New carb, super rich at idle, idle speed high, fuel dripping from boosters...

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Lars

Lars

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I swapped a new Speed Demon onto my Dart as the Road Demon that was on it doesn't match my cam specs. I ran the Road Demon on my old 318 and it was always great, ran fine on the 360 also. This one however is killing me. It is running stupid rich at idle, I can't get it to idle below 1500 rpms, fuel is dripping from the primary boosters (hence the rich condition). I never had this much trouble with the Road Demon, I swapped it cause I needed a new carb for the 318 in my truck, so I figured I would upgrade the carb on my Dart and pass down the Road Demon onto it. Anybody have any clue as to what my problem might be?

ETA: I did crank down on the float adjustments on the primary and secondary and the fuel level went down, so I assume they aren't sunk.
 
Sounds like either the fuel pressure is too high or the floats are too high. The only other possibility is that the needle and seat have trash in them.
 
Maybe the stupid power valve is blown or the gasket is not sealing good enough. Therefore you will have to "up" the idle screw, which opens the throttle blades which "pulls" air past the venturi's which pulls fuel out of the boosters!!! all negatives!!! How long before the plugs are black as coal & fuel fouled which will wash out the rings???
At the cost of fuel today, I figure you are using $$$$of fuel @ idle! "New carbs are thrown together by "China" here in lies the problem...they are not "assembled by Americans!"
Good luck!
 

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I changed the PV, no difference, I got it to idle at 1K rpm when I first started it up a second ago. However, if I blip the gas it hangs at like 1800, and won't idle down. The idle screw is completely backed off, the throttle cable is disconnected, it is completely at it's mechanical limits and it won't idle back down. When it was idling at 1k, it wasn't sucking any fuel through the boosters. If I screw the idle mix screws all the way in it'll run cleaner, but it won't die.
 
65Val said:
Does it have electric choke? Maybe the fast idle cam is hanging up holding the throttles open?
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It does have an electric choke, but the blades aren't open, I looked down it with a flash light while it was running. I got tired of jacking with it, wanted to make sure it wasn't something else. So I put the 625 Demon back on and it runs great (despite having carbon fouled plugs now). I compared all the settings on the new carb to my old one since they are physically the same carb and they were both setup the same exact way, one runs fine, the other one doesn't. All indicators point towards the carb being defective
 
If it won't idle down with the throttle blades closed it has a vacuum leak. If your sure you got it back together right after inspecting it it must have a problem in one of the castings. Do you hear air sucking anywhere?
 
Lars said:
It does have an electric choke, but the blades aren't open, I looked down it with a flash light while it was running. I got tired of jacking with it, wanted to make sure it wasn't something else. So I put the 625 Demon back on and it runs great (despite having carbon fouled plugs now). I compared all the settings on the new carb to my old one since they are physically the same carb and they were both setup the same exact way, one runs fine, the other one doesn't. All indicators point towards the carb being defective
Click to expand...

Ok...Just suggesting the simple stuff first. Any vacuum taps left open (uncapped), or voids in the base gasket to cause a vacuum leak? For the carb to idle that high, I would think you'd have to have a vacuum leak somewhere.
 
fishy68 said:
If it won't idle down with the throttle blades closed it has a vacuum leak. If your sure you got it back together right after inspecting it it must have a problem in one of the castings. Do you hear air sucking anywhere?
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Can't hear any whistling, must be a flaw somewhere in it in the baseplate or main body. I've had a lot of carbs apart before and I'm sure I did it right.

65Val said:
Ok...Just suggesting the simple stuff first. Any vacuum taps left open (uncapped), or voids in the base gasket to cause a vacuum leak? For the carb to idle that high, I would think you'd have to have a vacuum leak somewhere.
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No I gotcha, hate to burn all this time and send it back and it was something dumb I did. Everything is capped, I really acts like a massive idle leak, that is why I swapped my old RD back onto it, make sure I didn't make a mistake while installing the intake. It runs a lot better with the old carb on it. Guess I just got a bad one. :-/
 
I have a Demon doing the same exact thing. Every symtom you described. I havn't been able to get mine right yet either. I am going to just put my holley 650 DP back on mine.
 
It was a major problem on Demon carbs to have alot of casting shavings left in them, basically shitty quality control, i'm sure it was something minor in the idles metering, thats why i stay away from them, Not too long ago i installed a "brand new" Holley 650 dp on my 360 & it was damn near perfect OOTB, i think i had to turn the idle screws out 1/2 turn on each side.
 
Mr2.4 said:
I have a Demon doing the same exact thing. Every symtom you described. I havn't been able to get mine right yet either. I am going to just put my holley 650 DP back on mine.
Click to expand...

How old is it?

JoeDust451 said:
It was a major problem on Demon carbs to have alot of casting shavings left in them, basically shitty quality control, i'm sure it was something minor in the idles metering, thats why i stay away from them, Not too long ago i installed a "brand new" Holley 650 dp on my 360 & it was damn near perfect OOTB, i think i had to turn the idle screws out 1/2 turn on each side.
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I'd heard about this also, that's why I popped it apart as soon as I pulled it out of the box. Everything looked OK, so I thought it would be fine. My Road Demon that I bought back over ten years ago was gtg out of the box, and it still works great.
 
Return it and get yourself a Quickfuel or Holley h.p. the Demon carb i bought a few years back was a total piece of crap:pukerigh::pukerigh:my Quickfuel has performed great since i took it out of the box..:thumleft::thumleft:
 
stroked 340 said:
Return it and get yourself a Quickfuel or Holley h.p. the Demon carb i bought a few years back was a total piece of crap:pukerigh::pukerigh:my Quickfuel has performed great since i took it out of the box..:thumleft::thumleft:
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I'll likely leave the Road Demon on the Dart since it still works. Probably just exchange this Demon for a carb for my truck since it was the main reason I started this little endeavor.
 
I have yet to have a Demon product work properly out of the box. Over 6 years now, latest was 5 months ago. Usually shavings or machining crap left in them. The issues I had with rich idle were little shards left stuck to the holes in the metering blocks. The drill bit broke thru like it should, but the last flake of aluminum doesn't come completely off and was affecting the fuel flow thru the block's passages. I used a seal pick to break them off, cleaned it well, and it work ok after that. The biggest issue I have is you can get them perfect.. Then the weather changes and it goes way out. They can be excellent, but are a pain in the *** over time. I won't run a Demon product. The other possibility is the timing may be too high for that carb. they are much more efficient. Did you try backing the timing down a little to see if it would settle down? If there's fuel out of the boosters, there's airflow at the boosters.
 
Another quick thought...do Demon's have a secondary adjustment screw like some Holleys do...ie: the little screw you can get to under the baseplate that holds the sec's open a bit to get the primaries to close for proper idle mixture adjustment?

Just a thought....
 
moper said:
I have yet to have a Demon product work properly out of the box. Over 6 years now, latest was 5 months ago. Usually shavings or machining crap left in them. The issues I had with rich idle were little shards left stuck to the holes in the metering blocks. The drill bit broke thru like it should, but the last flake of aluminum doesn't come completely off and was affecting the fuel flow thru the block's passages. I used a seal pick to break them off, cleaned it well, and it work ok after that. The biggest issue I have is you can get them perfect.. Then the weather changes and it goes way out. They can be excellent, but are a pain in the *** over time. I won't run a Demon product. The other possibility is the timing may be too high for that carb. they are much more efficient. Did you try backing the timing down a little to see if it would settle down? If there's fuel out of the boosters, there's airflow at the boosters.
Click to expand...

I think an advance spring in my distributor broke or came loose, as it was idling last night at 900 rpm at 24 degrees (this was with the old carb). I need to pull it and check it out. While that isn't helping any, it didn't prevent the old Demon from running fine.

65Val said:
Another quick thought...do Demon's have a secondary adjustment screw like some Holleys do...ie: the little screw you can get to under the baseplate that holds the sec's open a bit to get the primaries to close for proper idle mixture adjustment?

Just a thought....
Click to expand...

Not that I can see.
 
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