Still trying to tune my new engine. I plan to take it around the block tomorrow to see how it runs for the first time.

Problem is, at idle it's running pig rich. I mean burn your eyes rich. My A/F gage pretty much stays on full rich while idling (rough). I've adjusted the transfer slots at .020 (looks like a square) , and then started the car with all four a/f screws 1 1/2 turns out.

Then I adjust my timing a bit and it's set at 18 BTDC initial. In order to get it to lean out, I end up having to turn all the screws in to about 1/2 turn from seated, then the a/f gage at least comes off full rich and bounces around. But then it wants to run hot (around 240) as if it's too lean or something.

No fuel coming out of either squirters at idle. The manual says ideally, I should have all four a/f screws in no more than 1 to 1 1/2 turns from seated. But I can't do it cause it'll run too rich when screws are out over 1/2 turn.

Plugs look pretty black. The jets the shop put in are 80/94 and that's what it was dynoed with. Total advance is 38 degrees. It almost sounds like the engine's missing at idle, but smoothes out when revved up. Where should I start???? Sounds like a top fuel dragster right now when idling.

 

i JUST went through the same thing. running pig rich. i tore apart my entire carb and fine tuned it. in fact, i'm still not done yet.

here's what i did (i have a holley double pumper):

get a vacuum reading. take a vacuum gauge and find out how many inches the carb pulls at idle. mine was 19" for instance. use this number to find out what powervalve you need. divide it by two. so i needed a 9.5 power valve.

next, jet down the primary jets 2 sizes at a time until the plugs look clean. then go up until they look tanish. for the secondaries, the way i found out what jets i needed was to drive on a open road and then get to WOT. hold it for a second and then cut the engine (while at WOT) and pull over. check your plugs same way as the primaries.

as for squirters, if you are having any hesitations immediately when you step on the gas, you may need larger squirters. i jumped up about 3 sizes on my carb.

hope that helps. again, this method worked for me, so hopefully i will for you too. good luck man!

 

Rich at idle right?If you haven't driven it yet don't touch the jets..either side.What amount of vacuum does the motor pull at idle when warmed up?What Power Valve do you currently have in the carb?I have the same cam in my 355 and it pulls 11.5-12" of vacuum at hot idle..fully warmed up.Split it in half and went with a 5.5PV.A little less than half but works perfectly.This is in a 355 again..so yours should more than likely pull more vacuum from the added cubes..but you get the idea on how to choose the correct one for your combo.Another thing I found to help lean out my Speed Demon 750DP at idle was to close the secondary butterflies to a fully closed position..then opened them up till I just saw the bottom of the transfer slot..less than .020...very little opening.

 

Demons are notorious for having an insanely rich idle out of the box. Your idle circut isnt controlled by the jets so changing them wont make much of a difference (to a certain extent). 1 1/2 turns out on my car is so rich it'll foul the plugs in less than 10 minutes and kill every bug in the neighborhood. Don't be afraid to turn them puppies in as far as you need. Also make sure you turn them all EXACTLY the same. These carbs are very sensitive. 1/8th of a turn is a huge difference. My car idles best with them at only 3/4 of a turn out.

 

That's just the info I was looking for. I had to go to the Barry Grant website to figure out what a "Power valve" was!!

Makes sense! I bet they only rejetted the thing for a couple dyno pulls and didn't tune at all for idle. I'll get a gage tomorrow and see what the vacuum is. Would a Holley replcement one work, or is it a Demon specific part?? No one has Demon anything around here.

I didn't plan to mess with the jets till I drove it, because it perks up off-idle nicely. Just pig rich at idle....my whole garage stinks like bad gas now!! lol

I guess I don't know as much about carbs as I thought. Up to this point, all the engines I've had in the past didn't require any carb tuning. They pretty much worked out of the box.

I'll post back on how it went. Thx again!

 

Yup all the basic tuning peices of a Demon are interchangable with a Holley.

 

I'm not completely familiar with Demons. Is this a Speed Demon? Does it have removable air bleeds? I couldn't tell from the BG website.

If so, you might want to put in larger idle air bleeds.

But, 1/2 turn out doesn't sound like the end of the world. There's nothing "magic" about 1 to 1-1/2 turns out.

Are you running vacuum advance? If so, try using manifold vacuum so you get the additional advance at idle. That may help as well (note that timing is the 1st thing they mention in their tuning tips for "rich at idle").

 

My Road Demon was another one that had to have the screws turned waaay in. Ended up being 1/2 turn out all the way around gave the best idle.

 

Well, here's what I've found out......this thing is a blast to drive!! Took it out for the first time since the swap yesterday. Runs great off-idle, doesn't seem to smoke when I open it up. It just wants more!

But - pig rich at idle still, and rough. Seems like it surges a little too. A bought a vacuum gage and I'm only getting around 10.5 to 11 inches of vacuum at 900 RPMs. Initial timing at 18 BTD.

Tried adjusting the transfer slots again, then backed out the a/f screws out 1 1/2, and went in using 1/4 turns while sputtering at full rich on my cheap a/f gage.....If I continue to turn the screws in it gets to a point where it will start to kinda "sputter", then I back out 1/4 turn. But still not right...rough rich...

This can't be anything serious judging by the way it runs off-idle!

 

1/4 turns are too much. Demons are VERY sensitive. 1/8th a turn makes a huge difference on my motor in the way it idles. Turn them all out like 1 1/2 turns then just very very slightly start turning them in. It may take you 45 minutes walking around the car adjusting them but your vacuum should start to go up. When it does keep adjusting them until the vacuum starts dropping again THEN back them out slightly til the vacuum rises again.

May also be best to set the idle with the car in gear. Just remember: very very sensitive.

 

Thanks for the help. I just got off the phone with a Demon tech rep. and learned that it isn't absolutley critical to keep the transfer slots at .020......

In a nutshell he says to try 16-18 initial timing, turn all four mixture screws out 3/4 of a turn, and reset the .020 transfer slot setting. Then after warmup, turn one screw in or out until I get a smoother idle, and go to the next and set it the same as the first. The manual doesn't tell you to do that! Then adjust both throttle plates at the same distance for correct idle speed. Both primary and secondary need to be set identical. He also mentioned lowering the float level.

Some of this stuff I've tried already, but I guess I'll go over it yet AGAIN to see if it improves. This has gotten frustrating to say the least.

I'll post back how it goes!

 

Well it didn't work. Seems if I tweak it just enough, I can get it to smooth out but if I shut the car down and try to restart it, first off it cranks over like it's way out of time, so it barely starts and it will idle lower then what I had it set at just before I shut it down!
If I rev it for a bit - then it will settle out. Something I'm not seeing here....

That's with 19 degrees initial timing for 37 full advance, holds 11 inches of vacuum at 950 rpms. Float levels set in the middle of the sight lenses. I don't just get it. Still wants to run around close to 240 degrees - too hot I think....but fan stays on the whole time.

 

Well, I called the tech line AGAIN - This time he took down more info. I told him it what problem I had and he said to change out the power valve and drill out the air/bleed screws to .076 (or a number 48 drill bit) and see if that will lean it out at idle.

Just before that though, he asked me what jet sizes I have installed. When I told him 80/94's in there, he said that's way too much fuel for my car. But I then told him I test drove it and it runs great off-idle - picks right up, a ton of power and no smoke that I could see.

So looks like power valve, air bleeds first, and if that doesn't work I may have to jet it down.

Then he said I should have gotten a 750!!!
These are the same people that talked me out of getting a 750 in the first place - they said 650! And I questioned it too...

 

Have you tried turning all 4 mixture screws in all the way while the motor is running? Does it imeditately stall? That will tell you weither or not the power valve is hanging open at idle.

 

Yes, if I attempt to turn even one screw in all the way it will stall. If I'm quick I can seat one and back it out 1/2 turn...

I turn them in until I hear it sputter slightly, and back out till it kinda smoothes out a little. Then I set the others the same way. Still ends up on the rich side. Then it wants to "wander" down to idle after I blip the throttle....the rep at Demon did say I'll need a 5.5 power valve. He did seem suprised at how big it was jetted. Maybe I'll end up having to jet this thing down??

 

Ok so if the motor stalls when you turn in the screws your power valve isnt open at idle, thus probably doesnt quite NEED to be changed (atleast right now). I suppose you should do what the Demon tech said and drill out the holes... but remember be EXTRA careful! one wrong move and you'll be all messed up. If you're really good you could drill out the holes and tap them for screw-in air bleeds.

One last shot... You said you have 19* initial. Have you tried giving it more? Do you have a vacuum advance canister? Try hooking it up to full manifold vacuum and see if the idle clears up any.

It took me weeks to get my Demon idling good tinkering with every possible thing. I finally found the perfect timing and idle mixture and now its ALMOST perfect.

 

Thanks for the reply 88IROC350TPI -

Turned out I didn't replace it anyway, for now. I couldn't find a 5.5 inhg power valve around here anywhere. I did decide to get leaner jets though. The Demon rep was amazed at how rich they were set and said I should go somewhere a couple steps up from the standard 70/78 jets that were there before I got it.

So I bought 74/82 jets and tried them. Much leaner when I rev, seems to respond quicker. I know jets aren't supposed to effect idle, but it seems to idle better for some reason, but far from perfect.

It seems to idle a little leaner - but still warm. On the other hand, the engine really isn't fully broken in yet.

If I advance beyond 19 initial timing it smoothes out but it won't start that way. I actually ended up backing down to 16 and I'm now holding 11-12 inches of intake vacuum at idle...???

Looks like I'm traveling down the same road...

 

Sure hope that advice was given with the understanding that the warranty will still to be honored if required.

 

If more timing clears it up than I'd say thats your problem. Do you have vacuum advance? Set your initial timing as high as you can get it without having start problems then hook the vacuum advance up to full manifold vacuum. The car will start perfectly fine but once it fires up you'll get a ton of extra timing at idle from the vacuum advance.

 

I have a brand new mechanical advance distributor on it now. I just got a loaner vacuum advance distributor last night that I'll try out. If nothing else, I should be able to put less initial timing on it (with the hose unplugged) so it will start easier. Hopefuly I'll end up with around 24 degrees advance when I plug in the hose.

If that clears up the idling problem then my only other concern is how hot the engine will run. At 19 initial, the engine wants to run too hot (around 235) but I hope this is just because the engine is not fully broken in yet. I am also smoking a tad white for some reason. I'm guessing that the rings hav'nt seated fully yet. But as I said, off idle this thing screams. Now I have traction issues, but that's good for now since I have the stock 10 bolt in it. Fastest car I've ever had!!

In general, does advancing the initial timing cause overheating or help prevent it? I'll post up what the vac. adv. dist. does for it. Thx!!

 

Ok – I’m totally frustrated with this thing. I went to a vacuum advance distributor, and hooked up the hose to the timed port fitting on the carb. I can now set the initial timing at 21 degrees and it idles a tiny bit better. I couldn’t set 21 advanced with the mech. adv. dist. and start the car up afterwards for some reason…

I also tried hooking it up to full manifold vacuum, and it will advance so much it kills the engine. So I think it needs to stay on timed vacuum. Engine temp gage still shows warm though (230)..And I have a 180 degree thermostat in it. Any suggestions on how to set this up?? I’m all ears!!!!

I just have a strong feeling that the timing is still not set right….engine sounds like it’s louder than the 305, no leaks, although the same exhaust is now on the 400. Also engine temps refusing to drop below 230 after warmed up with fan constantly running. Will not enough initial advance (retarded timing) cause abnormally high temps?? Still wants to run rich at idle. Starts leaning out and Rpm’s increase when I advance timing even further – anyone else running 26-28 degrees initial timing? Does that seem excessive? I already know my stock starter won’t turn the engine over if I have the timing that far advanced, but I should be getting a high torque starter in a few days.
I’ve heard of setting initial timing using a vacuum gage. Supposedly, you set idle to where the engine will barely run w/o stalling and advance timing to the highest vacuum you can achieve without pinging, then back it down approx. 1 to 1 ½ inches. Only problem is as mentioned above, I’ll end up with 26-28 degrees of initial advance – maybe more. Am I on the right track here?? I'm already thinking of putting the richer jets back in because it's looking way too lean when I open it up.

It seems I’m a tuning misfit…....Help!!

 

I'm holding off on drilling anything on a new carb, five7....I think the problem is with my tuning abilities, not the carb. Do you think I'm on the right track with this??

Still open to any thoughts!!

 

what your initial advance should be depends on the amount of mechanical advance. ultimatly you should have total timing between 32 and 36 for an iron head motor