Marine Carb - Rebuilt - Please help diagnose

[5stareventsdj]

I put a reman. 5.7 marine engine in my boat and have been having trouble reaching WOT RPMs (4200-4600). The boat has been topping out at 3700rpm.

I've been through just about everything on the boat from props to ignition. I'm working on the fuel now and it seems like my boat isn't getting enough. I replaced all of my fuel lines and just finished a carb rebuild. Today was my first time out and i noticed some improvement from the carb maybe 100rpm. Initial timing is 8 degrees and total is 26. Bumping initial to 10 gave me another 100rpm but I'm still seeing only 3900 rpm. It sounds like the engine is running too lean and I'm looking for advice. Should I change out the metering rods to allow more fuel to flow through my secondaries? Should I try to replace my fuel pump?

One thing to note is that I am also getting a new hard bog at around 2600rpm. I wasn't seeing that prior to the rebuild. It bogs for a second or two and then picks back up.

I'm really just looking for some guidance. If you can help, thank you in advance.

One thing I noticed is my total advance is in by about 2600 rpm. Would this effect my WOT RPM?

Thanks,
Greg

[Cliff Ruggles]

Greg, did you use one of our Marine kits?

They contain an upgraded accl pump assembly and high flow Viton needle/seat assembly.  Far superior to what's showing up in the over the counter kits.

I suspect fuel inlet seat is too small.  Accl pump shot may be insufficient.

Check the choke pull-off as well, and install a new secondary cam/spring to get rid of the stumble in the mid-range when you go heavy on the throttle......Cliff

[5stareventsdj]

Yes Cliff,

I used your kit. Although I did buy another kit before finding yours and may have used the needle and seat from the other kit. I will swap the two out. The choke pull off is working - I believe. It opens the choke at idle when the engine is cold. After that, I don't know.

Do you sell the secondary cam spring? I will buy it.

Greg

[Cliff Ruggles]

Secondary plastic cam/spring/screws are $8....thanks....Cliff

[5stareventsdj]

OK I'm looking for ideas. I rebuilt my carb with the CHP marine rebuild kit. At first I used a needle and seat from a kit I purchased before finding CHP. I replaced the needle and seat with the proper one that came with my kit. What a difference in hole size. The other was much smaller.

I also used the bushing kit to fix a leaky primary throttle shaft. It no longer leaks gas when I mess with the throttle while the engine isn't running. The kit was fast and easy just like described.

The problem is I am still not reaching WOT rpms and am looking for suggestions. I went out today and was topping out at 3600 rpm. My combo should be giving me 4200-4600rpm.

In addition to rebuilding the carb, I also replaced the distributer. My initial advance is 8btdc my total is 28btdc@3000rpm. That's what was spec'd by the engine builder. It's a reman marine engine.

I'm really stumped and am considering:

Replacing spark plug wires although they look like they are in good shape. There are no splits or cracks. They don't appear to be shorting at all.

Replacing the fuel pump. It's the original fuel pump (1989). Is it likely that the fuel pump is working fine until demand is high?

Replacing ignition coil? I have no idea what condition it is in? Is it possible that is producing enough spark except at higher rpms?
 
Checking cam advance??? It's been suggested on another forum. I just bought this engine in February. It maybe has 40 hours on it. I hope I don't have to tear down the engine.

I had my auto mechanic friend with me a week or so ago. He said it sounded like it was starving for fuel under load.

I would appreciate anything you can come up with.

Greg

[429bbf]

greg i dont know what tools or parts you have good access to. what i would do is get a 5 gallon can (im guessing your boat has a inboard gas tank ) grab some 3/8  gas line and a electric pump .i bought a holley from napa a few years back. hook the bad boy up and go for a ride . (i dont know whats legal on the water ) this will determine if you have a fuel supply problem. that way you can eliminate  one problem at a time.fwiw dean

[5stareventsdj]

Well I never thought of that. I may just give it a go. :-)

Greg