This sounds like the making of a nice tech article (with photos). Some of what I just read sounded a little confusing and photos would be great. To sum up all the inputs so far:

1. buy the jet kit
2. drill the plates (do you drill 4 holes or just 2?)
3. get A/F meter
4. get vacuum gauge
5. check the plugs (I am sure mine are fouled by now
6. ???? There has got to be a #6

 

You don't really need a jet kit because you end up with so many that you won't ever use.

You have a mild 454 so just go buy two 78 & 82's and when you have the metering blocks off note what power valves you have. I use a black felt marker and write that jet and power valve info on the bowls. So 3 months later I don't have to wonder what size I'm at. It will get you in the ball park for driving. You can do Norval’s wire trick and or drilling. Take the carb off the motor. Drill the primary throttle blades with an 1/8 inch drill bit. The hole center should be 3/8 of an inch from the front edge. When I drilled it left some ruff edges so I just used a larger drill bit to round and smooth out the holes. In reality .125 holes might not be enough and Norval once told me to just continue up in number drill sizes till it’s right. I just called it good enough and opened a beer!

I also bought a vacuum gauge (must have item) for about 16 dollars at post tools. Warm up the motor. After the drilling set all four corner idle A/F screws to 2 turns out. Set your idle up to 1000 rpm with the vacuum gauge on the full manifold vac port on the side of the carb. Watch your vacuum readings and listen to the idle speed and quality as your turn each of the screws equal amount in. With your holes drilled it should be in the 1 ¼ to 1 ½ turn out range. Different motors may very though. As you get closer to correct your rpm should start to climb so keep turning the idle down to 1000 rpm. When it’s right you will have the highest vacuum reading. When they are all set turn down the drivers side (Primary) idle speed screw to what ever you desire. Maybe 750 rpm in your case. That leaves the secondary cracked just a little more open and help with the transition from part throttle to wide open

When ever you pull the bulls on a Demon it’s a little tricky to get the accelerator pump arm in place before you tighten anything down. Never over tighten the bowls. Demons come with reusable gaskets good for 20 or more times on and off.


When ever working on carbs only make one change at a time after this initial setup I've even confused myself on how to change it next because i made to many variables. After you do some test driving and some plug readings only alter things in small steps. Like your primary will be close at 78. So take a 10 mile open highway cruise without ever opening up the secondaries. Pull one of the outer four cylinder plugs (Because they run leaner than the inner four) If you think that it's to brown go to 77 if it to white go to79. Secondarys are best done with someone following you down the highway. You should have a small hit of black smoke when you go to WOT from the squirters and then you should not see any smoke.

 

I almost ordered the kit from Jegs but I went to Autozone instead. They had the kit for $29. I now have all jets from 64 to 99. Summit sells the same kit (HLY-36-181) for $37. I know I'll never use most of them but I'll never be lacking jets.

Tomorrow morning, I will be putting in 78 and 82s and drilling holes in the plates. Do you recommend removing the plates or drilling with them on there?

 

I just pulled the carb. Then made a little ding with a ***** punch and went to drilling. Never bang on or torque the throttle blades because you don't want to tweek the shafts.

Another tid bit of information: NHRA requires two throttle return springs. I found that with the spring within a spring trottle return and the two Demon shaft springs that the gas petal was hard to push on. So I just took a needle nose pliers and popped the spring off the primary side of the carb and stretched out the twin springs a little. I also now use Max jets because they come in true sizes. So you can really dial in a carb when a max jet might be the equivolent of a 78.5 Holley size. Where Holley has only 78 or 79

 

Wow, it had some biguns!!! The jets that were in there were 93/85. I just put in 82/78 and came up here to doublecheck on the drill size for the holes in the plates.

 

If you had 93/85 in there...its no wonder your rear bumpers are 'painted' black !!!

Can someone explain EXACTLY what is taking place within the carb, when the primary jets are increased or decreased in size (diameter) ??? Thanks.

 

As I understand it RR your sqaure jetting is made for WOT operation. Road racing and drag racing so you get more equal max torque Air fuel ratio.

For the street you want 4-6 jet spread. Because at max economy cruise on the primaries only you need a high 14 to 15-1 AF ratio. Max power is attained at high 12 to 13-1 AF ratio. So the richer secondaries kick in and jump the overall to max power :seeya

 

NO MORE ADJUSTMENTS!! For now. Until I get a vacuum gauge, I am not going to change anything else. The holes in the throttle plates cleaned up the idle. The off idle still seems rich with lots of smoke. There is also a little stumble off idle.

 

Well how about an update? :smash: Vacuum gauge is the only way to tune a carb. I think that mine was $16 at Harbor Freight tools. They have an online web page.

 

[EDIT] D'oh! I'll read the whole post before replying next time. :yesnod:


[Modified by The Dude, 9:53 AM 7/30/2002]

 

No updates yet. I did get a belt to fit so now it is time to get tuning. Tomorrow night has been set aside for fixing this thing so I can go racing thursday night.

Dude: Mine is running rich at idle and under power. I am trying to fix both and have been following the advice of others. I drilled the throttle plates which seems to have fixed the idle richness.

 

I still don't have a vacuum gauge. Looks like I have to go mail order on that. None of the local places seem to carry on. I thought about trying the junk yard and steal a boost gauge from a turbo or something. Would that even work??

The idle seems great now. I pulled the plugs and took a peak but they are too dark from when I had the big jets to tell anything. I cleaned them and tried again but did not see anything in that short of run to tell anything about the A/F ratio. It is still a little smokey when I rev it but it also has a very minor stumble just off idle. That confuses me because the smoke indicates rich and the stumble indicates lean???

Gkull, any last minute advice before tomorrow night? I am going to a different track wirth a bunch of C4 and C5's. I know the big advice would be to tune it with an A/F meter and/or vacuum gauge. I am planning on it.