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I was going to ask if the secondary vacuum was pulling enough,,,, 3rd gear full throttle. You can see where the paper clip was pushed down.
But then I noticed the threaded hole in the carb base. What is that for? I have never noticed it before. I guess i need to plug it. DOH!
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THe base maybe interchangable with other models. It could be for the accelerator pump lever on a double pumper. Next time the carbs off the car look up the numbers. You may be able to find out of the base cross references to other models
The 4165 series of Holleys probably use the same base plate and they are double pumpers. That is where the secondary accelerator pump arm would be attached.
Thanks,,, makes sense... whew. How about my little paper clip. I'm trying to see if my secondary vacuum is pulling in as much as it should. The clip shows 3rd gear full throttle pull. It doesn't seem like it pulled that much secondary. It has the softest white spring in it.
Put a lighter spring in it...do the paper clip test again....did it open further? Chances are it won't as the springs really only control the rate of opening and not the total amount......if the engine has demand under throttle, eventually it will open to what it needs. Looks like it moved quite a bit to me....remember, it is only going to open as far as the engine needs......and if it doens't need the secondary wide open, it is not going to open all of the way......no matter what.
I have the white spring in it. I think it is the lightest. It seems to accelerates ok. I held it wide open up through about 5000 RPM's. It's the 327 350 HP engine. I'm just going through the carb to make sure it's tuned correctly. Thanks
That is what I didn't know. So the secondaries only open full at wide open throttle?
It opens fully based on engine RPM at wide open throttle and the spring used and the size of the engine.
What spring did you start with yellow or black, don't know which 4175 you have?
The 4175 intended for your year comes with a yellow spring
Look at the chart for the springs on page 2. Holley springs
I misspoke,,,,, What I wasn't sure of, is that it needed to be at full RPM to fully open the secondaries. Like I said,,, It has the white spring already. It doesn't seem to have any stumbles during acceleration.
I misspoke,,,,, What I wasn't sure of, is that it needed to be at full RPM to fully open the secondaries. Like I said,,, It has the white spring already. It doesn't seem to have any stumbles during acceleration.
No, the secondaries will open by engine demand (vacuum drop).....and will only open as much as needed. The primary has to be open all the way before this will happen though. On most vacuum secondary carb applications, the secondaries never open all of the way. If it is running fine and no stumbles....do not try to change anything or look for something that isn't there. Leave it. Your paperclip test proves it is opening.....
Holley 4175
