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]

update - AND ALSO MY 100th POST!!! (IMG:style_emoticons/default/cheer.gif) (IMG:style_emoticons/default/cheer.gif) (IMG:style_emoticons/default/piratenanner.gif)

I know this isnt the whole carb tuning process but ive done the official weber guide start to finish like 3 times now so.. just going with it... I know carbs are synched by this point.

To fix the closed throttle position I backed off the idle speed screws from where they were and turned them in 1/4 turn just to keep it from dying. Thing ran like a tractor, but ran. As i turn the mixture screws in (clockwise), the idle kept raising until I screwed them all the way in - as in it never started running worse.

specifically this step:



Does this mean it's still too rich? I think tomorrow when I take it to the local P-car shop I'll ask them to try their hand at tuning them, whatever they can do - just to make sure I'm not missing the mark totally - if they can't do It either I'll know I need to change something in the setup. Would that still indicate the venturis are too big - I have the 28mm stock ones on but wouldn't that decrease air to the engine?


and I'm borrowing a timing light from my boss so I can check timing / retime it on my own.

Now as for setting timing, IE finding TDC, spinning the wheel in 5th sounds great but do I need a piston stop or something to see when it hits TDC?

[emerygt350]

update - AND ALSO MY 100th POST!!! (IMG:style_emoticons/default/cheer.gif) (IMG:style_emoticons/default/cheer.gif) (IMG:style_emoticons/default/piratenanner.gif)

I know this isnt the whole carb tuning process but ive done the official weber guide start to finish like 3 times now so.. just going with it... I know carbs are synched by this point.

To fix the closed throttle position I backed off the idle speed screws from where they were and turned them in 1/4 turn just to keep it from dying. Thing ran like a tractor, but ran. As i turn the mixture screws in (clockwise), the idle kept raising until I screwed them all the way in - as in it never started running worse.

specifically this step:



Does this mean it's still too rich? I think tomorrow when I take it to the local P-car shop I'll ask them to try their hand at tuning them, whatever they can do - just to make sure I'm not missing the mark totally - if they can't do It either I'll know I need to change something in the setup. Would that still indicate the venturis are too big - I have the 28mm stock ones on but wouldn't that decrease air to the engine?


and I'm borrowing a timing light from my boss so I can check timing / retime it on my own.

Now as for setting timing, IE finding TDC, spinning the wheel in 5th sounds great but do I need a piston stop or something to see when it hits TDC?

just put it in gear (engine off of course), and roll the car till you see the mark on the flywheel line up with the case halves (from the top). Then you can pull the #1 spark plug. I use a chopstick (que the yelling and screaming) but if you only use pushing the car in 5th gear, you are not going to snap it off in the cylinder. You will feel the piston move down from TDC as you roll the car in either direction. Move the car back and forth until you feel confident the piston is at its highest point. Then check the flywheel again, and then the fan. The mark on the fan may be toward the engine side (if it exists). If it doesn't exist, now would be a good time to mark TDC on the fan if you want to keep using that for timing. As I said, I like the flywheel better, but in some cases the tin or air cleaner might block your view of the flywheel from above (probably not with your carbs) so the fan may be where you want to go. Remember, this mark is TDC so not to be mistaken for the 27 deg. mark you might have been using before.