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Discussion Starter #1
Okay over the weekend at the track I started helping a guy pitted near me with a 67 Mustang with a 351W with a supercharger and a Demon carb.
When he goes WOT it will run good for a few sec's and then die out and if backs off the trottle it will stumble of a little bit and then start working better at about 1/2 throttle.

when he drives it on the street there is no issues until he tries to go WOT

We changed the fuel line at the track to a big 1/2 inch line.
We also tried different fuel pressure setting 6psi on idle goes up to 9 when revved up on low boost in the pits
we also tried idle 9psi and boost 12 psi

it has a MSD box with boost controller

What info do you need? This is a good older guy that I want to help out.
 
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what the gaps on the plugs sound like he blowing the spark out take it down to .023 as a starter. That Deamon carb is not the best for a blow thur look at csu or cs carb alot better hope this helps. Jason
 
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If the plug are not blowing out look to see if he has gets extsions. Dont cut the fuel back a real fast way to pop a heads gasket keep it at 6 to 8 psi base and what reg is he running.
 

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Discussion Starter #6
If the plug are not blowing out look to see if he has gets extsions. Dont cut the fuel back a real fast way to pop a heads gasket keep it at 6 to 8 psi base and what reg is he running.
I'll look to see what he had all I know is it was blue with a vac line to the cover on the carb, was running over there in the middle on working on my car kind of a crazy day :)

if it was blowing the plugs out would they take a little bit to clear up after?
 
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no as soon and you get out of it a little it will come right back. most of the time people keep the .032 to .035 gap and thats just to much on a turbo or supercharged motor.

Yea try to find out what reg he is running you want to stay with a 1.1 boost ref so every psi of boost the fuel will go up 1 lb so if your base is 6lbs and you run a max of 12psi of boost you want it to be 18 lbs at max boost. Hope this help you out a little Jason.
 

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Sounds like either the fuel pump or regulator isn't up to the task. A lot of guys like the aeromotive boost referenced regulator for reliability and a true 1:1 ratio of fuel pressure to boost press. Can he see what the fuel pressure is doing (after the regulator) when he goes wot?
 

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i was going a turbo with a blow thur carb and i dont remember what they had to do to my carb but it had to be made for a blow thru set up also i had to add the aeromotive reg for boost. it adds 1:1 and i had the reg on the wrong side and the fuel pressure would fall off and it was doing the same thing. he needs to check the fuel pressure and make sure the pump can make that pressure
 

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you must have a boost referenced regulator.......I have one for sale that has very little use, made by C&S Specialties..

also, the carb you are using is going to give you nothing but a headache. I ran a successful blo-thru setup and these 2 pieces are KEY to making it work.
 

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How much does it rev before cutting out? Is he into boost yet? Can he get into boost with light throttle? Does it stumble if he stabs the throttle from a low RPM (no boost)? The answers to these questions should help point you into the right direction.

Is his squirter shot coming out too quickly...and not allowing the airflow to start pulling additional fuel out of the jets? Try to borrow a wideband O2 sensor to get it tuned.

$0.001 no change given :).

Have a good day!
Michael
 

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I believe it would be worthwhile to have a look at the plugs. A supercharged engine builds horrendous cylinder pressures and even with an MSD 7 you can be down to about a .020 plug gap to make it light...
 

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Discussion Starter #16
it's acts like someone turned off the motor I think we have 2 things going one one the plug gap is to large and also the fuel pump can't keep up. part throttle seems to be okay but full throttle will kill it, he will get through 1st he's saying by then it will die out and need time to recover.
He has a bigger fuel pump we will install this weekend and reset the plug gap and re-ajust the fuel pressure then we will have a good base to go from and I hope to be running good or a least have better info.

Thanks guys
Dan
 

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it's acts like someone turned off the motor I think we have 2 things going one one the plug gap is to large and also the fuel pump can't keep up. part throttle seems to be okay but full throttle will kill it, he will get through 1st he's saying by then it will die out and need time to recover.
He has a bigger fuel pump we will install this weekend and reset the plug gap and re-ajust the fuel pressure then we will have a good base to go from and I hope to be running good or a least have better info.

Thanks guys
Dan

Which regulator and pump is he running? I'm not the smartest guy in the world but I do run a blow through myself. The fuel pressure needs to rise 1psi for every 1psi of boost. I run a C&S barb and have had absolutly no issues with it. I also switched to a C&S belt drive fuel pump and it works awesome on both the strip and the street. Not saying he needs a belt drive but a good fuel pump is a must with a blow through. Also, if he has a dead head fuel pressure regulator it needs to be replaced with a return style.
 

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True that if there's any time you should go overkill on the fuel pump is when dealing with boost. Even the best mechanical fuel pumps should only be used with about 6psi of boost or less (talking about the normal type mech pumps, not belt drive). And yes absolutely to the suggestion of a return style fuel system also. I hope his pickup tube in the gas tank isn't the stock size. I know for my '69 stang it's only like 3/8" or slightly smaller. Definately sub par for blowthru performance use. More like 1/2" is needed all the way from the tank to the carb. The regulator is a big deal too. Needs to be a high flow type that well do justice to the big pump and lines.
 

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Discussion Starter #19
True that if there's any time you should go overkill on the fuel pump is when dealing with boost. Even the best mechanical fuel pumps should only be used with about 6psi of boost or less (talking about the normal type mech pumps, not belt drive). And yes absolutely to the suggestion of a return style fuel system also. I hope his pickup tube in the gas tank isn't the stock size. I know for my '69 stang it's only like 3/8" or slightly smaller. Definately sub par for blowthru performance use. More like 1/2" is needed all the way from the tank to the carb. The regulator is a big deal too. Needs to be a high flow type that well do justice to the big pump and lines.
He did have a 3/8 line but we changed it at the track to 1/2 inch but the tank line was stock so that is going to be changed and a BG 400 pump will be installed.
I think his reg was a aeromotive boost referenced regulator but right now it's set as a dead head setup not good but I think he was planning on changing that also.
 

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He did have a 3/8 line but we changed it at the track to 1/2 inch but the tank line was stock so that is going to be changed and a BG 400 pump will be installed.
I think his reg was a aeromotive boost referenced regulator but right now it's set as a dead head setup not good but I think he was planning on changing that also.
It needs a return style system for sure. It will make the pump quieter and the pump will live longer. A BG 400 pump is not enough. It doesn't put out enough pressure. If you have 7 psi as your base pressure and add 20psi of boost you end up at 27psi of fuel pressure. The BG 400 only puts out 25psi. Also keep in mind that the higher the pressure the less volume the pump flows. Here's the pump and regulator that it should have on it.

http://www.jegs.com/p/Aeromotive/Aeromotive-Eliminator-Fuel-Pump/750192/10002/-1

http://www.jegs.com/p/Aeromotive/Aeromotive-A2000-Carbureted-Bypass-Regulator/751924/10002/-1

Run -12an line from the fuell cell or tank to the pump. Run -10an line from the pump to regulator. -8an from regulator to carb. finally, run a -10an return and the fuel system is done. Also remember that the referance line for the regulator needs to be plumbed into the carb hat and not the manifold. If it's plumbed into the manifold it will see vacuum and cause some nasty issues.
 
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