Finished my build today, need help tuning. Just sucking air.

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Webygail13

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Finished my build today. 87 Alumacraft 1756. 2003 Merc 90/65. I used the CMC static riser. I tried to set it up with the leading edge a 1/4" higher than the bottom. I put it in today and when i opened up the throttle, it just revved and sucked air. Would get on lane. The motor also shook really bad. I eased up and throttled up slowly and it did better. I got it on plane and it ran about 30mph. It was lnt peeing a good stream though and was making a sound like it was sucking air. When i stopped and got back to idle, it almost sounded like it had an exhaust leak in it. So, two questions, is my motor too high and could i have possibly hurt my motor when i ran it. I only went about 500 yards down and 500 back. Thanks for the help.
 
This is one of those deals where you are best off taking the tools along that are needed to adjust the engine. 1/4" doesn't sound like it would be a big deal but it's hard to judge without pics.
 
Pretty sure i have to remove the motor to move it down. Not sure that would be feasable at the boat ramp.
 
1/8" made the difference between planing and just sucking air on my jet. I had to redrill the bolt holes from factory to get it the right height.
 
Is there any chance i hurt my motor sucking air? If i drop it one bolt hole, ill be dropping it somewhere between 3/4" and an 1".
 
I think the standing recommendation is to line up the front grate pin hole with exactly even with the bottom of the boat. In your pic it looks like it might be a tad low but it's hard to say.
 
It took me about 4-5 adjustments before I got it where I like it. When I had it where I thought it was best, it sucked air and sprayed back over the transom so I had to go back down one hole. Try dropping down one hole and see what it's like. I needed to add transom wedges to tuck my motor in to get rid of porpoising. But I have a tunnel jet so it behaves a little different than a flat bottom.
 
You can always slot the holes on you tilt and trim bracket to give finer adjustment. That's what I've done to my motors. I could be looking at it wrong but looks like you have a semi v bottom so you might have to run yours a little lower then a flat bottom to get clean water. Shouldn't of hurt the motor for no more then you run it. Might double check your impeller clearance and while your looking see if the impeller nuts still tight it's possible all the jarring from the cavitating could have bumped it loose. Probably not but can't hurt to take a peek.
 
Lil' Blue Rude said:
Might double check your impeller clearance and while your looking see if the impeller nuts still tight it's possible all the jarring from the cavitating could have bumped it loose. Probably not but can't hurt to take a peek.

I'd do this first. Is it a new or used motor?

If your impeller & liner aren't in good shape and have proper clearance, any height adjustment is premature. It's also much easier to take care of these items than change height on a larger motor like a 90/65.

Different note: is that a factory paint job? I like the looks of that from the little bit you can see above. Do you have a pic of the whole boat?
 
Webygail13 said:
Pretty sure i have to remove the motor to move it down. Not sure that would be feasable at the boat ramp.

It can be done, block the engine at the pickup grate and use the trailer jack to adjust the 'height' of the engine once the bolt are loose. You just have to be careful.
 
Sorry I haven't updated, but I've been busy. I moved the motor down one hole and it made a world of difference! It jumped on plane immediately and topped out around 30mph. I'm too low now though I was getting tons of splash back onto the back deck. I built a splash plate and installed it the other day, but haven't gotten to run it to see if it helps. I feel like it needs to be in between those holes. I guess I could slot the bottom and just drill a new hole at the top in the bracket once I get it dialed. I actually painted the boat myself last week. I bought a stencil kit from red leg camo. It looks close to factory. I'm really excited about how it came out. I'll post some more pics in a few.
 
Here are a few of the paint progressions. The bottom pic was how it started, the top is the finished product.
 

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