Blower fastener torque, motor "rolling, rich"
05-18-2003, 06:14 PM
#1
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Blower fastener torque, motor "rolling, rich"
Anyone
My buddy has two Merc 900sc' in his scarab and he's having problems with stalling and loading up when docking and putting around in no wake zones. The motors "roll" at idle and in off idle cituations, causing the stalling. As far as we know, this setup is 100%...very well done no details overlooked. At cruise and at speed it runs perfect. 5600 rpm and high 90's no problem. I've seen this problem or charactoristic in a lot of blown set-ups and we're just wondering if there is a way to make it better or just more bearable. He has chillers and pulleys that were on the motor when it was a west coast racer...but we don't want to compound a problem with a more dense, cooler fuel mix if its already rich. Anyone with baseline specs for this set-up; 540 with 420 B+M blowers MSD ign. 4150 mechanical Holleys Stellings 5" full exhaust...unknown cam specs or internals?? I know this is a mess, but even approximate boost levels, timing and jetting bases would give him somthing to compare to. The boat is right there, but for the down low missbehavior it would be great. Maybe its just the nature of this beast? Power valves are blocked out, and it will stay at its idle all day, but when you engage the drives, the problem comes out.
My buddy has two Merc 900sc' in his scarab and he's having problems with stalling and loading up when docking and putting around in no wake zones. The motors "roll" at idle and in off idle cituations, causing the stalling. As far as we know, this setup is 100%...very well done no details overlooked. At cruise and at speed it runs perfect. 5600 rpm and high 90's no problem. I've seen this problem or charactoristic in a lot of blown set-ups and we're just wondering if there is a way to make it better or just more bearable. He has chillers and pulleys that were on the motor when it was a west coast racer...but we don't want to compound a problem with a more dense, cooler fuel mix if its already rich. Anyone with baseline specs for this set-up; 540 with 420 B+M blowers MSD ign. 4150 mechanical Holleys Stellings 5" full exhaust...unknown cam specs or internals?? I know this is a mess, but even approximate boost levels, timing and jetting bases would give him somthing to compare to. The boat is right there, but for the down low missbehavior it would be great. Maybe its just the nature of this beast? Power valves are blocked out, and it will stay at its idle all day, but when you engage the drives, the problem comes out.
05-18-2003, 09:31 PM
#2
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Are the chillers hooked up to a constant water supply ???
If so that will cause the fuel to form back into a liquid at an idle. Hook them up transom mounted pickups that will only feed them when needed, which is while underway at speed.
If they are not getting constant water then I would look at float bowl levels--they might be set too high. Set them lower and then reset base idle mixtures.
Good luck
If so that will cause the fuel to form back into a liquid at an idle. Hook them up transom mounted pickups that will only feed them when needed, which is while underway at speed.
If they are not getting constant water then I would look at float bowl levels--they might be set too high. Set them lower and then reset base idle mixtures.
Good luck
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05-18-2003, 09:37 PM
#3
Charter Member # 55
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So what you're saying is that it stalls at idle situations due to the surge of the blowers?????
What are the rpms at the high and low side of the surge???
Might just have to turn up or richen the idle mixture depending on where the rpms are.
What are the rpms at the high and low side of the surge???
Might just have to turn up or richen the idle mixture depending on where the rpms are.
05-18-2003, 10:32 PM
#4
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Griff and Bigwavz
The stall only occurs when you engage into gear and try to bump it around like getting on a trailer or docking. It idles at 900-1000 rpm and yes the surge is what kills the motors unless you bump the throttles...which has a tendency to load the motor up a little. The chillers are currently not installed, but came with the boat as well as the proper size up pulleys, etc. The chiller piping has a sort of bypass valve that seems to be to keep the water in the chillers from either flowing through them or raw uncirulated water(freshly intook) from flowing through. We're not too sure yet. We're going to take down one carb and see what it has for idle jetting and mains as well as how it flows...just to get an idea what he has going on. The motors run excellent underway and drivability is flawless even with alot of throttle input(waves!!!)
Besides when it gets unruly at the docks, its a great ride. The chillers were going to be put on for the Hudson river Pocker run, but we need to work this bug out before we put them in. Any torque specs on the blower studs/nuts? We figured around 45-50ftlbs. And heres a doozy of a question...38' Kevlar Scarab 900sc's #4 with 26" wheels(Spinelli 3 blade) completely set-up yo go 8000 lbs-how fast should it be? We have a Gps, but by the time the dumb thing starts reading we're slowing down as it still climbs (around 90+)... just figured I could get a few opinions.
The stall only occurs when you engage into gear and try to bump it around like getting on a trailer or docking. It idles at 900-1000 rpm and yes the surge is what kills the motors unless you bump the throttles...which has a tendency to load the motor up a little. The chillers are currently not installed, but came with the boat as well as the proper size up pulleys, etc. The chiller piping has a sort of bypass valve that seems to be to keep the water in the chillers from either flowing through them or raw uncirulated water(freshly intook) from flowing through. We're not too sure yet. We're going to take down one carb and see what it has for idle jetting and mains as well as how it flows...just to get an idea what he has going on. The motors run excellent underway and drivability is flawless even with alot of throttle input(waves!!!)
Besides when it gets unruly at the docks, its a great ride. The chillers were going to be put on for the Hudson river Pocker run, but we need to work this bug out before we put them in. Any torque specs on the blower studs/nuts? We figured around 45-50ftlbs. And heres a doozy of a question...38' Kevlar Scarab 900sc's #4 with 26" wheels(Spinelli 3 blade) completely set-up yo go 8000 lbs-how fast should it be? We have a Gps, but by the time the dumb thing starts reading we're slowing down as it still climbs (around 90+)... just figured I could get a few opinions.
05-19-2003, 10:48 AM
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Check the timing at idle, both in & out of gear. If the timing is moving at all then that could be your problem. You want the timing to be stable while in or out of gear at idle. Some time the timming starts advanding at this low rpm & it make the motors unbearable at low rpm. Either lock out advance or not start advance until about 1500 rpms.
05-19-2003, 06:43 PM
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Hey Darkhorse, I would definitely run 30 deg. lockout on ignition.I am currently building 572's talldeck with 420 megas, Msd and Holley 750's. Havent completed yet but would like to know what you are running for jets and such. I will look into mine as well. thanks
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05-19-2003, 07:40 PM
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Thanks for the input guys...I'm going to call Nickerson tommorow and in the meantime, we set the float levels and leaned out the idle mix just a hair then raised it 50 rpm. Splash time this weekend and we also installed the chillers...they're valved in the intake side for about 10-15 psiwater pressure, so they shouldn't even open until we're almost at cruise speed(the water pressure is usually around 4-5 putting around then 10+when we're cruising). Hopefully all goes well.
