new 81 sport fire - remove jack plate?!

[Needafunboat]

Well, I just got the new checkie home (sportfire w/ an '87 150 XR2 black max). The prev. owner, Curt a good guy and member on this site, was on his way to setting up for pure top end and put a manual adj. plate on. About 6" of setback and 6" of lift.

Boat ran about 63 (per spedo) with 3 of us in at close to 6000 rpm (quicksliver 23P) and I don't think was trimmed outthe whole way - it started a pretty gentle chine walk. He said he's seen 65 on the spedo. It also cavitates at WOT just as it's getting on plane - not badly but not desireable. It alos has a BIG bowrise for about a second as you take off.

I'll be doing more wakeboarding and pulling tubes so my first priority is a boat that will plane and handle well. Of course I'd prefer to have as much top speed as possible too - it is a checkmate!!

A buddy suggested to remove the jackplate, but I think this is an extreme step. He also said something about older checks not being made for jackplates, but it seems like it's as secure as the orig mounting, where it was hanging on the joint of the two hull halves.

Obviously I'll try moving the motor down an ?inch?, but any other advice is welcome - I'd also like to try a different prop - seemed like it didn't plane as fast as boat that light should with 150hp. Is a jackplate with less setback a better choice to get a little more weight forward? Any advice is appreciated!

 

[JW]

Keep the jack plate so you can play with engine heights. 6" isn't making that much difference with that light motor anyway.

You can help planing by adding a plate to the bottom of the jack plate, to keep water from 'bucketing' into the jack plate and also create a flat surface to add buoyancy to the rear. If you don't already have one there, the plate mounts along the bottom of the jack plate, closing in the 'hole' created by the jack plate side walls. Second, get a High 5 prop, which helps hole-shot for pulling. Next, you can add a bunch of weight to the bow area. Maybe do a reverse fat-sack. Pump the bow sack full of water for sports, then drain it for top speed. Be carefull adding too much weight to the bow though.

 

[kct11]

did you get it out today? my recomendations, as i gave you when you picked it up. for tubing and sking would be lower the motor using the jack plate, and 21 or 19 picth prop. the prop will get you out of the hole a lot faster making the boat drive through the bow rise very quickly making it less noticable....... if need be put the kids in the bow for weight untill your up on plane. also, make SURE it is trimed al the way down, even with a little trim up, it will increase the bow rise while getting up on plane. btw, it only took this boat 3 seconds max to go from stand still to plane when it left. good luck

 

[Boston Predictor]

All of the checkmates Ive ever been in had horrible bow rise and cavitated when getting on plane. Im no setup expert so I dont know if this is normal.
One other thing I noticed contrary to everyone elses' opinion is that it planed alot faster and with alot less bow rise with the jackplate almost all the way up.
Goodluck

 

[fiftyp]

I've run mine with and with out a 10" jackplate.... can't really say there is a diff. in getting on plane. I just tuck the motor and and go.

 

[kct11]

my main reason for sugesting lowering the motor was for all the sharp turns he most likely will have to make while sking and tubing. i did notice as i raised the motor up, it really suffered while making sharp turns, it was real easy to blow the prop out. i think a lower pitch prop will make a big improvement, as it smeemed the engine was lacking the power to turn a prop with that much bite so low in the power range....... or a nice 200 merc might do the trick

 

[Needafunboat]

Thanks for all of the advice - good to know there are some options and that the rise / cav. are somewhat normal. No - didn't get out today (don't these people at work know I just got a new boat?!!), but I'll try tomorrow.

Yeah curt - not like the boat was slow getting on plane or anything, I'm just not used to the cavitation based on my previous experiences with less perf. oriented boats. Before I do anything, I need to get a feel for her a bit and also see how it is with a load (skier) on back. If that little cavitation feels the same with a skier - I'll probably leave as is and maybe tweak a little. Based on our brief meeting I suspect you put a bit of effort into setting up that boat - so before I mess with what you did, I want I want to get a good baseline.

One we were moving, I'm not sure you lifted the throttle at all!

Saddly in MI I really won't get enough time to experiment until the spring. Just trying to gather options and stuff. Thanks again!

 

[Needafunboat]

Is that Lower trim stop the answer?!

OK after that last post, I just went out to the garage. There is a long bolt stopping the motor from trimming the whole way down. It was in the second from lowest position. I removed it and the motor trims down maybe 20 degrees further and is nowhere near touching the jackplate or transom (3" to 4" of clearance).

Any problem with letting that motor trim the whole way down for holeshot and turning. I'd guess it will make everything a little better and pull the bow down a bit further. I can't see what's stopping the motor, but It looks like that big hinge kinda bottoms on itself and looks pretty secure w/o that trim stop.

Could someone confirm I'm OK running with out the stop.

Curt - was there any reason for that stop in there that I'm missing?

Thanks.

 

[kct11]

hmmm.... i noticed that also, that is the way i got the boat and i never thought about moving it, as the bow lift was not a issue for me.i would not run with out it, but try it with the bolt in the last hole. i would think that may help matters out.

 

[175checkmate]

Could you take a pic of where that bolt was?. Never seen one that would keep the motor from tucking all the way in. I have seen where they hit the trim limit going up when running, but never in the down position.

 

[JW]

I think that long bolt is probably the standard 'pin' that is used to keep the motor from tucking under too far. As long as you're not hitting anything tucked all the way down, then you're all set. Just be very careful running at speed and tucking it all the way down! It might be OK, but it also could be dangerous if you plant the nose and the rear rises enough for the boat to 'hook' and come around on you. Testing will tell.

 

[Needafunboat]

OK - I feel kinda dumb but can't figure out how to post pics.

Anyhow, yeah, it's the standard pin that doesn't let you trim down too far - I think it's really intended to keep the bottom of the motor away from the transom on boats with much deeper hulls than cm's and with a jackplate, you're far away from the transom anyhow.

Had the boat out today on a pretty small lake with the fam and even with the trim the whole way down (pin removed), it still cavitates in very tight, turns. So I don't think it's trimming too far down. I FORGOT THE GPS!! doh! - crowded lake and only ran to an indicated 52 with the fam / waves anyhow. Maybe on Sunday...

Also was the first time I drove the boat and it needs some minor carb work. Curt was thinking it was a timing issue, but based on my experiences it feels like it's running real rich. Very little power until you hit full throttle, then it comes on pretty strong. And if you go from idle to WOT quickly, it bogs bad and once it actually never cleared out and ran. - I'll post in teh OB forum though, probably the more correct place.