New Engine, Same Prop, Lower WOT. Need help.

[fvmerl]

I have a '99 Albemarle 242 center console. It had a Volvo Penta 5.0 GXI throttle body engine and would turn around 5000 RPM at WOT. This was paired with a Volvo Penta duoprop outdrive with a 1.95 ratio. The props are VP also and are SS F4's. Being VP, nothing gives you the pitch of the prop, just their designations.

So, I installed a new Mercury 350 Mag Bravo carbureted engine paired with the same outdrive and props. My WOT is now 4000 RPM. The stated WOT for this engine is 4400-4800. I only have about 4 hours on the engine so it has not been broken in yet. On muffs with no load the engine will reach 4800 RPM but in the water only 4000. This tells me that the props should be reduced in pitch to increase the engine RPMs. My problem with this is not understanding how you can install a more powerful engine with everything else remaining constant and it not being able to spin the props up to 4800 RPM.

The mechanic who did the work said I would not have to reprop with the new engine. Now, he says I should reprop. Can anyone explain what is happening in my setup that would cause this anomaly?

 

[bruceb58]

You shouldn't have to reprop. You either have to wait for your engine to break in, your fuel delivery isn't right or your new engine has something wrong with it. I would do a compression test for peace of mind if it was my boat.

With the engine off and your console throttle fully open, go back to your carb and make sure your throttle plates are completely open. Maybe it wasn't rigged correctly?

I would also consider checking the RPM with a shop tach just to be sure what you are reading at your tach is correct.

 

[Scott Danforth]

by changing from a 305 to a 350 you should reprop to an F5 (higher pitch for the new found power). however it sounds like something is amiss with your new motor.

did you keep the volvo fuel injection on the carbed motor? or are you running the carb?

 

[fvmerl]

I didn't bring the TBI over to the new engine. It is straight carb. Hope to visit the boat house tomorrow and talk to the mechanic about the problem and see if he can figure it out. Is this something I shouldn't worry about until after the engine has been broken in for 20 hours? I don't think the break in period would make that much difference of almost 800 RPM. It engine also has a hesitation or oscillation in the RPMs between 1800 and 2000 RPM.

I will check the carb plates because on the sea trial we had a problem with the choke not opening and it had to be loosened. Had not thought of that. Good call. Will let you know.

 

[Scott Danforth]

you have a carb issue if you have hesitation.

I suspect dirt in the jets or passages

 

[Tail_Gunner]

It would pop or backfire if you had fuel problem's....one would think anyway's....What size carb did you use and how was the HEI dist setup done...TBI use's the ecm to control timing a carbed version is done by the module in the dist....It would be intresting to see how you have rewired.


EFI

To this i presume

 

[bruceb58]

how was the HEI dist setup done...TBI use the ecm to control timing a carbed version is done by the module in the dist....It would be intresting to see how you have rewired.

Very good point. Definitely need to look at that. If the distributor isn't advancing properly, that would be an issue.

 

[fvmerl]

I really appreciate all of y'alls input and suggestions. Since this is a new engine and I will be out of town for a few weeks I dropped the boat off at the mechanic. Since he is a certified dealer and mechanic for Mercury he should be able to get things back to where they should be. A little disappointed that it wasn't like that when he first gave it back to me. I will update y'all with the details and see who was the closest to the real problem. Thanks guys!

 

[fvmerl]

Well, I should have gotten back on here sooner but after you fix one problem you find another and eventually have to fix some things twice.

The reason that I couldn't reach WOT with the new engine was there was a clip or pin that was not installed on the carb and I was running on 2 barrels instead of 4. Runs up to 5000 rpm now. Thanks for all of the ideas.

After getting the boat back I was going to take it out and see how she ran. Got to the marina and while boat was still on the trailer I started lowering the outdrive. The outdrive didn't move, no sound of pump running. Open the hatch to the bilge and water is running in around the jackshaft. Has to be a bellows gone bad. Take the boat back to the shop and have them put in new bellows and gimbal bearing. Outdrive still won't move. Start messing with the relays. Every time I attach one of the quick connectors to the relay the blades on the relay push the wires out of the connector. Somewhere along the line someone had replaced the wire terminals with a different type that doesn't lock into the quick connector and the blade will push the wire out without connecting. Took some doing but got everything connected and the outdrive works. Decided to clean the stern part of the bilge and added some cleaner and water and started scrubbing. When I turned on the bilge pump nothing happened. Took out the bilge pump (had to remove the raw water, strainer and baitwell plumbing to get the old one out) and started cleaning it up. After 2 years of sitting outside with the T-top leaned back and engine change out there was so much grease and dirt that the float switch was stuck to the bottom. Cleaned things up and noticed that the motor housing of the bilge pump was split. Probably because the float switch wouldn't work, water was in the housing, it froze and split the housing. Had to order a new pump and install it.

As I write, everything works and I hope to be fishing this fall. Thanks guys. Always nice to have experienced people help with advice.