Holley/Demon Carb stumble

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PRH said:
A carb configured like the 850MD, 1.560v x 1.750, downleg booster, DP, can be a challenge to get to leave hard....... even when it’s the right size for the motor combo it’s sitting on.
Which in this case...... it’s def not.
Add in the 8000’ DA and it just gets worse.

Watching the vids of it on the motor, looking down the carb during the attempts at winging the throttle and seeing it’s not anywhere even remotely close to working as well as it would have to, to get good launches by footbraking.......it’s time to accept that no matter how much you mess with it....... it’s not going to work as well as something that’s just a better match for the overall combo.

If you’re having a good time messing around with it, that’s fine.
The fact that there’s .2+ gain in the 60’ by swapping to another carb tells the tale.
On that combo, at that elevation...... it’s the wrong carb.
Click to expand...
JUST A NOTE TO THE VIDEO. it was in gear during the 2nt video that i just posted up a couple week ago,looking down the carb.

100% agree and i'm done with the Mitty Demon. I will keep it around just for the fact if i have a problem,and i know how this one works. i can throw it on to verify if it a carb problem or say ign problem. It worth keeping around for that. but have NO intention of putting it back on to try and tune it to my car.
Thought it was 2 mile an hour faster carb.........held on to that theory which made the carb worth keeping on. not any more. done with it.
The proform still need some work and i have idle and hi speed bleeds for it.
Beside it just runs cleaner all the way around, compared to the Demon.
IT ON THE SHELF!!!!
 
IF any one whats to take a look at the slow mo taking on top of the carb go back to post 683 and click on it.
 
Last edited:
Cudafever said:
IF any one whats to take a look at the slow mo taking on top of the carb go back to post 863 and click on it.
Click to expand...
You're only on post 752!!!???:realcrazy:...
Toke.gif
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So i never got a chance to do a full throttle pull with the Proform at the track.
Sneeked out today to do so. first one was a full pull in high gear from 4000 to 6000.
2nt one is from 4000 to 5000.
 
yellow rose said:
The sound quality is not good, but you can see this doesn’t stumble.

This is what I tuned on tonight.
Click to expand...

But you didn't have it in gear:p
All kidding aside hope to get my Proform to be just a little bit more crisp. Going to start with dropping 2 or 3 jet sides.....
Last time i did that. It popped and banging in the exhaust so bad i thought it might come threw the floor boards........but that was when i had the Demon metering block in it.
Hopefully that will get me leaned down enough to start learning how to play with air bleeds or maybe it will require PVCR changed. I know the first step is main jets.

The Proforms o2s say it's richer then the demon and i feel the demon is to rich as well. Demon around 12.5 and Proform 11s o2s when down to 11.0
When it was popping and banging the air fuel ratio was 13.5 to 14.0 at full throttle and couldn't get above 5 grand.

So i think 3 number down is a safe bet?????
 
Last edited:
Cudafever said:
But you didn't have it in gear:p
All kidding aside hope to get my Proform to be just a little bit more crisp. Going to start with dropping 2 or 3 jet sides.....
Last time i did that. I popped and banging in the exhaust so bad i thought it might come threw the floor boards........but that was when i had the Demon metering block in it.
Hopefully that will get me leaned down enough to start learning how to play with air bleeds or maybe it will require PVCR changed. I know the first step is main jets.

The Proforms o2s say it richer the the demon and i fill the demon is to rich as well. Demon around 12.5 and Proform 11s o2s when down to 11.0
When it was popping and banging the air fuel ratio was 13.5 to 14.0 at full throttle and couldn't get above 5 grand.

So i think 3 number down is a safe bet?????
Click to expand...

If reducing the main jet makes it pop and bang, you are probably too small on the PVCR’s. Use the primary main jets to get the cruise as lean as you can without surge and and then correct WOT with the PVCR’s and the secondary main jet.
 
I would have to put exhaust back on it first to draw less attention when i sneak out for testing.
Idle and full throttle is really all i can tune for.
o2 is only accurate at full throttle. o2 sensor is 5 inch away from the open exhaust
 
race car only? get it to idle and transition off idle cleanly, drive around pits @2k and tune for WOT around 12.8 afr. Put 12" extensions on the headers to get a better sensor read. Get the plugs front to rear as close as you can get. Unleaded pump gas leaves virtually no color even @12.8 Once your in the 12.8 ball park jet up or down for best mph and you are done.
 
mderoy340 said:
race car only? get it to idle and transition off idle cleanly, drive around pits @2k and tune for WOT around 12.8 afr. Put 12" extensions on the headers to get a better sensor read. Get the plugs front to rear as close as you can get. Unleaded pump gas leaves virtually no color even @12.8 Once your in the 12.8 ball park jet up or down for best mph and you are done.
Click to expand...

12.8:1 compression HYd roller cam 408.
4200 stall and 4.56 gears out back.
Race Gas
 
mderoy340 said:
race car only? get it to idle and transition off idle cleanly, drive around pits @2k and tune for WOT around 12.8 afr. Put 12" extensions on the headers to get a better sensor read. Get the plugs front to rear as close as you can get. Unleaded pump gas leaves virtually no color even @12.8 Once your in the 12.8 ball park jet up or down for best mph and you are done.
Click to expand...

3A657B26-6CA6-49D5-8659-4481F03D77C1.jpeg

AF6CA690-82B6-4DB8-BE73-B6F36FC3B70D.jpeg


These are all pump gas photos. They leave color.
 
i installed the o2 before i remove my exhaust system
o2 sensor.jpg


Us to open the exhaust at the track. Then just remove it all, after my muffler rotted out.
 
mderoy340 said:
flip that extension around and you will get a better reading. Jet down slowly to be safe 1 or 2 sizes.
Click to expand...
The instructions say that it should be a minimal of 10" after the collector and the pipe has a slight bend to clear the cross member.
 
Cudafever said:
The instructions say that it should be a minimal of 10" after the collector and the pipe has a slight bend to clear the cross member.
Click to expand...
I run an AEM Summit Brand Wide Band sensor 2" aft of the collector been there several years, works great.
 
mderoy340 said:
Not going to argue. I jet by MPH off timeslips.
Click to expand...


I 100% agree with that. Plug reading is as much an art as it is a science. We can’t see into the chamber. What we can “see” in the chamber is just a very tiny window of the chamber, local to the plug. What happens further away from the plug may not (probably is not) the same as what happens near the plug.

Sooooo...you may not be able to get the “perfect” plug or the “perfect” a/r ratio on the meter (is there ever a “perfect” in any of this?????) so MPH is the best way to settle on WOT jetting. Even when looking at cruise and idle, the plug may not look “perfect” but it has to idle and cruise clean and not stumble or choke you out with fumes.

I haven’t had a chance to go strip with this guy yet. I’ll get a better handle on WOT when I do. Certainly that will be by MPH. And then I’ll let the plug say what it says and take pictures so the owner will know what to look at.
 
I spent 2 year trying to get this !@#%$#^^$ o2 sensor to work. In the end the muffler shop welled the bung off set and i was crushing the o2 sensor and it would last 1 or two eng starts. Blamed it on the leaded racing fuel! When threw a dozen of them $$$ o2 before i figured it out.
Same sensor for about a year now.

So i'm a little bit gun shy about testing fate right now. Beside high gear pull is all i'm trying to do right now. Idle and tip in is grate with this Proform carb.
 
Cudafever said:
I spent 2 year trying to get this !@#%$#^^$ o2 sensor to work. In the end the muffler shop welled the bung off set and i was crushing the o2 sensor and it would last 1 or two eng starts. Blamed it on the leaded racing fuel! When threw a dozen of them $$$ o2 before i figured it out.
Same sensor for about a year now.

So i'm a little bit gun shy about testing fate right now. Beside high gear pull is all i'm trying to do right now. Idle and tip in is grate with this Proform carb.
Click to expand...
Remove it and jet for mph. I realize the sensors are $$$ and not race gas friendly.
 
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