Larson 310 cabrio 5.0 gxi won't plane off

[jdbarbor]

I just purchased a 2003 Larson 310 cabrio with 5.0 gxi, 270 h.p.. My issue is having a hard time planing off. I will push throttles wide open and the boat will run up to 2500 rpm and won't plane off. Worse in rough water, worse with 4 or more on the boat. If I turn sometimes that will make it go. I have the trim tabs and drives down. If it does plane then it goes 40 mph. Bottom is painted but clean. Props look good. I have replaced fuel filters, plugs, cap and rotor, timing is at spec 8deg, no fault codes in ECM. I checked to make sure throttle plates are going open the whole way, 200 hours on boat. I also think fuel economy is poor. One of the reasons I bought this boat is all the blogs I read about the conical hull and how efficient it is. I'm getting less then 1 mpg and was expecting 1.5 mpg from all I have read. Any ideas would be appriceated.

 

[55evinrude]

Re: Larson 310 cabrio 5.0 gxi won't plane off

a 310 is a big boat i'm assuming at least 30'?? a 5.0L is a small engine for a boat that size, so 40mph doesn't sound to bad. how ever your wot rpm's is low almost sounds like your prop is to high pitch you should be around 4300-5000rpm wot. what is your prop now? almost forgot welcome aboard!

Nathan

 

[500dollar744ti]

Re: Larson 310 cabrio 5.0 gxi won't plane off

i'd say go down in prop pitch. the boat is under powered as it is, whatever prop is on there is probably too much to turn for your setup.

do you know what size prop you have? does your boat have trim tabs?

 

[NoExcuses]

Re: Larson 310 cabrio 5.0 gxi won't plane off

I also have twin 5.0GXi engines on my 2004 Four Winns, I've been dealing with fuel issues all summer due to paint peeling off the fuel pump assembly and clogging fuel pump screens, fuel pressure regulators and fuel injectors. One place that is easy to check for peeling paint is the area where the fuel filter screws into the fuel pump assembly.

 

[Maclin]

Re: Larson 310 cabrio 5.0 gxi won't plane off

Sounds like 1.) The person you bought it from took the good prop with them or 2.) You found the reason they sold the boat

If when it does eventually plane out and hit 40mp what is the RPM? Some of your issues may be better addressed in the Prop topics forum.

 

[jdbarbor]

Re: Larson 310 cabrio 5.0 gxi won't plane off

I guess I didn't state that it has two engines. Total hp I'd 540. Boat weight is 10,400 lbs. I have thought about changing props. The current prop sets are f5, so which way do I go f4 or f6?

 

[Maclin]

Re: Larson 310 cabrio 5.0 gxi won't plane off

The smaller the number the lower the pitch in DuoProp talk. An F4 set woud be lower pitch than F5, F5 lower then F6, etc.

The smaller the pitch the better the holeshot but also lower top speed.

F5's are considered more of a power prop set, lower in pitch. As an example, a 22 footer with a 260hp+ or so would be able to swing F7's. So with twins in a boat the size of yours I would think F5 should be ok unless you are boating at 5000 feet or something like that.

Be sure the trim tabs are in working order.

 

[Senior B]

Re: Larson 310 cabrio 5.0 gxi won't plane off

A friend of mine who knows little about boats, but has deep pockets, is the proud owner of a similar craft (Rinker) 31 footer with twin 5.0GXis. It's VERY sensitive as to how you get it on step as the 5.0s are a bit underpowered for a boat of this size and weight. The trim tabs must be full up (retracted if you will) or they put up too much drag while coming out of the hole. Both motors must be trimmed full down and it takes full throttle from both motors to get on plane. Once on plane it takes a minimum of 3300 RPM to keep it on plane but 3500 is best. It does 42 MPH flat out on GPS and spins the motors to 4900 RPM. His boat has F5 prop sets I believe. When I first drove it, the bottom was cruddy and there was a lot of growth on the props that just killed it. Very difficult to get on plane and wouldn't go over 3800 rpm. Before you change prop sets at $1200-1500 a set, ensure everything is clean and free of growth. If you're getting close to 5000 rpm and 40MPH, I'd say your propped right but a bit under powered. F4 prop sets would help you on your hole shot, but top end and cruising range will take a hit. Good luck.

 

[500dollar744ti]

Re: Larson 310 cabrio 5.0 gxi won't plane off

I guess I didn't state that it has two engines.

that makes much, much, much more sense.

 

[jdbarbor]

Re: Larson 310 cabrio 5.0 gxi won't plane off

Great news, found my answer. Fuel pressure was at 99lbs on both engines. Found a volvo bulletin for fuel pressure restriction, removed regulators and removed regulator screens and replaced with e-clip per the volvo bulletin. Fuel pressure now at 52 lbs. ran boat Sunday, it's like a different boat, has power, planes quickly, the response and feel is 100% better. First thanks to iboats for blogs that allow us boaters to share information. Second, instead of spending thousands on props and guessing at replacing parts, I spent 1 dollar on 2e-clips and my issue is fixed. Knowledge is a valuable thing.

 

[tpenfield]

Re: Larson 310 cabrio 5.0 gxi won't plane off

That is a great thing when you can find an easy fix to a problem like that.

I am curious if you bought this boat without a sea trial and a survey??

You can only imagine why the boat was for sale . . . probably the P.O. could not find/fix the problem.

 

[NoExcuses]

Re: Larson 310 cabrio 5.0 gxi won't plane off

Great news, found my answer. Fuel pressure was at 99lbs on both engines. Found a volvo bulletin for fuel pressure restriction, removed regulators and removed regulator screens and replaced with e-clip per the volvo bulletin. Fuel pressure now at 52 lbs. ran boat Sunday, it's like a different boat, has power, planes quickly, the response and feel is 100% better. First thanks to iboats for blogs that allow us boaters to share information. Second, instead of spending thousands on props and guessing at replacing parts, I spent 1 dollar on 2e-clips and my issue is fixed. Knowledge is a valuable thing.

Was there anything on the screens? I had the same problem with high fuel pressure on one engine. I haven't done the e-clip thing yet, but my screens were clogged with something that looked like paint from the fuel pump assembly. I cleaned the screen and got the fuel pressure within spec.

 

[jdbarbor]

Re: Larson 310 cabrio 5.0 gxi won't plane off

Yes there was debris on the screen, I'm not sure what it was but could have been paint.