I have a street/strip 55 chevy with a 427 SB chevy and a turbo 400 trans set up to shift on its own at 5500 rpm. It ran fine last year on the street and strip with no problems, at the first test and tune this year it launched fine but started to slightly hesitate at about 330 ft. and then fell on its face at about the 1/8th mile mark, when I let off the gas and then accelerated again it took off and pulled hard the rest of the way. It felt like it wasn't getting enough fuel. I've replaced the fuel pressure regulator, the electric fuel pump, checked the fuel filter, fuel lines and fuel cell and and taken it to several more test and tunes and it still does the same thing. It only breaks down at WOT at the track, on the street it runs fine. Another thing is that I can take the car to a back road and go from a rolling start in first gear and it will go through the gears at WOT and never break down like it does at the track. That just leaves the carburetor ( 780 Quick fuel vac. secondary )but it hasn't been touched since last year when it was running fine. Maybe I need to go in a different direction but I'm just a parts changer and not much of a mechanic, so before I take it to someone that knows what he's doing, I thought I'd check here for some help.
Changing the fuel pump and regulator may have just confirmed that they're not up to the job. What's the pressure set at? Do you have fuel pressure gauge? Where does it read from. The diaphragm on the vac secondary may be leaking and not doing it's job. Unless you're 100% race fuel the new shit we have to use will screw up the soft parts in any fuel system. It's been a cold winter and any water in your system surely froze and caused issues if there was enough in it. Not knowing your car, and from the outside looking in, it sounds as though the carb can't deliver in a true race environment, as if internally it lacks the necessary volume.
I keep the car in a heated garage so their's no freezing problems and I drove it at least once a week and started it several other times a week during the winter months. Quickfuel recommends that the fuel pressure be set at 6.5 so that's what it's set at. If the carb is the problem, since it did the job fine last year you would think that the problem would be something other than it's too small.
Thanks for the reply. I ran the car last year into November and it seemed the colder the weather the better it ran. I know the carb I have will do the job because it ran fine at the track last year, I guess that , even though I made sure the car was driven regularly over the winter, something happened to the carb that's causing a problem now.
I crewed for a buddy running a B/G 56 Chevy. We had a similar problem. It turned out to be the fiberglass hood scoop getting sucked down and choking the carb. No scoop, then new scoop worked fine. Hope this helps.
I'd say carb issue. A lot of times, just clearing the jets and passages will fix it up. Check the vacuum lines for cracks. Make sure there isn't an air leak at the baseplate of the carb.
set your pressure gauge up where you can see it on the windshield, or with an isolator.. make sure it connects between the regulator and carb. .. then see if pressure is dropping as you go down the track.... long shot.. but maybe something with the timing not advancing for some reason? what kind of advance is it? vacuum? mechanical?
you need to know where your pressure 3/4 the way to the end of the track as much as the first 1/8th..
The Jalopy Journal
