I think I may have made progress with the flooding overnight issue as today it started and ran fine. I found the accelerator pump for the secondaries had too much stress on at and may have been slowly leaking out as I could hear a very slight noise after I shut the car off that I isolated to this. Will see how it goes, just thought I’d post back if someone else has this issue in the future.

 

So I was wrong again. Still flooding, the bowls just slowly drain. I’m at a loss and will call Holley to try and get warranty.

 

Did you try taking the carburetor off with the bowls full to the normal running level and setting the carburetor on a blue paper shop towel (or some other paper that would show the leakage) and watch if for a while to see where the leak is coming from.

Don
Williamsburg, VA

 

yes, it appears to be fuel pressure and or warm engine related.

 

Does it leak into the paper towel then when sitting on the work bench? Can you isolate where that would be if it does?
Fuel pressure doesn't appear to make sense as there's zero pressure when the engine isn't running wouldn't you say?
With the carb on the engine, can you observe through the sight glass the level steadily decreasing?

 

There is still pressure in the system after shutting off the car. It doesn’t happen so quickly that you can observe it lowering. When the carb and fuel and engine is hot is when it happens. Not on the bench.

 

Would pressure in the fuel tank cause this? As I know I build pressure.

 

As Skinny says, the fuel line doesn't make sense. When you turn off the engine, the fuel pump stops. There will still be fuel in the fuel line from the pump to the carb inlets. When those fuel lines heat up (engine off), it is possible that the fuel in the line would expand or vaporize and push "some' fuel into the fuel bowl. That shouldn't be enough to flood anything. At some point the pressure would drop to point that the floats would cut it off anyway.

If the fuel bowls are empty every time you start (after the passage to time), it is something else.

I also question the heat issue. Typically, heat would cause the fuel in the bowl to boil or turn to vapor and it would be hard to start. Heat soaking the carb. Heat shields help. If you think this is heat related, then the test would be to start your engine cold. Once it starts, the fuel bowls should be full. Turn it off. Now you have a cold engine with full fuel bowls. Come back the next day and see what has happened. If the bowls are way down (there is always some lowering of the fuel through evaporation) and the car flooded, it ain't heat, it's something else (including a bad carb casting or machining).

Don
Williamsburg, VA

 

Just to update this. I have done lots to just be right back in the same situation. I called holley, they asked a bunch of questions and figured it was a faulty unit and suggested I return it to where I bought it as it was under warranty. Got another one, same issue. So it is something with my setup, definitely heat related. Bought a holley heat shield kit, still does not fix the problem. It actually seemed to make things worse when hot, car too rich stumble at light throttle. Now I'm back to Sofkingdom's suggestion of a stock style mechanical fuel pump with a return line. I'll install this and post back.

 

If you would, can you run down all of the symptoms once more. There's been a bit of back and forth and I've sort of lost track.
Quick question. When say "car too rich stumble at light throttle", how do you know it's rich and not a lean stumble?

 

I thought the problem was the carb was draining out overnight and flooding the intake manifold. Now it sounds like vapor lock when the car is running, which is easy to fix with recirculating fuel lines

Don
Williamsburg, VA.

 

This is why I was asking for a recap. Seems there may be multiple problems and possibly one attempt at correction causing another problem.

FWIW, on the hottest days at the track, and this is where the real heat soak scenario comes to the top, I always experienced some degree of "vapour lock" when I was dead heading my fuel pump. This was with both mechanical and electric pumps. The installation of a properly sized return line was the cure for all of that. I had greater success with the electric rather than the mechanical and was later forced to go electric due to a fuel pump cam lobe failure.

 

I converted this ZZ502 from TPI to Carb. I have an intank fuel pump capable 60 GPH at 75 psi that was there for the TPI setup. I did not change the pump. It has a 3/8 feed and 3/8 inch return line to the tank. I have a dual stage regulator. Aeromotive 13220. The first stage drops the pressure to below 15 psi and has the return line. The second stage drops to 6.5 psi for the carb.

Don

 

I'd run a deadheaded mechanical pump for years. It was during my personal horsepower wars that this flat spot mid track started showing up.
I went to a Carter return style (mech) pump but soon found that the advertised capacity through the online store I bought it from didn't match the actual output. Fuel line pressure was all over the map too as the return line size wasn't ideal.
After the cam lobe failure it was the old Holley Blue pump to the rescue. I think max PSI on that 14 PSI. Holley's bypass regulator keeps the pressure carb friendly and keeps the fuel circulating. I had to up the return line to 3/8" although it necks down to 5/16ths at the tank.
Very stable and steady fuel pressure now and no falling over mid track. It's been ages since I was stuck in traffic on hot day so I can't comment on the stability there although I would think it would be fine.
Still need to address the lack of heat shielding at several key fuel line locations as well as the brake lines.

 

Sorry for the delay, I haven’t had time to deal with the car. A recap is a good idea as I have went down a huge rabbit hole of doing too many things at once.



it started with a new rebuilt stroker, originally had a Holley 670 street avenger with vacuum secondary. I wanted to switch to a 750 double pumper with mexh secondaries as I have heard that is the carb of choice. Bought a new brawler 750 and put in a afr gauge to help tune.



After starting my carb tuning and initial setup with the 750 I noticed my fuel pressure gauge started to have a considerably lower psi and was fluctuating especially when hot. I thought it was a fuel pump issue so I bought another one and a new gauge. Everything seemed fine at first then went for a bit of a bag drive and lost all fuel pressure and the car died. Since it was a new Chinese fuel pump I assumed it just failed when hot after driving the **** out of it. So I bought an edelbrock one and installed it. All seemed ok other than I started noticing that my car was flooding after sitting overnight after shutting off hot. Then I started getting other issues that appeared to also be heat related. Engine temps are fine but after all this, it would start to make me think there may have been some Vapor lock and or hot fuel boiling issues.



Then I put on a Holley 108-70 shield and spacer and started noticing other random issues when engine hot like rich stumble as per afr gauge. Otherwise ran fine when cold.



Now as of today I’m back to my original 670 street avenger and a new Carter fuel pump with a return line and the car seems to be running excellent even when hot so far. Once I make sure everything is running good with the street avenger I’ll try to go back to my new 750 brawler to see if I can get it to work right. If not I may just pawn it off and keep my vacuum secondary 670 I just hate to give up. I like the way the engine responds with the 750 better. Another major problem with that 750 carb is that I can’t seem to get it to run lean enough at wide open throttle. I’ve jetted the secondaries down from 80s down to 67s and it still was rich at WOT. That was also with my edelbrock fuel pump however. Maybe this Carter will react differently but doubtful. I’ll keep messing with it and report back.



Sorry for the long winded response, I just have went all around the world with this damn thing. thanks again everyone!

 

There are several key takeaways from your post. The most significant to me is "Now as of today I’m back to my original 670 street avenger and a new Carter fuel pump with a return line and the car seems to be running excellent even when hot so far".
That would at least say one thing and that's that the return feature is working to keep the fuel cooler. Something I see with your update is that the fuel issue was happening after the car was put away hot. So it's not an overnight thing but a right away deal after shutting the car down. That makes more sense. I could be wrong on that though but the remaining heat and no air circulation could easily evaporate and or boil the fuel out of the bowls. If it was draining, and something you may want to check if the problem appears again, is whether the engine oil is getting diluted with gasoline.

Leaving it at that, I have to ask why you would want to go to a mechanical secondary carb? Are you a drag racer looking for nth improvement? In all of my experiences, there's really nothing a vacuum secondary carb can't do that a mechanical carb does. The ease I see is in the track tuning. One less element to deal with and that would be the vacuum secondary deployment as to when and under what conditions. If the throttle response of the 750 appears better than the 670, then that's a tuning issue with the 670. By most accounts, your response should be improved with the smaller carb given the reduced venturi and throttle blade sizes.
There are other details that are to be considered between the two as well. Booster type is one. The Avenger will (should) have a annular booster which in and of itself improves fuel metering . Read that as increased response. I can't say what the Brawler has at this point of the day as I'm a little too lazy to look it up. Downleg booster perhaps? One, the former, tends to be more street related, the latter, more racy.

Anyway, thanks for the update and I'm happy to see that there's progress. Even if it's not the progress you were necessarily looking for.

 

I am not a drag racer, just looking for to get the most out of what I have. The street avenger is definitely not as responsive feeling when revving while stopped but seems to feel more torque and low end responsiveness with a bit less high rpm pull if that makes any sense. Not sure what type of booster they both have.

I don’t think I have gas in the oil but not sure hot to tell, can’t distinctively tell from smelling. And in hind-site all misbehaving was when engine was hot on a hot days, that’s why I went the fuel pump route after sofakingdoms recommendation. Even the flooding after shut down seems to happen when hot. It did not bleed down on the bench. I also don’t have a vacuum canister so my gas tank seems to also create vacuum and or pressure very easy which I’m wondering may also be contributing to the problem. Idk

im assuming the warmer the carb and fuel gets, it provides a more rich condition? Seems that that shouldn’t be right, but that’s what my afr gauge reads even with my street avenger. Even at startup when cold I’m idling at 18 afr and once warmed up it’s around 14.

im a very novice but don’t mind tinkering. And my situation does appear to be better. Will see after more test drives.

 

Is your gas tank vented?

 

Personally, I'd go with the VS carb for a street application. AFR is AFR as far as I'm concerned so your WOT performance, if at an optimum value (12.5-13 is a general average) then the power is the same.
Cruise AFRs are another matter and I'll say the VS is better in this regard. And as for driving around town in stop and go, you've one less accelerator pump dumping fuel in.
It does sound like a heat soak issue with the fuel not leaking out (which will kill the rings in short order if left like that as it washes the oil off of the cylinder walls (ask me how I know!)) but rather boiling off.
Keep driving and keep the updates coming when you can.
​​​​​​As for the fuel tank venting, make certain that it is vented in one manner or another.

 

So I'm running a 650 Quickfuel DP and have a similar situation (not with the fuel boiling and flooding and so on, just a tune question). It runs around 15:1 at cruise, idles at 12.5:1, and runs around 12:1 at WOT. Jets are now 69 primaries and 71 secondaries. I've been operating on the assumption that drive around cruising is mostly on the primaries, and probably mostly on the primary jets. So if I need to further increase the primary jets, then it's basically going to be square jetted from here. My concern really is just that I figure it's too lean at cruise, and I feel like square jetting the carb doesnt make sense if it has a power valve. I dont want to accidentally get myself into a detonation situation on long cruises in the summer.

For what it's worth, I've already changed from a .070 idle air bleed on the primaries to a .055 idle air bleed, which dropped the cruise AFR around 0.5 points at cruise, so it did make an improvement. Since this has a four corner idle I'm wondering if I should repeat this for the secondaries?

 

Just to give an update after all the tinkering and help from everyone in this thread, I’m running like a bat outa hell now. Got some things figured, car is 95% there. No more heat soak issues, no more flooding at cold start, runs clean and good for the most part.

I can live with it the way it is but I have a small lean issue during very slight throttle at higher 3k+ rpm light cruise, according to my AFR (15-17 range) and the car starts slightly surging. So if I shift up to a higher gear it goes away and operates in range, or if I step on the gas a bit more adding a bit of a load as it adds more fuel/opens power valve. Any suggestions? I don’t know if this is dangerous to the motor or not. Also not sure if raising my primary jets is the best idea as all other conditions seems great. Any suggestions from here on how to add a bit more fuel at very slight throttle higher rpm range?

thanks again everyone!

 

Next higher # power valve

 

I currently have a 10.5 installed. I’m not sure they make anything larger in a standard flow power valve . I will see what I can find. Thanks again!

This is what I am currently running.

Power valve 10.5

Primary jet 64

Secondary jet 66

 

They do. (or at least, did at one time) 12.5.

 

looks like the largest one is a 10.5 now. Any other suggestions? Is surging during slight throttle harmful to the engine?

 

If it's surging, that indicates a lean condition. Which could result from jets that are too small or a vacuum leak. Your power valve rating should be at least 2 numbers less than your vacuum reading at idle (in gear if auto trans) and preferably half of that number...

 

If they don't have that PV anymore then you're kinda out of luck. One way or another you have to get more fuel into it under those conditions. It might be possible to modify a 10.5 by messing with the spring but I wouldn't guarantee it, never tried it, never even heard of anybody trying to do that to one.

What's your cruising vacuum? What's the vacuum while it's misbehaving? Specifically, if the vac is higher than 10.5, you don't have alot of other options.

 

As suggested, you need more data to determine exactly what's next.
As an example, I can observe engine vacuum at cruise and AFRs. Acceleration from cruise to moderately fast will see the vacuum drop. I've an 8.5 PV and will see the AFR jump several points richer when I pass through that value.
FTR: My cruise AFRs are in the 15-16 range. No surge. At least that was the last engine's results. Still sorting the new one.
Didn't see it mentioned (might have missed it) as to what your advance would be at that surging condition.
Mine is old school with a centrifugal distributor with vacuum advance. It was quite a chore to develop and make a record of my advance curve under various conditions while parked in the driveway. But I do know I'm north of 45° during lean cruise. Very drivable and excellent MPH. (My apologies if I've repeated myself).
Data notwithstanding, have you tried jetting up the primary side? That'll force a revisit to other mixture conditions but if you see cause and effect you might be on to something.

 

sorry for the delay. I needed a break from this. Maybe I’ll do a bit more before the end of the season. I’ll hit ok up my vacuum gauge and report back.

 

all good stuff. I have a similar setup. Old school hei with vacuum advance connected to ported vacuum. Not sure what the timing is at right now at various points, didn’t mess much with the curve. I do know I’m at 36 degrees total timing all in at around 3500 rpm from what I remember.