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

[fiacra]

Lance, not everyone tuning in right now knows the back story. You should give a bit more detail about how you got to this point. It might be helpful in getting trouble shooting insight.

Did you drive the car from the Bay Area to San Luis Obispo? That's a good long drive to shake it out on. I'm assuming it was running well when you got it back from the shop after the engine install? Correct? I can't imagine that they let it leave the shop running like it is now. If all that is correct, something had to have changed in the interim, so it is unlikely (in my opinion) that the carbs are improperly set up. That should have shown up rather quickly, and before it left the shop. I don't know where you had the work done, but your dad was pretty clear about their level of expertise and having a long history with them.

So...have you pulled the jets and cleaned them? Even just a little bit of debris in the jets will give you trouble. Since everything has been apart recently the chances of some contaminates getting into the fuel system are pretty high. I'm for sure no expert on carbs, so I'll let other more competent folks weigh in, but that's probably where I would start. After that, I'd check the timing and valve adjustment. You can get a timing gun reasonably inexpensively. I invested in a good set of tools when I was about your age and other than the cost of my marriage license it was one of the best investments I ever made.

I know you can figure this out! Keep "pretending" you know how to fix your car and pretty soon you will know how to fix your car (IMG:style_emoticons/default/biggrin.gif)