Dcd Vs Twin Su Carburetors

[rob83ke70]

A little bit of background:

 

I currently have a worked 4k in a ke55 (eventually going in a ke30 rally car) which has a 280/286 degree duration camshaft, has been balanced, had flywheel lightened to 5.6kg, regraphed electronic distributor, thermofan fitted, 10.7:1 static compression ratio, 4-2-1 extractors and heat shield, 2" exhaust 4.3 ratio diff, 195/60r14 road tyres OR 185/65r14 rally tyres, and a lynx manifold with twin 1.5" hs4 su carburetors with needles that the carburetor guy said would work well....

 

issues: does not idle consistently - does not return to idle consistently. Have spent unbelievable amount of hours syncing carburetors and fussing over things. seems to be reasonable at the moment, probably need to fuss over it some more... seems to be really REALLY fussy over vac leaks from throttle shafts, I sent them to be rebushed and the carburetor guy said they were nearly new and he put new butterflies in them instead (they were worn).

 

Performance seems to be ok most of the time, it revs to 8000rpm, idles lumpy and doesn't do anything exciting below maybe 3000rpm give or take. It can seem a little boggy at wide open throttle with low revs (less than 3000rpm).

 

Air filters vibrate and crack, filters don't last too long (rubber splits etc). The car runs twin pancake type paper air filters made by redline, it does a lot of dirt events so I'm reluctant to use foam filters.... I am considering twin velocity stacks and foam filters though - undecided.

 

now for the recent developments:

 

I have purchased a weber 32/36 DGV carburetor, and it came with two weber 28/36 DCD carburetors. I am putting the DGV onto a Toyota Dyna with a 4y 2.2lt engine, and picked that because it is common and you can buy an air plenum for a cold air induction system readily for this carburetor. Anyway, I now have TWO weber DCD's, and I was wondering (just a thought at this stage) about the possibility of putting one with an adaptor plate onto a 4k manifold and replacing the twin SU's with it. I've spent a lot of time effort and money on the SU's so as I said before, this is just a thought and it might not eventuate yet...

 

The question is, will it be a performance improvement to go with the DCD? I know there are a few people here using DCD carburetors on 4k or 5k engines, and there are a few people with SU's. The SU's look much cooler, nothing beats the look of twin carburetors IMHO! However, I am considering this to increase reliability and possibly performance.

 

From memory, the reasoning was that with the standard manifold and a DCD the air had a longer straighter shot at the inlet valve (after the initial turn at the base of the carburetor) whereas the lynx manifold (very very short thing!) had a nasty "kick" in the air path where it joined the inlet ports, which was too close to the valve for the air speed to recover...

 

I'm after some opinions and thoughts on this! I'd love to get the car more reliable (less time playing with carburetors to make them work right!) and more consistent to drive, and a performance increase would be really really good too!

 

Car currently uses 7.75 litres per 100km when driven on the highway too.

 

Robert.

[Felix]

If you have a DCD, just try it.

 

I'd hunt around for a 24-25mm primary venturi on your 4k. Once you get the jetting optimised they are set and forget carbs.

 

Really cool the way you can change the idle and main jets in them without having to take the top off (you need a rag to soak up the fuel from the float bowl when doing the mains).

[altezzaclub]

Yeah, give it a go bro!

 

Its the only way to learn really. ..and I know you haven't got a lifting pin on one carb and who knows what else... ;)

 

When you have them off we can go over them with the pair I've got sitting on the shelf and make sure they are 100%

 

The richer needles sorted the over-run problem I was having and John Kane said the residual it is from the cam as it gets down under 1500rpm. It idles happily at 900-1000 and doesn't die when you turn the headlights on.

 

I ran to Sydney at 6.4L/100 on the lean needles, but I haven't got a comparison yet. It won't be as good, I'm sure. What needles do you have in there? I've now got a couple of spare sets around...

 

The air filters need to be replaced by an air box. Ugly but efficient! The oiled foam socks should be OK if you want to use them, that's what we used on motor cross bikes.

 

How about machining up an adjustable cam timing wheel. You could move the power down 500rpm if it worked well.

 

 

Nah, what the hell! get down to the motorcycle wrecks and I'll give you a hand.. quads!

 

http://www.rollaclub.com/board/uploads/mon...40263_thumb.jpg

[rob83ke70]

plan of action after consultation with the other half (who drives the ke55):

 

Going to try and probably go with the DCD and a remote mounted airbox to get cold air. Going to redo the exhaust so its a little quieter as well.

 

Going to install engine and good bits into the ke30, not going to stress about the cage, and we will use it as a daily driver as ke55 shell is too rusty and has a few too many hard k's on it...

 

Scheduled to happen AFTER the toyota dyna is back in one piece and on the road again...

 

Robert.

[rob83ke70]

dumb question: where do I buy a venturi for a dcd? can't find anything for a dcd (plenty of dcoe stuff) on the internet. is a local parts place going to laugh at me?

 

Robert.

[snot35]

I've found it takes digging. If I recall www.dellorto.co.uk carries DCD stuff, however to find it you really need part numbers. Search the internet for Weber DCD and you should be able to find an exploded parts diagram. Then search using the weber part number. There are a few places around that do them, but it will most likely be mail order from OS.

[rob83ke70]

email to dellorto uk sent.

 

another dumb question: how has everybody got the throttle cable hooked up on their weber dgv/dcd etc? they all come with a funny looking U shaped bracket that I can't work out and the throttle wheel turns the wrong way.

 

How does everybody have their choke hooked up? last time I ran a weber I had to run the choke cable the whole way around the engine compartment in order to not put tight u turns in it and make it acceptable to pull on and off. Any other way of doing this?

 

Robert.

[rob83ke70]

doesn't seem to be a lot of pictures on the internet of throttle cable setups d'oh!

[Felix]

My original DCD weber was previously fitted to a Mazda 1300. Think the throttle wheel is a modded item from a stock Mazda 1300 carb.

 

I moved the cable from the heater tap (which was removed from the car before I got it) to the choke linkage on the DCD.

Edited June 23, 2010 by Felix

[rob83ke70]

you can buy a kit from redline for hooking up the throttle cable to a weber dgv or holley 180. The picture in the book showed a holley 180.

 

if only linkages were that easy to come by for a pair of SU's!!!

 

Robert.

[altezzaclub]

I have a jar of various carb linkages and stuff if you want a look through it...

 

If the quadrant rotates the wrong way turn it upside down.

[bLinded_]

I used the stock throttle wheel off an Aisan carb, and 'modified' it to mount to the DGV Weber throttle shaft. Wasn't overly difficult to do, but you will also have to make a little bracket to mount off the tappet cover to brace the throttle cable. I would put up a photo of it, but, I honestly can't find the photos of it anywhere, and have since done away with the DGAV carby. Another member on here shauns ke30 has/had my old setup. You may be able to find out more if you ask him to take a photo of it etc. :yes:

Edited June 23, 2010 by bLinded_