ok. i bought a speed demon 650 off of a guy from work. i had a holley 670 street avenger on it before. well with the holley it ran pretty good, but if you have the chance to buy a demon for a good price why not take it right? in hindsight i wish i didn't get it. im having problems with idling and moderate to heavy throttle. when i drive normal, it works fine, but when i get on it; it hesitates and stumbles. right after that though it picks back up and runs halfway decent. i had a 5.5 power valve in it, which it came with a 6.5. so i put a 6.5 in it. im still in the process of getting everything tuned back up because i just did a small cap/external coil conversion.
what my question are....
is there anything else that can effect performance in the mid throttle range?
what is the factory setting for the idle eeze screw? which way adjusting it lets more air in or lets less air in?
or any other tuning tips that you can help me with?
my engine specs are in my signature
thanks for any help
kent

 

My demon worked fine with the car in park, nice crisp idle to throttle snap. Once I had the motor under load it developed similar problems.

Mine's not EZ-Idle type, but I've found the Barry Grant Website has a lot of material on it that is very helpful. I solved my problem by setting the timing, adjusting the transfer slots to closer to square, then fine tuning the transfer slots and the idle mixture screws.

Here's some good links:

http://www.barrygrant.com/pages/manuals.aspx

That page has the guide included with your demon and the EZ idle instructions.

I've also found this to be helpful because it talks about Barry Grant recommend'd timing depending on camshaft:

http://www.gnetworks.com/v4files/bar...withimages.pdf

 

Looks like you have to much duration on your cam for the speed demon. They say up to 240. Looks like you should be running a Race Demon or a King Demon. Not sure how big of an impact it makes?

 

Is that 270 advertised or at .050? Mine is 248 duration at .050 and 294 advertised, it's within the specs to use a Mighty Demon. The Speed Demon I used to have worked fine too.

Personal opinion on the EZ Idle stuff, keep it closed off unless you really really need it. Put the stock jets in if they've been changed, same with the squirters, set the butterflies to get those square transition slots and set the idle mix for best vacuum. For the power valve size, take a vacuum reading in gear for an auto, say it's 12 inches, go 2 to 2.5 below that. You'd end up with a 9.5 or 10 PV. Make sure there is no slack on the pump arms at idle, when full throttle the pump arms should still have a very small amount of travel left so they don't bottom out.

Maybe BGTech will step in on this one too.

 

Looking at the lift numbers the duration numbers he has listed are most likely the advertised numbers not the @ .050", so he should be OK.

The first thing we'd want to do is get the idle situation taken care of, and then work from there.

A few questions:

What RPM is the engine idling at?
How much vacuum is it producing?
Where do you have the adjustments on your carburetor right now?
How much ignition timing are you running at idle?

 

my engine is ideling at roughly 750 rpms. like i said i have to work a few bugs out of it. im not sure exactly what my timing is set at, i tried to set it at 12 degrees advanced but it seemed too retarted. with my timing set at 12 degrees initial, i had 3-5 hg of vaccuum, and it ran like crap i advanced the timing and i started pulling 13-15hg and it ran better. that is another one of my head scratchers? my timing tab and my balancer notch line up at 0 on tdc but my timing readings don't agree with it. i have tried two different lights and they both show the same, way advanced. the only thing i can think of is my balancer im using, its off my old 305 and i have a 70 model 350. but why would my timing marks line up?
the whole pwer valve thing im not too sure of. ive heard 2-2.5 points, but the valve from the factory in my carb is 6.5, that would mean it would work with a engine that had an idle vacuum of 8.5-9.0. how many engines would have that low of idle vacuum? it would make sense with my hesistation if thats true, but i dont know of many people that change power valves in their carbs.
as far as where my carb is set now
69 primary jets
78 secondary
6.5 power valve
31 squirter(factory)
idle screws turned to slightly rich setting (dont know number of turns off my head)
idle eeze screw??? dont know where it is in relative to what would be a base setting?
butterflies slightly cracked for fast idle

that is advertized duration
thanks
kent

 

Kent,

You're probably going to want to be somewhere close to about 16 degree BTDC on a combination like yours. That is going to be the first thing you'll need to check. It sounds like there is an issue with your timing light. You'll want to borrow a different light to check your timing. Some lights will give you issues with different ignition systems.

 

im going to work on it tonight. im going to try to set it around 16-18 degrees advanced. im also going to try putting my buddy's 600dp holley on it to see if my demon is messed up internally.
kent

 

ok set my timing 16-18 degrees advanced. slapped on my buddy's 600dp holley and it runs like a champ, no hesistation, real smooth acceleration.
whats going on with my demon???? is it too big for my engine? put too much fuel in? what can anyone suggest? im going to rebuild it, anything else i should consider?
kent

 

OK, at least we know the engine is working OK, and we can move forward.

I'd go through the carburetor, clean it out, install new gaskets, and put it back to a baseline to start with.

 

which components can i soak in berrymans? also what kind of seals are on the throttle shafts, ive heard they can be o-rings or nylon. do i need to worry about those? is there anything in particular that i need to look for when i rebuild it? and lastly im going to use a rebuild kit for a 4150 holley right?
kent

 

You'll be able to soak everything.

No seals around the shafts to worry about.

Best bet is to go through each of the holes with your cleaner, and spray them out with some compressed air.

No, you'll need a kit specifically for a Demon. The main body to baseplate gaskets are different.

Mechanical secondary carburetors use Barry Grant rebuild kit P/N 190004.
Vacuum Secondary carburetors use Barry Grant rebuild kit P/N 190003.

 

Bo seals around the shafts to worry about.

so are those ok to be put in berrymans? where can i get a rebuild kit pretty quickly?

 

No problems with your Berryman's...

You should be able to get a kit through any Barry Grant distributor.

 

ok im about to go to work and rebuild my demon and try to work that bug out. its been soaking in berrymans since last night and im going to go through it with carb cleaner and compressed air before i rebuild it.
now is there any suggestions for my problem? im having a problem with any quick throttle snap more than 1/4. it falls on its face hard and sputters then it starts picking back up and runs relatively allright. i noticed some gunk in my emulsion holes, maybe that will help out some. any suggestions will help me out!!! first thing im going to try (if the rebuild is not enough) is put a power valve in it that is 2-2.5 below my idle vacuum. after im going to see if putting a different secondary spring (to make them open sooner) in will help. anything after that.........thats where your ideas come in. and if you have a suggestions for me please explain how it will help, or what specifically it does. im trying to learn as much as i can about carbs because im not very savvy.
thanks for any input!!
kent

 

well the rebuild itself helped. i got better throttle response and it doesn't want to sputter as quick anymore. the sputter is still there. ill be at a dead stop and then pin the throttle, it takes off initially like the squirt from the accelerator pump is good, but then it starts bogging and sputtering, then it starts clearing out and takes off like a scalded dog. its worse when im cruising and pin the throttle, my tranny downshifts and my engine fall on its face. sputters for longer and then gets better. so my guess is its a problem between the accelerator pump and the metering circuit. can't tell if its too much fuel at the wrong time or too less fuel. i didn't get to try a 8.5 power valve, thats my only guess.....
kent

 

you need a stiffer secondary spring

 

ive gone 1 spring stiffer and 1 spring lighter. didn't make too much difference, i didn't get to mess around with the springs that much though. im going to try the next up from a purple. the bogging seems to happen before the secondaries should be opening.

 

ok last night i messed with the idle. i went out and drove it and now its not sputtering like it used to. now its just a big hesitation. the only other thing i did was put a different secondary spring in, i still have the purple. it seems like once the secondaries open, the hesitation stops and it starts running great. what else could it be?
kent

 

anyone.......my buddy BG TECH..........

 

"it seems like once the secondaries open, the hesitation stops and it starts running great. what else could it be?
kent:"

Leave the secondary springs alone for now..

I myself would start tinkering with primary pump cams and discharge nozzles...but one at a time.

What color primary pump cam is in it? What size discharge nozzle?

From what I have read it seems you have the baseline adjustments set rather good..so time to look elsewhere.

 

it has a pinkish pump cam and 31 size discharge nozzle.

 

Try a 32 or 35 nozzle first...may take car of the dead spot. But from experience with my Demon..if that doesn't work try the blue #427 pump cam on the #2 hole

 

Maybe I'm just slow, but I'm not clear exactly what it's doing now.

If it surges under cruise, your primary jetting is too lean.

If it has a dead spot as you slowly go from idle to power, like a smooth take-off from a stoplight, you need a larger number power valve.

If it sputters and pops when you first hit the throttle a little more aggressively, but not floored, you need more accelerator pump shot.

If it bogs out when you nail it, then recovers and takes off, you need a stiffer spring in the secondary diaphragm because the secondaries are opening too quickly. You shouldn't be able to feel them open when you floor it from a stop.

I would start fixing things in the order above.

 

it sounds like more of your last suggestion. it has a nasty flat spot when i nail it, then it recovers at about 3000-3500 rpms and starts taking off hard. 2000-3000 rpms is when it has its flat spot approximatly. right now i have a purple spring in it which is rated at 1915rpms when it starts opening its fully open at 6950rpms. next up is the plain which opens at 2240 and is wide open at 8160. should i go with that one or the next up from that?
kent

 

Start with the stiffest spring. If it still does it, you've got another problem.

If it goes away, go with the next lightest spring. Keep going lighter until you get a slight bog (remember, that means you can feel the secondaries open), then go back one stiffer.
----------
http://www.holley.com/data/TechServi...wer_valves.pdf

The PV # is 1/2 your idle vacuum.

 

Okay, I'm still a little slow. This is a Demon vacuum secondary? If so, I'm not sure of their design, but I know the Holley vacuum secondary carbs have a check ball in the secondary vacuum circuit that people sometimes take out, thinking it's keeping their secondaries from opening quick enough. If the Demons use that, too, and yours isn't there, you're never going to solve the problem by changing the spring.

 

yes it has a vacuum secondary. as far as the check ball, when i rebuilt it i didn't see one. now if there was one i don't know where it would go. the vacuum port goes straight from the underside of the throttle blade through the baseplate into the main body and is sealed off with an o-ring from the main body to the vacuum pod.

 

That doesn't sound right, because the vacuum source should be the primary venturi. But, I'm not completely familiar with Demon design.

 

ok i got some more info. first off i put the plain spring in and drove it, it didn't make much more of a difference with the flat spot/hesitation. i brought it back and advance the timing a bit, put a 35 squirter in, and went out and drove it. i paid attention to my rpms and when it happens. on nice moderate acceleration the flat spot is barely there. i put it in second gear and cruised at 2000 rpms, then i nailed it. the rpms shot to 2500, then is started flatlining, about 3000 rpms it started picking back up and by 3500 it was gone.
i have a quesition..... when the secondaries open what happens to the secondary main circuit? since it has no power valve, does it instantly start letting fuel in? if so maybe im getting too much fuel and not enough air at that point in time, since the secondary butteryflies are just opening up. the secondaries have 78 jets.......

 

Here's the main circuit theory, whether mechanical or vacuum, primary or secondary:

When the thottle is opened off-idle, there hasn't been any fuel flowing through the main metering circuit (or power circuit, for that matter). It takes a little bit of time to get the fuel flowing through the circuit as the vacuum builds in the booster due to the flow through the carb venturi. During the time it takes to get the fuel flowing, you have a lean mixture. With the primary circuit and mechanical secondaries, the accelerator pump squirts some fuel into the air stream to keep it from being too lean until the fuel gets flowing through the main metering circuit. With vacuum secondaries, the secondary throttle blades are opened gradually so the air flow will start building booster venturi vacuum to start pulling fuel through the main metering circuit - in practice, this should happen before the total mixture going into the engine gets so lean that you get a miss or "bog". If you let the secondaries open too soon, a vacuum secondary carb will bog due to the too-lean mixture while the fuel gets to flowing to the booster venturi.

There is a chance that the problem is coming from too rich a secondary mixture, but 99 out of 100 times (perhaps more), it's due to a too-lean condition.

Keep trying the heavier springs to see if it will go away. I haven't been able to find info on the BG website for specifics about their VS circuitry, but I know for certain that Holley VS carbs have a check ball in the secondary diaphragm vacuum circuit that if it's missing, you'll never get rid of the bog.