Let's play "Diagnose this symptom!" (Six Pack-related)

[Grec]

Here's my issue:

Car can can be sitting for days, in 40 degrees. Go in, pump gas pedal twice, hit the key... Vroom! Roars to life IMMEDIATELY. Perfect.

BUT... drive the car for 30 mins, go into a store for 10-15 mins, come back out... turn the key... (without touching the gas pedal) and it struggles to start up. This happens every time without fail.

It definitely has the feel of a partially-flooded carb.

Any thoughts? This is really annoying... and a bit embarrassing to have my bas a$$ car struggling to start.    Lol.

[70chall440]

A number of possibilities, however what comes to mind is

- venting issues in the fuel system (try cracking the gas cap)
- sticking needle/seat - run some cleaner through the system or take them apart (or gently tap on the carb with the handle of a screw driver)
- heat soak in the coil causing a weak spark
- cracked vacuum line that is opening up when the line warms up and gets soft (unlikely but...)
- warped carb bases that are creating a vacuum leak once warm
- loose carb/s creating/allowing a vacuum leak when warm (check all studs, hand tight with a wrench)
- poor carb venting (unlikely but possible) (my 440-6 doesn't have the rod for the vent and I have never had this issue, but I read somewhere that the vent on the center carb was designed to help hot starting issues)

I am sure there will be a lot more opinions posted, but this is what I am thinking.

[Oldschool]

What is the timing set at? Timing that is a little too high will cause that. When the engine gets hot, it doesn't like timing. When it cools off it's great again. It also could be some vapor lock issues, but at 40* ambient temp, that isn't very likely. Back the timing off 3-4 degrees and drive it see if it takes care of the issue...   

[70chall440]

What is the timing set at? Timing that is a little too high will cause that. When the engine gets hot, it doesn't like timing. When it cools off it's great again. It also could be some vapor lock issues, but at 40* ambient temp, that isn't very likely. Back the timing off 3-4 degrees and drive it see if it takes care of the issue...   

  I meant to list timing as well, I did have this exact issue as well.

[dfrazz]

I know my 6 barrel is sensitive when shutting off for just a couple minutes and trying to start again, very easy to flood.  I have learned when I can start it without touching the gas (usually 5 min or so), to when I need to give it one pump of the pedal, to hours or overnight and I need to pump the pedal a couple of times.

[Chryco Psycho]

What do the plugs look like ?
 It ould be running rich making for easy starts but difficult restarts

[Grec]

I'll try to address all at once. :-)

- My gas cap doesn't even seal well enough to keep gas from coming out on hard cornering, so I doubt it's a venting issue. Lol
- Center carb was just re-built by a guy who supposedly knows his stuff. Outboards were gone through as well and checked out.
- Coil is brand new MSD Blaster II
- All vacuum line is brand new
- warped carb base(s) or loose... I'll have to check

- Timing is set at 12* / 32* (or very near that)

- Plugs I'll have to check


Would the issues you guys mention show other symptoms as well... other than the rough re-start? This thing runs damn well otherwise...

[734406pk]

As CP says, check your plugs and post back their condition, which will help with diagnosis. BTW are you running factory cast iron cylinder heads with an exhaust cross over to operate the bi-metal choke element?   

[Grec]

Running factory 915s with a repro Edlebrock Six Pack intake and the "factory" choke setup.

Will check on the plugs and post results.

[734406pk]

Ok Great! Check the plug color and post back. Also would you know the jet sizes that you're running in the center and outboard carbs?

[Grec]

Also would you know the jet sizes that you're running in the center and outboard carbs?

That I do not know. I would think it's whatever standard size Holley sends them out with.

[70chall440]

4 additional things to consider

1. check the choke and make sure it is functioning properly. When hot, it should be open or mostly. I experienced this issue once.
2. in stock form, BB 6 packs ran fat (rich) which was done purposely. You really have to be spot on with the timing, choke, etc
3. I was running a "brand new MSD" coil as well, it took a dump and I spent a lot of time trying to figure out what the issue was and eventually ruled out everything else. In other words, trust nothing, test everything.
4. while you are pulling your plugs, inspect the wires to make sure nothing it arching (had this issue as well)

I have run BB 6 packs for a very long time, I cannot say I am an "expert" by any stretch, but I have spent countless hours diagnosing and adjusting.

[HP_Cuda]

Can you smell fuel when this problem occurs?

The reason I ask is that it could be electrical but I'm with Cryco - check your plugs and then move on from there.

[Grec]

So... I pulled 5-of-8 plugs. The all looked exactly the same and I didn't feel like dealing with the PITA ones. 

They look pretty spot on to me...

(This is drivers side, front to back, and rear pass side.)

Oh... and this is after about 800 miles of driving

[70chall440]

They look pretty good.

If this was my car, I would look hard at the electrical side first; make sure the timing is good, distributor is set up and working right (vacuum advance is functioning correctly); coil is producing the needed spark in all conditions. After that and assuming no changes, move on to the fuel system (or start here, doesn't necessarily matter).

I will say that I had somewhat of a similar problem on my Challenger; I could start it, it would run seemingly well, get it hot, turn it off and then it didn't want to start. Let it cool and it would fire right up. What I found out was that I was running a view all fuel filter that looked clean, however it turn out that it was actually clogged and while it was running it was slowly clog up and while there was pressure in the line it would not allow the bowls to fill or was presenting a vaccum. Once I figure this out (replaced the fuel pump, the pump rod, etc); all was good. During this exercise, I also figured out that my coil was sporadic in the amount of fire it was producing.

Take one thing at a time, make a change and test it. You will figure it out. I also went with the best spark plugs I could get and replaced each part with the best I could get as well.