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

[NotLance]

Good call fiacra - so to recap the story,

My engine ate a bearing and I got a new one from fiacra - the engine is good and can feel it wants to run good, but suspect something else is amiss, and was with the previous engine too. It wasn't what made it go kaboom, but it never quite ran exactly right. Fresh plugs always made it happy, for a while.

As for the shop that did the work installing the new engine, I trust everything they did was competent work. Long story short, they grew up with my dad, and have been taking care of his 911 for decades. It'll cost but they do it right. They swapped the short block, and reused everything from my old engine on my direction. I'm interested in FI in the long term, but for now would like to make the carbs work for the next year or so until I hopefully move once I graduate.

As they knew it was my intention to mess with it, I decided it was running properly enough to send out the door and avoid hours of fine tuning my wallet could not afford. Now its time for the futzing around

On the drive from Martinez to SLO I noticed these issues

Maybe I'm just being picky, but it just doesn't feel 'right' and idle up to about 3000rpm - and while I'm not convinced its the carbs, I am convinced the motor has more to give to make me want to drive it, not worry about it running rough, hurting it. Most importnantly to me, I want this new engine to last longer than the first so hearing/feeling it unhappy is not conducive to the daily driving I used to do with it. (only car (IMG:style_emoticons/default/biggrin.gif) )