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Bass Tracker Tournament 17 w 48SPLcavitating

C

catfishguru

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"I recently installed a 1993 E

"I recently installed a 1993 Evinrude 48spl motor on a 1991 Bass Tracker Tournament TX17 that I am rebuilding. I finally got a chance to take the boat to the lake this past weekend to try it out. The motor runs perfectly, but it seems to be cavitating when I give it full throttle. Everything is fine as long as I take it easy on the throttle...the boat will plane out fine as long as I keep it at half throttle or less but as soon as I hammer down on the throttle it just revs like it is not in the water enough. I brought the boat home and lowered the motor on the boat to the lowest setting on the motor, but that was only about 1 or 2 inches lower than it was. Is that enough to make a difference? The motor is a 20" shaft and I'm really hoping this motor will work...I have spent countless hours and no telling how much money rebuilding this boat. Any suggestions would be appreciated."
 
"The key question is not where

"The key question is not where the engine hangs on the transom, but where is the cavitation plate with reference to the bottom. My guess You are more than 1" above, which might be too high for that gear-case and prop. Another thing might be the trim angle.
If possible, upload a pick ."
 
"Thanks for the reply. I'

"Thanks for the reply. I'll have to take a picture and upload it tomorrow in the daylight. As far as the trim angle, it does seem to me to be trimmed a little too high at the lowest setting but I've already moved the lower pin that holds the tilt/trim in place to the hole closest to the boat. Will look at it more tomorrow and upload a picture. Thanks again!"
 
"Hi, I had the same problem wi

"Hi, I had the same problem with a 28hp SPL. It may not be cavitation. The rubber in the prop hub is turning, very common problem with this type SPL prop. As soon as you get to much RPM on it the rubber hub spins and dosnt make contact with the prop housing. Easy replacement/fix by a pro prop shop, you wont be able to fix it at home unless you have a prop press to install the new one. It will make contact at low RPM but spin at higher speed when worn."
 
"If not mistaken the 28SPL did

"If not mistaken the 28SPL did not have the through hub exhaust?
Secondly hubs are normally spinning just when going into plane where the torque is at maximum. Once spun, it just get worse."
 
I thought about the prop hub s

I thought about the prop hub spinning but kinda ruled that out because if I am running on plane at half throttle and just touch the trim up button it will do it...that made me think it wasn't in the water enough.
 
"The 28SPL dosnt have the thro

"The 28SPL dosnt have the through hub exhaust, Im not sure if the 48SPL is the same but suspect it is. My dealer told me that the SPL models were designed around older OMC engine parts that have proven to give satisfactory performance for a reasonable market price. When the hub goes out the first thing that comes to mind is that the lower gear unit is the problem. It only gets worse with a worn hub...keep the oars handy!"
 
When you trim it up it is prob

When you trim it up it is probably causing more pressure and different water flow at the prop hub and slip. Check your current prop to see if it has been rebuilt. I had one come out of a pro rebuild shop that was not angle/pitch adjusted correctly and caused cavitation.
 
Check where the cav plate sits

Check where the cav plate sits in relation to the bottom of the boat. If your not getting the ability to trim your motor in enough use a wedge between the transom and the engine to tilt the engine in more.
 
Mate the cav plate on your boa

Mate the cav plate on your boat running a std type prop should be level orslightly below the bottom of the hull any higher will result in ventilation. If you want better performance you need to change your prop
 
I don't understand...You&#

I don't understand...You're saying that if I change the prop on my boat it will correct the problem? I looked at the plate and it is slightly higher than the bottom of the boat. I took a picture of it but cannot upload it...it keeps telling me the file is too large.
 
"See my first reply!
Cav plat

"See my first reply!
Cav plate on the 'old' gear cases must be below bottom, or You get in 'trouble'. The newer ones with though prop exhaust, should be level or HIGHER, depending on V-shape (angle) of bottom. You may have to cup Your prop to get better grip, but You may run into problems with overheat as water intake may not run in clean water!
Lower the engine or change/modify prop."
 
Thanks again for the replies.

Thanks again for the replies. I thought my motor exhaust was through the prop but I guess not? I have lowered the motor as far as I can and the plate is still a little higher than the bottom of the boat. I did keep an eye on the motor when running across the lake and the water pump never missed a beat even at the higher setting. The weather here has been horrible since I made this post so I have not had a chance to try the boat again since lowering the motor. Is there anything I can do if I still have the problem and the motor is as low as it will go? You say "change/modify prop"...what prop would I need to put on the boat? Thanks again for helping a boating dummy!
 
"To my knowledge You HAVE thro

"To my knowledge You HAVE through prop exhaust, and Your engine (cav plate) should be slightly above bottom. If it gets too high, You may loose water.
However if Your transom is too straight, Your engine trim , even at inner hole, may be to much. In that case You will need a cupped prop, or make a wedge/spacer between transom and engine to get trim reduced.
Suggest You test first with engine at lowest setting and then report back. In the mean time find the numbers stamped at the prop, that might give us a clue."
 
"My guess You will need a 15 o

"My guess You will need a 15 or 17' pitch prop on that rig. Bring a tack on next test trip. You may even borrow an ignition lamp with built in tack if possible. Just note that it has to be set on 2 stroke! If a prop shop in vicinity, I'm sure they will help out."
 
"Well, I took the boat back to

"Well, I took the boat back to the lake today to give it a try. The boat did much better, but still seems to be doing it slightly. I changed the prop with a spare one that was on another boat of mine and it did the same thing with it so I know the hub is not spinning. It was the same size and pitch prop though so I guess I'll have to try a 15 or 17 pitch prop as suggested. Thanks for all the help to everyone that responded."
 
"If the tack on the boat was a

"If the tack on the boat was accurate it was 5200 at WOT. But, to be honest, I don't think it was working properly because when it did rev, the tack still never went over 5200."
 
I know this post is old now bu

I know this post is old now but I wanted to give an update. I finally got around to buying a 15 pitch cupped prop for the boat and it works great. Still can't trim it up like I would like but at least it holds the water now. Thanks for all the help!
 
"If You may trim the engine un

"If You may trim the engine until the prop shaft is parallel to water +10Degrees, You are ok. No need to trim more. Unfortunately the gearcase You have is not of the best ones when it comes to trimming.
What rpm did You get?"
 
There isnt a problem with your

There isnt a problem with your gearcase and i would say that your boat transom angle is spot on being a comercialy built hull and i havent seen a boat builder stuff up a design of the transon since early seventies.

If you want the best performance from your boat you need to think about changing your prop a std omc prop is good for the intended use but if you want to be able to trim the motor out to lift the bow of the boat you need to go stainless as they will hold and not ventilate as soon when trimmed out.
 
"The 'problem' with th

"The 'problem' with the late 80's gearcases is that they shortened the anti cav plate compared to the earlier ones. That modification unfortunately made it a bit easier for the prop to 'suck' down air when trimming. That apart and some bearing problems on the earlier versions, there is nothing 'wrong'."
 
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