525SC can't get above 4500 RPM
07-15-2003, 04:29 PM
#12
Charter Member # 55
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Originally posted by THRILLSEEKER
BTW, any of you guys know what valve pressures should be on a sbc, it has the old angled plug heads if that matters
BTW, any of you guys know what valve pressures should be on a sbc, it has the old angled plug heads if that matters
07-15-2003, 04:29 PM
#13
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Specs for SBC 260/270 hp engine:
78-86lbs closed, 170-180lbs open
I could only find specs for the 370, 400, 420 hp 454:
115-125lbs closed, 305-325lbs open
Gary
78-86lbs closed, 170-180lbs open
I could only find specs for the 370, 400, 420 hp 454:
115-125lbs closed, 305-325lbs open
Gary
07-15-2003, 04:43 PM
#14
Geronimo36
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My gut tells me you have a fuel problem, hard to tell without hearing it.
I have seen this problem on many different occasions. It usually happens because something is clogged in the needle & seat on the secondaries. While you are cruising the primaries are supplying enough fuel but when you give it more throttle the secondaries open and lean out the motor and cause a lean pop/sputter.
I have seen this problem on many different occasions. It usually happens because something is clogged in the needle & seat on the secondaries. While you are cruising the primaries are supplying enough fuel but when you give it more throttle the secondaries open and lean out the motor and cause a lean pop/sputter.
07-15-2003, 04:47 PM
#15
Geronimo36
Gold Member
Thrillseeker, what kind of ignition modules do you have? Sometimes the module goes bad, or moisture gets into the connection. Try swapping ignition modules.
I have also seen valve cover leaks short out ignition wires. Also check the cap and rotors, I have seen brand new defective caps and rotors. I have also seen cracked ignition coil stems.
I have also seen valve cover leaks short out ignition wires. Also check the cap and rotors, I have seen brand new defective caps and rotors. I have also seen cracked ignition coil stems.
07-15-2003, 05:01 PM
#17
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Panther, I had switched the carbs from engine to engine, as I did with a ton of other parts listed above, I put the carb from the problem engine on the good engine, and vise versa and the carb off of the "bad" engine" worked fine on the opposite engine. The only thing I havent had time to check yet is the fuel pressure @ the carb at WOT, I switched the ignition modules that are inside the distributors, rotors, and caps but I havent had time to test the boat yet: I will take a good look at the ignition harness tonight to look for "bad spots"
I am real tempted to swap the entire wireharness from engine to engine.
I am real tempted to swap the entire wireharness from engine to engine.
Last edited by THRILLSEEKER; 07-15-2003 at 05:07 PM.
07-15-2003, 07:53 PM
#18
Remember you can have sufficient fuel pressure and still not have the volume you need. It sounds like fuel probs to me. Don't forget to check the fuel tank vents, fuel lines, switching valves and whatever else is between the tank and carb. I had a fuel line collapsing internally at the end of the fuel inlet barb that had me scratching my head for 3 weeks. It was a WOT only power loss, OK below 80% throttle.
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07-16-2003, 08:41 AM
#19
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I'm with Panther and Go4broke.
Fuel or ignition. A valvetrain problem would like show up at even part throttle.
Try the simple stuff first. Blow out the fuel line and pickup. Believe it or not, I had styrofoam clogging the fue pickup on one boat.
How is your ignition seconday system. Wires, coil, can both cause that kind of problem.
Gary
Fuel or ignition. A valvetrain problem would like show up at even part throttle.
Try the simple stuff first. Blow out the fuel line and pickup. Believe it or not, I had styrofoam clogging the fue pickup on one boat.
How is your ignition seconday system. Wires, coil, can both cause that kind of problem.
Gary
07-16-2003, 08:49 AM
#20
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well, I blew out the fuel lines last night and nothing came out of them, I blew the feed hose back into the tank and if there was anything plugging it, it blew back into the tank, I could hear it bubbling inside the tank and air comming out of the fuel vent. could there possibly be something stuck in the mecanical fuel pump?? I am going to try to go to the lake tonight to test it, if that doesnt work, I will try changing plugs, then, tachs, then As a last resort I am going to swap wiring harnesses, after that I give up
Krumbsnatcher, have you had any luck yet??
Krumbsnatcher, have you had any luck yet??
Last edited by THRILLSEEKER; 07-16-2003 at 08:53 AM.
