Need some HELP! Promax modded Holley 3x2bbls installed, "surging" "pulsing"

[biomedtechguy]

Might need to change springs in the vacuum pods.

I appreciate all replies, but that doesn't make sense. My outboard carbs and their opening performance has been flawless since I had the car for a few weeks-5 years ago.
When I first got the car, the outboard carbs were not opening. The rod that connects them needed adjustments. Ever since I got them working, almost 5 years ago, every aspect of their performance has been outstanding.

Could be end carb jets are incorrect size.

They are 86s. I am not sure what the stock metering plates equate to.
I did the Promax mods to make tuning the rear carb idle mixture screws easier, and for the improved design center carb metering block (in particular for hot cams), and the ease of rejetting the outboard carbs.
Either I get this straightened out or look for the carbs for sale because I'm not going to put them back to stock condition, although I have all of the original parts, which would go along with them.
My next move if I can't get them right is:
Either the F&B direct port injection throttle body 3x2 setup,
OR MORE LIKELY this:
https://www.forbbodiesonly.com/moparforum/threads/fitech-3x2-bbl-system.153635/

https://www.forbbodiesonly.com/moparforum/threads/fitech-3x2-bbl-system.153635/page-2#post-910987137

 

[68 HEMI GTS]

How much total advance to you have with the vacuum advance hooked up when you bring the engine up to 3g? And is it steady?

 

[biomedtechguy]

It should be around 36. I may have a chance to check that later. I did bring the timing light and vacuum gauge with me to Crusin the Coast.
THAT is how badly this "ba baba ba ba" sputtering crap is bothering me.

 

[PurpleBeeper]

Dang, Promax is good, but they're only human. Maybe they jacked up your center carb?

For what it's worth, I had my carbs all modified 8-ways come Sunday and it ran terribly. I rebuilt them again at 99% stock configuration (only change was lighter outboard springs & center jets) and the engine ran night/day better....burning rubber in 1/2/3rd gear. I'm running a stock center metering block (#61 jets, fyi) & Promax outboard plates set to stock specs. I had to call Promax and order the idle bleeds (?) not listed on their website that go up in the top corners of the outboard plates. I wish I still had my notes on exactly what I did, but that computer died. I just remember that those outboard "idle bleeds" were substantially smaller than what the plates came with & I installed them with a tiny allen wrench.

 

[biomedtechguy]

REPORT:
I called and sent a few emails to Promax since I installed the carbs, describing in as much detail as possible the problems that I have NOW that did NOT exist before.
No reply....at all....whatsoever.
I became accustomed to a lack of communication while they had my carbs.
What they said was "well I can spend time on the phone and responding to emails or work on carburetors".....
Unless something MAJOR improves in customer service, I will never recommend nor do business with Promax again (although there's not really much of theirs for the 6bbl I haven't already bought except for the fuel bowls they make)

Even IF it's NOT carb related, I should have received a reply.
This customer service is

 

[biomedtechguy]

So I heard from Promax and they sent me 3 clear sight plugs. I am finally taking some time today to get started on troubleshooting the problems. I haven't driven my car at all since Cruisin the Coast which was the 1st week of October.
So the first thing I did was pull the Promax upper fuel line 40 micron inline filter off and opened it up. This would have trapped any debris from: the section of the fuel system going from the outlet of the new WIX 3/8" filter I installed (replacing an identical filter that came with the car 5 years ago) that is at the front end of the 3/8" factory fuel line from the tank, the new Carter M6903 mech fuel pump, and the new Promax lower and upper fuel lines. The only unfiltered lines that may have held debris are between this fuel filter and the fuel inlets at the 3 fuel bowls.
Tiny amount of debris in this filter:

 

[BSB67]

Kinda hard to follow this thread. A clear chronology of events including symptoms is helpful on where to start your focus. How and when did it run before FBO and Promax? What and when was the first change, and how did it run? What and when was the second change and how did it run, etc.....

The initial problem you started this thread about, the surge at 2000-3000 rpm is usually too much timing. Manifold vacuum is very high at cruise and coupled with your mechanical you could have 45 - 50° at cruise. For that problem, simply disconnect the vacuum and give it a drive.

If that is not it, it is likely lean. In this case, and in the case of when there is a part throttle stumble, I always just go through and clean the center carb. If that does not fix it, then you start looking at the other pile of things things could make it lean at cruise. And there are several.

The transition bog thing is a carburetor(s) problem. Is the transition problem new, or always since the carbs came back from Promax?

Your problem is unlikely fuel delivery.

Today, this is what I would do. 1) change your spark plugs, 2) check your float bowls fuel levels, 3) disconnect the distributor vacuum and plug, 4) check/set initial and total timing, 4) go for a test drive. Report back

 

[biomedtechguy]

The transition bog never happened, ever before Promax modded the carbs.
My mechanical timing has not changed. The vacuum source changed location but not source, both vacuum locations provide manifold vacuum, which is what Don at FBO insists on.
My next move is installing the clear sight windows in the fuel bowls and setting the float levels in all 3 carbs.
Your to do list sounds reasonable, and is what I will basically follow.

 

[BSB67]

The transition bog never happened, ever before Promax modded the carbs.
My mechanical timing has not changed. The vacuum source changed location but not source, both vacuum locations provide manifold vacuum, which is what Don at FBO insists on.
My next move is installing the clear sight windows in the fuel bowls and setting the float levels in all 3 carbs.
Your to do list sounds reasonable, and is what I will basically follow.

You're still not being clear.
I have no idea when you got your Promax carbs. In September it was just a surge. In October it was a transition problem. When did you get the Promax carbs and have they always had a problem with transition?

When did you get the FBO ignition? You said it surged before the Promax. So that problem existed before the Promax carbs, although maybe not as bad. Did it surge before the FBO stuff?

 

[biomedtechguy]

Part of this thread was venting, which could contribute to it not being easy to follow.
I have had the FBO ignition system for at least 3 years. No problem with it for the purpose of this topic. I haven't changed anything about the distributor other than I went from a manifold vacuum source under the center carb that should have been hooked up to the choke diaphragm (and is now) to a manifold vacuum fitting in the back of the intake manifold that I installed, and I'm sure that the fitting is not leaking.
I haven't had any problems with transitioning to the outboard carbs since I first made a mechanical adjustment a month or so after I got the car 5 years ago until now that Promax modded the carbs. Previous to their mods, the transition to the outboard carbs opening was smooth and powerful under ALL circumstances.
Before the mods, if I maintained a light throttle to where the outboard carbs did not open, I would get the slightest occasional miss or sputter in the firing of my cylinders. I had to listen for it. Now it runs that way but worse, 90% of the time or more, when I am on the center carb.
It is absolutely down on power under those conditions and when it occasionally clears up the power increase is easily noticeable (center carb only).
At WOT it is down on power as well.
All of these problems are since
I changed the fuel pump to the upgraded high flow (120 gph) STOCK fuel pressure Carter M6903, changed to the stainless braided upper and lower fuel lines w/integrated inline fuel filter and pressure gauge, eliminated the vapor separator and plugged the vapor return line, replaced the existing WIX fuel filter (that came with the car) that is at the front end of the 3/8" hard fuel line from the gas tank with an identical WIX fuel filter (3/8 in and out) and Promax modded the carbs.
I wasn't expecting problems or I would have only changed one thing at a time, for example I would have only reinstalled the carbs, then done the other changes one at a time. Because I was under a hard time constraint, and I was working with all of the fuel related items from the engine end of the hard fuel line forward, I thought it was time to do everything I did since it made sense to do it. I have had that Carter M6903 mech fuel pump BNIB for 2+ years now.
Maybe this will help you understand what happened.

 

[BSB67]

Part of this thread was venting, which could contribute to it not being easy to follow.
I have had the FBO ignition system for at least 3 years. No problem with it for the purpose of this topic. I haven't changed anything about the distributor other than I went from a manifold vacuum source under the center carb that should have been hooked up to the choke diaphragm (and is now) to a manifold vacuum fitting in the back of the intake manifold that I installed, and I'm sure that the fitting is not leaking.
I haven't had any problems with transitioning to the outboard carbs since I first made a mechanical adjustment a month or so after I got the car 5 years ago until now that Promax modded the carbs. Previous to their mods, the transition to the outboard carbs opening was smooth and powerful under ALL circumstances.
Before the mods, if I maintained a light throttle to where the outboard carbs did not open, I would get the slightest occasional miss or sputter in the firing of my cylinders. I had to listen for it. Now it runs that way but worse, 90% of the time or more, when I am on the center carb.
It is absolutely down on power under those conditions and when it occasionally clears up the power increase is easily noticeable (center carb only).
At WOT it is down on power as well.
All of these problems are since
I changed the fuel pump to the upgraded high flow (120 gph) STOCK fuel pressure Carter M6903, changed to the stainless braided upper and lower fuel lines w/integrated inline fuel filter and pressure gauge, eliminated the vapor separator and plugged the vapor return line, replaced the existing WIX fuel filter (that came with the car) that is at the front end of the 3/8" hard fuel line from the gas tank with an identical WIX fuel filter (3/8 in and out) and Promax modded the carbs.
I wasn't expecting problems or I would have only changed one thing at a time, for example I would have only reinstalled the carbs, then done the other changes one at a time. Because I was under a hard time constraint, and I was working with all of the fuel related items from the engine end of the hard fuel line forward, I thought it was time to do everything I did since it made sense to do it. I have had that Carter M6903 mech fuel pump BNIB for 2+ years now.
Maybe this will help you understand what happened.

Thanks. That is helpful.

Let us know what you find out today

 

[biomedtechguy]

Thanks. That is helpful.

Let us know what you find out today

Thank YOU for getting involved, and to everyone else who is offering advice.
Unfortunately today I'm working, and with the warden aka SWMBO aka wife off this weekend, my time is not my own...

 

[BSB67]

Thank YOU for getting involved, and to everyone else who is offering advice.
Unfortunately today I'm working, and with the warden aka SWMBO aka wife off this weekend, my time is not my own...

Don't get too excited, haven't fixed anything yet. I'm not good at solving problems over the internet. But if you take a systematic stepped approach and report back, someone will figure it out.

 

[Joske2]

From all the info he gave, it sounds like a to lean or to much vacuum advance on low load conditions.
Would not be surprised if you put a vacuum meter on, that it show's nearly 20 inches at 3000 rpm at low throttle.

 

[biomedtechguy]

UPDATE!
After procrastinating, being busy with work, and other excuses, I finally buckled down and got on with the problem solving...
The first thing was removing the triple carb Promax stainless steel braided fuel line. That fuel line and the large, single lower braided line was part of "what changed" from before when the engine was running fine, and AARRRGH aka after I got the carbs back from Promax and the engine ran really bad. To recap, I also changed the stock fuel pump to the
Carter M6903 mech fuel pump. New WIX fuel tank to pump fuel filter. Promax lower braided fuel line, Promax inline fuel pressure gauge, Promax reusable fuel filter, Promax upper 3 carb braided fuel lines, Promax jetable metering plates in the outboard carbs, Promax angled idle mixture screws throttle plate in the rear carb, Promax center carb metering block.
Problem was rough, down on power at every throttle position that was especially evident when I was on the center carb only, but very noticeable even at WOT.
Between the 3 Rochesters on my wife's GTO and the 3 Holley carbs on my car, and other prep for the 8 days of Cruisin the Coast, well that and the braided fuel lines being "new" I didn't flush the lines out...
So I found a couple of tiny, hair shaped metal particles in the Promax inline fuel filter. Looked like stainless steel BRAID CLIPPINGS. Yesterday when I removed the braided 3 carb fuel lines, I flushed them out with carb cleaner and here is a zoomed in picture of what I found:

So it looks like I really messed up not flushing the NEW braided lines, and after putting probably 400 miles on my car this is what was still left in the lines.
I took all 3 carbs apart (the reusable float bowl and metering block blue gaskets are AWESOME). Used carb cleaner and sprayed/flushed out every orifice and put them all back together, started it, let it warm up, checked for fuel leaks (tightened 1 fuel bowl bolt a little and that was it, it was leaking at the bolt head bowl hole) and called it a night.
Drove about an hour to my car club's annual car show, the first car show of the season, and IT RAN GREAT!
The only additional tuning that is critical is a slight hesitation when I stand on it and the outboard carbs open. I never had that before under any circumstances. I guess I have to play with the jets in the metering plates. When I run the RPMs up on a roll and the outboard carbs open, it pulls hard, but I am getting a little pinging that wasn't there before so I'm thinking the new jets vs the stock plates may be a little leaner than the stock plates.
Thanks again for all of the help and suggestions.
My takeaway: when you install ANY new fuel system parts, FLUSH THEM OUT!

 

[moobster]

Persistence pays off.....eventually. Glad to hear your making progress.

 

[kiwigtx]

My takeaway: when you install ANY new fuel system parts, FLUSH THEM OUT!

Very important but easy to overlook. After installing new SS braided lines and fittings on my A100, we ran about half a gallon of fuel through the system before connection. Found only minor particles, but saved a lot of guesswork later.

 

[biomedtechguy]

I didn't think about flushing them until after I had a problem.
Doing too much with not enough time, and ***-U-MEing since they were new, they were clean.
Thanks guys.