HELP needed for my Mighty Demon 750.

[VETDRMS]

(this is a carbon copy of the email sent to Lars, but I have heard he is busy and don't expect a reply by tommarow....so I would appreciate some opinions from the carb gurus we have on the forum! ) Thanks in advance I have talked with you previously on my 406 and tuning requirements of my Mighty Demon 750. I am having some problems with it and hoped maybe you could shed some light on my situation. Barry Grant just told me to send it back. When I first got the 406 running it was WAY rich. After I turned the car off I could see fuel pouring into the intake. I wasn't aware of this condition until after it stalled on me after a few miles when I slowed and let off the gas. Turns out a piece of machined aluminum was stuck in the secondary needle and seat. I cleaned it out and hadn't had that particular problem since. Almost since I first got I have been getting a small amount of fuel puddling on TOP of the baseplate. There is a little valley on the drivers side behind the primary linkage that fills with fuel every so often. Fast forward a bit and I notice I'm getting fuel on my intake. Fuel is leaking from the linkage. After reading the tech section at Barry Grant I concluded I had the butterflies open too far so I took the carb off and set it per your instructions. For some reason I cannot get a high enough idle with the transfer slots set at .020", no matter what I do to the mixture screws. So in order to get it to idle I have to open up the butterflies more, but I'm afraid this is the cause of my fuel leaks. Fast forward to tonight: My intake has been leaking some oil off both rear corners and I decided to pull it and seal it up. Upon removal of my intake I notice the intake runners are a light brown color, and "wet". After looking down the ports with a flashlight I notice a fair amount of fuel deposits built up on the stems and valve surface. So I have concluded that this thing has not only been leaking out the leakage, but pouring fuel into the intake when not running as I could see a standing puddle of fuel on top of some of the closed valves. This motor has 2000 miles on it and I really hope this has not caused any major damage (washed cylinder walls?). Also, what is the best way to clean the fuel deposits off the valves? As far as getting the carb so it doesn't do this: Is this just a tune problem as I suspect or should I send it back to BG? Would drilling 1/8" holes in the primary butterflies allow me to get the idle I need and keep the .020" transfer slot? My cam has a fair amount of overlap (which is evident on the intake runners), and I'm just having issues getting it tuned without moving the butterflies. Also, BG recommends 18-24 degrees initial advance, but my MSD Pro-Billet distributor does not have the bushing to provide less than 18 degrees mechanical advance. Could I just lock out the advance and run 34? Here are the specs of the 406: AFR 195 Heads 10.25:1 CR Victor Jr. Intake CAM: Comp XR288-HR 236/242 @ .050; .555I(1.6)/.540E(1.5) 110LS 106CL Any suggestions or ideas would be appreciated,

[The Green Rocket]

You know what, I had similar problems with a 750 Race Demon on a 406. After numerous attemps at carb and ignition tuning changes it was no better. So I decided to get rid of the devil. I'm thinking the Demon carbs have too many fuel circuits and emulsions. Swap out to a Holley HP series and I think you'll be happier, plus tuning will follow easier.

Thomas

[VETDRMS]

You know what, I had similar problems with a 750 Race Demon on a 406. After numerous attemps at carb and ignition tuning changes it was no better. So I decided to get rid of the devil. I'm thinking the Demon carbs have too many fuel circuits and emulsions. Swap out to a Holley HP series and I think you'll be happier, plus tuning will follow easier.
Thomas

After consulting various people who had similar problems I found the quick easy solution.....and....it runs GREAT! Turns out it is hard to get a decent idle off the stock idle circuit when using a cam with any significant overlap and duration. The idle circuit is far too rich, but if you use the butterflies to lean it out you are exposing too much of the transfer slot and it starts to draw off the transition circuit. This causes it to run excessively rich, and to leak fuel no only out the linkage, but inside the plenum.

The quick fix is to drill a single 1/8" hole in each primary butterfly centered on the side closest to the fuel bowl.

Results: EXCELLENT idle, starts right up (first crank), great response, no fuel leaks at all.

The Holley HP series carbs come with an 1/8" hole already drilled in all 4 butterflies...just not sure why Demon didn't do this as everyone i've talked to about the demon carbs has had to drill these holes.

So, I will stick with the demon as its running perfect, and before anyone decides to replace theirs, get out your drill.

:cheers: