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markpw

205 Rallye Euro spec DCOM

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markpw

Gentlemen.

I've been entrusted to try and sort out the poor running of a friend's 205 Rallye Euro Spec. As far as we know, the engine is standard. It has the correct (we believe) 40DCOM carbs. My friend has rebuilt these and all the jet settings are stock. No air leaks.

 

Most of the problems with poor running and flat spots have now been sorted but we are left with a flat spot on part throttle at around 3000 revs. It's possible to drive through it, but it's annoying. Did these cars ever carburate perfectly cleanly? Gut feeling suggests that a 1300cc engine with that much cam and 34mm chokes is never going to drive like a modern injected car. I should say, by the way, that I am very familiar with DCOEs, having several car equiped with them. 

 

We're trying to establish baseline settings for the carbs, but can't find a manual that covers these. Can anyone steer me in the right direction please. I'm also looking for a base setting for the screw arrowed in the picture. This doesn't seem to appear on any exploded diagrams. Any picures that I can find online show this as an undrilled boss. Should it be seated fully or screwed out several turns? What does it even do?

 

Any help would be much appreciated. Other than the flat spot, and the steering wheel on the wrong side, it's an exquisite thing to drive.

 

Many thanks 

 

Mark

Weber dcom.jpg

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Wallby

I have a tu24 head with dcom carbs (albeit with a different bottom end) that took me a long time to iron out all the flatspots. After changing many different jets I ended up with the stock main jets and I think some slightly richer idle jets.

 

The pump jet adjustment underneath the carbs can also have a big affect on smooth running.

 

From memory, I think those screws are air bypass screws. Don't hold me to this but they can be used to balance the carbs if they cannot be balanced using the main adjustment. If they balance up ok then these should be screwed tight. I may have a book with this detailed in, I'll have a look.

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DamirGTI

Seems like they all suffer from this "flat spot" at around 3000rpm , i did an full tu24 rallye engine rebuild for my mate 2 years ago .. that one also had this issue with "flat spot" jerky power delivery at mid revs .. which was really unbearable for road car . 

Additionally , someone fitted smaller jets which only made it even worse ... i tried a little bit bigger jets as an trial and error basis and it worked , after adjustment it ran smoothly all the flat spots and jerkiness disappeared .

 

Can't remember precise which jet numbers i fitted , need to dig my database to find out ... but , odds are that they may or may not work on you're 205 as each engine/carbs could be a little bit different .. i did the head porting and some other stuff too , thus i needed the mixture on "the rich side" anyways ..

 

And yes , it's really an interesting car to drive .. not as fast as the GTi , but certainly feels faster while driving ... much lighter on the front than the GTi . Plus i fitted 2.6 PAS rack on that car ,  from ZX 16v , which made the entire package even more fun to drive .

 

 

D

 

 

Edited by DamirGTI

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Thijs_Rallye

Start off with taking the carburettors apart completely, clean them thouroughly and renew all seals. Replace the throttle shaft bearings and seals as well so you basically have new carbs.

 

The rallyes I've driven didn't have any flat spots at all. Cold starts and cold idling is a bit finicky and that kinda goes with that type of car.

 

Also considering the age you'll probably will have to have the distributor reconditioned. The combination of the webers plus the advance curve of the distributor does make the engine happy.

 

I don't have time to translate it all now atm, but google can help ;) 

 

IMAG1681.thumb.jpg.71149515cda99de95e9391bd672644a9.jpgIMAG1680.thumb.jpg.1005fc9b9e95985d4f26591f70ee68fc.jpgIMAG1683.thumb.jpg.9fc3c90d8544f02eaee1bd37d0d53f64.jpgIMAG1682.thumb.jpg.df88da3d2f4ed67915d106cfdf95367e.jpgIMAG1683.thumb.jpg.9fc3c90d8544f02eaee1bd37d0d53f64.jpg

Edited by Thijs_Rallye

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