Tuning a Demon...need advice.

jfrenum · Jul 8, 2008

I have just got my car back together and am in the process of tuning. I need some help since i haven't tuned a carb except about 10 years ago with help from my dad(i didn't do much).
Here's what i got: 393w, rpm air-gap intake, AFR 205's, 10-10.5:1 compression, BG 825 GC Demon, 93 octane, 15 degrees base and around 33 total advance.

So, it idles good, and is pretty easy to manipulate for that, but my problem is that when accelerating from any RPM, it has a decent hesitation when i hit the gas. I am pretty sure it is lean, because right now i am running 7.8psi fuel press. and when i dropped it down to 7, it got worse. Also, engine gets HOT fast, which looks like a lean condition, it has a 2 core afco radiator, with high flow edelbrock WP, and new coolant, so the cooling system is fine.

I have read up on demons, and made most simple adjustments recommended, but i think i will be stuck changing jets or ??? Maybe something else if i get good recommendations.

Whats the best way to find out what jets i should start with, and anyone with a similar combo, what do you use?

thanks in advance,
Jake

jfrenum · Jul 10, 2008

So i got a change to go run it and read the plugs, looked pretty lean, but not detonating as far as i can tell by plugs or sound.
How many jet sizes should i go up for a start?
Anyone?

Shaker455 · Jul 10, 2008

Jake,
Jettting should start about 74/84.

How many turns out are you idle mix screws?

You could use more initial and 18 degrees is a good place to start.

31 squiters, and make sure there not too much pre-load on the accel pump arms.... on the car you want to just barely take any play out of the arms so they don't rock between the cam and accel lever.

Bench setting use a .018" feeler gage between the arm and the pump lever, move to WOT with feeler in place, then pull it out and watch to see if the lever comes back out of the pump housing a bit.....
Jeff

kim · Jul 10, 2008

because of BG's wierd rating system, size of engine, and carb size I wager your going to dial in close to 82/88 jet split on that carb on that combination. If the second posters jet sizeing is correct.

Jet up till it slows down.

jfrenum · Jul 10, 2008

Thanks, i have zero lash on the squirters with no preload, and haven't checked the free play at full throttle, but will. Also not sure when the mech. advance comes in full, i know it has around 35 total, but i might need lighter springs to let it come in sooner.
I need to re-gap my plugs based on another thread i have been talking to guys on, and will advance my base timing some.
My idle mix screws have been between 1 and 2 turns open for all the adjustments i have made so far.
When i check my plugs from an idle, they look good, a light tan, with no speckles or sludge type stuff, but from a mid-heavy throttle run, the ceramic was clean white, and the ground strap looked white and dry.
Would my initial timing make for a hesitation at mid and full throttle? I haven't checked vacuum at idle, but it runs smooth, cold and at about 180.

jfrenum · Jul 12, 2008

So i was gonna advance timing some and rejet today, and when i took the dipstick out to check the oil, the tip was missing...so i guess i will have to wait until i can change the oil and get a new dipstick to see how it runs.

jfrenum · Jul 20, 2008

Finally got a chance to pull it apart, the jets in it are 70/76. i will start going up and see how it goes, thanks for the advice.

jfrenum · Jul 23, 2008

Finally got set with a 76/86 split, 18* initial timing and out of the box settings on the carb. Haven't checked vacuum yet, but it idles smooth at about 750 rpm, pulls strong at all throttle positions and RPM, and will blow the tires off at 45mph.
So until i can get some track time, i am very happy.
thanks for all the help.
jake

Tuning a Demon...need advice.

jfrenum

jfrenum

Shaker455

kim

jfrenum

jfrenum

jfrenum

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