I asked around here and other sites about Barry Grant Demon carbs,got good feedback on them. So I bought a new 525 cfm Demon carburetor for the 305 SBC in my El Camino.This is a later roller cam engine with a 206-212 degree duration at .050 cam and 9.25 compression.Older Ram's horn exhaust manifolds and these modifications are just right for a 525 Demon according to Barry Grant's website.This engine is not some top end screamer so a small carb is good.This engine idles with a very slight lope at 700 rpm,pulls about 16 inches of vacuum at idle. I bolted it on,started right up with a decent idle out of the box.A road road test had the engine falling on it's face at part throttle even with a warm engine.Cl***ic case of lean main jets.So I checked the timing just to be sure,10 degrees initial,36 total at around 3000 rpm.Then I hooked up the vacuum advance,no change in the timing curve.Put a vacuum gauge on the timed vacuum port,nothing until 3000 rpm,what the ****? And the full time vacuum port showed no vacuum at all. Pull off the carb,flip it over,run a small drill by hand through the vacuum ports,they were full of something like Loc***e.Good quality control!!! So I changed the #58 main jets to #62's cause that's what I had on hand. Another road test,better but no cigar,still stumbles on application of light throttle and has almost no power off idle.The power valve test ok.And the timed vacuum port still doesn't pull vacuum to nearly 2000 rpm's which isn't helping throttle response.I have a lot of experience with Holley's and 4 steps up on a main jet is quite a change for part throttle. I checked for vacuum leaks,none to be found. I gotta say at full throttle the Demon does pull better than the 600 Edelbrock I had on the engine.But the Edelbrock does perform nicely at part throttle. Oh well,I'll call Barry Grant and if my experience with them is like other carb manufacturers,they are gonna tell me there's something wrong with my engine.........
I had a 350 2bbl Demon on the Peter Beater w/an AMC inline 6. Awesome carb. Yes, it took some tuning to get it just right but when it was there, good golly, Miss Molly....hold on to your lolly! (Geez, that was gay!)
From my past experience with Holley's I'm thinking the idle restriction jets are too small.So the throttle coming off idle isn't getting enough fuel through the transfer slots which provide fuel until the main jets come on line..With the engine idle set the transfer slots are just uncovered like they are supposd to be.The idle restriction is.028 ,that's kinda small perhaps for the 16 inches of manifold vacuum.And smaller air bleeds might help to get the main jets come on sooner,but they aren't replaceable so I'll try sticking fine strands of wire in them and see what happens. Keep messing with it until it woks........
there is a BG tech guy on here. Try PMing him. Can you imagine the number of calls per day they get dealing with people who are total idiots... give them a chance. Explain your problem and what you did to correct it. Once they see you've done your homework and you know what you are talking about you'll see a different side. Tech @ BG http://www.jalopyjournal.com/forum/member.php?u=9727
Thanks for the info.I know about stupid questions,I'm an electrical contractor.................But still I get the impression the Tech help lines are undermanned and they just try to get through it all as fast as possible............ I'll PM this guy and call Barry Grant Cars tomorrow if necessary.
With the engine off and you hit the throttle do you get a good shot of gas over the throttle plates. If not check the accelerator pump linkage.
The accelerator pump works as it should. I've heard some past stories of **** Demon carbs.I've also heard bad stories on Holley's,Edelbrocks,AFB's,Rochesters and so on.And let's not forget old Strombergs that squirt gas 100 feet if the fuel pressure is more than 1/4 PSI. This carburetor will not kick my ***,it will not be a a door stop,I will fix it!!!
send 'em to me. I will trade You for the dozen or so Edelbrocks becoming a modern art masterpiece in my junk room.
lol, I'm king of the Edelbrocks these days, I fix the good, or so they tell me. I'll take them off your hands. Wish I had some Holley's to give you.... on another note, I do not put a carb on straight out of the box these days. I check them over real good, check the floats, all orifices, etc.
Let me know if you get that figured out. I have a 650 Speed Demon that's been doing the same thing. I'll whip out my demon this week and see what I can get it to do, but things probably won't change too much. I talked to a BG guy once who told me to drill out the idle air restrictors if I remember correctly.
the ones I've dealt with have been a joy. I'd really like to try a 750 on my 425, but the Edelbrock on there seems to be fine for now.
It seems the Demons have more than their share of QC issues. For bolt-on and go, the old Edelbrock Performer AFB's are hard to beat. The Holleys will usually make just a little more power but are more finicky on a daily driver.
Nope,it isn't a secondary problem.If I run the engine up to around 2500 rpm ,then floor the pedal,the engine responds real nice and pulls hard to 5000 rpm through the gears The engine is weak at part throttle only,idle is fine. It acts lean,but going from stock 58's to 62's on the primary made little difference and it should have made a big difference,good or bad.
Power valve not opening or channels plugged? If the vacuum ports were full of Loc***e looking ****, no telling where else the stuff is.
Call the tech he will walk threw you problems I love demon carburetors. Some times you have to adjust out problems.If you want a out of the box carburetor you should of bought a carter or Edelbrock.My 2 cents
shinny polished junk, I bought a 675 drag race demon when the first hit the market I wanted to go bigger but the tech guys talked me into the 675 (really a 650 that flowed 675). put it on my street strip car and it ran good but nothing to jump up and down about. long story short I had a NOS back fire and damaged the idle circuits on the carb. I called BG and explained the problem and was put on hold then later dumped, called back and was put on hold and then dumped again! I emailed 3X over a 2 month period asking for advice or part numbers to replace & fix this 5 month old carb and got no response. I ended up putting a Nickerson prepped holley 750 and then I started jumping up and down, WOW what a difference at the track with only that change. fast forward2 years I meet a guy who has an "in" with BG and I tell him my story, he says to call this guy direct (gives me his number) and drop his name and he can hook me up. I explained all I wanted to do was fix the carb that still looked brand new and sell it. I originaly paid $650+++ for the thing. I call this dude and get his voice mail, I drop my guys name and a brief discription with my return number & email address....no return call comes, I call again and get the same thing so I leave the same message....no return call. So as far as I am concerned and from others I've talked to the have manufacturing probelms ,a poor tech department, there phone and web systems leave alot to be desired + BG's prostock team ****ED (that should say something right there??). last I heard they will fix any demon carb for nor more then $200 like new, if I do that I could feesably have almost $900 into this carb that is already "like new" shrink wrapped sitting under my work bench...and I'd be luckey to get $150 for it in todays market. For racing I'd take a holley based carb over anyones on the market anyday! Paul
Bolt on carb?Even the Edelbrock 600 I had before the Demon needed a change to the metering rods to get best performance. Tuning to me means changing jets,accelerator pump rates,secondary opening.This problem is beyond that it seems. I always read if a carb doesn't respond to jetting changes,chances are it not the right carb for the application.But I have a hard time believing this carb won't function right on a mild 305 V-8 with maybe 250 HP on a good day. I've been through this ******** on four barrel carbs on my past inlines.
Any chance you could send me one of them to fool around with? I'll send it back if I get it dialed in and I think I can. Around 750 cfm, but a 600 would work.
No, but carb tuning is. if it were an e.f.i. question, then we could lynch him. till then, lets try to help him out.
Try this before anything gets too fancy- source Yourself a "blue" holley acc. pump cam. it sounds like a no-go, but it has a real quick ramp. with the smaller resevioir to feed from at part throttle, you may not be getting a very good shot. with the blue cam, it has a bit more left in the bucket. also- and this is going to sound stupid- is this one of the "ez-idle" carbs? with the additional idle adjustment in the air cleaner stud hole? I had one of those play hell with me. I had the ****erflies way outta whack with the idle transfer slot, and the resulting performance was less than stellar.
Yeah that's what I'm thinking, I've never gotten that lucky that one was right out of the box. Now I have had a few that could be run out of the box, were livable, but they could all use a little love. Yep, but I think it's becoming a lost art.
it's really not...it's just getting harder to find a copy of "super tuning Holley carbuerators" anymore.... Heh.
I ran a Demon carb, 750 Speed Demon variety on my 427. I really like that carb, comparable to the Holley but gave me better fuel economy and more power. But I researched everything I could before making my purchase. I had heard several people talk about the extra that BG would give you. Extra as in casting flash and shavings. Pretty standard to clean everything you get these days and when I received my carb, I pulled it apart and sure enough there was aluminum/zinc shavings in the bowls and one of the transfer slots was partially obscured with flash. If I didn't trim it back with an Exacto knife before re***embly I am quite sure it would have given me the same grief you are now experiencing.
I think there are more people on here that can tune a carb than in the whole state of North Carolina. And my parts guys will probably back me up on it. Maybe I need to get them to carry some books.... nah... those guys can't read...
My speed demon was full of what looked like gl*** beads. It sure look like the carb had been wetflow quality tested with dirty fluid Honestly though, it's been a decent carb performance-wise. But I did the research beforehand & knew enough to take apart a BRAND NEW carburetor and clean the **** out. Anyone pondering a demon purchase would be wise to note the debris theme in this thread.......few minutes and a lil bit of carb cleaner before install will payoff...... good luck
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