750 street demon on mopar big block not getting full throttle......

[HAHNAGON]

First, thank you for letting me join. I greatly appreciate it. Heres my current issue. I'm restoring a 70 charger and have a big block with the holley street demon 750. I can't get it to open full throttle!!. I'm only getting 2 barrels, if that. I tried factory throttle cable and kickdown and currently using lokar style cables and brackets. I've adjusted, adjusted, adjusted and adjusted....no luck. It did stick one day and that was fun. Geometry issue or something? Idk. I'm close to getting this car finished and could use the help.Thank you, Alex

 

[BeepBeepRR]

Make sure your secondary butterflies aren't hitting anything. I had a set hanging up on a 4bbl gasket.

 

[Geoff 2]

[1] There is likely a secondary 'lock' out adjustment on the choke. If The choke is not fully open, secs will not open.
[2] This one is more tricky. The throttle cable connection point on the throttle lever may be too far from the t/shaft. This lengthens the distance the cable has to travel to get full throttle [ WOT ] & it may not reach WOT. The fix is to locate the cable anchor lower down on the lever. If your old carb was getting WOT, measure that as a guide.

 

[Beekeeper]

Make sure your secondary butterflies aren't hitting anything. I had a set hanging up on a 4bbl gasket.

The street demon is designed to be used on an open plenum intake if I’m thinking correctly. The secondary butterfly looks like it would have interference with the plenum divider on a factory intake and would never open.

 

[RiverRaider]

It's possible even with a spacer the toggle valve (third barrel) may catch on that intake which I guess you have a "69 301 383 with four holes. On my 440 I machined the intake to clear the google valve. I did not use a spacer on the 440 on my 70 Charger because I use the stock air cleaner. As it is the hood insulation just touches the pie tin.

 

[Beekeeper]

We don’t know what the opening of the spacer installed is as well so maybe a little more info on that would be helpful.

 

[HAHNAGON]

Thank you but throttle Blades are NOT hitting intake. No clearance issues. Throttle can be fully opened by hand from under hood. I can put a weight on gas pedal, holding it to the floor and it barely travels halfway at the carb.

 

[HAHNAGON]

[1] There is likely a secondary 'lock' out adjustment on the choke. If The choke is not fully open, secs will not open.
[2] This one is more tricky. The throttle cable connection point on the throttle lever may be too far from the t/shaft. This lengthens the distance the cable has to travel to get full throttle [ WOT ] & it may not reach WOT. The fix is to locate the cable anchor lower down on the lever. If your old carb was getting WOT, measure that as a guide.

Ok. So far you are only person to give any good advice, lol. Thank you. I can hold my pedal to the floor with a weight and see the carb throttle doesn't travel but about halfway, so I think it is #2.

 

[BeepBeepRR]

When you hooked the Lokar cable to the gas peddle did you pull the cable all the way forward before cinching it down at the throttle linkage?

 

[kiwigtx]

When you hooked the Lokar cable to the gas peddle did you pull the cable all the way forward before cinching it down at the throttle linkage?

A second person is handy for doing that.

 

[dadsbee]

Ok. So far you are only person to give any good advice, lol. Thank you. I can hold my pedal to the floor with a weight and see the carb throttle doesn't travel but about halfway, so I think it is #2.

Not the only one seeing you have two threads going on the same issue....

 

[steve340]

The problem could be how you attached the Lokar cable to the gas pedal. Any of the attachment stuff must not be between the gas pedal and the firewall.
I have seen another guy who made this mistake.

 

[BeepBeepRR]

A second person is handy for doing that.

It can be done by yourself pretty easy.

 

[HAHNAGON]

When you hooked the Lokar cable to the gas peddle did you pull the cable all the way forward before cinching it down at the throttle linkage?

Yes. And the gas pedal is at it highest point(closest to driver). If I do it the other way...ie: hold pedal to floor and cinch down cable while carb is at wot, then the throttle will not return to idle and blades are being held open.

 

[steve340]

You could try a lower mounting position on the carb throttle linkage plate - this will "gear up" the throttle action.

 

[HAHNAGON]

The problem could be how you attached the Lokar cable to the gas pedal. Any of the attachment stuff must not be between the gas pedal and the firewall.
I have seen another guy who made this mistake.

I don't quite understand. Do you mean just let the cable hang? I just don't see enough travel in the pedal bracket...

 

[HAHNAGON]

You could try a lower mounting position on the carb throttle linkage plate - this will "gear up" the throttle action.

Ok. Thank you. But I will say i don't have another hole. There are only 3 really low holes for kickdown and the currentone im using. I would have to make an adapter or something. I just find it hard to believe this isn't common because the pedal travel is not very far. I'll be pissed when I find out the issue but I need to fix it, lol.

 

[steve340]

You are on the right track - work out how to synchronise both pedal and carb travel.
The pedal does appear to be right - but you need to work out what is required to get more gas pedal travel.

 

[threewood]

If that is a typical Holley throttle arm on the Demon you may need an adaptor to get the geometry correct. Holley 20-7 is the part.
Holley 20-7 Holley Throttle Lever Extensions | Summit Racing

 

[RemCharger]

Is there a spacer under that cable bracket?

You should try to get the throttle cable mount lower. By whatever means.

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