No RPM increase

[78anniversary]

Hello all, i have a stock 78 corvette with a 17058204 that i rebuilt this spring.  The carb is rebuilt to stock specs and has ran great up until yesterday.  I pulled on the the expressway last night and mashed the pedal to the floor, when I thought the secondaries should just be opening, right about 3-3500 rpm, the motor just went flat and stopped increasing power and wouldnt accelerate and increase rpm from that point.  driving the car it accelerates fine under normal driving conditions, as long as i dont ask for the secondaries, once the pedal is pushed to activate them, then it flattens out...

where do i start?  its funny, it ran great last time i drove it. 

[73 Z28]

It sounds like the small holes that feed fuel to the secondary fuel wells are blocked preventing fuel from feeding the secondaries when you get into the throttle. To fix this your going to have to remove the airhorn and remove the float, then you'll see 2 small holes about 1/4 inch off the floor of the fuel well one on each side. These allow fuel to flow into the secondary wells. These holes can be cleaned out with a .040 drill bit using a pin-vise. While you have the airhorn off, you should also readjust the spring tension on the airvalve to about 5/8 turn after the screw makes spring contact, and inspect the smaller brass tube ends that hang down from the airhorn. Make sure these aren't restricted, but if they are, use a .036 drill bit to clean them out. Then reassemble and test drive.

Paul

[Frank400]

I'm thinking secondary lock-out.  Throw this away.

[429bbf]

78  start simple .warm it up and pull the air cleaner and rev it up by hand and see if the secondaries are tring to open.if there not see whats stopping them.if they are then id look for a fuel problem . just my 2 cents. dean

[78anniversary]

Thanks guys  i took it out this morning for a drive with the air cleaner removed, so i could hear if the secondaries are opening, and they are.  But as soon as they open is when it goes flat.  Im thinking its not getting fuel, because if it it got too much fuel it seams it should finally catch up and go.  But it doesn't, just stays flat.  I guess I'll try what 73 Z28 mentioned and make sure its got fuel in the bowls back there. 

Any other suggestions please chime in.

[von]

Sounds like it might have a fuel flow problem from the tank. I'd change the fuel filter(s) first and see if that helps. Or could be a weak fuel pump. The last resort, and I've had this happen before, is the mesh sock that's on the fuel pickup in the tank is getting clogged with sediment in the tank. If it is the best cure IMO is to remove the sock from the pickup and install an in-line filter between the tank and pump.

[429bbf]

i forgot about it until von said something . my wifes car 1981 vette would do the same thing. if you held it to the floor in passing gear it run up about 85 to 90 then fall on its face and them rev full bore again. it was still under warranty.so we took it to the dealer and they found a bull duram sack on the screen.for the guys that dont know what that is .its what tobacco used to come in for folks that rolled there own smokes.dean

[78anniversary]

Thanks for the info guys, unfortunately, I am out of town for work until the 11th.  So won't be able to dig into it until then.  Doesn't it stink how work seems to interfere with our hobbies?

[78anniversary]

For anyone still following this thread.  I found one of the secondary metering rods came off of the hangar and was just sitting down in the bottom.  Problem solved. 

[Cliff Ruggles]

Good news.  Had the same thing happen on my last outing to the track.  I changed metering rods and one fell off during the install and I didn't see it.  Had to abort the run....Cliff