Had TBI on my 91 rs swapped it over to carbureted timing is 6BTDC initial, when the throttle blades are opened quickly from a stop engine bogs and wants to stall if opened slowly it’s fine I think it’s from running rich because the plugs are black now it had .28 jets for the accelerator pumps and changed them to .25 still have the issue the jets are .69 primary and .72 secondary and the carb is a Holley 650 double pumper my thoughts are to change the jets about 8 sizes lower and go to a .21 or .18 jet for the accelerator pump just wanted to know if anyone had experienced this before

 

Did you change anything besides the TBI to a carb? I assume you addressed your fuel pressure. You need to change the distributor too, to a non-computer controlled unit (or get a box that can run the TBI one I suppose) if you haven't done that yet.

This might help.
https://www.thirdgen.org/carbswap/

 

Yes I changed the distributor and installed a fuel pressure regulator

 

Does it do it just when cracking open the primaries quickly or when you get into the secondaries? With double pumpers you have a very quick opening of the secondaries and sometimes that can overwhelm an engine if it’s not able to handle that quick burst. Possible you may need a larger accelerator pump shot to start the process. Maybe less. There are also kits to make the secondaries progressive linkage so that they open in unison with the primaries making a smoother transition that may help some. Assuming all other variables are ruled out like timing fuel pressure etc.

 

Timing is good fuel pressure is good, it happens from idle to full open when it happens rapidly that’s why I think I need smaller jets because it seems the car is just drowning in fuel

 

Yeah my guess would be that when you open the secondaries it’s causing your bog. Does it come out of it after it does it? A 650 dp might be a bit much if it’s a stock 305 otherwise. I’m guessing the majority of your problem is at the rear half of the carb. Make sure front and rear accelerator pumps have the correct preload on them as well. I would always adjust the spring to wear it was just touching the arm but not depressing it any and no slop in between. If there is a gap between them and you crack the throttle the engine won’t get the initial shot of fuel it needs to level out the burst of air it’s getting, and will likely bog down like you’re experiencing. Check those first.

 

You probably need more timing. Get your timing ironed out before you worry about the carburetor at all. You probably need something like 10 more degrees of advance at idle, depending on your combo. Most engines want 32-36 all in, which puts you somewhere in the 12-16 degree area assuming you have 20 degrees of mechanical advance. Plus vacuum advance.

 

Okay, I’ll set it to around 10 BTDC and then I’ll adjust the accelerator pumps with a feeler gauge and see how that turns out

 

Yeah you’re timing may be off as well if you’re using the factory settings. You don’t have a computer making adjustments for you any more so they will have to be set manually. If you have a dial back timing light or access to one get it set in that 32-36 total range and then see what it does. Odds are you will still need some fine tuning of the carb. They don’t tune themselves and are rarely bolt on and leave it. Let us know what you find!

 

Personally, I'd get a helper and set the all in timing and then see how it runs. Bring the RPMs up until the timing stops advancing (hopefully around 3K or so). Then, rotate the housing counter-clockwise to advance the timing to about 34 degrees BTDC. If it's higher than 34-36 you'll want to turn it clockwise to retard the timing. Do all of this with the vacuum advance unhooked and plugged, if applicable.

Afterwards, check to see what your initial (or idle) timing is. If you're using a standard HEI it'll probably be around 12-16 degrees at idle. Then go ahead and hook up your vacuum advance again to manifold vacuum.

All done? Take it for a bore and see how she reacts. If it drives better, great. Increase your timing a degree or two. Still better? Great. Do it again. No change? Pull it back a couple degrees. Is it better? If so, bring it back a couple more degrees. Is it better? Rinse and repeat. When you have no change go back to the previous setting and leave it alone.

Next move on your carburetor. Follow Sofakingdom's sticky for optimum results.
https://www.thirdgen.org/forums/carb...ey-tuning.html

 

The advice regarding the timing should be first on the list. Your 6° initial isn't going to cut it and the suggestion of another 10° for a total of 16° at idle is probably a good starting point. That's not the end of the timing tuning and checking what maximum available mechanical advance is important. But get the idle advance sorted out and test for throttle response then. You don't need to go 100 mph to figure if you're going in the right direction with the timing. Then sort out the WOT stuff as pointed out above. There's also the vacuum advance component to consider if that wasn't already mentioned.
For what it's worth, timing is easier to work with on the basic level because it' simpler to do. Getting into carb internals can get a little complicated. And messy.
Timing first.
Carb second.
Don't neglect your vacuum fittings and hoses either. That stuff gets knocked around during these swaps.
What do you have for tools? Timing light, vacuum gauge?

 

Just put the timing to 12 degrees, doesn’t seem to have changed anything I also tried putting a bigger jet for the secondary accelerator pump doesn’t seem to have made a difference also I’ve checked for vacuum leaks there are none I’m going to give it 4 more degrees and see what happens, it’s fine until the secondaries start opening that’s when the bog happens it acts like it wants to die for half a second then it revs back up quickly

 

That *sounds* like it's going lean, but I'm not there to see\hear\smell it. Is this a brand new carb, or is it used? If used, you may need to rebuild it. Normally the first thing I look at with a bog at WOT is the accelerator pump. Too small of a shot will not correct the momentary lean condition at WOT.

At any rate, finish with the timing first.

 

It smells rich it burns your nose and the plugs are black I’ve messed with the timing for a few hours it’s at around 12 ish base and when I rev the engine I can see the timing mark advance, went around looking for vacuum leaks again couldn’t find any sprayed carb cleaner over the intake and over every vacuum port I went 3 sizes up and 3 sizes down for the pump jets didn’t really seem to change much going to put .31 in the front and rear tomorrow and see if it improves both of the accelerator pumps have been checked with a feeler gauge and there’s no preload on them seems to get worse when the air cleaner is on which also points me in the direction of it just being too rich, this carb is used but the guy I got it from had it in the box and only used it for 2 weeks I went through it took it apart and cleaned it anyways everything looked great he told me he put bigger jets and when I checked them they were .68 and .72 he had the carb on a 383 making around 600hp so putting it on my 305 making maybe 200 seems like it would cause a huge rich condition I’m thinking .58 and .64 jets and the .28 for the accelerator pumps because I’ve ruled out all the other variables it has to be the carburetor at this point

 

How rich\lean it is at idle doesn't really correlate to how it reacts at wide open throttle. They use different circuits. Your idle mixture screws will help sort that out. Do you have a vacuum gauge? If not you can try doing it by ear. Did you read through Sofa's Holley sticky I posted above?

Also note that too little timing will cause the "burn your eyes" at idle effect, too. The gas doesn't get lit soon enough to burn completely before it's dumped out the exhaust valve. Also note that if you have catalytic converters still, they'll hate you for this.

You really need to go through the entire timing process before moving onto the next step. Otherwise you're really not eliminating anything. Right now you don't know what your maximum timing is. Knowing that it moves only tells us that the mechanical advance isn't locked out. For all we know you're only getting 10 degrees of advance. Trust me - skipping around from one thing to the next will only make things harder to diagnose. You might get lucky, but most of the time you spend three times as much effort and\or money trying to nail it down.

For clarification - are you using vacuum advance? Are you connecting it to ported or manifold vacuum?

Get the timing info you need and then get it set, and then follow Sofa's advice to a T. Don't skip any of the steps - they're all equally important if you want the engine to run right in all circumstances.

 

It was ported until about half an hour ago I changed it to a manifold vacuum port to see if that would change it any

 

If you're confident that the timing is set properly (a dial back timing light would be helpful here) and that there no vacuum leaks, follow the link to tuning a Holley carb the right way. And for the time being, put the vacuum advance back to ported. Tuning full manifold vacuum advance can get very difficult and there's no tuning that can be down with a stock distributor anyway. Manifold vacuum will keep things stable.
But if you'd rather not follow the links, I'll re-post it here. Chances are the carb's original owner made some significant changes and following the advice to follow, in order as the steps are laid out, will help you to restore and then tune to the about as good as it'll get.
Get a vacuum gauge.

Look at your primary jets. Whatever size they are, buy some that are 2 sizes, 4 sizes, 5 sizes, and 6 sizes smaller; and 2 sizes larger. You'll be needing them.

First, set the fuel level. If it has sight plugs, set the primary one to where gas dribbles out while the engine is idling, when you just bump the fender; and set the sec one to where you have to jiggle the car pretty good to get it to come out.

Lean the primary jets (using the "step size" description above) until the car just barely starts to surge while cruising (55-60 mph) at a steady speed on a level highway and it starts going up a hill. Ignore all other misbehavior of any kind for the time being. Once you find that point, go back up 2 jet sizes.

Once you get it to do that, look at the primary side power valve. If it's stock, it's probably a 65. Stupid. Raise the value until the flat spot goes away when you're in high gear and driving along at about 35 mph (basically, as slow as you can possibly go in high gear), and you give it gas. It'll take a MUCH higher number power valve.... probably a 105 or a 125. If it starts giving you the burn-your-eyes idle, go back down one step.

When you get that right, set the idle speed right (800 RPM out of gear, say); then get the idle mixture right by turning each pimary idle screw in until the RPM drops, then back it back out 1/8 turn. Shut the motor off, and average the 2 screws (like, if one is 5/8 turn out, and one is 7/8 turn out, set them both to 3/4 turn out), and restart the motor, and check them again. Repeat until they're equal, or until you have determined that they absolutely CANNOT be made equal. In no case should they be more than 1/8 turn different.

Take the carb off, flip it over, and look at the transition slot. You want less than .050" of it exposed below the pri throtle blades. If more of it is exposed than that (it will be), open the sec throttles with their idle screw, 1/8 turn; put the carb back on; re-set the idle speed and mixture; then pop the carb back off and look at it. Repeat until you have between .030" and .050" of the transition slot showing.

At this point, the thing should run like a bat outta hell, on the primaries. The secondaries could be just about anywhere. Put a 65 power valve in them, if they don't already have that; and select jets for max ¼ mile mph.

At that point, you'll have your Holley set up better than about 95% of all other Holley owners. You'll be getting nearly the same gas mileage as you would with a Q-jet, and you'll be making 20% more power than most cars with the same cam & heads, and FI.

 

Okay thank you, I went out and bought a vacuum gauge today idles around 21hg I’ll go out and get larger and smaller jets today if I can find some in store took all the plugs out today and they changed color from dark black white so I’m guessing it’s a lean bog I’m going to follow all the steps and hopefully that fixes it, when revving it, it seems like if the secondary accelerator pumps opened faster than they are it would help a lot a

 

Keep this is mind when looking at the mechanical secondaries:
The formula for calculating how much CFM (cubic feet per minute) an engine requires is: CFM = Cubic Inches x RPM x Volumetric Efficiency ÷ 3456
So, lets give your 305 a 5000 RPM limit and say it has 85% volumetric efficiency. The engine would need about 375 CFM. A little more than half of what the carb is rated for.