Final Weber 38/38 Jettings

[Jellobmw]

Well......almost final.......
This is as close as I've gotten it. Still a very very slight stumble in the 2500-3000 rpm range. Feeling a little lean there and I'll play with the idle settings.

Mains = 135
Idle's = 60s
Idle's at 1 3/8 turns
Power Valve modification per Jim Rowe at Metric Mechanic

Engine is a 3.5 liter, with a Schrick 384(?), Crane/Allison ignition, balanced, ported, polished etc. K&N filters on the carbs, and the big center muffler has been eliminated (sounds beautiful).
Timing is stock, plugs are NGK BP6ES, and carbs have been synchro'd.

There is also an occassional hiccup, which I suspect is ignition related.

Car is overall running great, and much more responsive and powerful than when I had the Weber 32/36s on there. Gas mileage is down, but I measure the fuel economy in tankfuls per year (as compared to a Harley Davidson where its dB/gal). I did a 50 mile drive early Sunday morning, and there was more of a stumble but then again it was 38 degrees here in Vermont. On the way back it was 60 degrees and it ran fine.

As I was driving back from Sugarbush, I started seeing a lot of British cars, and then recalled it was the British invasion weekend at Stowe. Saw the usual Morris Mini's, MG Bs, Austin Healey's, Jag's etc, and then along came 4 newer Aston Martins one after another. Beautiful cars!

And they were all on the proper side of the road.

 

[decoupe]

I'm guessing you have a 284 cam in what sounds very similar to my motor. A stumble at the 2500 rpm usually means the idle jet is too small and the 1 3/8 turns on the idle mixture confirms that (to me anyway). Put in a 65 and try to get down to 1 turn and see if that helps. I'll see if I can find my settings but I'm at 4000' so may be deceiving.

 

[jmackro]

A thought and a question:

- Might your engine benefit from additional ignition advance? I doubt it would solve the stumble as you transition from idle to main jets, but it might improve performance overall. Timing is easy to experiment with, and even my bone stock 2800 is happier with > than the factory setting.

- What is the "Power Valve modification per Jim Rowe at Metric Mechanic"? A modification to the 38/38's?

 

[decoupe]

Further to my previous reply my idles are 50, the mains 130/135 and the air jets 200 or 205. Given my altitude - this doesn't seem unreasonable. I believe total advance is 32 degrees.

Everything I've heard (and confirmed with my own obsessive adjustments) is to try and get a smooth idle with one turn or less on the idle mixture screws. Your idle mixture screw is adding air and fuel when you increase the turns on it so you are leaning out the carb with 1 3/8ths turns.

G'luck

 

[dang]

ar is overall running great, and much more responsive and powerful than when I had the Weber 32/36s on there.

I'm glad to hear this. The parts car I picked up last year has 38/38's on it and the engine sounded awesome when I fired it up. Both of my last CS's had 32/36's and it always felt like they were dragging an anchor. I'm getting more and more excited about swapping carbs.

Dan