Need more power to pull a skier, Could it be a carb Problem?

[imq707s]

I thought everything was going pretty good in the power department until I tried to pull a wakeboarder this weekend. My boat is a 1985 21' Scarab with Jasper 350, Alpha I drive, and 22P turbo 3-blade prop. My boat runs great at WOT, about 59 on the GPS at 5000rpms. I always thought that it took a little longer to plane off that it should, but pulling a wakeboarder proved it. I had three people in the boat including myself. It took about 30 seconds for the boat to plane off, but once the boat started to plane off and the rpms got over around 3500 the motor pulled really hard and then I'd have to slow down for the guy I was pulling. I know that my boat really isn't designed to pull a skier, but why is the motor down on the midrange power? I pulled the carb off yesterday to rebuild it, and noticed that the previous owner has pinned the secondary throttle blades on the Holley 750cfm 3310 vacume secondary carb. So when the primary blades start to open , so do the secondary blades. I've always noticed a bog when I hit the gas, but I just learned to ease into it and it was fine. I guess I found the cause of the bog, but would that also cause the low midrange power? The carb has 75 jets up front, and the stardard metering plate in the back ( around 78 jet size). I did a WOT runna few weeks ago and noticed that after I stoped and pulled a few spark plugs, they were bone white. Could the lean WOT mixture cause the low power while planing off? What about ignitoin timing, I think right now total advance is around 32 degress, should I bump it up to 34 or 36 and see if that gives the motor any more torque? My buddy has a boat similar in size and power to mine and it will jerk a skier right out of the water and tops off about the same speed as my boat. Thanks for the help, any tips would be great.

[lovemyultra]

try a 21 4blade you will get all the holeshot you need

[imq707s]

I've got a 23P 5-blade Merc High-Five prop and it pops the boat out of the water much faster than the 3-blade I've got, but it still seems to slow.

[Costello]

707, I wouldn't add anymore timing until you address the already lean condition present. You need to fatten her up with jetting, or look at the heat range plug you are using to ensure it is correct.

[Mandelon]

What happens when you play with the trim?

[imq707s]

It's trimmed in all the way but it's still a hog out of the hole. It seems like it just doesn't have any power at all untill it finally planes off after about 30 seconds, then it pulls hard to 60mph. I'm going to try jetting up the primary jets and see what it does this weekend, maybe it's just so lean it doesn't have any power untill it planes off and then the secondarys open up after the rpm's get high enough.

[lovemyultra]

Too much pitch !!!

[imq707s]

I thought about putting a lower pitch prop on it, but it already runs 60 at 5000 rpms, and the motors max operating RPM is supposed to be 4600. I think putting a lower pitch prop on the boat would help, but I don't think that's the problem. Thanks

[Nokomis]

imq707s, you posted that you have a Jasper 350 in the boat. Maybe the cam in that engine doesn't make torque in the power band that you need. Is it a marine cam or a "car" cam? Post the cam statistics and one of the guru's on the board can tell you.
BTW a 23P HiFive should plane that boat out in less than 30 sec! My $.02

[Hotcrusader76]

First off....aside from the blades, trim, etc etc....Deal with the timing first!
Is this a vacuum advance distributer? If so how much advance and at what RPM does it MAX out? (I am refering to the internal advance springs)
Now the carburetor...What is your manifold vacuum? Then you need to tailor that power valve to this reading (usually 2.0 hg less). Also you need to consider ditching the secondary "plate" for a 4150 metering conversion block. This will allow complete adjustable jetting. I think you shouldn't jet more than 80 up front, and your getting close...and still lean? WOW...
Honestly it sounds like your carburetor needs TLC and tuning. If you need some advice or help....call me at 1-619-920-5871 Texas Performance Carburetors
Or contact me at sales@tpcracing.com
Thanks
Ty Lofstrom
Texas Performance Carburetors

[imq707s]

Thanks for the tips. You might be right, I know it's a Jasper motor, but it could be one of the automotive motors. I'll have to call Jasper and see if I can get some more info on the motor. Maybe they can give me some cam specs. The primary jets were 75's, and I put 77's in, I'll see if that helps. The distributer is a standard Mercrusier unit controlled by a mercruiser Thunderbolt ingition module. The advance is all in at around 3200 rpms. Total timing is around 30 deg. That seems a little low to me, but I'm used to running 38 degrees in my 350 small block in my street car. I agree with you when you say I need to ditch that metering plate and jet a jet block to put in there. I think I need to ditch that whole vacume secondary carb and get a 650 double pumper. Thanks again for the advice.

[Hotcrusader76]

Anytime bro! Goodluck! and give me a ring if you need some help
Originally posted by imq707s:
Thanks for the tips. You might be right, I know it's a Jasper motor, but it could be one of the automotive motors. I'll have to call Jasper and see if I can get some more info on the motor. Maybe they can give me some cam specs. The primary jets were 75's, and I put 77's in, I'll see if that helps. The distributer is a standard Mercrusier unit controlled by a mercruiser Thunderbolt ingition module. The advance is all in at around 3200 rpms. Total timing is around 30 deg. That seems a little low to me, but I'm used to running 38 degrees in my 350 small block in my street car. I agree with you when you say I need to ditch that metering plate and jet a jet block to put in there. I think I need to ditch that whole vacume secondary carb and get a 650 double pumper. Thanks again for the advice.