Holley 600 Vacuum secondary tuning issue.

[eric76]

Bad Camaro where did you get that guitar string as I would love to do that with mine. I did finally find out the problem and it was the base plate the whole dam time and never would have thought that it would have been the issue. I got to thinking and put my cards down on the table as a figure of speech and got to thinking what was different in the previous 600 Holley carbs I used and a 670 street avenger and the base plates were the only things different then the older design base plates being the difference on the carbs I used. The three different ones I used all were done with the older design base plate and I measured the transfer slots and the primary side was about near .400 from the bottom of the base plate and the newer design ones that Holley has used now for ten plus years the transfer slot is only about .360 from the bottom from the best I can measure.

Then on the secondary side the transfer slots are longer on the older design and the newer design they are a lot shorter but I can't say by how much as I don't have my note book out. Bottom line installed my new 600 Holley on today and got all my pre adjustments done and started it up and wow it started up a bit sluggish at first but its normal before you get the proper settings and stuff. After a few adjustments and looking at my vacuum gauge and it got up to temperature the engine sounded so healthy now and the carb adjusted like it should have done with the last one. I had my primary transfer slot open up about .015 and my secondary side open up half a turn and my idle mixture screws would all adjust excellent just like it normally should have been before but that older base plate for some reason with the such shorter transfer slot did not allow for a proper butterfly adjustment and even if I did not have the transfer slot exposed the opening would still just be too much.

It was not warped as I used a straight edge and I could drag a .001 feeler gauge at all angles and it was like new condition. Like I stated I have worked on these things for so long I knew it had to be something out of the ordinary that would be the issue. I am glad it was not a camshaft grind issue as I was just trying to figure out the culprit as this was one of the curve balls that can come ones way. After comparing the carbs and then noticing the needing 1 and a half turns on the older style base plate versus the only 3/4 of a turn needed on the newer base plates, I knew that would have somehow have a big effect on idle and other factors.

Bottom line I would hate to throw them away since I could never use it at least on my build if I ever needed it. if I could make them longer that would fix it. What got me to thinking about that is because of the history of the Quick fuel carbs having to long and to wide transfer slots compared to the old design Holley carbs and the troubles it caused folks in some instances and that is where I figured I would try that theory and bam I was correct and it fixed my problem completely and the idle is not smooth and the throttle is snappy and no popping and the engine runs good in idle and in park again like it should have. Now just to get it out and do the finer tuning and then enjoy it finally after all this time of a year battling this thing and it was that one little thing that caused the biggest problem.

Cases solved.