ok so i have a fresh rebuilt 305, stock heads, 0.030 over, some kind of 350 cam or so i was told by the person i bought it from, headers and full exhaust, 625 road demon carb with vac seconds, 5-speed, 3.27 gears, new wires, new ac delco plugs, new accel ignition control module in the HEI cap.

The problem is, at idle it runs really rich and idles at 1000rpm or higher. and under light throttle it surges and stumbles on itself then gets power and takes off. the new exhaust i put it on it is black already after maybe 30 miles. it does eat gas more than it should. the idle is horrible, the whole car shakes and feels like a few mis fires, and the acceleration is really poor and rough.

I have tried messing with the idle screws and if i can get it to smooth out the exhaust makes your eyes tear, then if i fix that it idles rough and wants to stall when any load is put on the engine at idle.

So i am at a loss as of right now, base timing is at 11* btdc as per demons web site with the cam i have. any help or ideas is greatly appreciated.

 

To me it sounds like it has to much fuel pressure I would say buy a fuel pressure gueage. Install close to the carb for a accurate reading. It really shouldn't be anymore then like 5-8. Whenever mine would act like that the fuel pressure was to high.

 

what kinda demon u have... they tend to be jetter rich from the factory....

 

the mechanical fuel pump is self regulated at 6psi, it is just a carter stock replacement. the speed center i bought it from is pretty good about knowing this stuff, but he just closed shop and is no longer around to help :/

It is a road demon 625 4barrel, i bought it with 2 hours run time on it. the guy never opened it or touched the jets.

 

Put all the settings back to factory and start over including adjusting the throttle blades to their correct posision. You should have what looks like a small square showing for the transision slot BELOW the throttle blades. Make sure float levels are correct and check no gas dripping in from the boosters while the engine is running at idle.

Here's a link to the manual for that carb if you don't have one. It'll help you a bit with the 4 corner idle settings and high speed idle.

http://www.barrygrant.com/fromBarryG...n%20Manual.pdf

I had a 750 speed demon on my old 305 and ran without problems. Now I have a 750 Mighty Demon on the 350 and it idles at around 800 rpm without burning your eyes. All it takes is a little bit of time to get things dialed in.

 

ok, i know there is no fuel dripping from the boosters at idle, the float levels are correct, they are at the bottom line of the fuel window cause its a street car. the only think i have not checked is the throttle plates. i will do that tomorrow.

 

ok so i unbolted the carb today, found out the secondaries had play in them while the throttle was in the rest or idle position causing the engine to use as much air/fuel uncontrolled at idle as it wanted to. I fixed that, bolted the carb back on and so far its a world of a difference. it is not as rich, still to rich but it doesnt burn your eyes anymore. The idle is still really rough though, as if there is a few cyls mis firing.

 

I just ran my car on a chassis dyno with a Demon 750. The carb was brand new out of the box. IT was running PIG rich and when we took it apart there were NO jets in the back of the carb. When we put jets in it corrected the problem quickly.

My engine builder swore against BG carbs because he has had problems with 9/10 of the ones he used. Including finding a piece of a love letter in the bowl in one.

My next carb will be a Holley HP

 

that's a new one, usually it's just metal chips left in the bowls. Been pretty happy with my older model used mighty demon but still went through it checking all the passages I could. Had to do a bunch of cleanup stuff to a brand new 850 I had bought which is now sitting on a shelf. Really disappointed with that purchase.

 

yeah im not too impressed, i have an old holley that has seen better days appearance wise but runs great that i have been tempted to put back on.... it doesnt matter too much tho cause in the fall im putting tpi on and ill be done with this constant adjusting bs.

oh and BG's tech line is useless. i explained to the guy 5 times what was happening and he said it was normal. he told me that play in the secondaries while the throttle is in its resting/idle position is normal....while any other carb that i know of there is no play so the idle can be controlled; not idle at 12-1300 rpms with the idle screw all the way out.

thanks for your help guys, ill just have to keep playing with it and maybe get it to run smooth...

 

I've never messed with a road demon before but it looked like to me there was a fast idle cam on the thing. Maybe try adjusting the choke and the fast idle to where they don't come on at all. Then you might be able to adjust with the regular idle screw to get it down.

 

I HAVE A 650 SPEED DEMON ON 1969 350 AND IT IS A BITCH TO TUNE. MY GIRLS CONSTANTLY BITCHING ABOUT HER EYES TEARING. I'LL GIVE YOU A REASON TOO CRY!!! I HAD TO PLAY WITH THE FUEL LEVELS TO HELP KILL THE GAS SMELL

 

the choke is off completely, i have to hold the gas when i first start it cause i took off the choke. i dont really need it since i only drive it in the summer and it usually stays running without a problem.

the floats are as low as they can be and where demon says for a street car.


it seems to be running better, not as rich anymore, but it still stumbles on light accel while driving or starting up from a stop.

 

Sure you've done this but... check the accelerator pump arm adjustment. It should have no slop at idle so it squirts as soon as the throttle is touched. At full throttle, you should still be able to push down on the pump arm a very small ammount. You might have to play around with shooter sizes too.

 

still chasing this one guys,

i added some advance to the initial timing, it is at 11* btdc, helped out a lot. idle is smoother not as rich and the car is much more responsive, no more light throttle lag or stumble.

the only problem now is slowing down and stopping, if i dont downshift threw all the gears including first to slowly settle the engine down it just dies. it happens every time when its hot. if the car is sitting idling without being driven its fine.

im thinking its still to lean on the idle screws? the throttle plates are set correctly, and when it does idle it is at 900, any lower and it wants to stall and starts shaking. so im out of ideas?

 

ok so i helped the situation a little, i riched the idle and raised the idle to about 1300rpms. it still stalls when it gets hot then when it does run it has a nasty shake to it like 3-4 cyls are not firing and you can def hear something is not right in the exhaust. I am going to swap out coils today, my friend has a brand new one so i hope that is the problem. if not i am out of ideas. the ignition control module inside the HEI cap is brand new, plugs are new, wires are good, vacc advance is good, it was tested in front of me, the dizzy is straight and good. ill keep you updated.

 

How many turns are your idle screws out ?

 

Im thinking your settings are way off on your carb and you need to set everything back to original settings. You need your transfer slots .020-.030 exposed yours are more and thats where the rich idle is coming into play. Your probably going to need yor idle screws under 1 turn on all 4 corners mine are set to 3/4 turn on my 650 mighty demon. And the whole lowest float setting for a street car is "BS". This is the reason your car is dieing when coming to a stop becuase the fuel is sloshing to the other side of the fuel bowl and leaving the carb with no fuel. The fuel bowls need to be set at the middle line on the sight plug a little over or under with not hurt.To tune out the rest of your rich idle you need to deal with your IAB and your IFR.

 

i have adjusted the transfer slots back to 'stock' and at the same time i returned the idle screws to 1.5 turns out as per demon to start with. now if i tighten the idle screws to about 1 turn out the engine starts shaking and has really bad lag and wants to stall.

One of my friends is gonna look at it for me, he was in the car with me and witnessed it. i drove the car 2 miles if that, and it ran fine...until we stopped at a light then it died. then it wouldnt start and i was stuck in the middle of the road, i had to hold the petal to the floor for it to finally kick over then it ran like total crap; meaning violently shaking at idle wanting to stall and while driving car having no pickup and very shaky acceleration (stumbles).

The idea i might have the wrong fuel pump was brought up, seeing as how i have a main and return running to the tank but the pump only has a single in and no return. could that cause anything??

oh and about the floats, this carb came off a running 350 that ran fine with the floats where they are, never stalled at any light or anything so i dont understand how the float level would be wrong for this motor and not the other one? (correct me if im wrong)

 

Pull the carb off and start over with stock barry grant specs. Put the transfer slots on primary at about .020". (Should be a square) Raise the carb up to a light and notice the light coming through on the Primaries. Mimick that on the secondaries. It will probably be less than .020". Take your Idle mixture screws and turn them in till they lightly seat and back them out 3/4 of a turn. Checky and make sure the the gas is at the bottom line of the site glass on the primary bowl and somewhere between the bottom and middle line of the secondary bowl. Make sure the shooter squirts just as soon as the throttle is touched, if not adjust the pump arm. Put the carb back on the carb and start it up. After it starts put a vaccum gauge on the maifold vaccum port and start tuning your idle mixture screws. You want to turn the screw in 1/16-1/8 turns and tune for maximum vaccum. Adjust your idle evenly between primary and secondaries. Hope that helps..

Andy

 

Do you have a mech. or a electric fuel pump and what psi is it at ? Just casue the carb ran well on a 350 dosent mean it will run well on your 305. Put the floats to be set at the middle of the sight glass for now and try to re-adjust your idle screws after.

 

replace your plugs since they're fouled out.

 

i pulled them to see if they were but they are clean, not even wet.

the fuel pump is mechanical self regulated at 6psi, i dont have a pressure gauge to confirm that tho.

 

if your plugs are clean and have a nice tannish color then your eyes can't be burning from it running too rich. Can't have a rich running motor if the plugs don't show it

 

yeah i fixed the rich problem well better, it still smells a lot at idle but its ok idc how rich it is. the problem is when it gets hot it stalls then wont run. for the first 3-4 miles of driving the car it runs and drives like a million dollars, great response a lot of pep and take off for a 305 and i mean it throws you back in your seat, which is impressive... BUT as soon as it gets warm and been running for a few miles it stalls out at the first stop then it doesnt want to start for a few minutes and i have to hold the petal floored to get it to want to try to start....then once it finally starts it feels like its running on 4 cyls if that and it has no pickup, no go, nothing and the exhaust has totally different tone like its misfiring and all that. the ICM under the rotor is new, the coil is new, plugs are new, wires are only a year old. so im thinking it has to be a fuel problem. any ideas?

 

as the motor warms up it needs less fuel, i would lean out the idle screws a bit... remember they are VERY sensitive and they all must be out the same amount. everyone's bashing on demon, i learned how to tune on a demon and have barely adjusted it since the initial tune

 

To me its sounds like it could even be a bad vacum leak from some where. While the motor is just started everything is still cool it runs prefect and after a few miles the motor heats up everything starts to expand and then theres your motor running like crap. Also did you adjust everything on the carb at operating temp ?

 

ok so i talked with a guy that has had a lot of exp with carbs, he said it sounds like my gas tank isnt vented and its creating a vacuum and when the engine idles down the fuel pump cant keep up, then when the car sits and not running the tank settles down and the car runs till it happens again. so if i have time tomorrow ill try unplugging the return line so it acts like a vent.

 

just get a vented gas cap

 

A vacuum leak is going to cause more problems cold than hot.

Personally, I like the idea of a fuel pump with a return, just to keep fuel moving in the line to give it less time to pick up heat. A Carter M6626 pump works well for most street performance engines, I can't imagine it not keeping up with a 305.

High vacuum in the tank at idle doesn't make any sense.

I don't see anywhere in BG's information anything about lowering the fuel level in the float bowls for street use. Mid-window is their base recommendation, I doubt you're doing anything to require tweaking that. Try putting them mid-window and making adjustments from there.

From the horror stories I've heard around here, it might be a good idea to completely disassemble the carb and clean out all passages, especially the idle and air bleed passages. Having a piece of debris or an incompletely machined passage will really cause havoc.

 

there is no vac leak, i checked it while the engine was hot and cold.

the carb is clean, i heard the horror stories so i pulled it off and opened it up and made sure i put it back together right, and there are no leaks after.

I wanted a return line fuel pump but i was told it didnt matter...so now im stuck with this pile of crap.

as far as the floats go, i think it was in the video you get with the carb. i dont remember where i heard it but the speed shop i bought it from said that is where they need to be so i never touched it.

I wont have time til after vacation to mess with the car. so when i get back i am going to try the vented gas cap.

my main problem with this is that the carb came off a running motor. it ran perfect on my 350 and i know for a fact that the 305 is a good motor because it was running perfect in another car right before i bought it. the ONLY thing i did to the 305 was put roller rockers on it and i had them adjusted by a speed shop.

 

ok so the fuel pressure problem is non existent. i unscrewed the gas cap when it stalled and nothing, had a hell of a time restarting it like usual. so when i just got it running, i reset all the idle screws to 1 turn out. it runs better...doesnt stall anymore, i raised the idle a little to 900. it still shakes a lot at idle tho and is rough going through the rpm range. but i can live with this for now. the engine is getting a new cam, heads and tpi come fall/spring. thanks for the help

oh and i had a little race with it, my friend just bought a stock 89 iroc with 305 tpi auto, when my car decides to run i am faster but he puts up a fight