2x4 guys, anyone running jet extenders in their primary bowls?

[6667fan]

I don’t feel my launches are compromised without them but down the track there is a high gear stumble. Could be any number of things but throwing some money at two extension kits is easy.

Thanks

[SSdynosaur]

Yes, I do race primary jet extensions on 2x4 Hi-riser 715 factory carbs. Full disclosure; I use the old (first) style Holley extensions that press into the inside of the slotted outer ring of the jets, the reason being, that I also use the original rectangular brass floats. The smaller Holley extension O.D.s clear the rectangular brass floats without any modifications to the floats.

[Posi67]

I don't but couldn't hurt I suppose. Given the Carbs are on backwards I don't think there's the need as much as if they were the other way around. JMO

[Rory428]

I pretty much run single 4 barrel carbs, but the only time that I ever noticed issues that were corrected but jet extensions, were on the launch. If you have a stumble in high gear, I would be looking at fuel delivery issues. Back in the 70s, I was racing my 66 Fairlane 390 GTA, and it started to lay down in high gear, turned out the gas was uncovering the pickup tube of the stock gas tank, when the tank was much below 1/2 tank. Added a couple of gallons of gas, and it was cured. To check to see if jet extension may help, try raising the primary float levels and see if that helps. I did that on my Fairmont when I first installed a transbrake many years ago, the harder launch caused a stumble on the launch, raising the rear float 3/4 of a turn cured it, but you have to be careful that the higher float level doesn`t cause other issues, like dumping fuel into the boosters at idle, or downtrack further.

[6667fan]

Thanks much Rory. The stumble is probably not uncovered jets but I wanted to know from the 2x4 guys if adding the extensions should be SOP.
 I have been bit at the track by running too little fuel in the stock Fairlane tank. My rule now is the car has to have a half tank.
The car has a RobbMc fuel system from the pick-up to the carbs.  Even with good parts the owner can work against himself. It’s all 1/2” from the pick-up to the big RobbMc mechanical pump but I had a 90 degree turn in the run and that is not good to have on the suction side. I have since corrected it.

[mike7570]

My tunnel port had 660’s and didn’t need them (backwards carb) I also used a single 1050 that would leave better off the line but ran into fuel problems. I raised the floats and added extensions which fixed the problem . The 1050 would mph lower than the 660’s in super gas so I switched back to the dual carbs.