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jvest
10-20-2006, 10:23 PM
I just bought a new 750 mechanical secondary speed demon to go on my 383 small block in a 68 Camaro. I did the intial setup with the butterfly settings and idle-eze screw before I installed it. After getting it started and up to temperature, I set the idle mixture screws using the vacuum gauge. I had to run them in a lot, because it was so rich. They're about 1/2 turn out from bottom. I'm reading around 15 on the vacuum gauge. I also set my intial timing to 15 deg. For some reason I have to use the primary butterfly screw to adjust the idle speed. I moved the idle-eze screw from bottom to 4 turns out and it didn't make any change in the idle speed. I'm still preping the car for paint so I've not been able to take it out on the road yet. I've just wacked the throttle in the shop. It sound pretty good when you wack the throttle from a high idle, but is a little stugish (No stumble, just rich) from idle. It also will not start unless I hold the primary butterflies wide open. If you don't, it'll fire off for a 1/2 second then go dead. I had an edelbrock carb on it before this with great throttle response and started up with a bump of the starter, but it loaded up bad at an idle. I know it will be better to get it on the road before I start tuning, I just thought I could tweak on it a little in the shop while I'm tired of block sanding. I listed below info that may help.

Thanks for any help,
Jim

60 over 383 small block with 5.7 rods.
Two valve relief flat top pistons (Eagle Stroker Kit)
Cast iron heads with 2.02/1.60 valve & 64cc chambers.
Edelbrock performer intake.
Standard HEI ignition.
292 Comp hydraulic cam(.501 lift / 110 CL)
Comp roller rockers
15 inhg vacuum at idle (850 RPMs)
3" flow master exhaust with dynamax headers.
floats set at bottom of site glass.
1/2 turn out on the idle mixture screws.
15 intial timing & 38 full advance.
vacuum advance connected to the timed vacuum port per BG tech line (front port).

z28orshoot
10-21-2006, 02:16 AM
sounds that the box jetting is a tad rich for your combo or floats might be sticking.

what is the fuel pressure at the carb??? should be 7.5 lbs.

on the ez idle..... does the performer intake have a ridge dividing left and right sides or the planes. is the gasket on the bottem of the carb covering the ez-idle hole? the manifold might have to be clearanced for the idle. it is possible that this is happening.

you might take the metering blocks off and jet down about 4 jet sizes to begin.

check the above and let me know. hopefully this helps

jvest
10-21-2006, 08:32 AM
The out of the box jetting is 76 primarys and 83 secondarys. The primary power valve is 6.5 with 31 squirters in both front and back.

The fuel pressure is 6.5 to 7 psi.

The intake has a divider between the left and right sides, but I don't think it goes all the way to the top of the intake. I think it's about 1/2" to 3/4" lower than where the carb sets, but I'll check. The gasket came with the carb and is open in the center.

Would you go 4 jet sizes smaller on front and back or just the front.

Thanks for the help,
Jim

z28orshoot
10-21-2006, 10:21 AM
both prim and sec to start.
i would go p70 and s78.

dont forget to reset your floats after you rejet.

also as the car is idling, look in the carb body and see if fuel is dripping or running out of the boosters. it will not "look right." you should only see fuel out of there when the throtte is opened pilling fuel from the boosters. not the squirter but booster. the
if you see fuel then the floats are too high.

turn the idle mixture screws together. make 1/4 turn adjustments to them to rough them in and then 1/8turn to final set.

a good reference is to seat the screws the 1.5 turns inital start. then listen to the engine or have a fine rpm tach. turn each screw 1/4 turn until the car stumbles. you will notice a sound difference. then 1/8 turn counterclockwise( richer) and you are there. it is hard to set those with a vaccum gauge.

keep us posted

Skip Fix
10-21-2006, 01:17 PM
The idle Eze feature is just to help add some idle bypass air for BIG cams to get the air moving to suck more fuel throught the idle curb circuit with less vacuum. I have yet to need that feature(or drilled butterflies) for any of my motors, even with a medium roller cam. If you are pulling 15" at idle I doubt you need any extra air.

For some reason equivalent Demons are jetted richer than Holleys. My Demon and Holley 850s with way different jetting gave the same HP and BSFC on the dyno. Air bleeds and metering block emulsion holes are some of the diffrences. Demons do seem to be a little fatter on the idle side.

The primary butterfly screw is what is used to set the idle on almost all carbs. Sometimes a little turn on the secoindary throttle blade screw can help a little.

vintageracer
10-21-2006, 02:37 PM
I purchased 2 different Demon carbs new and both ran like absolute CRAP out of the box. Called Demon to bitch/complain. I was advised both times to send the carb back to their location in GA. In both cases the same carb was returned to me and they both ran FANTASTIC!!!!

Virtually no adjustment needed. Apparently the mexicans ain't doin so well on the original assembly of the carbs. When the carbs were sent back to their tech group for repair both carbs ran perfect.

My advice is to bitch and complain to their tech group and send it back! Both of my carb purchases were road race prepared carbs that would not idle at less than 1500 RPM. After repair, 700 RPM's with perfect idle with no other engine changes.

jvest
10-21-2006, 09:31 PM
I did have the Mopar Holley Tuning kit I bought for Jegs about 12 years ago. It had two little plastic containers full of jets, but I loaned it to a friend and hadn't seen since. I'll pick up some this next week after work. Does everyone think the 70 -78 is a good starting point?

I fired it up this afternoon and didn't notice any fuel coming out of the boosters.

I took it for a little ride in front of the house with no windows and lights (Not to safe). It actually ran pretty good, it's just a little slugish from an idled stop. From a 10 - 15 MPH roll it'll haul a@@. From an idle it'll sputter (not a stumble) just a second before it opens up.

I think its still a little rich at an idle after setting it with the vacuum gauge. I'll try resetting it tomorrow going from rich to lean then turn it back out 1/8 turn.

I think it's close, I just need to do a little fine tuning on it. The biggest issue right now is the starting. When I first hit the starter it'll fire off for just a second then go dead. Then I have to open the primarys wide open before it'll start. It's like its flooded. Readjusting the idle mixture screws may help this issue.

I'll run the idle-eze screw back down to close it off.

I'd hate to complain to much to BG Tech right now because I've not been able to do a good road test on it yet, but it may be several months before I get it back on the road. I hope they'll still take it in and tune it if I can't get these issues worked out. It would be nice to send it in to let them fine tune it for my application. I don't mind working with it, but I've got alot of work ahead of me trying to get this car road ready. The speed shop I bought it from in St Louis said I could send it into BG and they would tune it to my application, it just doesn't say that in the manual or on the BG web site.

Thanks for all the help,
Jim

LS6 Tommy
11-09-2006, 07:53 AM
I purchased 2 different Demon carbs new and both ran like absolute CRAP out of the box. Called Demon to bitch/complain. I was advised both times to send the carb back to their location in GA. In both cases the same carb was returned to me and they both ran FANTASTIC!!!!

Virtually no adjustment needed. Apparently the mexicans ain't doin so well on the original assembly of the carbs. When the carbs were sent back to their tech group for repair both carbs ran perfect.

My advice is to bitch and complain to their tech group and send it back! Both of my carb purchases were road race prepared carbs that would not idle at less than 1500 RPM. After repair, 700 RPM's with perfect idle with no other engine changes.

My best friend Eric IS the tech group at BG. He's one of the best carb guys I have ever seen. The BG's are getting better, but even he admits they have had QC problems. It's also funny that any carbs he does for outside customers are Holley's.


Tommy

Tech @ BG
11-10-2006, 11:51 AM
Jvest,

It sounds like you’ve got things going the right direction. For your combination going down 4 jet sizes from and rear would be a safe starting point. The majority of carburetor problems are being out of adjustment to the requirements of the engine. If you’re still having problems once you’re able to do some actually road testing please let us know, we’ll gladly go back through the carburetor to make sure that everything is working properly.

Vintageracer,

Sorry to hear you had issues, but we’re glad that everything is working properly for you now.

LS6 Tommy,

Eric is a great Tech, but hasn’t worked on a Holley® in over a year since he’s been with us.


Technical Support,

Barry Grant, Inc.

www.barrygrant.com (http://www.barrygrant.com/)