Port Engine is short on RPMs
05-23-2004, 04:45 PM
#11
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Re: Port Engine is short on RPMs
I agree, I am certain Rod's motives are good. He helped me out last year when I was in a pinch with my stearn drive. I felt bad after thinking about it for a while and was going to edit what I had written, I really did not mean to throw him under the boat so to speak, just started typing away with-out thinking. NOTE TO SELF: Do not respond to emails with a splitting headache and after waking up on wrong side of bed!
I never really paid to much attention to if it was pulling, if it is, it certainly is not pulling a lot that I notice it, but since the ride and handling of the boat are still so new to me, I could be missing it. As far as sound goes, I can not hear a difference at idle and at speed...it is anyones guess.
Thanks for the suggestion on PM 10x, I will do that.
Griff, thanks for the info on the fuel pump numbers.
I never really paid to much attention to if it was pulling, if it is, it certainly is not pulling a lot that I notice it, but since the ride and handling of the boat are still so new to me, I could be missing it. As far as sound goes, I can not hear a difference at idle and at speed...it is anyones guess.
Thanks for the suggestion on PM 10x, I will do that.
Griff, thanks for the info on the fuel pump numbers.
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05-25-2004, 08:26 AM
#13
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Re: Port Engine is short on RPMs
Most boat gauges are disappointingly inaccurate.
#1) verify tachs reading the same (which is different than "properly" but is more important). Run up to 75% WOT (wide open throttle). Play with the sticks until you get an audible sync. You can sync by ear very easily. Just listen for the out of phase sound and adjust a little at a time until it the phasing slows to an almost perfect sync. THEN take note of the tach readings. They should be showing within 50 rpm of each other. Some tachs have adjuster pots on the back. Some don't.
Okay, now that you are reasonably sure your tachs are reading close to each other, repeat your WOT run and note the differences in all of the readings. More than 100rpm difference is too much.
Fuel pressure: fuel senders are notorious for odd readings. You need to also have mechanical gauges in the engine compartment to double check your electric gauges. You should see between 5 and 7 psi of fuel pressure regardless of rpm or load (assuming this is a normal Merc 525SC). Less than 4 psi will allow the float bowls to run dangerously low and cause a lean condition. If you do NOT have 6 or 7 psi of pressure, then check your regulator and fuel pump and fuel lines and tank vents. Get that situation fixed before you do anything else. If you DO have 6 or 7 psi at all times, then set the float levels in all of the bowls (2 each carb). Pull the level plug on the side of the bowl and adjust the level screw on the top of the bowls (flame arrestor off and fuel pump running - if you have mechanical pumps the engine must be running so you will need to pack rags around the level plug to catch gas that spills out - also have a buddy with an extinguisher in hand: I've learned that if you have a manned extinguisher around you NEVER have a fire).
Boost? At WOT the two 525SC's should show the same boost even at 400rpm difference. Unlike a centrifugal supercharger, the blower on the 525SC should show pretty close to the same boost as the othwer motor AS LONG AS THE THROTTLES ARE OPENING ALL THE WAY (oh yeah, check your throttle linkages to make sure the throttles are opening up all the way). Leaking manifold gaskets or abnormal blower wear can of course change this.
Holler back when you check some more stuff.
#1) verify tachs reading the same (which is different than "properly" but is more important). Run up to 75% WOT (wide open throttle). Play with the sticks until you get an audible sync. You can sync by ear very easily. Just listen for the out of phase sound and adjust a little at a time until it the phasing slows to an almost perfect sync. THEN take note of the tach readings. They should be showing within 50 rpm of each other. Some tachs have adjuster pots on the back. Some don't.
Okay, now that you are reasonably sure your tachs are reading close to each other, repeat your WOT run and note the differences in all of the readings. More than 100rpm difference is too much.
Fuel pressure: fuel senders are notorious for odd readings. You need to also have mechanical gauges in the engine compartment to double check your electric gauges. You should see between 5 and 7 psi of fuel pressure regardless of rpm or load (assuming this is a normal Merc 525SC). Less than 4 psi will allow the float bowls to run dangerously low and cause a lean condition. If you do NOT have 6 or 7 psi of pressure, then check your regulator and fuel pump and fuel lines and tank vents. Get that situation fixed before you do anything else. If you DO have 6 or 7 psi at all times, then set the float levels in all of the bowls (2 each carb). Pull the level plug on the side of the bowl and adjust the level screw on the top of the bowls (flame arrestor off and fuel pump running - if you have mechanical pumps the engine must be running so you will need to pack rags around the level plug to catch gas that spills out - also have a buddy with an extinguisher in hand: I've learned that if you have a manned extinguisher around you NEVER have a fire).
Boost? At WOT the two 525SC's should show the same boost even at 400rpm difference. Unlike a centrifugal supercharger, the blower on the 525SC should show pretty close to the same boost as the othwer motor AS LONG AS THE THROTTLES ARE OPENING ALL THE WAY (oh yeah, check your throttle linkages to make sure the throttles are opening up all the way). Leaking manifold gaskets or abnormal blower wear can of course change this.
Holler back when you check some more stuff.
