Demon Carb Woes
Thread Starter
Intermediate
Joined: Mar 2006
Posts: 42
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From: PENDERGRASS GA
Demon Carb Woes
Ok I Really Love The Look Of The Demon Carb But, My 72 Coupe Hasn't Run Right Since I Put It On. I Have Had A Lot Of Past Problems That I Have Got Cleared Up With Demon Tech Support But Now I Have One More Small Issue, A Higher Rpm (around 4000-4400) Pop Out Of Carb, And When It Pops It Feels Like Im Losing Power I Am Currently Running The Road Demon 625cfm With A 78 Primary Jet And A 86 Secondary Jet. The Motor Has Aluminum Heads With About 9.5:1 Compression, And A Edelbrock Performer Cam. Edelbrock Eps Intake, I Ran The Car With An Edelbrock Carb, 600cfm For A Few Weeks And It Did Ok But I Dont Have That Carb Any Longer, I Wrestled With The Timing In Several Positions And Vacuum Hookup Options But Still To No Avail, I Also Have The Ignitor 2 And The Plate Under The Demon Carb Recommended By Demon Tech.
Help Richard
Help Richard
Race Director
Joined: Sep 2004
Posts: 11,874
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
sounds like a fuel delivery problem.......what is the float levels set to? maybe try increasing them or at least immediately after the pop stop and see what level of gas is in them....perhaps clogged fuel filter or even a dying fuel pump
Tech Contributor
Joined: Aug 1999
Posts: 14,381
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From: At my Bar drinking and wrenching in Lafayette Colorado
Popping out the carb and loss of power are indicative of a lean condition. Lean condition at elevated rpm and high power setting can be caused by poor fuel supply/delivery, low float level, or lean jetting for the application. Put a fuel pressure gauge into your fuel line at the carb and tape the gauge to the outside of your windhield. Observe pressure as you drive and as the problem occurs. If pressure drops below 3 psi, check your fuel delivery system. If pressure stays normal, bump your jetting up 2 jet sizes after verifying float levels.
Racer
Joined: Apr 2006
Posts: 477
Likes: 43
From: Millbrae California
Originally Posted by lars
Popping out the carb and loss of power are indicative of a lean condition. Lean condition at elevated rpm and high power setting can be caused by poor fuel supply/delivery, low float level, or lean jetting for the application. Put a fuel pressure gauge into your fuel line at the carb and tape the gauge to the outside of your windhield. Observe pressure as you drive and as the problem occurs. If pressure drops below 3 psi, check your fuel delivery system. If pressure stays normal, bump your jetting up 2 jet sizes after verifying float levels.
if the fuel pressure stays above 3 lbs with the test Lars suggested consider borrowing another known good carb to try since my chart shows the primary jet should have been 70's and the seconday should have been 78's. if you are at 78 pri and 86 sec jets, have good fuel pressure and are still lean it could be a bad carb or maybe a ignition or engine related problem since going up 8 jet sizes over stock jetting to ME is not normaly required. if it runs good with a known good carb most likely the carb you took off was a problem carb
Thread Starter
Intermediate
Joined: Mar 2006
Posts: 42
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From: PENDERGRASS GA
im Gonna Try The The Fuel Preassure Thing, The Fuel Pump Is New But I Have Never Checked The Pressure, I Bought The Pump On Ebay.this Is The Second Carb, I Had To Send The First One Back To Jegs And They Sent Me This One And It Does Great Except For The Hi Rpm Pop, I Am Running Real Rich But When I Go Down On The Jet Size It Gets worse.
Safety Car
Joined: Oct 2004
Posts: 3,725
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From: Minnesota
Get your old Edelbrock back.
Seriously, I've been happy with my Performer 1406 and I've even done some successful tuning on it recently. Some around here make fun of it as being an "old AFB" non performance carb but so far so good.
Seriously, I've been happy with my Performer 1406 and I've even done some successful tuning on it recently. Some around here make fun of it as being an "old AFB" non performance carb but so far so good.
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Race Director
Joined: Sep 2004
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by FUNDERBURK
im Gonna Try The The Fuel Preassure Thing, The Fuel Pump Is New But I Have Never Checked The Pressure, I Bought The Pump On Ebay.this Is The Second Carb, I Had To Send The First One Back To Jegs And They Sent Me This One And It Does Great Except For The Hi Rpm Pop, I Am Running Real Rich But When I Go Down On The Jet Size It Gets worse.
Melting Slicks
Joined: Sep 2004
Posts: 2,412
Likes: 3
I just had this problem too with my Mighty Demon. It would pop or spit out of the carb at low rpm on the highway when I tried to accelerate. It was too lean. I thought that I was too rich because I was fouling plugs but that was just because I was too rich at idle, my PV was opening too soon. Put jets two or three sizes bigger in there, should fix the problem.
Pro
Joined: Sep 2004
Posts: 595
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From: Boston MA
I agree with lars, but you might want to also check the power valve in the front if you are getting the pop under heavy acceleration. If that is not opening, then it may be lean.
Based on what I have heard, increased jets, etc.. I would guess a fuel delivery problem..
It may also be timing though, are you sure that is correct? It is important to start there and then go to the carb...
Thanks,
Joe
Based on what I have heard, increased jets, etc.. I would guess a fuel delivery problem..
It may also be timing though, are you sure that is correct? It is important to start there and then go to the carb...
Thanks,
Joe
