I finally got my DCD's in a state where I could mount them this weekend and I'm having quite a few problems getting them to run correctly. My main problem is the float level. I've got the specs for a stock DCD but the carb that I have is equipped with a grouse jet, rather than a needle seat. This makes the measurements for float settings useless, as the grouse jet is shorter than the needle/seat assembly. I think that I can set the close distance properly, but the opening is completely out of my control.

I'm also concerned about the emulsion holes on the main jet holders for the primary and secondary jets. It seems like the holes have been ovalled out, possibly by Rotary Engineering when they sold the kit. What effect would larger holes have? I would assume that they would allow more air to enter the fuel stream, leaning it out, but I'm just guessing. Is such a modification normal? For those of you that have DCD's, do your jet holders show evidence of modification to those emulsion holes?

Overall the car runs very poorly at the moment, with little poor idle quality, bad part throttle and cruise and no power above 5k RPM. About the only time it does run well is at about 50% throttle at medium revs.

I'm kinda at my wit's end, so any help would be appreciated.

 

Wish I could help

 

No problem, it seems I've stumped everyone.

 

They appear to be round in this pic I have - If I get a chance to this weekend when I go home, I'll pull one out and have a look at it for you.

 

The 2 sets of DCDs I have, 12A and 13B, have the same emulsion tubes in all 4 carbs, no difference between them. The holes are not ovaled out either. I believe the carbs I have are still stock since the main jet #s on both carbs have been ground off, presumably by RE.

I had the same problem setting my float levels. I then ordered the true Weber rebuild kits. Turned out the ***** for the grosse jets in the Weber kit are smaller than the ones that were in the carbs. That seemed to solve my flooding problem. They are very touchy to get set right.

You will need to find a wideband and get your main jets set, then maybe work on the e-tubes. I had no idea where to start tuning mine until IanS and I hooked up the wideband and took some test runs. Nice thing we found was the Holley e-jets that Carl and Sterling use on thier modified Nikkis also work as mains for the DCDs.

What porting do you have on your engine and do you know what size of chokes the carbs have? I may be able to suggest a range of Holley jets to start with.

Once the DCDs are set up, I'm quite impressed with them.

 

Stock porting, but I really have no idea what the venturi sizing is. I was assuming that it was as configured by Rotary Engineering, but so much is either changed or wrong with this kit that I probably shouldn't assume that anymore. I want to measure the inside diameter of the venturies, right? As for the ovalled holes in the jet holders, I'll see how the car runs. If it still runs like ***, I guess I'll have to order a set of new ones.

The testing has been sidelined for a while because one of the carbs had a damaged seat for the primary main jet and I had to use some JB Weld to patch it up. Tomorrow is the day to see if my patch did the trick or if I'm going to have to turn the carb over to the professionals.

 

You don't need to measure the venturi, the size is in raised numbers on the upper lip of the venturi. The 12A carb set I have has 25/32 mm primary/secondary venturi. Pull your main jets out of the sides of the fuel bowls and see if they still have #s on them or if they've been ground off.

 

All the jets have the numbers ground off, so I know that they are original from Rotary Engineering.

Except the air correction jets on the primaries, that is. I had to buy a new set of those because they were missing from the carbs. Those are 220's.

 

 

That kid cracks me up every time I see that picture.

 

On both of my sets, there were no air corrector jets in the secondaries. I think they came from RE that way but it's anybody's guess what porting the engines they came off of had. Something to consider. The primary airs are 200's in the 12A. Fwiw, I have no bog/lag when the secondaries kick in.

Keep in mind, my porting is based on RB's 1/2 bp porting template.

 

Ok, so I had the sucker running again tonight and did some fiddling.

As of now I'm unable to make it idle. No setting seems able to produce smooth operations below 1500.

What fuel pressure are you running? Could the wrong pressure affect idle quality?

Do you think that the modified holes on the main jet holders would also have an effect on idle?

Thanks for your help thus far.

 

Fuel pressure should be 4.5 psi. Make sure that the secondaries are fully closed and that the throttle and idle screws for both carbs are turned out the same # of turns. I've also noticed that it's easy for the accelerator pump piston to stick if the sleeve has any wear or if there is any debris/crud/varnish or whatever in the carb.

Matching the turns on the idle mix screws is easy since they are needle/seat screws and can be bottomed out, then backed out. The throttle/rpm screws are a bit trickier. You have to turn each one of those in until the lever under the fuel bowl just starts to move and match that movement between both carbs.

 

Thanks for the help, trochoid!

Hopefully later on tonight I'll have this sucker licked!

 

Update:

I noticed that the valley between the two emulsion tubes is literally filled with gas. This isn't normal, is it? The levels are so high that it's soaked the airhorn gasket with gasoline.

I'm thinking that my floats aren't sealing correctly...

 

Correct, air only, no gas in that area. it could be either needles not seating/sealing or the floats are set to high. When you have the engine idling, do you notice gas seeping into the throttle bores, primary/secondary, any of them?

That was the problem I had. Bought 2 rebuilds kits from Pierce Manifolds, part# 92.1025.05. That's the full rebuild kit with needles/seats, gaskets and filters. Instantly solved my problem, no more seepage. The 2 kits ran a bit over 50 bucks, well worth it. Now I just need to get my fuel pressure down to a consistent 4.5 psi before I can finish tuning. For some reason my fpr constantly sticks at 6 psi and I can tell the difference when it does.

Keep at it, once you have them tuned, you will be very happy with them. You might want to pick up a synchrometer too, that will help you get the duals balanced to each other. That's another tool I need to pickup.

 

I've got a set of needle/seats that I started to put in last night, but I ran out of time. Glad to hear that I'm on the right track! The carbs came with the grose jet setup, which has proven to be nothing but trouble thus far. Hopefully after I get the needle/seats installed and the floats set I'll be able to get this sucker to idle and run at a constant RPM without coughing and spitting.

 

When I installed the new needles/seats, the Weber ones are the gross jets that you sent me a pic of. Odd thing was, the ***** on the Webers were much smaller than the ones I took out. When I said earlier that the float levels are tricky to set, it's because of those *****.

Pierce does sell Weber tools, including those little rods to set the floats, iirc. You might consider buying them or find dowel rods that are 13.5 and 5 mm in diameter, then cut notches for the seams in the floats. The rods would make setting float levels a snap.

Did you find the venturi size #s yet?

 

I think that I've got it running now, thanks to some help from a local Weber guru.

My other question is, how do you have the brake booster hooked up? There is a threaded port on the passenger-side rear of the manifold, but it's too close to the transmission for anything other than a plug to thread in and clear the bellhousing lip. There is another port on the top center of the manifold between the middle runners that I'm assuming would be for attaching a PCV valve, but I've got the brake booster hooked up there now so that I can stop.

I don't suppose I could get away with running a breather filter on the center housing nipple, could I?

 

I used a Uni-Syn many many years ago. Don't bother. The best thing to use is a length of hose to listen to the carbs.

 

Matt popped by today to show off the carb install. Fokkin' clean engine bay! It's basically just the keg with an intake manifold, carbs, and a header.

 

Both of my intakes have a brake booster barb on the rear runner. Neither have a port in the center. Rear one works fine for me.

 

I must have a different revision/version of the kit then.

In any case, the car seems to be running quite well. These carbs are very deceptive, when I first drove the car I didn't think it was any faster.

It was kinda disappointing, actually.

Then I did some pulls against my buddy's MkII Supra, and I was able to keep even with him up until 120 km/h without breaking a sweat (shifting at 6800). Before the carbs, he used to be able to stomp me after 1st gear.

So yeah, they work well.

There isn't any feeling of sudden acceleration anywhere in the power band, just a smooth pull to redline and beyond, the first time I've actually felt my car make power past 6500 RPM. These dual progressive Webers are a fantastic upgrade and didn't sacrifice any of the drivability of the stock carbs. At light and medium throttle, they feel just like stock, smoothly accelerating and cruising at all RPMs.

 

Good to hear you have them working well. Imho, they are the best carb setup for both street ability and power. I'm not even done dialing them in yet and am very pleased. I didn't think there was anyway to make a 1/2 bp street able, but these carbs seem to do the trick and that's no small accomplishment.

When you finally get it to where you have it dialed in, post the specs on your jetting. If you get a chance to take it to the 1/8 or 1/4 mile track post your times. I hope to be hitting the 1/8th mile in the near future, need to find a laptop to take along with me.

 

I don't usually drag race, but I may make an exception in this case, if only to try and determine how much power I'm actually making. Jetting-wise, everything is as delivered by Rotary Engineering, except the air bleeds on the primary emulsion tubes. There is a dyno in town, I may have to pony up some cash for a few pulls and see what the power really is and where the carbs may be running rich/lean.