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

[emerygt350]

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

This could be carbs, I am not at all familiar with those on a type 4 so I can't be of help there, but I would say it kinda feels like timing to me. Maybe a combination of the two.

I would verify TDC on the #1 cylinder, I just put the car in 5th and roll it till the piston is at the top of the bore on the compression stroke. Once you have it at TDC (recently I have gotten into using the TDC mark on the flywheel to time my car) check to see where your mark is on the fan (and the flywheel). I find the flywheel way more convenient for timing, and on my car TDC on the fan is just a smudge of paint.

I wouldn't trust any mark on the fan due to the different fans that can be added to these. I replaced my fan with one off of a bus 2.0 because I had some broken fins on the original. The replacement doesn't have any marks at all. I verified my flywheel mark and just go with that.

When timing, if you don't want to rev the thing all the way up to 3000 rpm to set the timing, you can just set it at 7-8 BTDC at 900 or lower rpm.