350 sputtering and popping at part throttle

[1989bmw535i]

Hello, I'm having some trouble with my pickup, it's a 350 with long tube headers, glass packs and turndowns, an edelbrock rpm air gap, an edlebrock avs2 650cfm and an msd street fire (I think) hei distributor with new plugs and wires. Transmission shifts fine maybe slightly late but could be nature of the beast. It idles fine but when part throttle, around town or cruising on the freeway it sputters and seems to miss and even backfires (out of the exhaust) if I have the throttle in the right spot. I've been playing with the mixture screws and the timing, I had base timing set to 12 degrees (vacuum hose unplugged carburetor capped) and it seemed to run better when I retarded the timing (spun clockwise) I also didn't notice a difference when I switched the vacuum advance hose to the other port on the carb (manifold vs butterfly vacuum) any advice is appreciated thanks!

[1989bmw535i]

Now that I'm listening it is missing at an idle.

[bd]

Recheck the firing order: 1-8-4-3-6-5-7-2.

[JohnnyPopper]

Usually 5 & 7 get juxtaposed.

[1989bmw535i]

I'll check the firing order in the morning and report back, thanks!

[1989bmw535i]

The firing order is correct, that being said why would retarding the timing make it run slightly better? I've also gained about 3000 feet in elevation, fuel metering rod springs? I've got 15in of vacuum

[bd]

Generally, exhaust popping represents either an ignition misfire or a mechanically compromised cylinder (i.e., very low compression).  Initial timing set to 12° BTDC in and of itself won't cause exhaust popping.  Check the following, in order:

• Make sure you are timing off of the #1 (driver-side front) cylinder. 
  
  
• Verify that the harmonic balancer is correctly matched to the engine timing plate.  If the balancer or timing plate has been replaced with one from a different year application, the timing marks may no longer align correctly.
  
  
• Take the necessary steps to verify that the outer ring of the harmonic balancer hasn't slipped, causing the balancer timing mark to rotate from its original position.
  

[1989bmw535i]

I will look into misaligned timing marks, could I just replace them as a set and not have to worry about it?

[1989bmw535i]

I sprayed carb cleaner around the top end and it bogged slightly when sprayed at the back of both intake manifold gaskets, thoughts? It only sputters and occasionally pops when cruising, pulling a load like up a hill and it runs fine.

[JohnnyPopper]

Definitely have a vacuum leak.

Could it be too lean?

If it's a 4bbl your secondaries kick in under load overcoming a lean condition.

How old is the carb? 

[1989bmw535i]

The carb is probably 2 years old, it only had like 30 miles on it until I drove it out here (650mi) it's an avs2. I'm not going wot when pulling a load just more like 40% opposed to 15%. The stuttering is itratic, if it was a compromised cylinder wouldn't it be consistent? There is also some hesitation.

[1989bmw535i]

Alright so I changed the intake gaskets as I already had an oil leak at tye rear China wall, it seems to run different now, it kinda chugs almost like a 2 stroke that's "4 stroking" if yall know what that is, that being said it stops doing that and smoothes out when I get on it, am I just super lean?

[VileZambonie]

Sounds like fuel starvation, lean miss.

Check fuel volume, check for kinked hoses or restrictions all the way back to the tank. Check float level and drop, while you are in there clean everything.

[1989bmw535i]

Hey sorry guys, it's a daily driver so I don't have the time or money to throw at this thing, I don't think it's a fuel starvation issue as while idling it was spraying fuel from the carb inlet and I had to tighten the clamp, lean condition maybe but not fuel starvation, it ran noticeably better today but it was 20° warmer than it has been in awhile, less oxygen when it's warmer. I think I'll get a jet kit and see what I can come up with...