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KNOT-RIGHT
09-24-2004, 10:12 AM
To boost reference or not.
My understanding of boost reference is to relocate the power valve vacuum signal from above the supercharger
to below it.
This thought has been bothering me there have been several posts concerning this.
Just do a search on boost reference and you shall see.
Considering the procedure you are about to see I decide to boost reference the following carbs.
This is the way I decided to do it. It does not mean it is the only approach just the one I went with.
Im sure there are others who will comment on my procedure but this is the way I did it.
Please do not hold me responsible for any of the following. In other words Attempt this at your own risk.
This info is provided for educational purpose only.
Remember this is specific to this demon carburator.
Power valve on primary side only.
850CFM street demon.
Gerry
http://www.***boat.com/forums/attachment.php?attachmentid=5930

KNOT-RIGHT
09-24-2004, 12:00 PM
on the primary side of this carb behind the meetering block there is the power valve chamber
three holes are apparent one (center one) is pluged by one of the philips head screws holding the base plate down. the smaller hole to the right makes it way to the base plate but yet it is not used.
The one we are concerned with is to the left this is
the vacuum source for the power valve we must relocate.
http://www.***boat.com/forums/attachment.php?attachmentid=5934

KNOT-RIGHT
09-24-2004, 12:02 PM
remove base plate removing 6 philip head screws.
located under carb
http://www.***boat.com/forums/attachment.php?attachmentid=5935

KNOT-RIGHT
09-24-2004, 12:06 PM
this is a shot of the center base phillips screw you just
removed. located normaly under the primary power valve chamber. You should see two small holes and of course the threaded hole you just removed the phillips screw from.
all of these holes including the threaded hole lead to the power valve chamber the two small holes must be pluged. Of course we dont need to plug the threaded
hole because the philips screw you reinstall will do that for us upon reasembling the base.
http://www.***boat.com/forums/attachment.php?attachmentid=5936

KNOT-RIGHT
09-24-2004, 12:07 PM
fliping the base over meaning looking down on it the way it would sit on the engine reveals a brass
check valve. Power valve protector in the event of backfire. This is removed by fliping over once again and looking into the smaller holes and finding the one that is centered to it. and lightly punching it out. I used a fliped over 3/32 drill bit. taping it with a small brass hammer
http://www.***boat.com/forums/attachment.php?attachmentid=5940

KNOT-RIGHT
09-24-2004, 12:09 PM
it should look like this when it comes out.
this is no longer used so if you get a backfire lator and you start following plugs ya might wanna check your power valves.
http://www.***boat.com/forums/attachment.php?attachmentid=5939

KNOT-RIGHT
09-24-2004, 12:19 PM
The base plate should look like this now.
This is looking down on it the way it sits on the engine
http://www.***boat.com/forums/attachment.php?attachmentid=5941

KNOT-RIGHT
09-24-2004, 12:20 PM
Now here comes the scary part looking at the base plate
from the side view. scribe a line spliting the hole in half
this is to establish a center line of the hole.
measure twice.
after scribing the vertical line I chose to scribe a small horizontal line. This is centerpunced .
Then drill a pilot 3/32 hole through this punch mark.
it will intersect with the original power valve vacuum
source hole.
You can view your depth easily by looking down the original p/v vacuum source hole.
http://www.***boat.com/forums/attachment.php?attachmentid=5942

KNOT-RIGHT
09-24-2004, 12:22 PM
I chased the 3/32 hole with a number 23 drill which is slightly smaller then my brass tubing I purchased from
mcmaster-carr.com
http://www.***boat.com/forums/attachment.php?attachmentid=5943

KNOT-RIGHT
09-24-2004, 12:24 PM
now I cut my brass thin wall tubing to a lenth of approx 1 inch. and with a liberal amount of Locktite red.
I gently tap it in taking notice of mt depth. Making sure I dont bottom it out. Again this is easily visible looking down the original p/v source.
http://www.***boat.com/forums/attachment.php?attachmentid=5944

KNOT-RIGHT
09-24-2004, 12:26 PM
Remember the the original two tiny holes near the screw hole underneath the base plate. We must plug them now. They are both 3/32 in diamiter. I purchased
some 3/32 brass solid rod. from mcmaster-carr.com
and cut a 3/16 peace and applied some locktite to it and carefuly punched it into one of the holes. the second hole I chose to use a very small machine screw with a large head. I applied more locktite red to it and screwed
it into the other hole. the size was perfect as to make its own threads while screwing into the soft aluminum base plate. The large head insures the brass plug installed a minute ago is held in.
http://www.***boat.com/forums/attachment.php?attachmentid=5945

KNOT-RIGHT
09-24-2004, 12:28 PM
it should look like this.
Notice the screw is actualy beneth the base plate.
http://www.***boat.com/forums/attachment.php?attachmentid=5946

KNOT-RIGHT
09-24-2004, 12:30 PM
The finished project.
(Lines not plumbed into manifold yet.)
I did four carbs in 6 hours with a minimal amount of swearing and throwing wrenches.
total cost of project was 26.00 dollars
There are many who operate blowers without
boost reference. I figured for 26 bucks and 6 hours
why not.
Gerry,
Please feel free to call me if anyone has
any questions.
401-255-5242
http://www.***boat.com/forums/attachment.php?attachmentid=5947

Infomaniac
09-24-2004, 07:37 PM
81 views so far and no compliments on the project?
Let me be the first to say: Great Job Man.
Mind If I spice it up a bit to make it a little more viewer friendly?

Some Kind Of Monster
09-24-2004, 08:17 PM
Very nice job. Should there be a performance gain?

KNOT-RIGHT
09-25-2004, 07:15 AM
Thanks For the Help Info!!
Some kind of Monster. Not sure If Performance is the word to use.
A brief description would be
The # on the Power valve is the measurement of the vacuum in "HG" meaning a 6.5 would open at 6.5 HG and remain open anything below 6.5. If you connect a vacuum gauge under the carb (normaly Asperated) and you read 12 HG of vacuum at idle a starting point would be 10.5. However Heavier boats and or different setups play a role. The Idea behind the power valve is it enrichens the carb circuit when the engine needs more fuel. Hence low vacuum (Load). Obtaining the correct
PV in a boat is a little different then the street. The Ideal situation would be
to have the power valve closed at minimal planing speed that way when
you give it throttle the vacuum would drop opening the power valve. Some
choose not to run power valves by installing plugs and upping the jet sizes
by 7-10. Please Remember to check plugs accordingly. Not to confuse you
anymore. Some Supercharge applications Boost reference the power valve.
meaning they block the signal from above the blower and reroute it beneath
the blower so the carb see's the engine vacuum not the Blower.
This is the above procedure.
Hope this helps
Gerry

78Eliminator
09-30-2004, 07:40 AM
Now THAT is what this forum is all about. I bet you just made a lot of people a lot more confident to take on that kind of job. Thanks for the information. Just goes to show, you don't need to drop big cash for simple jobs.

RiverDave
09-30-2004, 11:17 AM
Great Write up!!! :) To echo what 78 said, that's what the tech forums are all about!!
RD

hack job
09-30-2004, 01:07 PM
great job! we need more inof like this iam sure glad that they put this forum up