Bent MixScrew Options

[914ghost]

Hi All-
Have been fighting my 40mm Dellortos for a while now, haven't quite been able to find an obvious problem (until now).
Anyhow, the Screw you see is from #2, which only fires when the mixture is turned ALL the way out. And the car runs badly, ALMOST runs okay when VERY cold, but starts backfiring through carb and exhaust w/any thottle applied. The backfiring is at all speeds and all rpm and it is continuous (sounds like a 917 on the straight).
Also, I can cover #1 & #2 carb with my hand making a seal and hear suction from elsewhere inside the carb. Doesn't affect idle. The are NO vaccuum leaks, valves/timing are adjusted.
Compression is 160 on all 4. Carbs are in good shape, very clean.
Can my bent mixture screw be the root of ALL of it?
Regards,
Robert O

[914ghost]

Sory here's the screw:
Yes, I did try to straighten it and NO I haven't screwed it back in since I banged it up.
It wa REAL bent until I took the vice-grips (IMG:style_emoticons/default/aktion035.gif) to it- I have a new one coming and figured I couldnt mess it up more than it was.

[Brad Roberts]

I dont think that is causing all of your problems.. It sounds like a throttle plate is bent.

The engine should just about die if you cut off air to 2 cylinders.

Have you used a Uni-Sync gauge yet to detemine if they are remotely flowing the same amount of air ??


B

[914ghost]

Yeah, used the unisyn, and that side doesnt flow like the other.
Bent throttle plate is something I hadnt considered....
I thought possible o-ring that sits in the side of the auxilliary venturi, as I "tightened" the set screw for it I could feel a little more suction on my palm.
Maybe o-rings combined with the bent mix screw could be it.
If not, I'll take them off again, blow all through them reassemble one more time before I give away the carbs.
The car ran pretty good with 36's so...I'll check the throttle plate idea.
Regards,
Robert O

[Carl]

I agree with Brad that it's doubtful that the mixture screw is the entire problem. From the symptoms you described it seems that the car is running lean so there's either vacuum leak or one of the fuel passages is plugged.

Pull the plugs and see if they're uniform in color, etc. I don't know about Dell's but if the unisyn is low on that cylinder then a bent throttle plate is unlikely. A more open throttle plate would cause the unisyn to go higher. Check for worn bushings in the throttle shaft. Spray a little carb cleaner around the shaft pivot points and see if the idle smooths out any. That will help you track vacuum leaks.

Carl