More Questions - Rough running, What am I missing? Options

[NotLance]

My new engine is in, but I continue to have issues with rough running - and its gotta be something that was retained when i swapped the short blocks, as the behievor is similar to what I witnessed with the other engine too. Engine is good above 3000rpm, so I think the main circuit of the dual webers is good, but at lower rpm it surges on light-med acceleration, consistent on foot down acceleration. backfires out of exhaust on decel and at idle. All of that said, when I pulled one plug after 300 miles, it was very carbon fouled so leaned out that one to hopefully fix... it did not. Resyched and tried tuning carbs per factory weber procedure but still cant get it happy. I also can't verify running conditions at higher than 3500 rpm becuase I'm still breaking in the brand new block.

Fresh plugs and ignition coil, advance on 123 distributor set properly, theoretically timing set to the mark on the fan housing (27* i think), I do not suspect vacuum leaks due to the engine not picking up speed after spraying everywhere with starting fluid... STE reads synchronous airflows on all carbs

Plugs I pulled seemed out seemed okay, not super carbon, oily, or anything.

Maybe I just can't tune dual carbs to save my life? Or they need a rebuild or something (IMG:style_emoticons/default/confused24.gif) I've got it going to a shop friday just to attempt to tune the carbs for me becuase I don't know what else to do...

Consulting the 914think tank to see if there is something obvious I'm missing because despite pretending to know a bit about fixing my car, im just a kid (IMG:style_emoticons/default/biggrin.gif)

I dont have a timing light, can you rent one from somewhere so I could verify timing? I trust the people who installed my engine but starting to pull out my hair so trying to eliminate any variables possible

Its a -4 cyl GA case, dual weber 40 idf carbs and a 123 distributor set to curve 1. BR6ES spark plugs

[Jack Standz]

VW produced several different fans with various timing marks (L-jet, D-jet, etc). So, 50/50? Either the timing mark is at 27 BTDC or it's not. (IMG:style_emoticons/default/biggrin.gif)

A plastic straw (or a borescope or flexible camera, available for < $20 on Amazon.com) in the sparkplug hole of the cylinder head is one method of finding approximate TDC. But, you have to make sure the piston is on the compression stroke,. You can do so by removing the valve cover and checking to see that both valves are closed. Sometimes you can see the TDC marking on the flywheel by pushing the rear engine tin a small amount back towards rear trunk at the point by the engine case centerline.

Once you have found and marked TDC on compression stroke for cylinder #1, use the dial back timing light to set timing at 27 degrees fully advanced. The light comes with instructions that tell you how to do this or it's readily available on the internet (i.e. thunderhead289 on YouTube)