weber DCOE 45 help

I have a 84 vw rabbit 1.8L 8v running a single DCOE 45 with a long tube header, 8.5.1 compression pistons, GTI head and factory G cam. I have the vacuum advance removed and the base timing set at 12 degrees with a total timing of 22 at 4000 rpm. I'm trying to figure out how to get more timing in earlier, still searching this.

The weber has these jets,

175 air corrector F16 emulsion tube 140 main jet

40 pump jet

45 F9 idle jet

The car starts right up, idles great and seems to run fine up until 2400 rpms then it leans out and stumbles. When I bought the car the PO had a 180 air corrector in where the main jet should be. So I tried putting that back in and it ran a lot better but this isn't right.

Then I hooked up a cable to the starting feature (choke). I went for a drive and at 2500-3000 RPM I would floor it and pull the cable and it ran great.

I'm new to weber tuning but if I understand whats happening the starting feature is dumping fuel in which means I need to run a larger 180 - 200 main jet which is completely opposite of everything I've read for a 1.8L

I'm running the carter low pressure pump, no regulator and the fuel line connects to a T on the carb and the other side has the return line back to the tank. Not sure if this is right or not.

I checked the float level with a caliper in the main jet opening flush with the top of where the emulsion tube screws in and its about 25mm.

I don't know what size chokes are in the carb, I think I need to remove it to see.

I did put a AF ratio gauge on it and it is leaning out without the starting feature dumping fuel in.

Any suggestions? Just put some 195 or 200 main jets in it and tune of the AF guage?

You need to check what size main venturis you have in there before proceeding further. Does it stay flat all the way up, or does power return higher in the RPM range? You know that you're running lean, but the solution may not be as simple as larger mains. Smaller air correction jets and/or smaller main venturis may make for a better running engine across the range.

FWIW, I don't run a fuel return on my DCOEs. It's not necessary, but it shouldn't be causing a problem.

I've set up a ton of Webers on British and Italian cars at Eclectic Motorworks and used to fix a lot of Rabbits in the 1980s and 1990s, but I can't remember working on a Rabbit with Weber(s)...but this may help anyway.

My main piece of advice is to call Pierce Manifolds and ask them for a baseline calibration for your car/carb. Their baselines are usually very close. Lots of good tech advice on their website, too, but a little hard to find sometimes: http://www.piercemanifolds.com/ Beyond them, I'd offer the thoughts below.

First, I think you need more timing--likely somewhere between 28-32 degrees, all in (no vac), at 3500RPM or so. At 22 degrees, it's going to seem doggy. You may need to recurve the distributor, but you could check and see if it will work to just advance it. If you go 28 all in, I think you'd be at about 18 at idle, which may be fine. A lot of 1980s cars had little advance at idle, keeping the timing a bit retarded, basically as trick to pass emissions. If 28 seems good, keep going up a bit and see if that seems better.

Then, as O2Pilot says, you should to check your venturi sizes. 1800cc MGBs with a single DCOE like 32mm or sometimes 34mm venturies, and I'd guess you'll be good at that size on a Rabbit as well. I see a lot of Webers with way too big venturies as people seem to always oversize them. Unless you're spending a lot of time at high RPMs, smaller is always better than larger for street driveability. Large ones don't offer enough vacuum to proper atomize the fuel at lower RPM ranges. Looking at the rest of your calibration, I think you're probably in an okay range, but may need to go up or down a bit in certain areas.

Regarding your float level, remember that you set it with the carb vertical and there is an upper and lower limit. See: http://www.piercemanifolds.com/category_s/317.htm

Next, I think the most important thing about Weber tuning on the street is knowing where your throttle is. If the stumbles and driveability issues are at WOT, you're on the mains and air correctors (ACs). Bigger mains make it richer, bigger ACs make it leaner. If you're at cruise/part throttle, you're usually running on the idle jets, not the mains. If you've got a stumble in the transition (very common), it's about balancing transition from the idles and mains (one may be too rich/lean for its relationship to the other) or emulsion tubes.

If you're tuning with a wideband, remember there will always be a lean spike at throttle tip-in, so don't let that distract you. If you're tuning by reading plugs, remember to shut the engine off at the end of a WOT power run without letting it go back to idle--if you let it idle, you'll just be reading the idle mixture on the plugs. I don't recommend reading plugs anymore as it's kind of dangerous driving that on the street.

Long story short, though, is usually to call Pierce. We find most of the time their calibrations are very close and we don't have to do much more. When we do, we usually do it on a dyno.

Keep us posted!

It's running like crap because you have the vacuum advance/retard disconnected, why the Hell did you do something THAT stupid? Reconnect it or buy a mechanical advance distributor for it and you'll be fine, really !

Carl and 02Pilot thanks for the help, this is a track only car, it will never see the street. I'm going to pull the carb off and check the choke size before I contact Pierce Manifolds. The distributor I'm still working on, the little bit of research I've done suggest pinning the vacuum advance and to have 30-32 degrees all in by 3500 RPM. They must be using softer springs or drilling the weight because I can't find a re-curve kit for the vw distributor.

Could it be running out of fuel due to the return? I would either put an fpr in it or if you don't need a return eliminate it. My suspicion is that at wot it is wanting more fuel but the fuel is going back to the tank.

Simple test is to clamp off the return with a vice grips and see if it gets better. This is of course if the fuel system can handle the pressure generated by the pump and the pressure does not overcome the float valve.

The car starts right up, idles great and seems to run fine up until 2400 rpms then it leans out and stumbles. Then I hooked up a cable to the starting feature (choke). I went for a drive and at 2500-3000 RPM I would floor it and pull the cable and it ran great.

To me that sounds like your main circuit may actually be obstructed. How lean are we talking (whats your wideband afr) when you stay in it past 2400 rpm? We have to discern the difference between tuning issues and repair issues. If it's so lean the engine doesnt accelerate and is bucking and popping i would probably look into whether the main circuit is restricted. You said you swapped the main jet (or rather put an actual main jet back where it should go) and that made a difference which suggests that the inlet from the bowl to the bottom of the jet stack is not blocked. You could still have a problem between the jet and the actual mini venturi thing where the main circuit fuel actually comes out. The whole up-to-2400rpm thing suggests your idle and progression circuit is working fine, but once you open the throttle far enough the vacuum that sucks fuel out of that circuit is lost and it tapers off. The starter circuit also has its own jet and passageways unrelated to the main circuit. So in that sense it's good that you can narrow the problem down to the main circuit. You could probably take the little hat off, take the jet cover and the air correction jet out and just hammer air through there with a blow gun (might want to empty the float bowl first) and see if it clears up. If i'm picturing your setup right i'm guessing the carb is facing the firewall but if you can get a mirror or a phone camera or something to see down the throats you could just WOT it while parked and observe the fuel coming out of the main circuit and see if maybe one side is way less than the other, that would narrow it down even further.

Simple way to test Dean's idea of the float bowl running dry without actually using tools is to just cruise up to 2400+ (preferably way more) rpm at the lowest throttle it will reach that rpm at, and then floor it. If it will cruise up to high rpm at light throttle just fine and then give you a shot of power after flooring it and THEN lean out, it may well be the float bowl running empty due to your return line being the path of least resistance. A pair of vise grips can be used as a variable return hose restricting tool to further test on that. As Dean said, if you block it completely the pump could force your float valve open and overflow the the carb.

I pulled the carb and it has 38 chokes, filter is clean too. I thought about crimping off the return to see if it made a difference. I will call Pierce tomorrow to get base line jetting.

I'm waiting to get the AF files from a friend that had his AF gauge hooked up, it records the RPM and AF and saves it to a excel file.

A lot of DCOE issues are transition issues.

Assuming that the float level is correct, the DCOE tune is built from the idle-up. If the car wont idle with the throttle screw turned less than one turn, then you need figure out why that is and remedy. I used to turn the throttle screw until the car ran sorta smooth an then tried to tune out a bunch of weird behavior like a flat spot. Good way to chase around in circles.

Having lived with a DCOE on the MGB for about 15 years,and never got it perfect, I am no longer a fan of the DCOE for the street.

I've never had a single DCOE setup, but I wonder if the persistent rumors of uneven distribution (rich middle cylinders, lean outer cylinders) are a factor. Much depends on the manifold, I'm sure. For the OP, how do the plugs look? Any indication of cylinder-to-cylinder differences in mixture?

FWIW, I've run a dual DCOE setup on my 2002 for 20+ years. Aside from periodic synchronizing and trying several filtration solutions, they've been rock-solid and needed nothing. They are completely usable on the street in my experience, but tuning is everything.

02Pilot wrote: I've never had a single DCOE setup, but I wonder if the persistent rumors of uneven distribution (rich middle cylinders, lean outer cylinders) are a factor. Much depends on the manifold, I'm sure. For the OP, how do the plugs look? Any indication of cylinder-to-cylinder differences in mixture? FWIW, I've run a dual DCOE setup on my 2002 for 20+ years. Aside from periodic synchronizing and trying several filtration solutions, they've been rock-solid and needed nothing. They are completely usable on the street in my experience, but tuning is everything.

When I rebuilt the engine the outer pistons showed signs of leaning out. I though it was maybe a tuning issue but it seems like its more the design of the manifold then the tune. The outer cylinders, 1 and 4 have a slightly longer runner length on the manifold then 2 and 3.

The plugs look good, not lean or rich and they all look the same.

I talked to pierce and they recommend a 32 choke over a 38 but since its a track car that will live mostly above 3000 rpms he said I could keep the choke the same and run a 150 main jet.

Does going from 140 main jet to 150 make a big difference? I would think if it runs great with the starting feature pulled open then I would need more then a 150 main.

If you saw signs of lean running on the outer cylinders, then let me put it bluntly: IMO you will never get it running properly with that setup. DCOEs were never intended to run feeding more than one cylinder per throat. I would seek out a dual carb setup or switch to a downdraft single carb (a 38/38 would probably suit your application). Sorry if that's not what you want to hear, but trying to tune out a manifold design issue is going to be nothing but an exercise in frustration.

Choke size X 4 = main jet size 38 X 4 = 152 just as a starting point.

Main air Main jet + 30 = main air So about 180 Changing the main air size will move the main fuel curve to start at higher or lower RPM.

If the manifold is making 2 cylinders leaner, then you will have to go a little richer to ensure those two don't go lean.

A better set-up would of course be a twin weber set-up, but the single carb could work, just needs tuning.  You may end up buying a lot of jets, main fuel and main air.

    The mixture tuning will be partly based on throttle position and partly RPM, at part throttle it is running on the idle jets, at above half throttle it is running mostly on the mains.

 You may not really need vac advance, but you don't have enough timing.  For a track car the timing curve isn't to important, since it is mostly running at full advance, above 3,00 RPM.  But the total advance will need to be 30- 35 deg.  I ran a race car with the timing locked and set at about 35 deg, little harder to start like that.

I ordered a few jets and air correctors from Pierce Manifolds. 02Pilot thanks and I agree I will never get all 4 cylinders running the same with the way the manifold is designed. I'll just have to tune on the rich side for now and look at a different setup.

Ted_fiestaHP I did that calculation yesterday when I ordered the jets. Pierce Manifolds website has a ton of info on weber setup. I should have all of the jet by the weekend.

Update:  Bought some jets based on recommendations from pierce manifolds and stilled had the hesitation problem.  I charted the data from the AF gauge and did more reading on weber tuning.  Seems like the old timers would solder and drill the jets to make changes.  I also read about soldering the pump jet - inlet/exhaust jet - exhaust opening closed to deliver all of the pump jet fuel to the carb.  I soldered it closed and that made a huge difference.

Next I removed the idle jets and drilled them out from .45mm to .55mm and it was almost perfect.  I then drilled the idle jets to .60mm and now the car is a rocket!  No hesitation or stumbling, pulls from 1000rpm to 6000rpm with no stumble.  I didn't have an SD card for the AF gauge data logger but looking at the gauge while driving I could see it is around 11.5 to 12.0, rich.... finally!

I plan to make the final adjustments on the main and air corrector when I can get out on a track and make a few laps with the AF data logger.  For now its very close and on the rich side which might work out good given the single DCOE with this intake manifold.

One thing I'm surprised about is how far off the jetting recommendations from pierce manifolds and other data suggests.  I think this engine/head/cam combo moves more air volume faster, plus the carb has 38 chokes instead of the recommended 34 for a 1.8L

After I get AF data out on the track I'm going to change all of the modified jets to the correct ones.  Drilling and soldering the jets and drilling to your desired jet size is a great way to tune without having to spend a small fortune on a bunch of jets.  Thanks for the help everyone, except you two_tools_in_a_tent, you have a lot more to learn grasshopper.

The idle jets, you say? There shouldn't be enough vacuum at the idle/progression circuit holes to contribute much fuel at high throttle openings. For me, your statement just raises more questions. BUT, i'm glad the car is running well.