Weber DCOE's installed | Initial impressions

[T-Bone028]

Finally made the switch from SU's to triple webers.  Here's the basics:

 

3.1L with 470/280 cam,header, exhaust, MSD, etc.

 

40 DCOE 2's:

33 main venturi

4.5 aux venturi

130 main

180 air

50F9 idle

F11 emulsion

55 exhaust bleed

 

Here's a before pic with the SU's

 

Started rebuilding the carbs roughly a month ago with a couple of mis-steps here and there.  The carbs looked like they hadnt been touched in over 20 years, and they were filthy with dirt and dried gas.  Between the 3 carbs, I went through about 6 cans of carb cleaner and I still thought they were dirty.  Bought almost all of my replacement parts from Pierce Manifolds...great vendor.  For those who have never rebuilt a DCOE, heed the advice you've read....take your time and dont force anything.  I broke a pump rod due to trying to force a stuck accelerator piston and as I was checking my floats I noticed one of the support arms that holds the pivot pin was cracked.  It broke off completely shortly after.  Hopefully the gas proof "JB Water-Weld" I used to put it back in place will hold over time.  

 

As far as the actual rebuild, it was pretty easy.  Just matched up where the gaskets should go, and referenced the Weber manual.  I took my time to set the floats per spec to 8.5mm/15mm, turned out all of the idle screws to 1.5 turns from fully seated, and lined up the throttle plate edge with the first progression hole on each carb.

 

Regarding the actual installation, sprayed all the manifold bolts with PB blaster over the past 3 days and went through the tedious process of undoing all of the bolts.  I couldnt see a way to get them all out with anything other than a wrench and 1/8 inch turns at a time...there just wasnt any room!  That or I need better tools.

 

Got the SU's out and put in a new intake/exhaust gasket and put the redline intake manifold on.

 

After getting all of the bolts torqued down, things started moving a lot quicker.  I bought the plastic anti-vibration mount with O-rings, but after getting the 3rd carb on, I realized that it would be impossible to actually run the air cleaner I planned to use due to interference with brake fluid reservoirs.  So had to take all the carbs off and put on paper gaskets and re-install.  Hopefully it wont be an issue.  Ran the fuel lines, re-attached hoses, temporarily mocked my throttle cable set-up, and crossed my fingers.  Primed the fuel pump and started checking for leaks.  Found leaks and tightened everything back down, and started cranking.  It took about 4-5 minutes of cranking the engine before it wanted to fire up.  Kept at it and she came to life!  couple of blips of the throttle and it quickly settled to a steady 1000 RPM's.  Success!  Watched it smoke off all of the PB blaster and let it run for about 15 minutes.  Checked my fuel pressure gauge and was at 3.5 psi, and my AFR was fluctuating at about 10.5 - 11 at 1000 RPM idle (using an AEM UEGO w/b).

 

Revved her a few times to hear the glory, and noticed that I was occasionally getting what sounded like a misfire.  A couple of other blips, and I would get a backfire out of the front carb, on the rear barrel.  It happened twice, and was something I couldnt replicate consistently.  I'm going to try replacing my spark plugs in the next few days and start paying attention to how they look.  Hoping to actually drive the car tomorrow.  I still have yet to sync the carbs, tune anything, or completely address my throttle linkage...I probably should do all of those things...but I just want to actually drive her and see what its like under load!

 

My initial impressions, this is gonna be a hell of a "project" with a lot more work to go!.  I was hoping I could get the carbs on the car for about $500.  I got the carbs, manifold, and linkage from the PO with the car...with all the other misc pieces and "while I'm at it" stuff...so far I'm about $1600 in!  A lot of the cost came from air horns and new main venturi's (carbs came with 30's), but there were a lot of little odds and ends that added up quick!  

 

I still have to install my heat shield, dial in my throttle cable / linkage, and figure out my ignition timing.  For those thinking about going to triples, you have to admit they look awesome.  Now back to re-reading the Weber FAQ for the 15th time.  

 

[BluDestiny]

Same thing happened to me. I got them rebuilt by top end performance and as soon as I got them running they would randomly spit fire out the air horns. Never figured out why, and it eventually happened less and less as I got more miles on the engine. 

 

I believe I got my carbs for $650 with everything, but after the rebuild, ITG filters, air horns, heat shield, I was at around $1500 also.

 

Triples just look right in the bay of an s30 and the sound is intoxicating 

[310z]

Having good linkage is a key to keeping them in sink. The O-ring seals are there for anti-vibration and to keep heat from transferring from the head into the manifold, you need them. You can view my build thred to see how I got around the air cleaner issue. ITG makes a good option although is is pricey. http://forums.hybridz.org/topic/83577-the-build-of-a-240z-by-310z/

[duragg]

Sneezing = Lean.

[T-Bone028]

I wonder if the lean sneeze is due to the brake vacuum assist valve being place on that runner...I would imagine no, since it's not really pulling extra air from the vacuum canister, but maybe I'm wrong? Any thoughts?

 

310z...Regarding the anti-vibe mounts, i would have liked to put them on, but short of going to stack filters or a lower profile aircleaner, paper gaskets will have to do until I figure something else out for clearance. Your Z build looks great btw.

 

Bludestiny...couldn't agree more about the sight of triples. With a stroker, I just didn't have the bling bling vroom vroom impression with the SU's. Don't get me wrong, I was happy w the SU's...but triples are just the wow factor I wanted from an aesthetics standpoint. Here's to hoping that the performance is as awesome as I've read!

 

Day 1 of tuning starts today!

[srgunz]

The Weber thread in the FAQ section will help you a lot on

getting it to run the way you want. You may need to change

 out that idle jet for a larger one.

[steve260z]

Great. I'm right behind you. Re-jetting the carbs, got a couple of pump jets "unstuck" and drilled out an exhaust valve. Currently do a mock set up with the billet linkage.

My jets are different and I'll give you my feedback. Stroker as well. Off the top of my head, my main jet is 145. Chokes are 34, F2 emulision tubes and can't recall the rest. What about the pump jet size?

[T-Bone028]

I believe my pump jets are 40 or 45, but from what I understand, it can be more cost effective to play with the exhaust valve at the bottom of the bowl, since there are only 3 of them. I purchased "0" exhaust valves, but decided to wait on messing w them.

 

After being honest with myself, the car is slower w the webers in it's current state of tune (which is untuned) compared to the SU's.

 

So, bought a timing light and going to try and see where I am this week. Hopefully, my timing isnt advanced enough and that's why it feels a little sluggish. Got to check for vacuum leaks too just in case. After that, I'll get back into jetting.

 

Let me know how your endeavor turns out! Could be fun to compare notes.

[josh817]

MY DCOE's don't have vacuum ports just above/in front of the throttle plates. This meant in order to run the advance I wanted past 3000 RPM I had to mechanically crank the dizzy or run full vacuum advance at idle. The dizzy has two advance mechanisms, one mechanical where it flings out weights as it spins faster, and one vacuum so with more vacuum you get more advance. Some emissions dizzies are the other way where they retard with more vacuum. Nissan might not have done this but I know some British companies did.

Here is what I am getting at; I could never get my idle below 1200 because I had to run so much advance. If your dizzy is the type that advances with more vacuum, you need to hook up somewhere between the throttle plate and the air horns. This way when you crack the throttle, that vacuum port will start to see a vacuum signal. If you hook it up to the manifold like your brake booster, you see vacuum all the time and actually at 100% throttle, might not see any vacuum at all. With that being said, if you find (again I don't know if Nissan did this) a dizzy that retards with more vacuum, then perhaps you try to hook that up to the manifold directly.

I honestly can't remember if the manifold vacuum drops with increased RPM's. I may play around with that on my truck, you can just use a regular vacuum gauge.

PCV and brake booster go to manifold, dizzy needs to go to carb. Though, like I said before, I haven't seen any way to do this on DCOE's. On my truck I run a DGV (downdraft weber) and it specifically has a port just ahead of the throttle plate so it reads 0 at idle and as the plate cracks open you get vacuum. Double check your vacuum signal... When timing, you can test your dizzy by pinching the vacuum hose. If you disconnect it and don't plug he port on the manifold the RPM will just increase due to the vacuum leak. Can also plug that port temporarily and while the motor is running at idle, suck on the hose to the dizzy. Granted, it'll make you blue in the face but it should change enough to see.



I've always had this problem with my DCOE's:

Had an exhaust leak on EVERY port which is way it ticks and pops so bad. I never fixed my vacuum/dizzy thing I just explained either. The car ran, left it at that. In freezing conditions I never need a choke hook up either. Pump the pedal, Weber's have accelerator jets. Do it like 3 full times before you start and it should do just fine! Goodluck Edited May 14, 2013 by josh817

[T-Bone028]

Hey Josh, nice paint color!  Regarding Vacuum advance, I do not believe it applies at WOT, and is generally a fuel economy thing.

 

Currently, I have the block breather vented to atmosphere with a filter because I havent decided on location for a catch-can yet (so no PCV), and my brake booster is attached to a port on runner #2 (still need to replace hose and check for vacuum leaks because the same carb barrel is sneezing/spitting/coughing/ruining my life).  Vacuum advance is unplugged and the nylon hose is just hanging in the engine bay because I havent found a plug to fit on to the distributor I want to use yet.

 

I've been searching all day on setting timing, so just waiting on my timing light I order today so I can get started.  So basically, the only thing I'm happy about is that I got the car running and it sounds/looks cool.  Still need to make the heat shield I bought from ZCCJDM fit (it doesnt, at all, in any way, requires modification) and then start throwing different jets at it to see if anything makes it happier.

[josh817]

Hey Josh, nice paint color!  Regarding Vacuum advance, I do not believe it applies at WOT, and is generally a fuel economy thing.

 

Currently, I have the block breather vented to atmosphere with a filter because I havent decided on location for a catch-can yet (so no PCV), and my brake booster is attached to a port on runner #2 (still need to replace hose and check for vacuum leaks because the same carb barrel is sneezing/spitting/coughing/ruining my life).  Vacuum advance is unplugged and the nylon hose is just hanging in the engine bay because I havent found a plug to fit on to the distributor I want to use yet.

 

I've been searching all day on setting timing, so just waiting on my timing light I order today so I can get started.  So basically, the only thing I'm happy about is that I got the car running and it sounds/looks cool.  Still need to make the heat shield I bought from ZCCJDM fit (it doesnt, at all, in any way, requires modification) and then start throwing different jets at it to see if anything makes it happier.

Thanks! I was thinking the timing could be the reason for the lack of power so far, the tune as well obviously! Should be around 33-36º full advance and that is with vacuum advance. You will see that if you want to get that type of advance you are going to have to run high advance at idle unless you find a vacuum port in the correct location.

 

Lets just say you can adjust the advance infinitely by twisting the dizzy, then lets say mechanical advance increases that number by 10º, then lets say another 10º for vacuum advance.

 

Traditionally I would twist the dizzy to either set my idle, or set my total advance. Usually I would go for total advance and whatever the idle is just accept it. So lets say I set it so idle is 12º, thats strictly twist on the dizzy and some mechanical. Off idle, you get full mechanical so you're now at 22º. Above 3000 RPM you should be getting all your vacuum advance putting you at 32º. For this example we say we wanted our max to be 32º.

 

Now if I don't hook up advance, the only way I can get my 32º total is to twist the dizzy and set my idle at 22º, which then the mechanical takes up the last 10º. If I hook up the vacuum directly to the manifold so I am getting max vacuum at idle, well... I get 10º right away from vacuum, I could twist the dizzy to get another 2º so I have my 12º at idle, and then get another 10º from mechanical but that's only 22º total. The only way to get 32º in this case is to run 12º by twisting the dizzy and then you automatically get another 10º. Either way you are getting too much advance at idle however without it, you don't get full advance and advance timing has a lot of power potential in it!

 

My Z reaped the consequences of having more advance at idle, so I could get my full 36º that I wanted. With the idle screws fully backed off the stops on the carbs, I still only idled at 12-1400.

 

Setting the timing, I think factory calls for 12º at idle and makes no mention of max advance. I cranked mine up more to get the max I want but you can test your limits by twisting the dizzy, giving it more advance; the idle will keep going up until it peaks and drops back down. At that point, back the dizzy off a little. Go for a drive, load the engine down, listen for pinging. Do it again when its real hot outside, listen for pinging, and when you shut her down make sure it doesn't run on/diesel. If it does, back the timing off until it doesn't occur. I think you will find that you will be around what the factory calls for anyway. For my truck it calls for 12º but in the Texas summer it tends to diesel when I shut her down so really I'm only running like 15º at idle even though I could crank it further before the idle drops off.

 

I'm sure you already know this.... I typed all this because its late and I can.... For what it's worth, at the track most of the dudes don't run vacuum advance, subsequently the advance is cranked so high the motor is hard to start (you know when you crank it over, only cranks over once and won't go anymore, that's too much advance) so they have the 12v to the coil on a toggle switch. This way they can get the motor spinning up and then flip the ignition.

[Lazeum]

Power on engine is done with clean & efficient combustion at the right time. Timing is key!

If you have poor timing management, you're not going to use full potential of your build. DCOE or SU, it doesn't matter. With a stroker (so $$$$ invested), it is a waste not to invest on something good to manage timing.

- Either you get a dizzy recurved to proper specs (do you know them? ) with no excessive shaft play or wear in your system, of course! Mallory Unilite allows it but it costs some money.

- or you go with locked mechanism and timing management such as MSD AL2 system. You can play with timing with the box.

- or distributorless with full timing management - Megasquirt, Megajolt, Electromotive XDI, etc.

 

For "race engine", you're only focusing on WOT (intake fully opened => Intake pressure = Patm, so no vacuum). What matters is Max total timing. Good Idle timing is also good to have while you're waiting to go 

 

For street engine, where WOT is only a part of the use of an engine, the lack of vacuum makes the engine burn air/fuel mix too late since mixture will burn slower.

2 choices to overcome this situation:

- You run richer AFR - this is what you do with recurved dizzy with no vacuum advance. Fuel economy gets bad.

- You increase advance timing - this is what stock dizzy with vacuum does, this is what distributorless system with full timing management can do also. Engine efficiency is best.

 

Timing at idle should be set where engine run best. You should only limit the amount of air going inside the engine, you should set AFR where engine runs best, you should set timing where engine runs best also. Best means here  most efficient combustion.

With regular dizzy with no vacuum advance, it means you can get your dizzy a little loose, make the engine run and turn slowly the dizzy by hands until you've reached max rpm.

 

 

To get back on DCOE, you should tune first idle, it should run smooth first. With 50f9 & 33mm chokes, you shouldn't be that far off. This is what I'm running with L28 with head job & 32mm chokes.

You should also check everything on the carbs: fuel bowl level, shape of jets, etc.

When I purchased the Z with Webers, they were supposedly fully rebuilt but fuel level were not even & in specs, needle valves were shot & crushed (so one needle jet never got closed = fuel level never stop raising with fuel flow), idle jets were having grooves at taper, etc. I've made the engine running "good" before I noticed all the defects, I had to start again from scratch.

 

To set idle, there's 2 methods:

- get AFR at 14:1 or so with a wideband

- use best lean idle method - I've run this one with good results.

Edited May 14, 2013 by Lazeum

[ram75280z]

Honestly T-Bone028, 40DCOEs are woefully inadaquate(truly not better than the SUs) for the motor you have, particularly with 33mm chokes. But, the flow on them is going to max out with even 34-36mm chokes anyway and still not be anywhere near as good as 45s with the same size chokes. It really needs a set of 45s with at least 36mm(really 38mm) chokes to make the power it's capable of making. Naturally you need to have the timing set up relatively close. Any of the stock distributors set to around 14 degrees at idle will give you 32-35 total mechanical advance. Which is going to be about right, with your cam, depending on your compression ratio.

 

With the cam you have, which I assume is a 270/280 not a 470/280, a 3.1 should make peak power around 6300RPM. But with 33mm chokes, it will peak at around 5600RPM. Some folks think that they will save some bottom end power by putting smaller chokes on their engine. But, all they are doing is shortening their operating range. With a cam of 270 duration, or more, it's not going to make good power below 2200RPM. So, if it's not going to make power until around 2200RPM and peak at 5600RPM, that's 3400RPM of really useful operating range. Or 4000RPM if you take it to 6000RPM or so. When you could have 2200RPM to 7200RPM= 5000RPM. In addition, it will make A LOT more power!  The ONLY thing that will make any difference at all, for the low RPM range, is if you have the ovelap reduced on the cam which I recomend anyway.

 

If you don't want to go through the trouble of getting 45DCOE carbs, I would recomend getting a new cam that is made to peak around 5750-6000RPM. I think you will find that it makes the most power, for the least amount of money, with those carbs and the rest of your setup, and the engine will have a VERY strong low RPM range.

Edited May 14, 2013 by ram75280z

[310z]

Honestly T-Bone028, 40DCOEs are woefully inadaquate(truly not better than the SUs) for the motor you have, particularly with 33mm chokes. But, the flow on them is going to max out with even 34-36mm chokes anyway and still not be anywhere near as good as 45s with the same size chokes. It really needs a set of 45s with at least 36mm(really 38mm) chokes to make the power it's capable of making. Naturally you need to have the timing set up relatively close. Any of the stock distributors set to around 14 degrees at idle will give you 32-35 total mechanical advance. Which is going to be about right, with your cam, depending on your compression ratio.

 

With the cam you have, which I assume is a 270/280 not a 470/280, a 3.1 should make peak power around 6300RPM. But with 33mm chokes, it will peak at around 5600RPM. Some folks think that they will save some bottom end power by putting smaller chokes on their engine. But, all they are doing is shortening their operating range. With a cam of 270 duration, or more, it's not going to make good power below 2200RPM. So, if it's not going to make power until around 2200RPM and peak at 5600RPM, that's 3400RPM of really useful operating range. Or 4000RPM if you take it to 6000RPM or so. When you could have 2200RPM to 7200RPM= 5000RPM. In addition, it will make A LOT more power!  The ONLY thing that will make any difference at all, for the low RPM range, is if you have the ovelap reduced on the cam which I recomend anyway.

 

If you don't want to go through the trouble of getting 45DCOE carbs, I would recomend getting a new cam that is made to peak around 5750-6000RPM. I think you will find that it makes the most power, for the least amount of money, with those carbs and the rest of your setup, and the engine will have a VERY strong low RPM range.

 

That is good information. I would say spot on. I did not realize he was installing 40s I thought he was discussing 45s. I had to go back to the top and re-read.

[T-Bone028]

So finally got some time to play with the Z a little bit.  So you know how everyone says "Webers like a lot of initial advance"?  Well guess what, webers like a lot of initial advance!  I received the timing light I ordered and checked my timing this afternoon.  At idle, my timing was currently set at about -6 degrees without vacuum advance, which makes sense (I disconnected vacuum advance when I installed the triples).  I advanced the timing to about 13 degrees and watched the RPM increase from 900 to 1500.  From what I understand, this should put me at about 31-32 degrees total advance (really wish I shelled out the extra $25 to get a timing light with an ignition advance dial!). I gave it a couple of revs to see if I heard anything odd....my "spitting" that I was observing from the front carb on the 2nd barrel disappeared.  

 

Decided to take her out for a spin and....dear god, I thank the italians for my webers!  I run 245/50/15's in the rear and from about 15 MPH, I was losing traction when I stomped the throttle, and getting a little loose going into second!  I have a wideband installed, and I didnt even have the time to look at it through the rev range because I was too busy making sure I didnt crash the car or miss a shift.  The car was screaming through the rev range as soon as quickly as I was shifting gears!

 

I was running out of time and have not had a chance to start really tuning and sychronizing the carbs. Next step will be to try to lower my idle to 1000 RPM.  Currently I have 50F9's in the 40 DCOE's at 1 full turn out from fully seated.  I think I'm going to need to try out my 55F9's (Thank you LeonV) and start tuning the idle from there.

 

Honestly T-Bone028, 40DCOEs are woefully inadaquate(truly not better than the SUs) for the motor you have, particularly with 33mm chokes. 

 

Ram75280Z, let me say this in advance: I do not disagree with you. I think 45 DCOE's would be a better choice over the 40 DCOE's. I have a P90 head with unknown head work...from some searching, a number popped up that said the P90 head flows about 172 CFM intake per cylinder - stock (I assume this was 172 CFM per cylinder...the post did not specify).  Is this true?  I dont know, but its all I've been able to find.

 

As far as CFM's, I will share some numbers that I found during a search regarding CFM's for various induction methods posted by TonyD on Zcar.com back in early 2000's.

 

CFM's:
Stock early round top SU's (46mm plate with 32mm venturi X 2) 217 cfm (this was what I had on my stroker prior to the Weber install)
Stock late flat top SU's (46mm plate with 34mm venturi X 2) 254 cfm
DCOE/DHLA/PHH Triples with 32mm Main Venturis (x6) 650 cfm
DCOE/DHLA/PHH Triples with 34mm Main Venturis (x6) 761 cfm
Stock EFI 50mm Throttlebody (50mm x 1) 323 cfm
EFI 60mm Throttlebody (60mm x 1) 490 cfm
EFI 65mm Throttlebody (65mm x 1) 583 cfm
TWM / SK / Weber Triple 40mm EFI Throttlebody (40mm x 6) 1140 cfm
TWM / SK / Weber Triple 45mm EFI Throttlebody (45mm x 6) 1512 cfm

 

So I would Imagine with DCOE 40's and 33 chokes, I'm able to flow somewhere in-between 650-750 CFM's.  Does this mean that the P90 head is out breathing the carbs?  Probably.

 

P90 head: 172 CFM x 6 =  1032 CFM's

 

So yes, I may be out-breathing my 40 DCOE's with 33 mm chokes.  But is it an improvement over the SU's at 217 CFM?  I would say yes!  The reason for me installing the DCOE 40's was because I had them already available to me, sitting in a box in my garage.  If I had more disposable income for my Z, I would have gone with ITB's via Extrudabody.  However, this was just a "why the heck not" spring project that I'm having a great time with.  Maybe in a couple of years I will go down the path of EFI ITB's, but for now, the 40 DCOE's are just what I needed.

 

 

Hopefully tomorrow I can synchronize the carbs, finish up my heat shield, and refine my cable linkage set-up/geometry.  I'll be sure to post my cable linkage set-up...seems to be a topic of interest for the triple folks.

[Leon]

Nice! Welcome to the club.

 

You've got a lot of work ahead of you, but hey, it's all in the name of fun, right?

[Heroez]

I agree that 40s choked down to 33mm on a 3.1 motor is way too small, a rookie mistake, turning now into an epic mistake. Sad/Funny to witness.

Edited May 18, 2013 by Heroez

[steve260z]

I agree that 40s choked down to 33mm on a 3.1 motor is way too small, a rookie mistake, turning now into an epic mistake. Sad/Funny to witness.

 

Why don't you go re-read why he is running them then you won't be "sad/funny to witness"

[Heroez]

Because he had them laying around. Yeah, but no. Doesnt change it for me.

[T-Bone028]

Hey Heroez, thanks for the insight.  Complete rookie mistake on my part using the 40s.  45 DCOE's would have been the way to go...no maybe I should have gone EFI ITB's, or better yet forced induction for the most power out of the L6.  

 

Actually now that I think about it, I should have just done a motor swap (all of the members on this forum that stayed with the L6 are clearly rookies and its sad/funny to read their experiences)...Clearly the best choice would have been V8 or even better yet a V10 with twin turbo's and nitrous with a rocket strapped to the roof.  Wait, I take that back...I just had a moment of clarity. Every member on this forum that enjoy's the Z is a rookie.  So many better/faster cars out there.  

 

Maybe I should just sell the Z...dont want to be a rookie.  Thanks again Heroez, you just saved me a lot of wasted time.