well i just got a new 750 CFM holley w/ vacuum secondaries. it has about 30 mins of run time from the guy i bought it off of. basically brand new. well here's the problem.. it idles great but as soon as u try to take it off idle it starts sputterin out and fallin on its face..i adjusted the floats correctly (when i take the screw out the gas is just to the bottom of the hole and just barely trickles out) i'll do this and it runs great for about 5-10 minutes and then starts doing the same thing again. i'll mess with the float levels and then re adjust it and it will run perfect for about 5-10 more minutes and start doing the same thing again.. also when its acting up if i put it at half throttle it will rev up and start surging like its running out of gas. the fuel pump is brand new and there is no problems with the fuel system.. what could be causing this?? sticky floats or what?

thanks!

 

sounds like a fuel starvation problem.

Look for a crimped line or clogged filter.

Also remove the filters in the float bowls. They may be clogged.

 

But put filters back in before you run it again. You are also supposed to have another filter (in-line) before the carb.

 

30 minutes of run time...how long ago? If it has'nt sat for too long nothing "should be" varnished up internally, but ya never know.

Sounds like possible contamination of the needle and seat with crap/crud allowing fuel past when it should be holding it back. If you done have pre carb filter installed, do so immediately before continuing or you may have a crispy critter for a car....been there done that in HS

Are you running the right size power valve up front? They come stock with a 6.5" PV. Let the car warm upto temp at an idle, then have a buddy put the car in gear. Take a manifold vacuum reading and then divide that number in half...that is the size PV you should be running. Ex. 10" of vacuum you need a 4.5 or 5.5" PV, easier to get it on the small side. 6" of vacuum run a 3.5" or 2.5" PV, so on and so forth

Do you have the idle mixture screws adjusted properly. Just to do a double check, turn the screws all the way in until they just seat, then back them out 1 1/2 turns, this is the oout of box setting for Holley carbs and will get you close to where you need to be.

How much clearance do you hve in the front accelertor pump. Youo should be able to get a .015 feeler gauge between the arm and spring without squirting gas.

 

thanks for the help. i took the float bowls out and it was N-A-S-T-Y inside..cleaned it all out and now it works great! im gonna do the vacuum test for the power valve tomorrow..once again thanks for all the help