I just put a 650 Speed Demon on my motor. It is very responsive and great down low. But up in the higher RPMS, it does seem to give what it should. feels bland and dead up top. Im using the same secondary spring i used in my junk holley, but it doesnt seem to be where it should. Should i use a bigger jet in the secondary.

Get a secondary spring kit and try a lighter spring.

Don't ever jet for wide open throttle. Jets are for cruising. The way you set the jets is to cruise at various speeds and check for surging. If there is none, jet down until you barely feel a surge, then jet up four sizes.

*cough*

I meant jet up 2 jet sizes.

i know the jets are usually numbered even...so when you say two sizes do you mean say...66 to 68...or 66 to 70?

also, i have like the second lightest spring in it. it is the same on i had in my last carb which worked really good for that. I didnt think that would change from carb to carb...that comes off engine vac doesnt it?

Well thats absolutely, totally misleading and contains about a hairs worth of reason to it.

Granted. if your cruising and you feel a surge the circuit the carb is operating at that point very well could be lean. That is the circuit you would jet up. Under a cruise condition it very well could be the idle circuit that simply could be richened up and viola, everything it good to go.

BUT, under wide open throttle conditions you most certainly JET UP the secondaries if you experience high RPM lean out conditons. A lack of power and throttle response is a good indication that your VERY lean.

Airman, trust me on this, Demons are not Holleys. They don't seem to operate at all like a Holley on the dyno and seem to have their own way with themselves. So it MAY be safe to assume that the vacuum circuit to open the secondaries may not be consistant with a Holley. Therefore the spring may not be proper for that application. I would guess it highly likely that your on the right track thinking it's lean. I also suspect lluciano is correct that you at least have to verify the secondaries are opening. ON the Holley carb you can insert a paperclip into the secondary linkage to see if the rod is moving full travel. I don't knwo if that is setup the same on the Demon or not but you need to verify that. If it is opening all the way I suggest to jet up 4 sizes as a start on the secondaries. So if you have 66's in there than isntall 70's.

Other things you want to check. Make dang sure you have the floats set correctly front and back, fule level right up to the bottom of the side hole so that when you shake the fender a bit it splashes out. Low fuel in the floats will lean things out as well. Fuel pressure also must be good, 6 psi or so. I assume since you retrofitted the carb that all the fuel system is in fine condition to start with.

Well thats absolutely, totally misleading and contains about a hairs worth of reason/logic and truth to it. I'll give you credit on that answer if the question was "On my Mikuni 38mm Flat Slide carbs on my Yamaha FJ1200 how do I know if my pilot jets are too small"? Then we are in the ballpark, kind of.

Granted. if your cruising and you feel a surge the circuit the carb is operating at that point very well could be lean. That is the circuit you would jet up. Under a cruise condition it very well could be the idle circuit that simply could be richened up and viola, everything is good to go. In your case though your cruise and low speed conditions sound fine, so the primary circuits of the carb appear to be in fine shape.

BUT, under wide open throttle conditions you most certainly JET UP the secondaries if you experience high RPM lean out conditons. A lack of power and throttle response is a good indication that your VERY lean.

Airman, trust me on this, Demons are not Holleys. They don't seem to operate at all like a Holley on the dyno and seem to have their own way with themselves. So it MAY be safe to assume that the vacuum circuit to open the secondaries may not be consistant with a Holley. Therefore the spring may not be proper for that application. I would guess it highly likely that your on the right track thinking it's lean. I also suspect lluciano is correct that you at least have to verify the secondaries are opening. ON the Holley carb you can insert a paperclip into the secondary linkage to see if the rod is moving full travel. I don't know if that is setup the same on the Demon or not but you need to verify that. If it is opening all the way I suggest to jet up 4 sizes as a start on the secondaries. So if you have 66's in there than isntall 70's.

Other things you want to check. Make dang sure you have the floats set correctly front and back, fule level right up to the bottom of the side hole so that when you shake the fender a bit it splashes out. Low fuel in the floats will lean things out as well. Fuel pressure also must be good, 6 psi or so. I assume since you retrofitted the carb that all the fuel system is in fine condition to start with.

the secondaries came with 78 jets. I think i may know one more thing. My mechanic did this trick, where he put a small screw in the slot in the secondary linkage. This would allow the secondaries to open much sooner, and be fully open well before my redline. The first time he told me about this i was weary, but then he did it and it made a hell of a difference. im taking it to him later today for some tuning, and ill see if he recommends doing that with the demon. as for the floats. on the demons its not to the bottom of the hole like the holleys, its to the center of the hole. You can do this because of the clear sight plugs.

please don't put a screw in the secondaries, that defeats the vacuum secondary's purpose, the sound you hear when they open when done this way is a bog not acceleration.there is no pump shot to cover the fast opening of the secondaries.when vacuum secondaries are working correctly you won't feel them hit, it will be seamless acceleration.

A surge is caused by the power valve. Factory is 6.5 put in a 4.5 to help
forget what is good for others with the 2" under the vacuum hight point.
Jetting don't cause surging, its thru the metering system, I.E. power valve.
Plus what barnym17 stated, NEVER put a screw in the secondaries,when vacuum secondaries are working correctly you won't feel them hit, it will be seamless acceleration, a totally a stupid thing to do with putting in the screw.
Put the float level to the bottom of the site plug just like Rich explained :Qt:
Make dang sure you have the floats set correctly front and back, fuel level right up to the bottom of the side hole so that when you shake the fender a bit it splashes out. Grant carbs are set the same way.
The Knowledge Base has allot of info on carbs if one looks.
Here is Holley's site with a free down-loadable trouble shooters guide and manual.
http://www.holley.com/HiOctn/TechServ/TechInfo/FMCTech.html
Or go to Barry grants site.

__________________
Luv the smell of NITRO in the morning.

i know, and thats how it felt with the screw in the old one. my mechanic defined it as making a vac secondary a partial mechanical...but it works...and cut about a half second off my time.

if grant carbs are the same way...then when would the Barry Grant tech on the video that came with the carb say..."set the float level to the half way point on the clear sight plug"

Vac secondaries with jets, that must be nice!

And the screw will work if done right. The common way does not allow the carb to open fully. Some Holley's you can set up correctly with a screw if they have a certain linkage on them.
The kind that can work have TWO holes where they secondary shut bar links onto the primary linkage. You will need to move it to the lower hole. It will need to be bent to do that. Now when the throttle is opened it must reach 50% before the bar will begin to open the secondaries. The secondaries will then open at twice the rate of the primaries and be 100% open at the same time as the primaries are.

That allows a nice squirt to enter the manifold and chambers before the secondaries open(plus allows 100% open vs a screw or most vac secondaries where 100% is never acheived). If a bog is felt a 50cc accel. pump may be needed(rarely the case).

Allright foolio. Before you go bad mouthing my advice, pick up a Holley book and read it.

Jets + PVCR area = wide open throttle metering.

The idle circuit controls metering to about 45 mph.
The main jets control the entire part throttle range.

Once you get the main jet dialed in for part throttle cruise, you can work out the PVCR area if needed. Usually if oyu have the right carb you won't have to drill the PVCR. It is always a last resort thing to do because it is difficult to reverse.

Holleys tend to teeter totter with their adjustments. If you don't have the idle mixture right you can't set the jets. If you don't have the float levels right, you can't set the mixture accurately, etc.

Most people try to set their jetting by WOT runs and almost always end up being way to rich at cruise. Not only that but they end up with constantly fouled plugs, so they end up compensating other places that they shouldn't to try and clean everything up.

Don't ever do this. Not only will it not work well, but it will ruin your chances of selling your vacuum secondary Holley on Ebay later. If you want a double pumper buy a double pumper.