have not thought of vent. if it has a roll over valve it could be backwards. i will check.
ep-thanks

Pauley

Two possible causes, fuel delivery issue or air scoop problem.

First on the pump pressure, sounds like you are running a 16v system, common problem when going from 12v to 16v and increased pump pressure. They do make a different spring for this now.

Sound like no data logger? This would be very helpful to pinpoint your issue. Assuming you have no fuel tank issues like venting or fuel pickup etc. Are you running alky, if you are when was the last time the floats were changed? They absorb alky and get heavy which requires float level adjustments to lower fuel level. This reduces float drop, float bottoms out on the bowl before the needle clears the seat which restricts fuel flow so the bowl runs out of fuel,,, motor lays over reducing fuel demand which allows fuel to build back up,,, repeat, repeat...
Needle and seats too small for combo restricting fuel flow, drains bowl as a result. Other restrictions in the fuel delivery system.
If you make a large jet change with little to no results, this indicates a fuel flow issue.

Air scoop issues, air flow becomes too turbulent over the carb and messes the signal up to the boosters. Easiest check for this is to add an air filter or even a velocity stack on the carb which will smooth the air entering the carb. I have seen issues with both sealed to carb scoop setups and those that aren't sealed.

One other item to check, especially with small fuel tanks, where is the fuel bypass return located in the tank. I have seen these dump in at the top of the tank right over the supply bung for the fuel pump. This can be an issue; the return fuel flow can aerate the fuel in the tank which can cause air and fuel to be delivered to the carb. The bypass fuel return should have a line inside the tank with the exit well below the fuel level and away from the pump supply bung!

Good luck

quote:

Originally posted by 1320racer:
This ^^^

Further…

quote:

Originally posted by C Hodge:
Any carb builder will tell you two carbs are more consistent.

1. I’ve had many conversations with the top carb builders in the country and not one has ever stated that.
2. Look around, The Who’s who of bracket racing all run one carb.
3. 2 carbs aren’t going to make a car that is already deadly consistent, more consistent. One good carb is all we need and is more than enough for engines making upwards of 1400HP.

I would say that two carb setups are not any more consistent and are not as consistent for many running them out there now!

EXACTLY!

TOP38...KNOWS!

thanks TOP i will check these things out as well. I don't have room for an air filter so i suppose i could remove the scoop to see if it effects it or makes it better.

it is a gas carb. the smaller carb would not run at all. i went from a 1150 to a 1050.

ep

quote:

Originally posted by TOP38:

quote:

Originally posted by 1320racer:
This ^^^

Further…

quote:

Originally posted by C Hodge:
Any carb builder will tell you two carbs are more consistent.

1. I’ve had many conversations with the top carb builders in the country and not one has ever stated that.
2. Look around, The Who’s who of bracket racing all run one carb.
3. 2 carbs aren’t going to make a car that is already deadly consistent, more consistent. One good carb is all we need and is more than enough for engines making upwards of 1400HP.

I would say that two carb setups are not any more consistent and are not as consistent for many running them out there now!

No disrespect, but when it comes to a tunnel ram and 2 carbs, AND alky, you and Ed would be wrong on it NOT being MORE consistent. That setup is one of the BEST setups here in the midwest for consistency and speed. We do have some great alky carb builders in our area, and maybe thats the differce, but i have never seen a tunnel ram, and 2 alky carbs not be WAY MORE consistent, and .03 - .05 faster, minimum. This setup also doesnt slow down in summer like a single carb does.

I will continue to argue consistency and I'll put my car up against any over the course of an event, racing day into night. Matter of fact my car frequently puts up back to back runs that are identical to the thousand and when it doesn't, the runs typically vary by 1-3 thousands and you can't make blanket statements about alky as the performance gains diminish as the cubes get bigger and you'll typically run slower on alky with a 615 and bigger. Our own racerdude2054 and his father coolroy found that out after switching to gas a few years back after arguing alky's consistency and performance on their dragsters.

quote:

Originally posted by pauley:
my new car has a problem if anyone has any ideas. along the same lines as OP. it leaves fine but down track it lays over like it is starving for fuel then will pick up then lay over like no fuel. i have a magna fuel 500 pump as well front tank dead head regulator set at 7 psi. the only thing i have found is the factory bypass is the smaller outlet hole and stiff spring. i have run in to this on my camaro when i went to this pump on it. the pump pressure is probably above 30 psi. i drilled the bypass and cut the spring, run the bypass out as far as i could so now i am at around 18 to 20 psi at the pump. just with this change my regulator pressure went from 7 psi to 10.5 psi so i reset it back to 7. i have not run it since this change.

does anybody have any ideas as to what might be going on?

i tried a smaller carb before this and it was much worse. wouldnt run at all down track. on my camaro my regulator could not control the 30+ psi pump pressure. once i lowered the pump psi everything was good. wonder if something like tat is what i have going on.

ep-any help is appreciated

A too restrictive filter on the suction side of the pump could cause issues.

No filter or a large micron rated filter(100)on these real high output pumps or they will cavitate....

I had this issue with an Aeromotive A-2000 but it did it right away so I was not chasing the issue out on the track...

quote:

Originally posted by 329L:

quote:

Originally posted by TOP38:

quote:

Originally posted by 1320racer:
This ^^^

Further…

quote:

Originally posted by C Hodge:
Any carb builder will tell you two carbs are more consistent.

1. I’ve had many conversations with the top carb builders in the country and not one has ever stated that.
2. Look around, The Who’s who of bracket racing all run one carb.
3. 2 carbs aren’t going to make a car that is already deadly consistent, more consistent. One good carb is all we need and is more than enough for engines making upwards of 1400HP.

I would say that two carb setups are not any more consistent and are not as consistent for many running them out there now!

No disrespect, but when it comes to a tunnel ram and 2 carbs, AND alky, you and Ed would be wrong on it NOT being MORE consistent. That setup is one of the BEST setups here in the midwest for consistency and speed. We do have some great alky carb builders in our area, and maybe thats the differce, but i have never seen a tunnel ram, and 2 alky carbs not be WAY MORE consistent, and .03 - .05 faster, minimum. This setup also doesnt slow down in summer like a single carb does.

Jeremiah
Let's be clear here, first I said many dual setups are not, and I stand by that! No different than a single carb deal that's not right.
I never stated anything about yours, not to mention a carb or carbs is ONLY one piece of the combo that contributes to constancy.

The next thing is predictability, gas is more predictable than alky.

Some facts:
Alky is not faster in many combo's built today, example, large CID BBC running SR20 heads.
Alky hates moisture, it's humid on the east coast in the summer, alky combo's slow down, especially at night when gas combo's go faster...

I can go on and on here, but the point is both fuels work very good with the right combo and tuner! I have run gas and alky carbs along with alky injection and have won with all.

If I had to pick one item in a good running combo that is the most important, it's not the carb, it's the converter!

Jeremiah
Let's be clear here, first I said many dual setups are not, and I stand by that! No different than a single carb deal that's not right.
I never stated anything about yours, not to mention a carb or carbs is ONLY one piece of the combo that contributes to constancy.

The next thing is predictability, gas is more predictable than alky.

Some facts:
Alky is not faster in many combo's built today, example, large CID BBC running SR20 heads.
Alky hates moisture, it's humid on the east coast in the summer, alky combo's slow down, especially at night when gas combo's go faster...

I can go on and on here, but the point is both fuels work very good with the right combo and tuner! I have run gas and alky carbs along with alky injection and have won with all.

If I had to pick one item in a good running combo that is the most important, it's not the carb, it's the converter![/QUOTE]

100% AGREE ON CONVERTER.

Here in the corn belt, we see high humidity all day and night, we normally see 100+ water grains from june through september, and most alky cars run dang near the same et at 3 pm as they do at 10 pm, and on most combos up to 1100 hp run faster on alky MOST OF THE SEASON than they do on gas. Oxy fuels have got gas closer to alky in consistency, and will run within .02-.05 of alky in the heat, but WILL blow the doors off alky in mine shaft air, like we get 4-6 TIMES a year. For us, alky is the way to go for most bracket combos.

quote:

Here in the corn belt, we see high humidity all day and night, we normally see 100+ water grains from june through september, and most alky cars run dang near the same et at 3 pm as they do at 10 pm, and on most combos up to 1100 hp run faster on alky MOST OF THE SEASON than they do on gas. Oxy fuels have got gas closer to alky in consistency, and will run within .02-.05 of alky in the heat, but WILL blow the doors off alky in mine shaft air, like we get 4-6 TIMES a year. For us, alky is the way to go for most bracket combos.

I agree with this.

If you look at fuel flow and afr on a graph, compare/ correlate it to et given the weather conditions, it could help show which fuel is more consistent given the conditions changing on the track.

EFI gives you the ability to monitor this, along with following the desired afr, or changing fuel flow anywhere in engine rpm and changing conditions.

I ran gas on my 12 degree 632 because it wouldn’t run on alcohol and thats the only reason I’d ever run gas. 10k race today double entered and I’ve ran 6.071 to 6.078 flat out every pass and taking 2 entry’s to 3rd round as of now. No reason to run gas when I know how good the car is with my 33x16s and alcohol as ED says. My combo band-aided is as good as most that think there stuff is good. I’ve ran both Gas and Alcohol and know over the years what is best for my car. ED I will say I screwed my car up when I tubed it. It was more consistent and faster on a 28X10 tire but now that it’s set up for the 33X16 I’ll do what I need to with weight to make it work

quote:

Originally posted by C Hodge:10k race today double entered and I’ve ran 6.071 to 6.078 flat out every pass and taking 2 entry’s to 3rd round as of now.

Must be fixed...... Great Work and Good Luck today !!!

Not fixed but it’s good where it’s at for this weekend. I agree with top I need to get pump psi down but I have to get carb psi up first. Trying something almost every week to get pressure up and end up right back where I’m at now.

As I stated, your car, your time and your money. Doesn’t have to make sense to me but I can’t get excited about any car/combo running in the 6s today no mind with a sheet metal manifold and 2 carbs on alky, along with a dry sump and 16” tires, not when my door car runs 5.50s with a single 4150 carb on gas atop a Vic Jr. manifold and rolling on 12.5 slicks. Just saying seems like an awful lot of effort and expense to run that slow and still be chasing the same problem for 4 years.

This message has been edited. Last edited by: 1320racer,

I have made 460 runs in my S10 since we started racing it last season. Pretty mild 406, runs 6.40s.
Alcohol.
rear 8 gallon tank. #10 to MagnaFuel 500, #8 bypass to tank off pump with down-tube to 1/2 tank depth, and #10 to the regulator (inline stainless filter on the way there), 27 psi at the regulator, #10 return to tank (return line has a "down tube" that goes below 1/2 tank to cut down on aeration). Regulator is Aeromotive ByPass, #8 to either a Heller-bilt 750 or Rupert 1000cfm alky carb.
PSI out of regulator when dead-headed againt a $8 plug is 6.5 psi. Can never see or log more than .5 lb variation in pressure at end of the fuel log, never.
Truck has been unblievably good once I fixed the rear suspension and rear springs.
Not sure what would cause the N&S to not handle 7 psi or less pressure as I have never seen that unless the floats were "heavy".

Good luck, hope you find it.

Jok

Jok I’ve tried new floats and even different bowls with new floats. New APDs will be at the house Friday but I’m out of town this week so won’t get to try them. Gonna bolt them on and see if anything changes. If not I have a few more things I’m going to try.

quote:

Originally posted by C Hodge:
New APDs will be at the house Friday

As always ED your right I may be a little nuts. But I installed the APDs turned pressure up to 8 pounds and set the floats without issue and the pump still set at 38psi. So now I can turn the pump back down to where it should be and race. Now to figure out if the issue is the APD bottom feed bowls or if it’s something screwy in the carbs

Any improvement on carb situation?