ok im working on the tune on my holleys. two 600 carbs

im trying to work out a secondary stumble right now.

i had secondary PURPLE springs, they created a big bog when they opened.

i NOW have the BLACK springs in the secondarys. the bog is less but it is still there.

i pulled off one of my metering plates right now and it is stamped "39" which is equal to a 70 JET

i was going to open this up to a 72 jet which is a drill bit size .079

1969 HOTROD told me this:
I had spent some time tunninga a pair of those on a hot small block.
open up the transition holes in the secondary jet plate to .032 and this should cure your bog from the light secondary vacuum springs

what holes are these i have my holley book and it tell me "main metering restrictions" ( the jet size hole) and the "idle feed restriction"

what is .032 being referred to.

im looking for advice on taking care of the stumble.

if i start from a dead stop and run it thru the gears it feels fine (tire spin a lot) but if im cruising and step on the gas the car goes (tires light up) then a bog ( tires stop spinning) and the car recovers and starts pulling again.

let me say this it is the secondary's that are the bog NOT the primary side.

thanks for any input going back out and take other plate out to see if same size.

opening up the transfer slots willnot stop the lean bog!!!!!!!! THE SECONDARIES ARE OPENING TO FAST !!!!!!!!!!!!!!!!!!! you need to slow down the opening rate!!!!!!!!!! ............. OR get larger carbs to weaken the signal (if you already have the heaviest springs).

bigger carbs will bog more, not less. he's already running 1200 CFM. what's happening is that when you mash it you operate the primary accelerator pumps which cover the bog till the pump shot runs out. then it's bog city. to isolate the problem, try disconnecting the sec opening diaphragm from the throttle shaft. if that fixes the bog entirely then hook it back up and try raising the sec float level 1/2 turn. Don't take the sight plugs out, it'll run all over. just make sure it's right, then raise it a half turn. this will make it much easier for the sec main system to start metering. If it helps try running it that way for awhile. If your carbs are mounted fore and aft position it might cause stalling on hard stops. If they're mounted sideways it might do some other weird behavior.

It's been so long since I worked with sec jet plates I can't remember where the idle feed restrictions are. I believe that's what he was referring to. Maybe I'll go out a dig one up, look at it.

come on jason settle down, we all know the secondary's are opening to fast. and i already know that the secondary's need to be slowed down.

what im looking for is advice not a repeat of what is known. there is no need for bigger carbs.

thanks tom for a helpful direction.

sounds like a direction to take, the carbs are inline and the idle feed restrictions are located near the top on the plate. i think the stockers that i have are .028 dia.

i maybe able to change out pump cams to deliver a longer squiter shot. i may not need to much off idle as i have now i might be able to back off and changed the cam.

all in all the set up works great. it start on first try and idle nice and great to drive around the street. it runs thru the gears just fine to 6600 rpms (rev limiter) im just trying to get a few things dialed in better before i take it to the track.

bigger carbs will bog more, not less. he's already running 1200 CFM. what's happening is that when you mash it you operate the primary accelerator pumps which cover the bog till the pump shot runs out. then it's bog city. to isolate the problem, try disconnecting the sec opening diaphragm from the throttle shaft. if that fixes the bog entirely then hook it back up and try raising the sec float level 1/2 turn. Don't take the sight plugs out, it'll run all over. just make sure it's right, then raise it a half turn. this will make it much easier for the sec main system to start metering. If it helps try running it that way for awhile. If your carbs are mounted fore and aft position it might cause stalling on hard stops. If they're mounted sideways it might do some other weird behavior.

It's been so long since I worked with sec jet plates I can't remember where the idle feed restrictions are. I believe that's what he was referring to. Maybe I'll go out a dig one up, look at it.Tom his problem happens when the secondaries open !! THEY OPEN TO FAST! then he gets a lean bog!! NOT a overcarbed fat bog!! your idea might work though?

ddennis,
check your pm's

Make sure the check balls are still in the vacuum pods for the secondaries. I have actually had to double up the sec springs on motors that had I couldn't get the sec opening slow enough for the set up (mostly pickups that towed something). I never tried a vacuum carb on tunnel rams (the 6109 Holley works so good I used them on every tunnel ram I ever had) So you be up against something I haven't run across.

update on what i have done this afternoon so far.

i went and bought a .079 drill bit and opened up the rear metering plates on both carbs ...... so thats equal to about a 73 jet and i did open up the chamber to match what holley had with the other hole size.

i dug back into the primary side and i had 70 jets up front. not sure where i got 72 from but thats what i had marked on the bowls with a pen. but in any case since the engine appears to be fine from the rebuild and the plugs looking a little fat. i bought the primary's back down to a 65 jet.

i double check my float level and it was just barely comming out the rear site plugs like i had them set some time ago. so i added another turn to them to set alittle higher as Tom had said.

i took it out for a test drive throttle response is sure better as expected with a closer tune on jets. tested full throttle at 45mph there is a slight bog you can feel and see the front come down alittle then my tires light up again.

it seems to be getting better. still there, (bog) but i dont think near as bad.

mike the check balls was taken out long ago, my experience with them seem to work better without but since this is a tunnel ram set up i will put them back in. it just might slow them down enough to be effective to put them back in. i had totally forgotten about those. i will try that.

what's an overcarbed fat bog? big carbs lead directly to lean bogs as the velocity thru the venturiis drops to nothing as the throttle opens. air velocity is what creates the low pressure area in the booster venturiis that causes fuel flow from the bowls/jets.

If your initial pump shot is doing OK but it dying off too soon try using a smaller squirter. this will cause the pump shot to last longer. if it causes a lean bog you'll have to go back.

try using a an old accelerator pump diaphragm to increase the capacity of your pumps. Take an old diaphragm, use a razor blade or whatever to cut the rubber part out leaving the gasket part, install this extra gasket between the float bowl and the good diaphragm. It'll add a little capacity to pump without going all the way to a 500cc pump. Normally need to re-adjust the linkage, it might have slop in it. different pump cams are worth trying too.

I've used double springs in the secondary diaphragm housings too. A guy was trying to use 2 780s on a TR on a BB. A little crude but it worked. Find two light springs that together are heavier than one heavy spring.

and what Mike said about the check balls in the sec diaphragm housings. It was a popular trick to leave out that ball to a little quicker sec opening.

thanks to all that helped.

it looks like i got the carbs dialed in, at least took care of the dead spot or bog.

i moved my acc. pump cams to the number 2 position im running a 466 orange cam and that seemed to be enough to help cover the lean spot. took the car out to test drive it and i couldnt get it to bog like it did before.

i thought i removed the balls ( because i was going to put them back in) in the secondary pod but there was brass inserts there. it had been a few years since i messed with my set up and i thought i removed the balls but i guess there was no balls to remove.

in anycase it looks like i have the bog taken care of. now i can take it to the track and see how it does.

i will have to watch the plugs since im still running pump gas on a 11.8 to 1 motor. get my timing adjusted for max mph and then work on jetting.

thanks for all the advice. dennis