Choppy during cruising, but accelerations without any issue?

[kawahonda]

Curious on my current issue. It's "sputtery" when cruising, but once you floor it, there is no hesitation.

1) Fuel lines replaced. Gas tank replaced. Clean high octane gas.

2) Spark plugs replaced and gapped to .035"

3) Jets are clear. Primary venturi not checked, circuit not checked, and gaskets not replaced. Carb rebuild should happen.

4) Timing was set.

[Cuda Cody]

What carb are you running?

[kawahonda]

Carter AVS

[Cuda Cody]

A good rebuild might be all it needs.  I'm better with Holley's, but have a love for Carters.  If you want a fantastic rebuild back to bone stock try contacting @ScottSmith_Harms   He's not far from you either.

[ScottSmith_Harms]

Its really difficult/impossible to diagnose your issue from a description, that said it sounds like you covered the basics. Sometimes the tension on your secondary air door can be off and cause an idle issue (usually too loose). It sounds like you went through the fuel system, did you replace the fuel pump? Do you know your fuel pressure? How about your vacuum reading at idle?

*If you do decide on a carb restoration I'd be glad to help.

[kawahonda]

Thanks all. I ordered a rebuild kit from Mike's (guessing he has the best one out right now). Comes with a video any everything. Plus i have the service manual. I'm pretty sure we're gonna "kill it" when it comes to rebuilding the AVS!

I did not replace the fuel pump. I also have not checked the vacuum reading. I have not replaced fuel line from pump to carb (yet). It's sitting on my desk right now. From the looks of inside of the original line that I did replace, I expect the line from the pump to the carb to be just fine and not causing this issue.

It's most likely the carb needs to be gone through is my guess. But will certainly check all the other items you guys have mentioned. It's fine enough to drive around town in...drove it 10 miles today....to Autozone...and for lunch!

To be honest, today is the first time I did anything with the engine since obtaining it! Been busy elsewhere. Replaced spark plugs with Champions (yay). The spark plugs were definitely in need of replacing, lots of uneven gaps. Sadly, it did not improve the issue. So I really haven't done anything else to diagnose this. I'm a Honda motorcycle guy...my knowledge tuning V8s is limited, but that's what I'm hoping to learn. Was just wondering what the most-likely causes are. My pops is the carb-man, so I'll have him rebuild it next time he visits.

[RUNCHARGER]

My guess would be a passageway is plugged. A good cleaning and rebuild is in order. The fact that it runs fairly well otherwise is a pretty good sign.

[Chryco Psycho]

In cruise mode you are only using the jet cicuit so it could ba as simple as low float level [check this first] or jetting is too small

[RUNCHARGER]

Yep surging indicates a lean condition (which you probably already know).

[Shane Kelley]

I had this issue going on for a while. Chased everything I could possibly think of. Last thing I tried was the ignition box. Bingo!  Doesn't mean that's your problem but definitely a easy thing to try. Mine started and idled perfect. Acceleration was perfect. It wouldn't clear up until I was turning 3500 rpm. Lower steady speeds were choppy. 

[Bullitt-]

don't overlook the PCV valve

[kawahonda]

I had this issue going on for a while. Chased everything I could possibly think of. Last thing I tried was the ignition box. Bingo!  Doesn't mean that's your problem but definitely a easy thing to try. Mine started and idled perfect. Acceleration was perfect. It wouldn't clear up until I was turning 3500 rpm. Lower steady speeds were choppy.

Did you have to replace the box?

[Shane Kelley]

I had this issue going on for a while. Chased everything I could possibly think of. Last thing I tried was the ignition box. Bingo!  Doesn't mean that's your problem but definitely a easy thing to try. Mine started and idled perfect. Acceleration was perfect. It wouldn't clear up until I was turning 3500 rpm. Lower steady speeds were choppy.

Did you have to replace the box?

Yes.  I had a spare MP orange box on the shelf. I was running the MP chrome box.  You need to find one you can try before buying a replacement unless you don't mind having a spare if that's not your problem. But it sounds like yours is doing what mine was.  What ignition box you running now?

[kawahonda]

My guess is that it’s the bone stock one. I'll check today.

I’d its indeed the ignition system, may be a good time for this for a "set it and forget" option that isn't too expensive?:

https://www.jegs.com/i/Proform/778/440-426/10002/-1

I'll check the PCV and vacuum first. I have feeling my problem may "not" be the carb. It "may" be the carb, but would rather check the easy/fast stuff first! I'd like to resolve this before taking it to the transmission shop so they can focus on the transmission tune-up.

Shane, that's exactly what mine is doing. Starts up fine. Idles fine (though, I've killed it one by holding the gas+brake on a slight uphill). Usually after driving it and parking it (say I'm running in a store), then it usually takes a little bit of effort to start it again. Accelerates strong. But just "sputtery" while cruising.

Is there a way to test the ignition box?

[kawahonda]

Alright, some updates. Haven't driven it since this work.

1) Replaced bad PCV.

2) Did a vacuum test before PCV replacement. About 12.5-13.2. After PCV was about 13.5-14 but with less fluctuation.

I'll check fuel pressure next.