I've spent a few days trying to get my motor to not have the WOT stumble, if I go from idle to wot it happens any other time it doesn't. with the hood open and blipping the throttle it seems like it wants to missfire engine shakes and then it'll get started again, idle mixture is set, 30cc accell pump shot, tried both the 26 and 32 numbered squirters.

At idle vacuum is around sixteen, the power valve is brand new and a 9.5, I also have an 8.5, timing is locked down to 8 deg initial.


My engine specs, 355 with vortec heads 9.5:1, 600 cfm holley

Make sure the "pump shot" is happening as soon as the throttle is cracked. If it isn't, you can change the pump cam profile by purchasing a kit for around $25. The blue cam cured my stumbling problems. Also, transition slot adjustment is critical too.

I'll re adjust and check might need the bigger nozzle back on? and no kickdown cable installed

What is the total timing set at? May need to play with distributor curve. Try 14 initial with 34-36 total all in by 3000 rpm.

If it's not a vacuum problem and you have spark it's probably fuel delivery, anything from a pin hole in the gas line, insufficient gas line diameter, fuel pump, dirty filters, float level, jets or accelerator pumps ... etc

With that much vaccum you may very well be introducing to much fuel with the accelerator pump. The reason a carburetor has an accelerator pump is to make up for that split second of lower vaccum when you open the venturis. I'd try a smaller squirter yet on both sides.

well, here's my results so far, jetted carb down a little bit still just above the stock 66 jet size, have a slightly more aggressive accelerator cam in place. drove the car to work and back and had slightly better results, still had a stumble tho.

I've had a slightly annoying exhaust leak sound for the whole break in time that has been getting on my nerves, almost like a header leak, I ran a new exhaust on the car at work on saturday and did new header gaskets on monday. I still had an annoying header leak sound, I double checked the lash on the car a few weeks ago and only did the drivers side, passenger side had a loose valve when I just checked it.

I'm hoping this improves my performance a bit more

As a general rule, the more the load that the engine see's off the line the more pump shot that is needed in rate and volume to cover the launch. Example: A car with a 3000 stall converter needs less fuel off the line then a car with a 1800 stall converter. In most cases a bog at WOT is caused by fuel starvation not flooding. I suggest try bigger nozzles and if needed place a 50cc pump on the primary side with a sharp nosed cam. This will ensure you get enough fuel for a WOT slam until the primary circuit kicks in. I used a pink cam in #2 position with large nozzles and this fixed my WOT issues. Good luck!

Ap68, Funny as it sound spectre makes a very thick header gasket for cheap. My hookers super comps were also a problem at first. I actually ended up cutting in between each outlet to allow the header to seat better against the head then having one long solid piece. Do this as a last resort, but look for a thicker gauge gasket. Make sure to warm up the re-tighten again. Drive a while let it cool and re-tighten again. It may take 3 or 4 heat ups and torkings to get a good seal!

funny thing is so far I'm settling for a pink cam in the number 2 position, I've got a number 36 (or 32, i don't remember which) nozzle on the car at the moment.

I'm just using the cheap mr. gasket header gaskets right now (work got me a good deal, $4 for the pair) they're not to thin probably 1/8" thick or so, sealed for now at least.

What is the total timing set at? May need to play with distributor curve. Try 14 initial with 34-36 total all in by 3000 rpm.

I'll second what Mark said once you get the carb straightened out if that's the problem. Most weight sets and regular stops I've seen only have 20 degrees of advance with some of the brands like Summit only having 15 degrees. If yours are like most, with 8 degrees initial you're shorting yourself out of some power. I can't even get my car to start with less than 12 degrees initial for some reason, and run it at 14-16 for the timing advance to hit where I want it.

With more advance, you'll probably be able to back down on your idle screw as well.

well, I'm only idling at around 600 rpm in gear, 700 out of it. Well, little update around 2000 rpm, maybe more like 2250 rpm my air fuel gauge gets dangerously lean... like um, the lights went down to the red then went out, and the car began to surge and have a lean misfire.

I'm guessing this means I have to jet the carb up? this isn't accel shot related anymore is it?

Have you set the float levels? If it's a steady cruise and your float levels and fuel pressure is adequate, you need larger primary jets.

alright that's what I was figuring, I reset float level, only got as far as pulling the sight plugs and rocking the car.

I'll pop in larger jets and see if that helps

Look for a vacuum leak as well.

I'll second what Mark said once you get the carb straightened out if that's the problem. Most weight sets and regular stops I've seen only have 20 degrees of advance with some of the brands like Summit only having 15 degrees. If yours are like most, with 8 degrees initial you're shorting yourself out of some power. I can't even get my car to start with less than 12 degrees initial for some reason, and run it at 14-16 for the timing advance to hit where I want it.

With more advance, you'll probably be able to back down on your idle screw as well.

I didn't see a response to this...but I will state it 3X

I had a bad stumble and chased the carb settings for months, turned out to be an ignition timing issue. Every small block I have had liked more initial timing and I made sure it had 34-36 total.

Are you running a vacuum advance?

yes, running both mechanical and vacuum advance on the car, I haven't checked today I was picking up another toy to play with.


It's, well... a mopar, but that's another story, I'll check my total advance tomorrow after work

How old is the carb?Depending on what type of gas you are using{pump gas winter or summer blend}the accelerator pump may be hardened up.I replace mine about every year regardless of the car or carb has been sitting most of the time or not.With the engine off,crack the throttle.If the spring on the accelerator pump arm compresses more then about 1/4 the way,the pump is hardened up.$5 from any speed shop for a new pump diaphram,you can either take the carb off and swap it from underneath,or leave the carb on the car and take the float bowl off.Another thing to check is the pump arm linkage.There should be no slack in the linkage.If you can lift the pump arm off the lever that is on the pump itself,you have too much play.I can tell you how to adjust that if it is your problem.

Good luck.

How old is the carb?Depending on what type of gas you are using{pump gas winter or summer blend}the accelerator pump may be hardened up.I replace mine about every year regardless of the car or carb has been sitting most of the time or not.With the engine off,crack the throttle.If the spring on the accelerator pump arm compresses more then about 1/4 the way,the pump is hardened up.$5 from any speed shop for a new pump diaphram,you can either take the carb off and swap it from underneath,or leave the carb on the car and take the float bowl off.Another thing to check is the pump arm linkage.There should be no slack in the linkage.If you can lift the pump arm off the lever that is on the pump itself,you have too much play.I can tell you how to adjust that if it is your problem.A vacum leak is another good place to look.

Good luck.

yes, running both mechanical and vacuum advance on the car, I haven't checked today I was picking up another toy to play with.


It's, well... a mopar, but that's another story, I'll check my total advance tomorrow after work

Nothing wrong with Mopars...my parents and grandparents all worked for GM otherwise I would probably have one.

My car responded well to increasing the vaccum advance allowing a higher total timing at idle without killling it with too much timing at high speed full load. I am a believer in the adjustable vacuum advances...and that time spent getting your timing right first ususally pays off.

well, I've upped the timing a few times and am hovering around 30-32 total, the only issue is that I still keep getting a very random exhaust backfire once in a great while. I'm thinking I still need more initial timing?

The backfire only happens after cruising at highway speeds approx 70 mph at 3000 or so RPMs and then coasting or during braking.

oh and another question, when you press the gas pedal how far does the linkage arm on your carb move? mine only goes far enough to make the linkage attatchment point go about half-way thru it's total travel (I can pull back on it another equal amount until it's completely oppened.

It sounds like you arent getting WOT then.Make sure that all your linkage brackets are tight,and if there are any adjustments remove any slack in the cable.After that you need to recheck your travel.If you still dont have enough travel,try moving your linkage to a hole on the carb arm that is closer to the shaft.
Good luck.

I had a similar problem with a 600 cfm holley dp. When opening the throttle, the squirter only dribbled at first and then gave a squirt. It turned out that the needle check valve under the pri squirter was sticking. I had to return it for another carb. The needle check and seat were defective. According to Holley this was rare but wanted to share my experience.

I don't know what WOT is but I had a little stumble but it was only if I was to try and pull out slow and not really give it any gas, if I mash it to the floor it would burn tire and go.

I retorqued my intake, carb and exhaust manifold bolts again and it seemed to run much smoother and I upped the RPM about 100 to about 900 in neutral and about 7 or 8 in gear.

I don't know what WOT is.....

W= Wide
O= Open
T= Throttle

WOT= :D

David F.

yes, running both mechanical and vacuum advance on the car, I haven't checked today I was picking up another toy to play with.


It's, well... a mopar, but that's another story, I'll check my total advance tomorrow after work

Try unhooking the vacuum advance and see how it operates. Make sure of course you plug the vacuum line so it is sealed tight.

If this helps you may have a smog friendly VA on the car...when you stomp on the gas pedal and the carb blades open there is a decrease in pressure in the plenum and the vacuum drops considerably, takes a while for the airflow to get moving through the intake to create vacuum to make the VA work properly and put timing into the engine.

I'm not sure about mopars but on some chevys there was a number stamped on the vacuum advance, I would try to get the lowest number possible (like on a 76 vette) and put it on mine. This was before adjustable VAs were available, or affordable in my case.

no no, the issue is with my 68 camaro, not the barracuda, that one's in pieces right now..

Okay, a little update, with 12 degrees of initial timing with the VA hooked up I was running around 45 deg. total, disconnect vac hose and I'm right around 34 now.

I've been playing with my jet size and everything for a little while, got it so it has better response but if I'm cruising around 2000 rpms and press the pedal, even slightly the car starts to lean out, would this more likely be a jet issue or accel pump/cam?

Keep in mind..not all air entering the intake manifold is mixed with fuel.I have seen my share of incorrect or gummed up pcv valves lean the a/f ratio when transitioning to the main ckt .

I don't know what WOT is but I had a little stumble but it was only if I was to try and pull out slow and not really give it any gas, if I mash it to the floor it would burn tire and go.

I retorqued my intake, carb and exhaust manifold bolts again and it seemed to run much smoother and I upped the RPM about 100 to about 900 in neutral and about 7 or 8 in gear.

If you are getting better results from just tightning these bolts then I would say you have a vacuum leak. Try stacking 3 or even 4 carb gaskets, check the carb baseplate for warping or cracks beforehand.

has it backfired through the carb yet?

Also, after checking the baseplate-and inspecting the intake for cracks or warpage and eliminating the possibility of vacuum leaks if it is leaning out when gradually accelerating i would say go up to a bigger squirter size.

i had the same kind of problem with my holley.. i went with larger accelerator pumps now it is perfect.