914 Popping and backfiring out exhaust, Need help! Options

[SolarRT99]

I'm at my wits end with this. Background on car. Originally a 74 1.8 car. Now has a 1.7 engine block with an A&A 1911cc piston kit. All new bearings, scat c45 cam with new scat lifters. Rebuilt 1.7 heads with hp springs, shims and elephant feet adjusters. Pertronix ignition with flamethrower coil. Dual Weber 40's. SS 2.0 Heat exchangers with Sebring exhaust. New cap, rotor, plugs, and wires. I have set the valves 3 times and it still has a pop out the exhaust at idle. Carbs were rebuilt last year. I think 3 and 4 aren't firing completely even though it idles fairly well. I crawled underneath with my nc temp gun and 1 and 2 are at 500+ degrees at the exhaust pipe right off the engine, 3 is right around 350 degrees and 4 is around 220. Could it be a bad carb? I tried new plugs and wires and nothing changed. Any thoughts or ideas appreciated.
Thanks

pics here

https://drive.google.com/drive/folders/0Byp...d28?usp=sharing

[iankarr]

Just watched the videos. scared the hell out of me that you were under the car while it was running!

Tough to tell from the clips, but the valve train sounds loud and the pop almost seems like a timing miss.

Are all barrels breathing equally and in sync? If so, I'd try making the mixture a bit richer on the popping side and see if that has an effect. Popping can also be from an exhaust leak. I'm sure you'll get lots of suggestions here. Good luck and be safe.

[McLovin]

Don't know much about those carbs, but maybe your idle circuit jets are configured too lean...possibly because your displacement is bigger than the carbs were set up for.

Either that, or you have a vacuum leak, which can be found by spraying (carefully) around the engine with some starter fluid and seeing if you heard a rise in RPM.

[SolarRT99]

Just watched the videos. scared the hell out of me that you were under the car while it was running!

Tough to tell from the clips, but the valve train sounds loud and the pop almost seems like a timing miss.

Are all barrels breathing equally and in sync? If so, I'd try making the mixture a bit richer on the popping side and see if that has an effect. Popping can also be from an exhaust leak. I'm sure you'll get lots of suggestions here. Good luck and be safe.

Car was up on 2 jackstands and 2 floor jacks, was nice and steady! Thanks for your concern though.

[SolarRT99]

So I pulled off the 3/4 carb today. After I pulled the top off the inside was looking pretty nasty, even after only a year. A quick cleaning and a reset of the float and all seems way better. Some initial popping from the carb on restart, but some quick adjustments and now it is running good. Some final tidying up and it'll be ready for it's first drive.
Thanks for the help!

[iankarr]

Glad it's running better. IMHO the car is never safe to be under when primarily supported by floor jacks. Too easy for them to lose pressure and/or suddenly release. They're also not designed to hold a load for extended periods. Please also only use the pin type jack stands, as ratcheting ones can be inadvertently released. Sorry if I sound like a parent...I've heard and seen too many horror stories. Be safe!

[SolarRT99]

Well after a 10 minute jaunt around the neighborhood, was running well with good power. Towards the end the valves got loud and sound like they really need to be set again. Is this common with a new build, cam/lifters? Also the valve covers are leaking, come to a stop and get some smoke from underneath, brand new victor cork gaskets. I tacked them to the cover with some silicone to hold in place, but still leaking. Oh well, will have to wait until next weekend again. (IMG:style_emoticons/default/sad.gif)