Was running good

Here is a good one, 77 chevy k-10 pickup 4wd. 350 4bolt, mild rv cam was smooth idle. I have a performer intake with a 650 vac, sec. carb. Ok, built this motor in december got it running had problems from the get go when it warmed up idle drop, so decided to try a different carb, that was a big performance change but always would kill you standing behind it, tried increased timing, went from 44 plugs to 45 it carbons them all up, so I have dealt with that for a while now, I have had a vibration in my shifters at 2200rpm, so I just shrugged it off as the new clutch being a tad out of ballance, I was driving it for about an hour a couple weeks ago and I got into it ran it up a little ways then after about 25 min the motor idled down started running like it had about a 292 cam in it choppy choppy, so I tried to adjust the floats nothing, so heres a kicker and cant figure this out yet run the mixture screws in normally in all my years the motor will idle down, not this one, bottom out the idle screws it idles up, ok weird to me from having about 10 holleys over the years, so I replaced, coil, ign module, plugs again, cap rotor you know thinking I may have weak ign, nope still runs the same, so I decided to hook vac gauge to it, yea I know took a while huh, fluctuating from 10 to 17 very fast, so here I am carb has never acted right with the idle mix screws being like that, and now it runs like it has an internal problem, It will still run, I just never have figured out that running rich all the time at idle, did everything now and I am at a road block, tried floats, needles, power valve, so anything to suggest I am pulling valve covers tonight to inspect and probably going to pull the carb off again to see if I can find anything!:whacked:

I have no ideas, but someone here will come up with the solution, but welcome to best Hot Rod site in cyber space.

Jack

What kind of carb do you have? If you said in your post, I missed it. It sounds like you may have your idle mixture adjustment out of whack, and maybe your fast idle and/or choke needs a little tweaking. There are some (several) on here that can explain this better than I can, but do a search for "idle mixture adjustment". Good luck.

The Holley could have a warped body where the metering block goes. This warpage allows a vacuum leak, and sucks gas directly into a vacuum port. Remove the float chamber and metering block and check the face of the carb with a straightedge. If its warped, use a fine file and dress it flat.
The warpage is caused by overtightening the four long screws that hold the chambers on, tighten them gently and in rotation.
Also can be caused by the cork gaskets shrinking. The newer composite gaskets don't have this problem.

Pope has a good sugestion about double checking flatness and proper composition gaskets. Make sure (doubly sure) the meter block is super clean inside especially. Compressed air to gently blow out the passages in the booster passages on the body and anything thet appears to be a "hole". I am curious about the rapid vacuum fluctuation though. This is an indication of mecahnic problems. Possibly valves being to tight. How fast was the gauge flucuating?. If it was gradual up and down, it could still be a cause of improper fuel transition through the carb. If it's fairly rapid, Look for the mechanical things.

The carb is 650 cfm holley single feed vac. secondaries, I have the electric choke, all is set open no choke working on it, it is not hung on or binding, the floats have been set and checked, new needels and seats for them, the idle screws when turned all the way in makes the idle increase instead of decrease like I have seen so many times before, the truck is extremely rich to where you can hardly stand behind it. It carbon fouls every plug even with the delco 45's in it. It sounds like it has a full race cam now, used to run smooth and have a tad lope to it, now have wicked lope, sounds like some old race motors I used to build with huge cams,

I have gone through them, cleaned, there are all composit gaskets now, I will pull it apart tonight check it all again, see whats the real problem, and the vac. gauge was very quick on its movement like 4 times a second fast. So maybee the valves? I will try to pull the valve covers to see if I have a broken valve spring, just dont know why its always been so rich never has been lean since I have had this carb,

Go ahead and pull the covers. That's very supicious so take a look see.

If the main idle screw is cranked too far the blades will be into transition region and the curb idle screws won't work because you are no longer using them. This is a very common occurence. The valves being tight might be a reason you had to crank the fast idle out of the curb circuit too.

Also be very careful with the curb idle screws. Their seats are easily damaged and then they will never completely close off and might behave erratically (like my teenagers). :LOL:

Kitz

Isn't there a vac secondary Holley that has idle mixture screws that operate backwards?
Perhaps a smog model?

Well when its higher rpm like 2500 holding it there it stabilizes pretty good, then when you let off it snaps up real quick then recovers pretty quick too,, the valves may be a problem and it was a weekend cruiser now it has to be a daily driver soon, so I am trying everything I can, I guess a midrange vibration could be that the transition in the carb leaning out? I have a 6.5 power valve in it right now, Ill check it all out tonight pull the carb 100% down and go back again, see if Im missing something. I just didnt think a vacum issue due to having decent power brakes, lol, but could suggest why when I put my foot on the brakes the idle would go up about 75rpm, ??? new theroy I guess.

Sounds like you have more than one issue going. Get the carb sorted, check the valve settings, then look at your brake booster.

C9 may be onto the problem...get the list number from your carb and look it up on the Holley site....some later models had backwards screws so you screw it OUT to make it leaner....in is richer!!! They set differently too, not at 1 1/2 turns out like the old model.

mike in tucson

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Originally Posted by C9x

Isn't there a vac secondary Holley that has idle mixture screws that operate backwards?
Perhaps a smog model?

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the only ones i know that do that are the 2300 series 2bbls, specifically the ones for ford 390s, but there might be others as well

I will open her up tonight and let yall know tomorrow what I find thanks yall ,gives me some direction here, I will post my results either tonight or tomorrow. Thanks again!

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Originally Posted by DennyW

I thought those carbs were mostly on chrysler cars, as I remember. :LOL:

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i dont know for sure about that denny.... but i do know that i've found plenty of them on 390 fords.... but it does sound like something chrysler would do, they're always trying to be backwards on things :LOL:

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Originally Posted by thesals

i dont know for sure about that denny.... but i do know that i've found plenty of them on 390 fords.... but it does sound like something chrysler would do, they're always trying to be backwards on things :LOL:

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Backwards? Depends on your perspective i suppose........:LOL: :LOL:

Check this out. http://www.allpar.com/corporate/technology.html

ya know like left handed lug nuts :LOL: i've seen quite a few lube techs break studs on those trucks :LOL:

You're right.........no excuse for that one. :HMMM:

got the carb done last night, on the older holleys the acc. pump goes through the metering block into the main body with a brass shaft with o-rings on the end, the o rings were bad leaking fuel into the power valve, so thats where my stammer was I think, fired up alot easier and not having to crank up the throttle plates to get it to run, so step in the right direction but still have a miss and but alot more steady vac. holding 15 to 16 minor fluctuations now bout 1 ever 2 seconds, so major improvement. Heres what else I found, take a small vac line off the vac advance and the vac increases to 18 and holds steady with a vac leak! More vacum with an open line. weird to me. Also with the throttle open to about 2500 I can hear minor poping back through the carb, so thats my miss and why it dosent run good, so i think the carb issues are done so I guess I will try to pop the valve covers off and see whats next! Starting to sound like a valve not opening or closing all the way. But on a positive note she did start right up and didnt shake like she used to so making progress.