Squarefour1

Well I may need some help, I have pulled the old Dumas Cat off the shelf and fired the 90 up ran ok but the remote needle is spinning. I put new orings on and have not reinstalled it. I was told to update this carb with a OS 9b .47 id. Has anyone ran this carb. Also I am going to add about 2 inchs to the exhaust manifold, there doesnt seem to be enough to hold the silicone exhaust to pipe (a hose clamp wants to pull the tube off when tight) The boat was once real fast and now its time to bring it up to date. Any help or thoughts

Blackout

Sorry, no tech to offer, but is your boat a Dumas Skater 67? I have a Dumas Skater with a K&B .82 that I'm trying to get in the water again.

stempak

Same here, What prop is on your ops? There is a few things to do to those ops's of the 90's to get them to run really well. They are near bullet proof motors. I believe one was tightening the cleareance of the back plate, to the relation of the disk rotor.

Squarefour1

WELL IT IS NICE TO KNOW SOMEONE ELSE IS RUNNING A BIG BORE AS WELL. I HAVE HAD THE 45 INCH CAT FOR ABOUT TWENTY YEARS THE 15 CC OPS IS VERY STRONG BUT FINIKY. 78 MPH ON A RADAR GUN IS THE BEST RECORDED MPH. I DONT THINK ADDING OR CLOSING THE TOLERANCE IN THE ROTOR VALVE WOULD HELP, I BELEIVE IT HAS A CONSTANT VAC ON THE INTAKE SIDE WITH A SMALL AMOUNT OF REVERSION. I DIDNT WANT TO CHANGE THE PORT TIMING I JUST WANTED TO MAKE THE MOTOR MORE EFFICIENT. THE IDLE OR WOT CARB IS PROBABLEY OUT OF DATE WITH TODAYS TECH. . I HAVE MOVED THE REMOTE NEEDLE VALVE TO THE MOTOR MOUNT TO SEE IF THIS WILL HELP WITH THE VIBRATION. IVE TUNED THE PIPE FOR MAX RPM. DO YOU GUYS HAVE A FIX FOR THE SHORT EX PORT. I THINK I WILL TIG A TWO INCH PIECE OF STOCK ONTO IT. MY PIPE FALLS OFF OR BLOWS OFF THE PORT

Blackout

For what it's worth, the pipe length on my K&B's exhaust manifold is 1.25 inches.

stempak

That's what I was told, That there was like three things to make them run really well. It was someone on intnlwater's. Are you telling me this skater will do 78!!? I was told by someone that use to race them that they were only 60mph hulls.

Squarefour1

WELL THAT COULD BE TRUE FOR HIS "SKATER", BUT THE ENGINE POWER TO WEIGHT RATIO IS OFF THE SCALE THE 15CC IS RATED AT 6.2 HP AND PHOTO TACHED AT 20800 RPM AND CLOCKED WITH A GUN FROM OUR LOCAL SHERIFFS DEPT. I HAVE TO SAY THE BOAT IS VERY HARD TO KEEP RUNNING ALL THE TIME AND I HAVE HAD ALOT OF FUN WITH IT. THERE HAVE BEEN MANY WRECKS AND ROLL OVERS AND SEVERAL GOOD 15 MIN RUNS. I CAN TELL YOU GUYS THAT I REALLY MADE ALOT OF SPEED BY MOVING THE DRIVE SHAFT UP AND CUTTING THE RUDDER A 1/4 INCH AT A TIME. I WILL BET YOUR BOATS HAVE THE STOCK LENGHT RUDDERS, MINE IS 4.5 INCHS LONG STOCK IS 6 I RUN THE TWO BLADE CLEAVER (1/3) OF THE BLADE FROM THE BOTTOM OF THE BOAT ROUGHLY 3/4 OF AN INCH FROM THE BOTTOM OF THE SPONSUNS. AT SPEED THE BOAT IS NOT AS CONTROLABLE AS YOU WOULD LIKE BUT REAL FAST.

Squarefour1

THAT IS THE SAME AS MINE. WOW, THE PIPE JUST SEEMS TO GET LOOSE FROM THE MANIFOLD I WILL TRY THE EXTENSION I CAN ALWAYS CUT IT OFF. I AM USEING A GOOD SILICONE HOSE AND 1/2 INCH WIDE HOSE CLAMPS. OH AND BY THE WAY WHEN YOU GUYS START GETTING MORE SPEED YOU MIGHT WANT TO GO TO A 1/4 SCALE SERVO FOR THE RUDDER. I STRIPPED A FEW SMALLER ONES BEFORE I DID. THAT WILL FIX IT AND USE SOLDER LINKS AT EACH END.

stempak

Well how well do you expect a 45" inch boat to handle at nearly 80mph!(20yrs old) Have you tried a skeeged strut? I want to and believe it will help most of the time they do but not always. Also are you running a stock rudder configuration? I want to move it to the right to get a full roost.
I would post on intnl waters about your motor. That was exactly what I was told, that they are hard running unless you do a few mods. Also I was told that those ops's run very well moddified and last about as long as a stocker if ran properly. Also another thing that will help if not done is use 1 or 2 tanks in the bottom of the ride pads instead of infront of the motor aswell as the radio box/box's.

I guess since the hull is capable of those speeds I will build a new radio box/box's

stempak

What is your smallest prop? I'm trying to figure out what I need for this OS 81VR-M. My boat came with a 3blade. I'm asuming that this hull doesn't run with it? My and many gas cats won't run on anything but a 3blade.

I may have to invest in a mac 84 if this O.S 81VR-M doesn't perform like it should it's only rated at 4.2hp which I find very hard to believe.