Help, Might be wrong on my Demon carb.

[deputycrawford]

I have a complete MSD ignition with 6AL box and all.  My problem is my plugs don't color. Barry Grant company asked me a zillion questions about my engine, car, weight, intended use, cam size, vacum, and much more before they sent me the Mighty 750. I have jetted it up 9 sizes and can't get almost any color on my plugs and the cars is starting to slow down from a best of 13.19 to 13.35. The 13.19 was in 50 degree weather and the 13.35 was in 75 degree weather but everything else stayed about the same. I am now hearing that MSD boxes cause such a complete burn that the plugs don't color. Am I going in the wrong direction?

[dodge freak]

Well did you try going down? I have seen you should go 2 sizes at a time to make a difference but it seems like once it is close even one size makes a difference. This gas today can be very "clean" and without any lead anymore in it makes it hard to read the plugs. I would think 9 sizes would make a hugh defferance  how the engine ran. Why don't you jet it back like it was and drive it for a little while, then go up AND down one to three jet sizes and see if you can tell just by driving it if its any better. Go slow when you change the jet leave it alone for a day or two. This way you can tell how it runs when the engine is hot ,cold and at different speeds and rpms. You can always call back Barry Grant and talk to them again.

[Chryco Psycho]

I agree go back , I have seen a lot of cars on the dyno where the plug color seems off but the power & o2 sensor is reading great

[jg68]

Don't be to concerned about not seeing any real coloring on the porclein, look at the end of the threads, the flat part, you should have a full burn & medium color & chalky, if its black, your too rich, if you look way down in the plug at the base of the porclein, thats your fuel ring, it should be light brown or tan, the top part of the porclein coloring is idle & low speed, look for any black pepper spots also, they say thats detination, sometimes the plugs look white untill you compare it to a brand new one under a light, then you can see its not as white as you thought! make sure you have the currect heat range, check the ground strap for timing, the burn pattern should be in the middle of the bend, the hotter temps most likely affected your ET, that tells me you were on the rich side, if you find you have to jet up too much, you most likely need a bigger carb, this is ONLY if your fuel system is supplying enough fuel! pick a day, start with the stock jetting, keep jetting up F&R till it slows down, if the temps cool off or B/Pressure rises, you'll go faster with more fuel, you will go slower in the opposite with the same jets!

[deputycrawford]

ok, I have a 120 GPH fuel pump and a 1/2 inch fuel sender and line. I am also running a fuel pressure regulator. I have 6 psi at idle, 7 to 8 at light throttle and 4 to 6 psi through the traps. I have jetted down five sizes to start and found the car comes on really hard now. It even idles better. I will run the car and check the plugs. I will jet down until the car slows down. I went to big at first. Thanks for the info and keep it coming. I want my 4000lb car in the twelves with the original block 383.

[jg68]

ok, I have a 120 GPH fuel pump and a 1/2 inch fuel sender and line. I am also running a fuel pressure regulator. I have 6 psi at idle, 7 to 8 at light throttle and 4 to 6 psi through the traps. I have jetted down five sizes to start and found the car comes on really hard now. It even idles better. I will run the car and check the plugs. I will jet down until the car slows down. I went to big at first. Thanks for the info and keep it coming. I want my 4000lb car in the twelves with the original block 383.

You may want to check your voltage to the pump, you should be holding a steady pressure at all times! I had my blue pump at 7lbs. with a 3/8 line, it was rock solid at 7lbs. at ALL times, even through the traps, this could be some of your problem, also check your fuel regulator. there is definately a problem somewhere.

[deputycrawford]

I'm sorry. I forgot to tell you that it is a mechanical pump. The regulator does change the pressure at idle but I do have a return line also.

[Chryco Psycho]

you will be safer slightly rich than lean................ jsut so you know

[jg68]

I'm sorry. I forgot to tell you that it is a mechanical pump. The regulator does change the pressure at idle but I do have a return line also.

You may want to upgrade to an elec. pump, with the fuel pressure bouncing around like that isn't good, it will affect the metering on the carb, especially with it at 4 lbs through the traps, that would lean it out up stairs, what kind of pump is it?

[deputycrawford]

A new Carter 120 GPH mechanical pump. Oh, and Chryco, I did think about the jet down until it slows down. That soes sound kinda backwards doesn't it? Lean is mean to a certain extent. Then its just piston material on the plugs...lol  I will start at the Demon "factory" settings and jet up until it slows.

[Chryco Psycho]

down is OK too , just stop when it quits gaining power & possibly even up jet 1-2 sizes at that poinjt to be safe

[deputycrawford]

I will be careful.....and thanks for the info.

[Steve P.]

What fuel pressure gauge are you using and where is it mounted??

[deputycrawford]

My guage is an Auto Meter Sport Comp electric guage. I have the electronic sensor mounted in the end cap of my fuel log. I thought that would be better than running a pressurized fuel hose into my interior. It doesn't really bounce that much. I have adjusted the regulator. It idles at 6 psi. When the pump initially speeds up with the engine, it seems to go to around 6 1/2 under most conditions. I have not checked it throught the traps lately. I can check it under full throttle soon and let you know.

[Steve P.]

I wondered about the gauge thinking maybe you had a fluid filled gauge. VegasMike had quite the runaround with 2 of them. Then he tried a NON-fluid filled at the request of the BARRY GRANT tech. Guess what, no pressure loss at all. The fluid filled gauges lie when the get warm/hot. 

[deputycrawford]

Ok, no fluid filled guages here. I do like the Sport Comp guage. I just wonder if a mechanical pump is supposed to move around like that at certain throttle inputs.

[jg68]

Ok, no fluid filled guages here. I do like the Sport Comp guage. I just wonder if a mechanical pump is supposed to move around like that at certain throttle inputs.

What kind are you running, my Carter strip mech. pump held fairly steady at 10 lbs. it never blew the needle/seats off either

[deputycrawford]

I run the Carter street pump. It was supposed to be the 6 psi pump. I cheked it and found it stayed around 8-9 psi. Thats why I put the regulator on.

[jg68]

I run the Carter street pump. It was supposed to be the 6 psi pump. I cheked it and found it stayed around 8-9 psi. Thats why I put the regulator on.

When your at the track, turn the pressure up to 7-8 lbs. reset the floats & see if it runs better.

[Chryco Psycho]

I wondered about the gauge thinking maybe you had a fluid filled gauge. VegasMike had quite the runaround with 2 of them. Then he tried a NON-fluid filled at the request of the BARRY GRANT tech. Guess what, no pressure loss at all. The fluid filled gauges lie when the get warm/hot. 

You have to be kidding me the drawn out problem with fuel pressure was just a crap guage 

[firefighter3931]

I wondered about the gauge thinking maybe you had a fluid filled gauge. VegasMike had quite the runaround with 2 of them. Then he tried a NON-fluid filled at the request of the BARRY GRANT tech. Guess what, no pressure loss at all. The fluid filled gauges lie when the get warm/hot. 

You have to be kidding me the drawn out problem with fuel pressure was just a crap guage 

Neil, i'm sure there were more problems than just the guage....it was burning up fuel pumps at an alarming rate until Mike installed a return line. 

Those deadhead pumps don't appear to work as advertised....at least in this application !  The guage was merely giving a false reading from what i gathered.


Ron