Speed Demon problem..............
Thread Starter
Racer
Joined: Jun 2001
Posts: 460
Likes: 0
Speed Demon problem..............
Been having some issues with the Speed Demon 750 on my big-block. Been running way too rich with the idle varying from 900 to 1200 rpm. Pulled the vacuum advance unit (on the distributor !) to see if it was working properly and it was full of gas.................... not just a little, but pretty much full !!!
Anyone got any ideas on what the problem might be ????? ................. and what I need to do to alleviate the problem ! Thanx for the input guys, Rick
Anyone got any ideas on what the problem might be ????? ................. and what I need to do to alleviate the problem ! Thanx for the input guys, Rick
Melting Slicks
Joined: Mar 2008
Posts: 2,989
Likes: 198
From: Meriden CT
I'm not real familiar with that carb but, plug the port on the carb that the vacuum advance went to, and put the advance on full manifold vacuum for starters. Check the timing as the idle rises and falls. If the tining is advancing as the idle rises, put heavier springs on the mechanical advance. Hopefully someone else will chime in.
Intermediate
Joined: Jul 2008
Posts: 41
Likes: 0
From: Raleigh NC
Is this VS or Mechanical?
I have a Demon tuning guide that I have ben using with mine. They seem to like alot of base timing 16-18*. Adjust your dizzy to accomodate it.
Make sure your primary blades are not exposing the transfer slot more than a square. Go unported vac on your dizzy.
Floats on mine ended being under the slight glas a hair.
They are a PITA but can be v good carbs when dialed in
I have a Demon tuning guide that I have ben using with mine. They seem to like alot of base timing 16-18*. Adjust your dizzy to accomodate it.
Make sure your primary blades are not exposing the transfer slot more than a square. Go unported vac on your dizzy.
Floats on mine ended being under the slight glas a hair.
They are a PITA but can be v good carbs when dialed in
Thread Starter
Racer
Joined: Jun 2001
Posts: 460
Likes: 0
I should have mentioned that Lars set up the carb (and tuned the car) afew years ago ! The vacuum advance went bad and I put another one on a couple of years ago, but never got the engine tuned up back to the same specs.................... wrong vacuum advance unit !
With Carlisle coming up, I figure now is the time to get it tuned up right again............... especially with gas prices ! Milage has been pretty poor recently, since I was getting 20mpg (w/the tremec TKO) after Lars worked his magic.
I did notice tonight that gas seems to have leaked out between the main body and the base plate at some time............ it left a golden film on the top edge of the baseplate. This could cause a vacuum leak (and irregular idle), but I'm still at a loss on how the vacuum advance got full of gas !
Thanx for the input guys................ any other ideas ???? Rick
With Carlisle coming up, I figure now is the time to get it tuned up right again............... especially with gas prices ! Milage has been pretty poor recently, since I was getting 20mpg (w/the tremec TKO) after Lars worked his magic.
I did notice tonight that gas seems to have leaked out between the main body and the base plate at some time............ it left a golden film on the top edge of the baseplate. This could cause a vacuum leak (and irregular idle), but I'm still at a loss on how the vacuum advance got full of gas !
Thanx for the input guys................ any other ideas ???? Rick
Melting Slicks
Joined: Jun 2002
Posts: 2,844
Likes: 99
From: Orrtanna Pa.
Rick,
How big of a cam are you running? Is the idle smooth or pro stock like mine. I found I had to increase my idle feed restrictors , as well as bump up my timing,in order to get a decent idle without having to open the throttle plates too much. If the throttle plates are open to the point of exposing the transfer slots I can see how a lot of raw gas could get sucked into the distributer vacuum advance can.
Lucky you didn't blow that thing up.
How big of a cam are you running? Is the idle smooth or pro stock like mine. I found I had to increase my idle feed restrictors , as well as bump up my timing,in order to get a decent idle without having to open the throttle plates too much. If the throttle plates are open to the point of exposing the transfer slots I can see how a lot of raw gas could get sucked into the distributer vacuum advance can.
Lucky you didn't blow that thing up.
Le Mans Master
Joined: Jan 2006
Posts: 6,506
Likes: 139
From: Butler Pa
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Melting Slicks
Joined: Mar 2008
Posts: 2,989
Likes: 198
From: Meriden CT
Yeah, but how? The vacuum originates in the carb, not the distributor. That's why I say forget that "vacuum" port on the carb and go directly to the manifold.
Le Mans Master
Joined: Dec 1999
Posts: 8,627
Likes: 1
From: Houston Texas
CI 1-2-3-4-5-6-7-8-9-10 Vet
St. Jude Donor '03-'04-'05-'06-'07-'08-'09
Sorry to hear of your troubles. I had MD850 on my 71 BB convertible but having to build a completely new motor because the old motor's internals were not as advertised and motor is in the crapper.
I noticed more timing at idle helped a ton. No clue beyond the conversation so far though on what would have pulled gas into VA unit.
Maybe you need to step up to an 850! Mine is in a box all ready to send you!
Doug
I noticed more timing at idle helped a ton. No clue beyond the conversation so far though on what would have pulled gas into VA unit.
Maybe you need to step up to an 850! Mine is in a box all ready to send you!
Doug
Le Mans Master
Joined: Jan 2006
Posts: 6,506
Likes: 139
From: Butler Pa
No one is arguing with you. I agree something is not right with that vacuum port, but the fact remains that the VC is full of gas and could have potentially leaked into the distributor.
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
I know nothing about Demons but if you were pulling a vacuum thru the hose to the advance when the motor is running it would seem the only way gas could get into the advance would be when the engine is off. It must be draining back into the advance from the carb somehow. Wonder if the area where the hose is on the carb is filling with gas somehow. Floats too high???
Someone just posted the same problem with gas in the advance the other day but couldn't locate it.
Someone just posted the same problem with gas in the advance the other day but couldn't locate it.