Ok, here is my problem. I was adjusting the float in my primary fuel bowl on my 750 VS (4150) when i realized the needle and seat were stripping the threads out of the bowl. So, I was SOL yesterday and had to wait till today and ran to Barnett Performance and picked up a new bowl. I ended up getting the quick change fuel bowl and kit. Anyway, I transfered my hardware using new gaskets of course, but am now getting a problem that is stumping me.

Let me start from the beginning. I puchased this carb a few weeks ago, and have been tuning trying to get it just right. I have the jets where I want them, but I have been having trouble getting this thing to lean out while idling. No matter what I do it seems to want to stay rich. Well since I had everything apart on the primary side I purchased a 2.5 power valve to stick in there in place of my 4.5 that I was currently running, thinking that this would help me get the mixture that I am looking for. Well, got everything back together, and she is running richer than before. I set the float level, and its right where its supposed to be, but she still wants to run even with the idle screws all the way in. The secondaries are closed, and I checked for vacuum leaks extermally, and I highly doubt I have an internal one. I have been playing around with it all day, but haven't gotten it where I want it. It drives just fine, but idles extremely rich. Any ideas?

 

Some people will probably disagree with me, but if your throttle plates are open the correct amount at idle, the power valve can be completely open and not cause a rich mixture. That's because the power valve feeds fuel through the booster venturi, and at idle, there isn't enough air flow to draw fuel through them. The Holley web site has a page explaining the proper method for choosing a power valve. Your engine probably falls into the "mild street" catagory, meaning check vacuum under various cruise speeds, pick one 1 below the typical cruise vacuum (if cruise vacuum is 9, pick 7.5; if 10, 8.5, etc.).

But, speaking of throttle plates being open the correct amount, they should expose the transition slots about the same as the width of the slots. To check that, you have to have the carb off and look at it upside down. With the choke off, adjust the idle speed screw until that is true. Then, put the carb back on, and adjust idle speed primarily with the mixture screws (try starting at 3/4 turn out), then make final adjustment (without moving it too much) on the idle speed screw.

Oh, idle mixture screws all the way in is full rich on a Holley 4150/4160.

 

five7kid...

I just wanted to say thank you for always helping me out. I think every single post I have on this carburetor board you have responded to. I followed your directions to a "T" and the carb is running great. Thanks again