Carbed 502/502HP fueling issues on 1996 Baja 272 Islander
 

So my new to me Baja boat came to me with a bum motor, so I found an Eagle 502/502HP marine engine with 9.6:1, Edelbrock RPM heads, GM ZZ502 cam and had a local perfpormance boat mechanic put it in for me. So far it wont rev with a load beyond 4800 regardless of prop. I tried the stock Mirage plus 23p and got 4800 @48mph, and tried a Rev 4 23p at 4800 and 54mph. The stock 454 should push this boat easily into the 60s. I've verified ignition timing, so that seems to be out, and so I believe the fuel is petering out.

It has a brand new QFT marine 850 double pumper carb and a Holley red fuel pump which puts out 67gph. I'm no fan of the pump and will switch it out for a mechanical asap, but that should be enough flow as 500hp requires ~50gph.

Possible plugged pick up tube? Is it safe to blow air back through the fuel line to clear the lines?

Any suggestions for trouble shooting this beast? I can see the jetting being off a few numbers, but it seems like I'm missing about 100hp out of this set up.

I'd put a fuel pressure gauge on it and make sure you have good fuel pressure at wot.

It does have a fuel gauge on it, but it didn't occur to me to open the hatch and watch it while I was on the water, and I haven't had someone that could run it wot while I looked back there, but yea...that would've been some keen info to have.

Get a wide band guage and make sure you are not going lean...... It's the only way to tune your carb properly in the boat.... I.m getting 69MPH in my Donzi 26 with a 502 and 850 carb..... 26P B1 prop.... This was into the wind and against the current in mid 90* temps..... I would think you should be using something at least around a 24P prop.......

We use wide band tuning on motorcycles, but I've never heard of them for marine use. Works with factory manifolds? A quick check showed quite a few different makers of it, so I'll look into it. It sounds like a pretty key tool.

The stock Baja pickup tube is pretty small (5/16 I.D.) so you could possibly be running out of fuel but even at 4800 rpm with a 23m+ at 48mph is 31 percent slip (assuming 1.5 drive which is more then likely what's on it. If it had a 1.36 that's even worse slip). Or a 23 rev4 at 54 is over 20 percent slip.. Are you trimming the drive? No offense just trying to rule out the simple stuff, I know every Baja I've ever worked on or been on loves trim. And can gain upwards of 3-400 rpm trimmed up some and 4/500 rpm trimmed almost to the limit.

You can rig up a small temp fuel pressure gauge on a hose and lay it up near the seat to check while running with some hose and Afew fittings. Easier and alittle safer then trying to get the hatch open at wot. Obviously it isn't a permanent thing but just something for a test run.

The prop slip is ridiculous and have been trying to sort that out here;
https://www.offshoreonly.com/forums/...502-500hp.html

Also another troubleshooting thread here;
https://www.offshoreonly.com/forums/...ectations.html

It is a 1.50 drive and I've trimmed the heck out of it until it blows out.

Lots of good tips here to work on, Thanks!

Do you have a pic of the back of the boat out of the water and a good pic of the engine in the boat all rigged ?

What exhaust are you running? I have a spacer plate with a threaded opening for the O2 sensor on a 496 style exhaust....... Unless you had the motor dyno tuned its the only way to get the tune right...... From what I read, my Donzi hull did not perform well with a 3 blade..... 4 blade bravo seems to be best and I have pretty low slip numbers and excellent cruise...

Is there a anti-siphon valve, on pick-up?