kmiller

I have a speed marine demon 650 cfm carb that needs the power valve replaced ( rich idle and I can screw in the four corner idle screws and still idle ). Does this sound like a bad power valve? And how do you change it, I think theres only one, can the carb stay on the intake, is it on the front or rear metering block, and do I replace the gaskets????? Thanks I am hoping to do first thing in the morning and get this best in the water by 12 / 1.

kmiller

one more question what would cause a small amount of gas to be found on intake under center of the carb? Here is my orignal question or problem http://www.offshoreonly.com/forums/s...d.php?t=104304

MILD THUNDER

I think you will have to remove the carb and turn it upside down to change the power valve.

MILD THUNDER

I believe if the gasket on power valve cover is leaking, gas will leak externally.

gmhdfan

Did you check the float level? I would start there first.

KNOT-RIGHT

If it is truly a speed demon marine it should have j tubes
(vents).

You appear to beleave its the power valve leaking which
it may be however some simple things to look at first.

1) have you diconnected the carb linkage cable and varified
the secondary as well as the primary plates are both closed?
Evenly.

2) With the boat running in gear in water. Have you looked at the float level thru the site glass?

3) you say you screw in the four mixture screws but it does not stall . See #1) or possible vacuum leak.

4) removing the carb is not required for the powervalve
replacement. Just remove the 4 allens on the primary bowl
and the P/V is in the metering block.

5) another thought for proper Idle would be to remove the carb and flip it over and view the Idle transfer slots on each
butterflie they should be adjusted so it looks like a square
when viewed straight down throat. Even is important.

6) Read the info on the Barrygrant web site it is very informative.

Hope this helps
Gerry

Cord

The power valve is under the bowl cover. There are proably two of them on your carb. The primary may be blocked though. However, I believe that all of BG's carbs have PV protection. Do check the idle transfer slots as caveman suggested. Yes, a high float level will cause the fuel to over flow through the vent tubes and cause the engine to idle rich. With my carb, I could not get the floats to set correctly with having to bend the arm slightly. Bend the arms only after trying to set the floats correctly. The way to set them on the bench is to flip the bowl upside down and then adjust the float so it's centered and level. The leak could be a torn bowl gasket, a leaking bowl bolt gasket, a loose bowl bolt causing either of the two to leak or a loose fuel line fitting. I'm not sure if your carb has a vacuum secondary or not, but there could be a booster diapram under the bowl that also could be leaking. Typically, you can reuse the gaskets, but I have had them tear on me. I always keep an extra set of gaskets and bolt washers handy. I tear or loose one, I just replace it right away so I'm never without. If you take a little chapstick and rub it on the gasket, they'll release better with out tearing.

kmiller

Found the leak it was a bad gasket under the float adj screw / replaced power valve with the stock 6.5 , I checked my vacuum and in gear at idle I get between 7-9 diped less a few times, I get more vacuum at around 1100rpm I read 10-13. I did not think my cam was that hot, shound I get a different power valve?? Heres my cam card does the vacuum sound right that I am reading / I have dry gills and around
9.2/1 compression. Also I got a small amount of gas from the vacuum line when I removed the gage is that normal???


284*/290* @ .006”
223*/234* @ .050”
131*/141* @ .200”
112* LSA
108* ICL
IVO 28* BTDC
IVC 77* ABDC
EVO 79* BBDC
EVC 31* ATDC
59* Overlap
4* Advance
.309” I lift lobe/ .323” E lift lobe
.475”/ .485” valve, with 1.5 ratio which are inverted on the chart

FloridianSon

6.5 + 6.5 = 13 good to go on the power valve.