Blower Motor seems fuel starved
 

I have a Donzi Z29 that I recently built a couple of what should be some reliable strong running engines. I am having a couple issues that I could use a bit of advice on. Both engines are Identical and all new. 383cid chevys 8.3/1 comp.very good cranks and rods, mild blower cams, World sportsman 2 heads, sharp roller rockers, 671 blowers, full MSD ignition. Edelbrock marine 600cfm carbs with recomended modifications for these engines," larger neadle and seat set 101 jets pink springs,etc. Both engines were run in on a dyno with no issues 558hp @ 6000 rpm. When run in the boat they act like they run the carbs out of fuel when pushed over about 3800rpm.for more than half a minuite or so then one engine, usually the port, may die entirely unless the throttle is quickly cut. If it dies it restarts easily and runs fine unless I get up around 3800 again. each engine is fed by both mechanical and electric fuel pump in series each 140+ gph rated The lines are -10s and the filters are huge Baldwin comertial units that should flow more than enough. I first thought the tank suction tubes which were origional to the boat may have been the cause, only 1/4" id. so I made new ones just over 1/2" id. with no change. What am I missing? Maybe not a fuel issue? rev. limiters are set at 6500 any suggestions would be appreciated.

so are we to assume you do not have fuel pressure gauges? if not that would be a start.

time to hook up air/fuel ratio gage to see if it is getting lean.serious damage can happen very quickly when they go lean.

+100, AFR never lies.

Also, have you tried running without the engine hatch? Maybe you have lack of air, or an air pressure issue that is effecting carb tuning. I'm guessing the Z29 was not designed to meet the CFM you are demanding

The fuel pressure gauge holds at 6-7 lbs always. The air supply has been improved but I will try the hatch it needs reupolstering anyway.

I'd check fuel psi for sure. If the psi drops at 3800, you have a delivery problem. If it doesn't, you have carb tuning issues. Could be a tank vent issue, try running with the fuel fill cap off. I think your small on the metering jet size too.

Be careful, don't run it long that way, or you'll be draining pistons out with your next oil change

On another note, Im not a fan of the AFB style carb for marine blower application. I personally, would sell them, bolt on a pair of Holley 750DP carbs. Holley's dual needle and seats, large center hung float bowls, sideways mounted, just works well in marine.

Since you're fuel psi is steady, my guess, and simply a guess from where im sitting, is you're jets are being starved for fuel due to float height (running angle of boat), needle and seat capability, or simply too small of metering jet.

Man dude, you gotta get out of the garage more often :D

I think you mean the "Magic Room" :party-smiley-004:

I had the same issue a couple of years ago. Had boost referenced holleys, but the shop who did my carbs left the power valves in the secondarys which are not boost referenced. The motor ran great on the dyno but was doing the same exact thing in the boat. Leaned out the motor and toasted it. Ended up blocking the secondary power valves and jetting the secondarys up, and never had an issue again except for XR drives