Holley Carb Issues.... NEED HELP

[6600DURAMAX]

Motor is a 454 Big BLock with a Holley 750
Stock Lower end, Stock heads, mild cam, Edelbrock rpm intake, headers, HEI


Idle is perfect
Free Rev sounds good
When put in gear it idles fine and if you ease into the trottle everything is OK

PROBLEM: When in gear and mash the trottle it hesitates then takes off and sounds great but as soon as you get out of the gas it falls on its face and dies

I have made sure the floats are adjusted to were fuel barely comes out of the sight plug at idle

I put two carbs on and am still having the problem, although it is not as severe with this 750. IS it the carb,? Any help is appriciated, she is going to the Mud Run this weekend.......... MAybe??


Thanks guys

[Roland]

Is it acting like it is flooding ? Black smoke out the exhaust?

[6600DURAMAX]

I dont know if there is black smoke or not, but it does act like it is flooding OR like the choke is partially closing. BUT it is not closing as I have it wired opened.

Doing some more research it looks like I need to ensure my accelerator pump is adjusted correctly.

Any more ideas

[prostreetC-10]

There could be a few things going on here. First of all, when you say a 750, are we talking a 3310 style or a 4779 style (vacuum or DP)?

Just about all carbs will "free rev" as you put it just fine because there is no load on the motor/carb. The "slight" hesitation is usually an adjustment somewhere in the accel circut (shooter, pump arm, cam).

When you stab a motor you hop right into the main circut and get most of your gas from the boosters with some pump shot. When you lift off quickly, you snap the blades shut and immediately shut off the main circut so the only way the motor can run is off the idle circut. I'd be curious to know where your throttle blades are set at....mainly the front ones. Where are the primary blades resting on the transition slots? What's tricky to diagnose is if it's dying from too much or not enough gas. It can be hard to feel the difference sometimes. You say it's idling perfect. Holleys tend to idle a little rich (CYA principle) in the 750 vacuums.

Just a side note too......what is your initial timing set at? All my BBC 454+'s like around 18*. Might not be the problem but it sure can help with streetability issues.

[Roland]

The diaphragm in the power valve in the Holley metering block will sometimes break and allow gas to pour into the venturi. This usually happens when the valve is being replaced and the new one is tightened with anything other than a twelve point socket. Channel locks and other methods tend to deform the outside edge and tear the diaphragm. If yours idles OK, you probably don't have this problem, but you might. It's that little gold baby in the center with the rubber middle.

[6600DURAMAX]

ProStreet-

Are you sure you know what you are talking about

Just kidding you are talking way over my head - I am not sure I kow what the transitions slots are. Do you want to know where they are resting at idle?
If it is dying from too much gas are the jets to big?
If it is dying from not enough are the jets too small? Or is it the adjustment screws on the side that might need fattened up?

I am going to tweak on the accelerator pump tonight and see if that works/helps I will also double check my initial timing and see what I have it at

Thanks for your help

[cableguy0]

This shows what hes talking about http://www.candsspecialties.com/tuning1.html . Just slow down before you change too much stuff. If you take and rip into that thing and change everything you will likely end up with an ad on craigslist selling a carb for 100 bucks. Start with the timing and move on from there. Also ensure the advance is working and moves freely and isnt stuck. When you pull the cap off the rotor should move and spring back. Its likely you have a couple small problems that are acting together to make it seem like a big problem.

[prostreetC-10]

Originally Posted by 6600DURAMAX

ProStreet-

Are you sure you know what you are talking about

I have had a couple run through my hands. Cableguy is giving good advice though. Don't go blowing through the carb. Very easy to create a new problem that will affect the old one as well and now you have a huge mess on your hands.

As others will agree, it can be very diffucult to diagnose carb issue on the computer where 2 minutes under the hood would at least let us know what is up.

Once again, tell us a little more about the carb. New? Old? Just rebuilt? Did this just start happening? etc. Although jets and the power valve, at times, are the only way gas gets into the metering blocks, the size is not a factory here at all. Jet are a main circut issue and that's not what we have unless your needles are not closing all the way and you are getting the ole "booster dribble". This can be when you have a little extra fuel pressure or to the fuel level becomes too high after the "land on it", the pressure in the bowl will cause gas to dribble out the boosters a little.

The main thing to get right, and only you can do this, is the fact of if it is dying because it's leaning out or because it's loading up. I would bet loading up over leaning out because you are coming off a "land on it" situation. When you finally get it started again, do you have to pump the crap out of the accel pump (GAS PEDAL) or do you have to just crank it until it cleans itself out? Usually, what you have to do to get it started the next time will tell you what happened to cause it to die in the first place. Make sense???

[6600DURAMAX]

Perfect guys, I am working on it tonight and you guys have given me some great advice.

I will let you know what I find. I do beleive timing has something to do with it because I am use to setting on my other motor (full roller 468) and it has a degreed balancer and I set it around 32 with a locked out distritutor at 3000rpm. I only have a tiiming tab on this motor.

At what RPM should I be setting the timing to 18 degrees?

[prostreetC-10]

Okay....I just want to be clear here. You are not running a locked dizzy on the problem vehicle right?? If not......

You set the 18* or so at idle. It shouldn't really matter because there will be a little room in the RPMs before the curve starts to kick in. Remember too that if you are moving the advance, you will pick up rpms. You will need to bring that down with the carb idle circut. This is why it's always nice to kinda start over and make sure the blades are set right.

The only problem with Cableguys link he provided is that this is the usual for a 4 corner idle circut. You can see in the pics this is what they are working on. If you have a 2 corner DP or a vac carb, the rear has no way of metering the fuel because there is no idle discharge holes and no A/F adjustment so you don't want to do it that way. You really shouldn't have a problem though. Usually, people get the blades way too high because they are running their motor at the chilton's 4*-8* and it's the only way the darn thing will run. On the back of a vacuum carb (since you STILL won't tell us what carb we are working on lol) you want to close the rear butterflies and then give it an 1/8 to a 1/4 of a turn on the little and I mean little screw on the bottom of the base. If the back blades are too far opened, you will get unmetered (raw) fuel coming/dribbling out the rear boosters because the high speed bleeds can come in really at idle. Hope I'm not going over your head. Just stick to the first part of my post now that I have gone off on a tangent!!! LOL

[6600DURAMAX]

Sorry ProStreet it is a Vacumm 750 with an Electric Choke that is wired in the open position.

With all this info I should be able to get it running good tonight. I will start with one thing at a time and work from there.

[6600DURAMAX]

You are correct, I am not running my dizzy locked on this vehicle but my vacumm advance is plugged because I was told it wouldn't matter.

[prostreetC-10]

Originally Posted by 6600DURAMAX

You are correct, I am not running my dizzy locked on this vehicle but my vacumm advance is plugged because I was told it wouldn't matter.

WHAT??????? Not having your vacuum advance hooked up can really affect performance on a street motor. The vaccum advance really helps off idle/cruise performance. You need it hooked up....unless I'm missing something. Why were you told it wouldn't matter??

[6600DURAMAX]

Thanks Cableguy, I will also make sure the blades are correct now that I understand how/why the adjustment is critical

[prostreetC-10]

I'm not cableguy! lol

[6600DURAMAX]

You guys are too much ....

[cableguy0]

Originally Posted by prostreetC-10

I'm not cableguy! lol

Are you sure? We keep typing the same thing the other one types in all these posts. lol.
Now as far as timing. You basically want as much as you can get away with and not have a ping. I would start with around 34 degrees total timing and move from there. BBC's tend to like less timing than SBC's but still you will be in the 34-36 degree range said and done all in by 3k.Generally your hesitation issue is going to be accel pump related. It does sound like you have two seperate problems. Problem one being the hesitation and problem two the dying. Very possibly completely unrelated. It is hard to do this over the internet but we have managed to help a ton of people get there problems straight and things running tip top. The more info you give the better chance we have to nail it down.

[prostreetC-10]

The good news is that I bill out at about $75 an hour and I think Cable is closer to $90!

[6600DURAMAX]

The most timing I could get in it last night was around 8-10*, it runs better and doesn't die now. Do I need to try and get some more timing in it? If so I would need to adjust the blades per both of yours instructions. Unfortunatly I ran out of time last night finishing some other loose ends getting ready for the mud run on Saturday. It is good for now - next week I will get into adjusting the blades to see if I can get some more timing in it.

Thanks guys you really have helped me understand these carbs alot more.

[cableguy0]

As you add timing your idle should increase which will allow you to back out the idle screw. Once you have timing and idle set you can then adjust the mixture screws. The easiest way is to adjust one screw slowly until idle comes up once it peaks and starts to drop again go back to peak and adjust idle speed back down and do the same thing on the other side. I would imagine at that point You should be good to go. while your changing timing dont forget to take it for a ride to see how it feels. make sure your not getting any backfires or other odd issues. Also start it up and shut it off to make sure theres no dieseling or hard starting issues.

[prostreetC-10]

I still want to know why your vacuum advance is plugged on your dist and who told you it was better that way?

You also wrote that you were going to adjust the blades to see if you can get more timing out of it. Was that a typo? Your throttle blades have nothing to do with timing. Could you only get 8-10* because your vac can was hitting the manifold or something? Are we working on the "green giant"?

I can tell you your 454 will want more than 10*. I have both a lower and a little higher compression 454 and I am running them both at 18* initial. One has MSD dist with 6AL and one is bone stock HEI (with vac advance hooked up! lol). At 18* neither ping or hard start when hot. Given that it doesn't die now at 8-10*....I can't imagine how retarted that timing must have been to start with. On my prostreet truck, I noticed a huge improvement going from 14* to 18* and you are not even at 14*.

It's funny how many times I get someone's carb to run super good after bumping up their timing. I always like to do a rebuild where I can be the one to bolt it on so I can check that just to be sure.

[GASoline71]

Originally Posted by prostreetC-10

I still want to know why your vacuum advance is plugged on your dist and who told you it was better that way?

I'm curious to this as well. It'll be a contributing factor...

Gary