tuning help

have nearly racked up 200 miles on the refreshed 1641 and its freeing up nicely, my only drama is a very occasional pop out the exhaust if I accelerate lightly, it only does it the once then may not do it again for a while. I have tried adjusting the acc pumps slightly in and out with no change.
the other thing, when accelerating, 1st and 2nd its like a rocket without nailing it, 3rd is passable but if sitting on 2-2500 in 4th and trying to pick the speed up there is a lot of induction noise with very mediocre pickup, should I be upping my main jets? 120s at the mo

I bet you're running a 009 dissy. Vacuum advance (SVDA) provides some sort of engine control response to the engine being underload, such as acceleration or your foot burried at 2000 rpm ish, besides the initial accelerator pump.

what carb you got?

what colours your spark plugs? you can tell mixture conditions by that.

magnaspark 2 dizzy, twin 40 IDFs, pop is very unregular (is that a word?) need to pull the plugs to check. Valve clearances checked and set, no vac leaks.

Is it popping out the exhaust or the top of the carb?

Have you sync'd and balanced your carbs....... properly?

Are the Webers or other things?

What is you vent / jet set up?

Spanish Webers (brand new) 28 vents 60 idles and 125 mains. balanced as best I could with no snail. To my ear (with hose) they sound very close

what Weber tuning book/manual do people recommend? is there a gospel? tipping its not the Haynes one Ive seen

I will say I have never seen a 60 idle in a 40 Weber.
Not saying it is wrong - just very surprised.
I would have thought a 50 was more appropriate
Rule of thumb is 1.25 x body size

Does it pick up in revs and peak at 2-3 turns out on the mixture

Again - your 125's seem large for 28 vents.
personally, I dont like 28's
I ran 32's very successfully on a 1600 with 135 mains
Rule of thumb is 4.2 x vent size

you have set the carbs but are the opening "exactly" at the same time.
I assume you have a redline hex bar set up?

They can be a bugger to set the heim (sp?) joint drop arms

Have you read these articles?
http://www.aircooled.net/vw-carburetors-jetting-102/

http://www.aircooled.net/synchronize-dual-vw-carburetors-103/

DubbyDo wrote:what Weber tuning book/manual do people recommend? is there a gospel? tipping its not the Haynes one Ive seen

Personally I think the AC.net articles do the biz

What is the Haynes one you have seen?
Haynes does a good one that I have??

or this one

http://www.cbperformance.com/ProductDetails.asp?ProductCode=0103

I also like the Dellorto one
Similar but different idle jets size and emulsion tube numbers

http://www.cbperformance.com/ProductDetails.asp?ProductCode=0101

Yeah read those, would like to educate myself so I have more of an understanding of what effect any changes I make will have.
Have a CSP bell crank setup, Redline Hex Bar that was supplied with the carbs was missing the arms that the heim joint rods connected to, so glad I didn't go that way!!
could try dropping the original jets back in to see what the difference is (55s and 120s)

CSP = good

Are you getting reaction from the mixture screws?
How many turns out are they?

Exhaust leak?

started at 1 1/2 turns out, ran better when wound in, was exactly the same with the smaller idles

silver wrote:Exhaust leak?

checked that too, all flange joints (vintage speed), nice and tight with new gaskets, cant hear or feel any gas escaping out of the joints