Calibrating and tuning dual Weber DCD's
08-09-07, 11:06 AM
#51
I have a set for 13b 4port. For my REPU.
Pierce Manifolds is the best place for parts. And they sell excellent linkage. JPS rods, bought a set real easy to use.
Use the carb syncher from summitracing.com. It has a rubber mouth and a swept dial. Have to remove the stacks to use it but much much more accurate then uni-syn.
The primary throtle shafts tend to wear, letting air in which screws up the mixture and synch. There are brass bushings that I've replaced but they are not designed to seal - only the throttle shaft seals.
Pierce Manifolds is the best place for parts. And they sell excellent linkage. JPS rods, bought a set real easy to use.
Use the carb syncher from summitracing.com. It has a rubber mouth and a swept dial. Have to remove the stacks to use it but much much more accurate then uni-syn.
The primary throtle shafts tend to wear, letting air in which screws up the mixture and synch. There are brass bushings that I've replaced but they are not designed to seal - only the throttle shaft seals.
08-09-07, 04:45 PM
#52
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i was told that mine suck air through the shaft and that it would cost less to buy a new carb than to try and have them line bored to correct the problem... the problem being that vacuume doesn't scavenge enough for the idle jets to work correct... so i just idled it higher so it doesn't idle lean... it is a little on the high side for idle but i don't care, as long as it doesn't hurt the motor...
08-10-07, 11:38 AM
#54
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have you done this to yours??
(man do i feel bad for jacking this thread... but if you don't mind i would like to keep this thread alive longer because we are starting to find a few more people w/ dcd's)
(man do i feel bad for jacking this thread... but if you don't mind i would like to keep this thread alive longer because we are starting to find a few more people w/ dcd's)
08-10-07, 02:20 PM
#56
My wife bought me 2 RX-7s
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You're not jacking the thread at all, this is all good information. I don't think mine are leaking anywhere as I've done quite a few tests with WD-40 and found no vacuum leaks anywhere. I think my problem is a combination of incorrectly set float levels and fuel pressure variations. I think my pressure gauge is less than accurate. 
It's certainly harder to keep two carbs in tune than it is one, but this setup in particular has great low and mid-range characteristics while still allowing the engine to breathe at and beyond redline. They're a very good upgrade from stock, IMHO.
It's certainly harder to keep two carbs in tune than it is one, but this setup in particular has great low and mid-range characteristics while still allowing the engine to breathe at and beyond redline. They're a very good upgrade from stock, IMHO.
08-14-07, 04:29 PM
#57
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Morey987- i paid $400 for mine years ago... and that still seems to be the going rate, unless someone else says different...
DriveFast7- hey did you bore your carbs and fit the oversized shafts yourself???
MosesX605- thanks man!!! i really like my downdrafts and i haven't acually seen anybody else with them in person... ever! has anyone else seen them on someone elses car??? i think i would trip over myself if someone popped the hood and hadden't told me ahead of time that they had this setup...
DriveFast7- hey did you bore your carbs and fit the oversized shafts yourself???
MosesX605- thanks man!!! i really like my downdrafts and i haven't acually seen anybody else with them in person... ever! has anyone else seen them on someone elses car??? i think i would trip over myself if someone popped the hood and hadden't told me ahead of time that they had this setup...
08-14-07, 08:37 PM
#58
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Morey987- I drove two cars back in the late 80's with this setup and I can honestly say I never drove a smoother ported engine, on the bottom to mid range, until fuel injection started being available for custom setups. I think the main reason more people don't use these setups is that they were no longer available once Lake Cities Rotary or Rotary Engineering (I can't remember who made them) went out of business. I also think I remember reading somewhere that the reason Mazda went with a 4 barrell carb with small primaries was for the same reason. Folks modifying the Nikki carbs successfully for much greater flow these days might also explain why people are not using the dual DCD setups as much as the Nikki keeps in tune better. Tuning dual carbs is not hard but it does take a little more work and few people have much experience with this these days. Sure my Corvairs have dual carbs but they were made in the sixties.
Cheers,
Peacedog
Cheers,
Peacedog
08-23-07, 05:04 PM
#60
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http://www.youtube.com/watch?v=DkN2omI6y4o
i just found this and didn't know if we had heard from this guy or not... does anybody know this car????
i just found this and didn't know if we had heard from this guy or not... does anybody know this car????
08-23-07, 05:06 PM
#61
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http://www.youtube.com/watch?v=8FQBd92UyTU
didn't know if anyone cared to see my car run on the dyno or not but here it is...
didn't know if anyone cared to see my car run on the dyno or not but here it is...
09-04-07, 08:13 PM
#63
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It's alive after 22 years of storage! The R.E. engine came to life today in a new body. My friend sold me this engine with the 36 DCD twin carb set up after deciding to go with a Grannyspeed conversion for his SA. My biggest problem was finding/machining the parts he lost while cleaning the carbs years ago. After all the fabrication and modification to get it into my FC it started within 5 seconds - amazing after all this time. ( Don't flame me for having an FC, my heart has and always will be with the SA/FBs. ) He just sent me some of the original literature which I will scan and post so you can enjoy reading a little history.
Right out of my garage it runs very smooth from about 2500 to redline with no stumbles or flatspots. Below 2500 is another story, it seems to be way too rich. I set both mixture screws at 1 turn off of seat and will begin again tomorrow to see if I can dial it in. Timing is set at about 1*advanced for the leading. I'm not sure on the split yet but it used to be 10* when I had the dizzy on the other engine. I am also running Jeff20bs three igniter setup. If anyone has been down this road let me know if there are any things to try first. Thanks.
Right out of my garage it runs very smooth from about 2500 to redline with no stumbles or flatspots. Below 2500 is another story, it seems to be way too rich. I set both mixture screws at 1 turn off of seat and will begin again tomorrow to see if I can dial it in. Timing is set at about 1*advanced for the leading. I'm not sure on the split yet but it used to be 10* when I had the dizzy on the other engine. I am also running Jeff20bs three igniter setup. If anyone has been down this road let me know if there are any things to try first. Thanks.
09-05-07, 07:46 PM
#64
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I put my AFR wideband on it today and confirmed my suspisions. 3K holds at about 12.5 and stays that way if gently accelerating. WOT produces put to 13.5 and deceleration is 14 to 14.8. The idle at about 1500 dips to 9.6 to 10.0. I tried leaning the mixture screws but the top end numbers got too lean with little effect on the idle. I shot some great fireballs into the yard and scorched the grass. What is the next step? I have some pics and will get the original Rotary Engineering literature posted soon.
09-05-07, 09:06 PM
#68
go down one size on the idle fuel jet. be sure to measure it first with a jet gauge as RE drilled out several of the jets in there. Mine said 45 for idle fuel but my 45 would not go in there.
Oh, and my DCD setup will be up for sale very soon just need to take pics and come up with a price. Includes custom airboxes and new K&N air filters, new linkage rods and all rebuilt with new needle & seats and 2 carb synch tools FTW. I'll bring it to Seven Stock for pickup.
Oh, and my DCD setup will be up for sale very soon just need to take pics and come up with a price. Includes custom airboxes and new K&N air filters, new linkage rods and all rebuilt with new needle & seats and 2 carb synch tools FTW. I'll bring it to Seven Stock for pickup.
09-05-07, 10:09 PM
#69
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OK - that sounds good. I presume Pierce Manifold has the necessary jets. I also have two 36 DCDs (non RE) from a Fiat. Do you think the jets from them would be closer to what I need? Thanks for the help.
09-08-07, 04:52 PM
#70
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Turns out the idle jet is standard and not drilled. It is a 45(.018") as were the others from the Fiat. 40 is the smallest they ever made which boils down to a .016" hole. I am machining a 35(.014") set now to try in it. Once I get the bottom less rich I should be abble to sdjust the rest with the mixture screw. Mid range to top end a a little rich(2.5-13.3AFR) but it runs great.
09-09-07, 12:09 AM
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the dyno showed mine run rich on the bottom and sort of rich on the mid and high end... i posted a new thread in the performance section to see if i could find an adaptor for my twins intake... i would like to install my twins (currently on a 12a) on a 13bre motor that i have currently sitting on the engine stand... i have plans to turbo it in the future w/ fuel injection, but in the mean time i would like to put it in the car and run it... i already have everything i need to drop it in, but any help with the adaptor info. would be a big help!!! i know that i have seen adaptors in the past somewhere, but i can't remember where i saw them...
Last edited by dayton; 09-09-07 at 12:11 AM. Reason: fragments
09-10-07, 06:22 PM
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Would you post the scanned manual that you have? This carb set up is just too nice to let die. When I get done jetting my RE13b I will post the jetting so others can have a starting point. I have two spare 36 DCDs, bought off eBay, that I have been using for comparison and parts.