Guy's, This summer I installed a holley 600 and manifold off an ~83 into my 77, which has an otherwize stock 302. it's all running fine (even the automatic choke !) except for one little thing. If I'm cruising at about 60, and then just touch the gas, it will balk then go. It's almost enough to give you whiplash. The same thing happens if you are constantly gently accellerating, it will do it right about 2000RPM. If you accellerate aggressively, there is no problem... she's outa there. I tried tightening up the tollerance on the accellerator pump to no avail, and that really wouldn't explain the hesitation through constant accelleration anyway... Any thoughts ?
I'm not the greatest Holley tuner but I'll make a guess or two. Possibily too light of a secondary spring? If the secondaries open too quickly the carb has no way to make up for the sudden lean condition (like the second accel. pump on a double pumper), and you can get a hesitation when they pop open. That or make sure the seconardies are opening smoothly by hand. You can't make them work in neutral working the throttle, only while driving. But make sure the seconday linkage is smooth and not binding. Tim
Maybe... I might try a stiffer spring, but I'd expect that effect when you stomp on it, not for gradual accelleration. Any opinion ?
A vac. secondary carb doesn't or I should say shouldn't flop the secondaries open immediatly when you "stomp it". The engine vac has to reach a certain point when it overcomes the spring (if I am correct on how things work). as you gradually accelerate the vacume builds to a point to where they should open. Unless they are sticking slightly, and all of a sudden after vac. builds the sec. plates snap open. Maybe I'm wrong (quite possibly so). "But if you can't dazzle them with brilliance baffle them with "
Mine does the same thing and I have a 600 4 barrel edelbrock with a weiand manifold it kind of hesitates when I push the gas. It seems like it does it worst when its cold dont no what it is I always just thought it was giving to much fuel to my stock 302. If you figure it out would be a great help. Also I have notice sometimes when I get on it hard or when I start my car up it will puff out alot of black smoke. Defiantely like to know what that is from think its because my car is running to rich. Don't no hope its nothing serious, planning on getting one of thoughs K&N air fuel checker that tells you if your running to rich or lean.
when i was driving my car on a full time basis, i was using a holley 600 with vacuum secondaries. could never really get rid of that hesitation. made improvements but it was always there. when the II went to a fair weather ride i changed my engine combination and went with a holley dp with mechanical secondaries. no more bog. don't need to wait for the vacuum. my point is i dont, think you will ever get rid of the bog completly due to using vaccum to open the secondaries. from memory (which is getting worse) i tried: new pumps, new springs, accelerator cams, linkage springs, tweaking the linkage, all differnet types of lubricants on the linkage.
I've had the same thing happen to me with a 750 on a 302. You drive along fine, and just slightly ease into the throttle, just a bit. What I found was my problem was the power valve. If you were to hook up a vacuum gauge and drive around town, you would be able to see at what inches of vacuum this happens. Then get a powervalve about one step higher or a half say if the stumble comes in at 8 inches of vacuum (as in my case) I run a 8.5 pv and it took care of it. Another thing is, is that the powervalve could be blown, due to a backfire or if it's never been replaced.
Wow, Someone actually understands a power valve ! I'm impressed. But doesn't the powervalve run off venturi vacum ? The secondaries certaintly do. If so, what will manifold vacum tell you ? But you've got my attention !
How old is your accelerator pump? The diaphram could be cracked and not getting a full shot through the carb. For that matter how clean is the carb? The passages for the accelerator pump could also be blocked. Is the pump adjusted correctly. All the slack taken out of the pump action? How much is the engine modified. You also might try different squirter sizes, go up a step or two and see if it improves. Best bet buy a Holley book and read up on the problems and solutions. Dave
I had the holley 4160 universal 600 on mine forever I got the bog from day one. You don't ever get rid of it It subsides and is barely noticeable somewhat if the engine is running tip top, mine was like somebody switched off the key I tried spuirters, cams, even considered the 50 cc pump but never did I replace jets when is was TDY in New Mexico but had to switch back when I returned to San Antonio. The jets dont affect the idle circuit which is where I saw mine at the most. Hotrod had a article on how to cure the holley hiccups. I cured mine with a edelbrock 1406 with vaccum sec 15+ years later.
It shouldn't be like this. Maybe I'm lucky, but I've been able to get holley carbs to work well on everything. My car has had 5 different setups. 600 edelbrock, 600holley vac secondary, 750 holley vac secondary, 650 double pumper, and now a modified 750 double pumper. The thing is, is that every carb I have had has had to be tuned to the car. Sometimes what the experts say, doesn't work, and you have to figure it out. Books help, what helped me out the most was some good websites and trial and error. http://www.jason.fletcher.net/tech/carbtuning/carbtuning.htm
I know it was a lean condition right out of the box. Try opening the sec plates a little Holley cheap a** single pumper I changed stiffer vac springs nope --even wired the secondaries shut. That 4 barrel only kicks in at wot a few seconds later anyway. Don't get me wrong she ran like scalded dog just the slightest hesitation if I quickly but gently touched the gas[ floor it and it is non existent]
I must just get lucky with my Holleys too... The original 302 and the 5.0L in my Mach 1 both have never had that kind of hesitation with an "out of the box" Holley 600cfm 4160 vac. secondary. The only tuning I've done is running a stiffer secondary spring and I didn't do that until the 5.0L had been in there a while. My 351W has also been happy with the a Holley 600, and with the 750 I eventually switched to. The 750 had been on a 390 which ran like garbage, pumped black smoke, and gobbled fuel...I traded it for the Holley 600 and it has ran great since without even having to change the float levels initially. I have since switched to the second softest Holley spring and installed a secondary metering block, but haven't changed jets...still works great with no hesitation ever. I'm pretty sure I have adjusted accelerator pump cams on all of these though.
And I just remembered...when I set the secondary float levels, I usually test at idle by cracking the secondaries open without opening the primaries. If the float level is wrong, the engine will bog or backfire...usually when it behaves like this, you do end up with a hesitation just as the secondaries start opening.
