As some of you know, I've been getting ready to do a 5-8 PSI blow-through setup with an S5 turbo on my streetported R5 13B. I've got a couple of questions for the Weber guys.

First: I have two options as far as which carb to use. The first one is an old-style "made in Italy" 45 DCOE. It looks to have pretty high mileage and the throttle shaft seems like it's a little tweaked, and doesn't close fully without an external throttle return spring. Seems to work okay otherwise. The other carb is a newer "made in Spain" model that seems to be in a little better shape overall, though it's a bit dirty. It also has some weird brown/orange sand-like gunk in the float bowls, which will have to get cleaned out. I have heard the Italian ones are better somehow, but I can't find details as to why. Which one do you guys think I should use? I'll probably use the plastic floats out of the Spanish one either way.

Second: I'm currently having a very choppy cruise at less than about 1/4 throttle. More than that and it's smooth and has decent power. Deceleration is smooth, idle is acceptable. I read one post that suggested that the float levels might not be set right, which is possible since I haven't checked them yet. Any other probable causes? Current settings are listed below:

Main venturi: 40mm
Aux. venturi: 4.5mm
Idle jet: 65F9
Main jet: 180
Emulsion tube: F11
Air corrector: 175
Accel. pump jet: 60

Since I'm still NA, I'm not going to bother trying to get it perfect yet. I'd just like to solve the cruise problem for now and get it tuned for real once I have boost and an air/fuel gauge.

 

Having looked at both carbs, the Spanish one has an extra screw near each accel pump jet. This tells me it should have a smoother transition from idle to primary.

You should post a picture of the top of each carb so everyone can see what I'm talking about.

 

it could be your float levels, or the the 40mm chokes

 

Any luck on these carbs?

 

Hey we got it running better with the plastic floats.

 

Yea lots of luck my turbo Fb was blowthrough 45dcoe. and as far as i know noone has put more than I did to the wheels with a stock ported 13b with a 45dcoe still n/a.

 

Yeah, it's a bit better than it was, but still needs work. I need a fuel pressure gauge.

 

If it's a problem while cruising then it's probably in the idle circuit. Without a pressure gauge or a wideband you're pretty much shooting in the dark though. You can get a cheap guage and that will be better than nothing, or Respeed sells an expensive one that is supposed to be the most accurate one available.
I would recommend that you go ahead and buy some more jets too, odds are you are not in tune and will need some. I don't know anything about boosted applications with the DCOE, but something else to consider is that you might need some larger venturis when you do it, like 42. I've run with 36's up to 40's, and even without the main venturi to make it a true 45 (wacky's idea) on a 12A stock port, so on a 13B with a street port you might not be able to get enough air in there. For each venturi size you get different characteristics, smaller ones give you more torque but can't flow enough in the upper RPMs. Keep in mind that if you change the venturi size you will have to re-jet.

 

When you're turbo you want a smaller venturi. I had to run a 36 to get the thing to drive resonably well

 

I have considered removing the main venturis altogether, but I'm liking the powerband of the 40s, so I'll use them for now (I've still got the restrictive stock exhaust manifold and muffler). I'll see how it drives when the turbo is installed and see if I need to go smaller. Adrian, did you dyno your car with the 36mm venturis? What kind of numbers did you end up putting down?

As far as idle jets, too lean, do you think? Should I try 70F8? Yeah, I'm basically just guessing here. I need monies to buy a narrowband and a fuel pressure gauge (and perhaps the head of a neck, too).

 

I forgot to ask, but since you don't have a gauge I'm wondering, do you have a regulator or an aftermarket fuel pump? Like I said earlier it's guesswork without knowing if your pressure is right. The different circuits of the carb won't work as they should without that being right so fingering out problems is virtually impossible. The carb will "run" under a vast assortment of conditions, but it will only work as it is supposed to when its operating requirements are being met. Proper fuel pressure is the first requirement. Everything starts there in the diagnostic and tuning process. You can get a cheap gauge for like $10-$15 bucks man, do it.
I don't know of your turbo plans, or when they might happen, but it almost seems wasteful to try to get it tuned N/A on a stock exhaust if you're going turbo anytime soon.

 

Exactly. Probably pointless to even try speculating. I'll pick up a fuel pressure gauge when I have the chance. I just have a cheap reg that I'm borrowing (set to 3 PSI on the previous car) and the stock fuel pump (which so far hasn't had problems keeping up with full-throttle pulls, but could be sitting at a lower pressure than it should). Adrian figures that's probably the problem, and I'm inclined to agree.

 

I think that's your first problem, and once that's taken care of you can start addressing other issues to ensure a smooth progression of the carb through all of its circuits. You're on a journey down the long & fun road of carb tuning.

Everything I've read regarding carb upgrades insists that the stock fuel pump doesn't flow enough. Even Sterling's modified Nikki requires an aftermarket pump, and he says that the stocker barely even flows enough for the unmodified Nikki. I use the Carter pump on my 7 with the Weber and I've just purchased another one for my latest project to use with a Sterling I just got. Now I just need the time to install the stuff!

 

65 f9 is perfect. you're going to get a stumble with 40mm chokes I always did. there just insn't enough velocity to have a perfect transition. move down to 38mm chokes and it'll go away. especially since you're running a 4.5 aux venturi. if you remove your main chokes you're engine will only run well at 5k+ and WOT. The first day i drove my NA 13b car with my 45 dcoe I hit a huge lean surge at 6k in 4th gear. I put in a holley blue and the problem imidiatly went away. If you turbo your car and want it driveable you cannot put bigger than 38mm chokes in the weber. With 40's in mine it drove fine at full throttle, but it wouldn't drive well enough for me to even attempt to autoX it or drive it around town. Once I moved down to 36mm chokes it drove as well as a stock t2, except about 10x faster. I never dyno'd it turbo but I assumed about 220rwhp. That was on a street ported s513b running 12-14 psi non-intercooled. As already said. My car ran perfectly when it was N/A once I turbo'd it I had to change everything. The only thing I didn't change was the 65f9 idle jets.

 

Don't skimp on the pressure gauge! I got one for $8 one time and it ran .7 PSI difference with the Weber I had (set at 2.5) and about 1.2psi difference with my Holly (set at 6.3psi)

 

yeah i have a re-speed guage on order... my mr gasket pressure gauge reads 7 psi on the lowest setting of my aeromotive FPR.. it should be 3 lol sucks trying to be a cheap ***

 

Just curious, how did you know the variance? Upgrade of the gauge?

 

well said! a true jedi rotary warrior

 

Yes, to a better gauge that cost me only $15

 

Which one did you go with?

 

^ Yes, I'd like to know as well.

Okay, so 38mm chokes, then? I don't mind some mild drivability issues if I can get a few more HP out of it.

 

Stu I should've also asked how you knew that the new one was right and the old one was off and not vice versa. I've got a somewhat cheap liquid filled gauge from Summit and have no clue how accurate it really is. Maybe they make a pressure gauge to test a pressure gauge?

 

I doubt your gauge has any fault. The summit brand stuff usualy is reengineered Name brand stuff. Almost as good for half the price. Just like the bags of cereal at the bottom of the isle. best way to test it is to buy another gauge. but then you wouldn't really have a way of knowing whice one was wrong unless you bought a 3rd or 4th to create a control group.

 

Okay, bumping for updates. Finally got around to hooking up a fuel pressure gauge, and at idle and while revving it stayed at a reasonable 2.8ish PSI. However, rev it up a bit and hold it at a constant RPM, and the fuel pressure was all over the place, waving wildly between about 1 and 3.5 PSI. Could it be the stock fuel pump's internal bypass causing problems? Should hopefully go away with the upgraded fuel system.

 

What did i say young man? The stock pump cannot keep up.
It can't flow enough to stay at 2.5psi then it drops to 1psi so the regulator closes to bring the pressure back up and it bounces to 3 then the reg opens to get it back down to 2.5 but the pump can't keep up so the pressure drops to 1 psi so the regulator closes to...