DRLA Problems

[Marvel]

I came here looking for info on DIY fuel injection as I've had enough of my carbs and found this carb forum I've not seen before. I've posted messages all over the internet trying to find out why my progression and main circuits have a weak area at the transition but no joy. My set-up is as follows:
1776cc
W100
Standard heads
1 5/8 merged header (a bit big)
Twin 40 DRLA
28mm venturi
5mm float height
112 main jets giving 12-13.5 at WOT (should be too small but the AFR looks ok i.e. venturi x4.0-4.2)
180 air correctors (should be 160 i.e. mains+50)
9164.3 emulsion tubes (should be 9164.1)
55 idles giving 12 at cruise (could go down to a 52)
Megajolt set 32deg BTDC plus 10deg at cruise
I've tried every combination of the following:
28, 30mm venturi
112, 118, 122, 130 mains
160, 175, 180, 200 airs
9164.1, 2, 3 emulsions
50, 52, 55, 60 idles
It drives well enough except for the flat spot at the transition.

[Dale M.]

I came here looking for info on DIY fuel injection as I've had enough of my carbs and found this carb forum I've not seen before. I've posted messages all over the internet trying to find out why my progression and main circuits have a weak area at the transition but no joy. My set-up is as follows:
1776cc
W100
Standard heads
1 5/8 merged header (a bit big)
Twin 40 DRLA
28mm venturi
5mm float height
112 main jets giving 12-13.5 at WOT (should be too small but the AFR looks ok i.e. venturi x4.0-4.2)
180 air correctors (should be 160 i.e. mains+50)
9164.3 emulsion tubes (should be 9164.1)
55 idles giving 12 at cruise (could go down to a 52)
Megajolt set 32deg BTDC plus 10deg at cruise
I've tried every combination of the following:
28, 30mm venturi
112, 118, 122, 130 mains
160, 175, 180, 200 airs
9164.1, 2, 3 emulsions
50, 52, 55, 60 idles
It drives well enough except for the flat spot at the transition.

Huh?.... That would appear to me you are at 42° BTDC at cruse, if so its way to much advance... I would not go more then 30°.. But maybe I don't understand your Magajolt and your terminology...

Dale

[Marvel]

Timing is set to 32BTDC at WOT increasing to 42BTDC as the manifold vacuum increases just like an SVDA distributor.

[Clonebug]

Post a pic of your ignition map.

[shepherd]

That header, and those carbs, on a stock head 1776 is a poor combo, even with a small vent in the carb. A 1776 with a W100 really needs a 1 3/8" header, and then you might be able to get the carbs to run well. A larger air jet will bring the main circuit into play sooner, so if you're dead set on that header, use the 200 airs and nothing smaller. I experimented with several combo's on a pretty potent 1835 for years, and dual 36 dells, 30 vents, and a 1 3/8" header w supertrapp was the best combo.

[Marvel]

That header, and those carbs, on a stock head 1776 is a poor combo, even with a small vent in the carb. A 1776 with a W100 really needs a 1 3/8" header, and then you might be able to get the carbs to run well. A larger air jet will bring the main circuit into play sooner, so if you're dead set on that header, use the 200 airs and nothing smaller. I experimented with several combo's on a pretty potent 1835 for years, and dual 36 dells, 30 vents, and a 1 3/8" header w supertrapp was the best combo.

I fitted the 200 air correctors with 118 mains to compensate and it's better but the main circuit still doesn't come in soon enough. You say 200 minimum; would bigger AC and mains be better still?
I've always suspected the 1 5/8" header was too big but like the look of it and it was cheap. I've got plenty of 1 3/8" header so that's next on the list to try. I've also got some 36 Dellorto's with 30mm vents so can try them too if the header doesn't work.
It still goes well when the main circuit does come in I just need to fill the hole.

[Marvel]

Post a pic of your ignition map.

[Dale M.]

Timing is set to 32BTDC at WOT increasing to 42BTDC as the manifold vacuum increases just like an SVDA distributor.

Guess I'm stupid about timing because in performance engine workings best advice is set timing at anyplace above 3000 RPM is between 28-32° BTDC... First time I have ever heard of 42 BTDC° at WOT....

Dale

[squeakie]

Timing is set to 32BTDC at WOT increasing to 42BTDC as the manifold vacuum increases just like an SVDA distributor.

Guess I'm stupid about timing because in performance engine workings best advice is set timing at anyplace above 3000 RPM is between 28-32° BTDC... First time I have ever heard of 42 BTDC° at WOT....

Dale

good thing he ISN'T setting timing at 42° BTDC at WOT!