Weber DCOE 45 152...glutton for punishment. Any advice?

[Konish]

Okay, I just bought and installed some DCOE 45 152s. I installed these to replace a set of old DCOE 40s I had. The 40s ran pretty good for the most part and the plan was to get some Mikuni triples. The deal for the 45s was pretty good and parts are easier to get, so I opted to try the Webers one more time.

 

Trouble is, I cannot get my idle to settle down. Its +/- 100/150 rpm like a lean hunt. Average idle speed then would be really close to 1000rpm.

 

Valves adjusted, carbs synched across all barrels and the following jets:

Mains 145

Emm tubes F-11

A/C 185

Pumps 45

Needles 200

Aux Venturis 4.5

Chokes 36

 

Since I can't find starter fluid here in Japan, I used propane from a torch to check for vacuum leaks and there did not appear to be any. I tested how much my idle would come up by putting the propane right down the throats and it definitely picks up a couple hundred rpm. Anyway, I kept the torch in each area of the manifold (top and bottom...head to manifold and manifold to carbs) for 15 seconds or so and no idle increases noted.

 

I adjusted the floats using the direct measurement from the main jet well to 25mm which instantly cured an almost undrivable lean condition despite the 55F9 idles.

 

Idle stop screws are 1/2 turn past initial contact with the throttle levers. From the inspection port, the plates are *well* behind the first trans port (a known issue with the 152s which causes a just-off-idle lean spot).

 

Idle mixture screws are 2 full turns from bottom...I've read that the 152s may need as much as 2.5 to 3 turns to idle correctly.

 

I get 10 kg/h across the boards on the flow synch meter from barrel to barrel.

 

I'm totally guessing here, but here are my thoughts:

 

1. My chokes are too big and it's not allowing sufficient velocity to build through the carb. The slower speed then draws the fuel from the idle mix port at uneven and poorly vaporized state(?) I know, I'm grasping at straws.

 

2. One thing I did note in diagnosing my problem is that one of the teeth on my reluctor ring on my 280zx distributor was broken (not the stator) increasing the gap between the broken tooth and the stator teeth. I will say the car has always run fine prior to these 152s.

 

3. Even though the bowls are set, I'm still suffering the effects of a weak mechanical fuel pump causing fuel starvation. This would make more sense if that car acted like it was starving at higher rpm which it doesn't seem to be...I mean it doesn't break up or ping excessively. Actually, the car feels pretty good at above 3000 rpm under load, but I do still get a lot of lean popping on deceleration or closed throttle.

 

Also, I can make the car die in a very tight turn with the throttle closed. Before the float adjustment, the idle would increase a lot...say to 1500 rpm or higher, and then immediately die. It acted exactly like a small R/C motor right before the fuel runs out...runaway idle then dead. It's better now and it may or may not die (usually does), but I get a big drop in idle before it catches back up. Finally, it takes forever to warm up.

 

I have a Innovate LM-2 hooked up but it has its own issues (see their forums) so I don't know what to believe as at idle it always reads 20.9 AFR (sometimes it bounces around and reads crazy numbers like in the hundreds etc). At 1/2 to WOT it reads anywhere form 10.5 to 13. Until I can get this thing on it's own power supply directly from the battery, I'm not sure I can trust it's readings right now.

 

4. A combo of all 3 issues above, but I'm guessing issue 3 is the most likely the problem. I mean it seems obvious the car is lean and acting crazy as hell, but it just ran *so* much better when I had the DCOE 40s (30 mm chokes) on there with the same mech pump.

 

EDIT:

The more I think about it, I'm thinking that this is a fuel volume problem. Even though the fuel level looks good at idle and the fuel pressure is good (via a reg), it simply cannot replace the fuel fast enough due to the idle jets being higher in the bowl (which is why the mains aren't as affected due to their lower position in the bowl). As I start to use the fuel under partial acceleration, the idles "run dry" and start to go really lean.

 

I guess this all moot anyway as I have a Holley Red on the way so one or another I'll know in the future...still would love to hear opinions though.

 

These are driving me nuts.

 

R/

Dustin

Edited April 17, 2010 by Konish