RPM Loss wont plane

[Chuckyd973]

OK guys,

So i bring my 89 21' trophy w 3.0 and cobra into mechanic because it wouldnt run right. Hes not sure why or how but gets it running well. He checks points and dwell and does a water test. Boat planes and maxes out 4200 RPM's with trim tabs stuck down. My job is to get them up and he figures we can get the 3.0 to max out around 4600 rpms. Im happy with that. He also in forms me that the alternator is over charging and needs to be swapped out.

They pull the boat from the water for me and I get the tabs working that week and launch it the next saturday. Now I can only get the boat to run 3500-3700 rpms and it wont plane out no matter how I position the tabs.

Anyone have any ideas? Im running a 13.75x15 prop.....but that shouldnt explain the inconsistancy of the rpms. Is it possible the points are just shot? I have electronic ignition conversion coming next week. Could the alternator have to do with this?

 

[HT32BSX115]

Re: RPM Loss wont plane

Howdy,


It's pretty unlikely the alternator is causing this.....

Points gap/dwell and/or timing mis-adjustment could definitely cause it though......


Regards,


Rick

 

[Chuckyd973]

Re: RPM Loss wont plane

OK I checked the distributor cap and it seemed a little loose.......I tightened it down and it got more power......Ran all day around 3900 rpms and planed..with three passengers...top speed was about 21-23 mph.....Any ideas on how I can get the 4200 - 4600 that Clymer s telling me I should be able to get out this motor? So far this year I have done fuel filter, new starter, new plugs, head gasket, two batteries, new ignition coil, swapped the out drive, osco HO head to stock intake adapter, new shift cable, and I have a petrinox electronis ignition and cdi esa adapter on the way..Its timed at 8 degress atdc with the dwell and points recently checked .....Lemme know if you have any ideas!

1989 Bayliner Trophy Hard Top Pilot House 3.0 OMC and Cobra out drive with 13.75x15 prop.

Chuck

 

[Doernuth]

Re: RPM Loss wont plane

Have you had this boat for a while? Did it run ok with that prop before?

If the engine is running correctly the way to increase RPM's is to drop the pitch of the prop, try a 13 instead of a 15 should get you about 200 more RPM's.

If the prop was ok and at proper rpm range before than look at the engine/drive for problems.

Also check the manual for the proper timing and make sure 8 atdc is correct.

 

[HT32BSX115]

Re: RPM Loss wont plane

So far this year I have done fuel filter, new starter, new plugs, head gasket, two batteries, new ignition coil, swapped the out drive,

If you swapped the outdrive,


Did you replace it with a drive that had the same ratio as the previous one?

Has it EVER turned the correct RPM with the prop you're using?

 

[Chuckyd973]

Re: RPM Loss wont plane

I was thinking about going to a 4 blade 13 pitch. This boat needs to get up to about 3500 before it will plane and the more chop on the lake the harder this seems to achieve. Im considering an 4 balde aluminum 13.25 x 13 pitch. Any thoughts?

Chuck

 

[Chuckyd973]

Re: RPM Loss wont plane

Wow guys,

Im happy to report that the 4blade 13 pitch prop made this boat finally fun to drive. I actaully have a holeshot now and the boat gets on plane right away. Also goin from a 15 to a 13 pitch worked also. My tach finally shows the boat at 4500 - 4600 rpms wot which is what my lil 3.0 is speced to do. If any of you guys are feeling under powered I would highly suggest the 4 blade solas amita 4 to anyone.

Chuck