I recently put the set up that is in my sig. I can get the idle curcuit to where i want it, but i cant seem to richen up the motor through the powerband. Right now im mainly just trying to fine tune the primarys and have upped the jets from a 70 to 78 with no real results. The plugs are a little better than they were but still lean in my book. I figured by now it would be running rich and i could start backing down the jets but that isnt the case. I have taken it for a ride after every jet change, and its seems to running better with every jet change, but by no means making to the kind of power it should be making. Also i think its pinging alot due the lean condition but im not sure because i never heard pinging before this setup, but that also seems to be getting better with every jet change. I took a little total timming out of it to see if that would the pinging but that didnt help much. Btw total timming is set a about 30*.

My questions to all of you are, should i keep upping the jets or maybe i have a fuel pump that cant keep up. Last night i hooked my fathers OLD fuel pressure gauge up to it, but it seemed to bounce around to much. The gauge would bounce back and force really fast from about 4 or 5 psi to over 8 sometimes. I just took that with a grain salt, figured the gauge is bad, but maybe that means something to some of you. Btw the pump is a fairly new stock replacement.

Thanks for all the help.

 

I take it those FP readings are sitting there idling....

What does the FP do UNDER LOAD? Does it change over a period of time of WOT operation UNDER LOAD? Does the car seem to pull pretty good for a while, and then peter out? Does it pull OK on primaries only, and go lean when the secondaries open; or vice-versa; or is it the same all the time?

 

To clarify to FP readings. At idle the gauge goes from about 2 to 8 psi back and fourth, When i give it some gas or while driving it will go up and down from 4 to 8 or 9 psi. I figure to readings should stay steady, by i also figure the gauge is bad, because it is pretty old. I was thinking about getting a new that stays on the fuel line.

As for how the car runs, ive mainly been only driving on the primarys, primarly because it seems to start pinging when i give it more than 1/3 throttle and i wanted to get the primarys all dialed in before i started messing with the secondarys. It runs ok on the primarys under light throttle but i feel it should be running alot better. It doesnt feel as torquey as it should. I got on it a few times yesterday but it doesnt feel much better with the secondarys open. Pretty much feels the same as the primarys. Its a vaccum secondary carb btw, and i pretty sure there opening because they were a little dirty before, and they were nice and clean after WOT.

 

Any ideas fellas. I really want to get the car running good and want to know if im going in the right direction, because im pretty much guessing right now.

 

What's the fuel pressure, UNDER LOAD at WOT? That's the one that matters.

What happens if you disconnect the secondary vacuum diaphragm from the sec throttles, to disable them?

Remember: we need FP while running at WOT, UNDER LOAD.... like a blast up a freeway ramp all the wy through at least 3 gears. The rest of that is worthless, except that it sounds like it's higher than it really needs to be. We're looking for a restricted fuel supply.

 

Ok at WOT pressure drops to a steady 4psi and starts falling slowly after that. I didnt stay on it to find out where is stops, but it was almost at 3 1/2 psi when I let off. Which sucks!!! I deconnected the secondarys and that didnt help much, when I got on it I heard a couple backfires out of the exhaust this time but the FP was about the same a WOT.

So I take that i probably need a better fuel pump or have a restriction in my fuel line.

 

First, I hope you have a good multiple spark ignition system you need one (e.g MSD BOX) Second you did match your carb to your cam right??? Third, you can't tune primaries first you MUST do the same to all 4-corner idle screws at the same time the same way(amount of turns) or it just won't work. Fourth, STOP jetting up the carb, fifth, I heard that demons like enough initial timing and total timing to be set-- say at 34* with that said lets get that baby dialed in. "I suggest you reinstall the stock jets".

Now screw in the four corner air mixture screws until they bottom, your seating against a small rubber o-ring so be gentle or you'll crush and possibly tear the o-ring apart, wich will cause an air leak into the circuit and make adjusting impossible, now back .75 (counter clockwise) then hold the throttle open a little and start the engine, now ease the throttle to the stops, If it tries to stall DO NOT hit the throttle, tap gently on the accelerator pump arms...did it get better or worse?

you said that your car is running lean so in your case .75 of a turn may not be enough so go ahead and counter clockwise turn the 4-corner screws in equal increments out another 3/4 of a turn at the same time. Do you still hear the pingning? if so keep adjusting(turning the the 4-corners screws out until the pinging stops but only 3/4 of a turn at a time) this may take several times around the carb to get it right; making all adjustment equally to each of the 4 screws.

Now recheck your primaries and secondaries idle screws. In other words adjusting the 4-corner idle mixture screws is how you correct A/F mixture problems in a demon carb not by rejeting it. PLEASE USE PREMIUM GASOLINE ONLY your carb and engine will thank you I hope this helps solve your tuning problem.

Some references taken from "DEMON TUNING 101"
Author Don Gould
For more info or to order DEMON TUNING 101 go to: www.4secondsflat.com

 

Well im still hunting down this problem. I bought a new carter fuel pump, played with the timing, bought the demon tuning guide as mentioned above, but no luck as of yet.

A few days ago i sent my distributor out to get recurved, because i have a little to much mechicanical advance in it, but i dont think thats the problem. Ive been to talking the gentlemen you wrote the tuning guide and he says to address the distributor first so im trying that, because im all out of ideas. So when that gets back ill give him a call again.

Also i checked my vacuum and i was only pulling 10 inches at idle. but i plan on checking that with a new gauge when my dist. comes back. I figure i should be pulling atleast 15 inches. What should i be pulling with this cam?

 

My 355 pulls around 11.5-12" hot idle @ 800rpm or so with that cam.