start in the air intake, and then she'll fire, splutter a bit, perhaps die, but then go.

I have already changed the distributer cap, rotor and plugs. Good spark.
Absolutely no issues hot starting.

I have bought a carb refurb kit from Fast Road Cars, but have not got round to doing the job yet.
Too busy galavanting round the Western Isles in a silly Nissan Figaro!!!

1978 LHD SAAB 96
1978 MGB Roadster
2008 LHD "Classic" Renault Twingo
1991 Nissan Figaro
mellePosted - 08 May 2019 : 17:52:23
Yes, the enrichment system provides fuel and air for fast idle. The starting jet really is an emulsion tube with an interchangeable air jet. It's a pretty nifty system and I'm not sure why Weber went back to choke flaps on the later DGV-family of carbs.

I just checked J. Brejaart's book "Van Saab tot Saab", MYs 75b and 76 had the FoMoCo with manual choke, all other MYs had carbs with an auto choke. Passini suggests it's easy to flood a V engine with a manual choke, hence most were equipped with auto chokes. I've never had any issues with auto chokes on 2bbl Solexes, my experience with FoMoCos is too limited to say anything sensible about those.

www.saabv4.com
BorstlapPosted - 08 May 2019 : 17:29:46
Mine is MY1975B and it had a manual choke on the FoMoCo carb. Does that DCD fuel enrichment system also increase fast idle?

Alex
mellePosted - 07 May 2019 : 21:24:01
Yes, as most V4 carbs, the Solex 32TDID has an auto choke. I think the MY76 FoMoCo was the only one with a manual choke?

By the way, I found my DCD only needs about a third "choke" (the DCD doesn't have a real choke), it runs way too rich with the choke knob fully pulled out.

www.saabv4.com
BorstlapPosted - 07 May 2019 : 20:49:48
Does that Solex carb you refer to have an automatic choke? If I remember correctly the start instructions in the picture are for cars with an automatic choke. In case of a manual choke it is just to pull the choke knob and stay away from the gas pedal until the engine is running.

Alex

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