[12sec67]

my car runs hard till 6200 rpms then falls on it face like it has a rev limiter, when i pull the plugs they are all white like i ran out of fuel- the thing is it does it whether i'm under a load or if i'm just reving it up from an idile. i have a MSD6A not AL so i don't have a rev limiter, and i'm running the biggest jets on my carb which are .119's all around and the back are drilled out even bigger on an edelbrock 750 carb. I also have a new holley fuel pump that i thought might have been bad.i also went straight through without the fuel regulator to see if the regulator was bad. still no luck!
so now i'm at the point were it might be my distibutor which is welded and adjusted at a solid 36 degree total timming or my coil or MSD box. plugs are new!
could it be something as easy as my wires being bad?

please help ----- thanks Rich

[mr.b]

check to see if the float level is correct. You could be running the fuel bowls dry. A bigger jet will increase that problem also. You dont need 119s, especially with a power valve.

[12sec67]

Originally Posted by mr.b

check to see if the float level is correct. You could be running the fuel bowls dry. A bigger jet will increase that problem. You dont need 119s, especially with a power valve.

thanks for the response...

but edelbrock carbs don't have power valve.

what else could it be?

thanks
Rich

[jason2]

Hello,

Is it a new problem, have you reved cleanly past 6200 before? Could you be floating the valves?

Are you running a point type or electronic dist. If its a point type maybe you could drop the 6A box out of the loop and try it.

When you say the plugs are all white are you checking several plugs or just one? I have seen individual plugs go white if that cylinder isn't firing and the fuel washes it clean.



Good luck, Jason

[12sec67]

i have reved passed it before,
i pull all the plugs, none of the plugs are wet when pulled out....?
i have a duraspark distrib w/ MSD
thanks for the response jason!


i hope i'm not floating a valve heads only have 10,000 miles on them!

[mr.b]

its sounds like a fuel or valve float problem. Is it a flat tappet hydraulic cam? have you checked your valve spring pressure? Definitely check that. I don't know much about edelbrock carbs, just make sure you are getting enough fuel to it. Are you running a mechanical or electric fuel pump?

[jason2]

Hello again,

New plugs are tough to read, are they darker at a lower RPM shut down like 5400-5800 and then go white just at max RPM. If so I would keep looking for fuel problems. Does it pop or backfire at all just before or as it falls on it's face


I don't know what to say about it having the same symptom while reved in park other than don't stand in line with the fan while reving it. I dont think the engine is moving much air then because of throttle blade position.


Untill your sure your not floating a valve, I would use a little caution with the higher RPM testing. You don't want to cause any more problems especially those expensive ones.


Also keep checking those electrical components. I think losing one cylinder(bad plug wire, etc.) would kill the power but I don't think it would make the other plugs white.

Jason

[12sec67]

Originally Posted by mr.b

its sounds like a fuel or valve float problem. Is it a flat tappet hydraulic cam? have you checked your valve spring pressure? Definitely check that. I don't know much about edelbrock carbs, just make sure you are getting enough fuel to it. Are you running a mechanical or electric fuel pump?

hydro roller, electric fuel pump see sig!

heads only have approx 8,000-10,000 mile on them.

[12sec67]

Originally Posted by jason2

Hello again,

New plugs are tough to read, are they darker at a lower RPM shut down like 5400-5800 and then go white just at max RPM. If so I would keep looking for fuel problems. Does it pop or backfire at all just before or as it falls on it's face
Jason

plugs are dark brown at idile then white after W-O-T.

it startes to squaken like a duck(missing) like out of fuel.

i'm going to put bigger fuel hard line on and see what happens.maybe the stock fuel line can't flow fast enough?

we will see

thanks again for the responses

[mr.b]

what kind of electric fuel pump are u using? your not using the factory fuel injection lines to feed a carburetor are u?

I would invest in a cheap valve spring tester that you can use on the rocker arms. i use this just to see how bad my springs are. It is fairly accurate. I then use the benchtop to set up a new set. BTY, just because your heads have 8-10,000 miles on them, doesn't mean the springs couldn't have been set up wrong.


Here is a formula you can use to test your fuel system. It is best to test through the fuel bowl, needle and seat. If all else fails, just take the fuel inlet off the carb and measure your fuel amount out of the line. This will give you somewhat of an indication if you have enough fuel or not.

All the below information is from magnaflow racing fuel systems.

How can you plan your racing fuel system?
Use a hand held calculator and plan on .5 lbs/hp-hr (gasoline). Methanol Alcohol requires about 1.0 lbs/hp-hr. Use .7 lbs/hp-hr when planning a gasoline system for nitrous assist.
EXAMPLE: You have a 650 hp engine. 650hp x .5 = 325 lbs/hr (gasoline). Although you need to know how much your fuel weighs, assume for this example that it weighs 6.2 lbs/gal. 325 lbs/hr 6.2 = 52.42 gal/hr. Dividing by 60 (minutes per hour) yields .847 gal/ min (GPM).


Fuel System Requirements
In order to consider how much fuel flow your race car needs, it is necessary to consider how much power the engine makes. Although it is desirable to have reliable dynamometer data, it is not totally necessary. If using GASOLINE fuel, each 100 horsepower needs to have at least .134 GPM (gallons per minute) at an appropriate pressure to overcome the g's (g is 32.2 ft./sec./sec.) of acceleration. If using ALCOHOL (Methanol) fuel, each 100 horsepower needs at least .25 GPM.


So if your car made 400hp you would need at least .54 gallons of fuel in a minute. (this is based on race fuel weight, through the needle and seat) you would want to see more than this through the fuel line.

[12sec67]

mr.b i still using my stock fuel hard line that the car came with from the tank to the pump to the regulator to the carb.

do i need to upgrade the fuel line size to 3/8"?

[mr.b]

if it was me i would definitely upgrade to 3/8 line. But if you want to save money go do the test i posted, since it doesn't cost anything but time. hot wire your fuel pump to run with the key on or with a switch. Run the test for a minute and see how much fuel you pumped out. See if you can use a good measuring container (i use a glass beaker) then we will go from there. You may be pumping out enough fuel.

Also, are u using a fuel injection pump? Because a 155lph pump is only 41gallons per hour, which is only .68gallons per minute. This flow number hasn't been subjected to fuel line, regulator and carburetor restrictions, which will reduce it further. Remember you need at least .54gpm (after all your restrictions) to support 400hp.

[12sec67]

thanks mr.b