Still Having problems with the PROBLEM CHILD-Lean/miss/stumble/backfire!!!!
05-18-2003, 05:45 PM
#31
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I don't have any reference materials with me for specifics, but you plumb the gage into the intake, and at idle watch how the needle fluctuates. There are specific patterns to look for that will tell you many different things. I think seloc has a section in the merc manual telling what to look for. That, or when you buy a vacuum gage it generally comes with the specific things to looks for.
BT
BT
05-19-2003, 04:50 PM
#34
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Well..........................Lets see. I ran a bead of silicone down the intake/head surface yesterday. I took the boat out today and the symptoms actually MIGHT have gotten a tad worse. But the intake leak (or whatever it was) is now gone.I shot the starting fluid down the areas and finally there was no change at all at idle thru-out the rpm range when I shot the fluid down. I put the vacuum gauge on and it was between 14-15. The needle moved pretty rapidly between the two amounts but the amount itself was small. I re-checked the plugs and still WHITE AS A GHOST. I figure the only thing left to change and what several here have suggested is the fuel system....I orderd a Hi-output 6-8lbs & 110gph new fuel pump. So it should be here Wed. So I should have something by Thursday evening......I have a VERY Bad feeling that that it's not the fuel pump but I can't think of ANY thing else to check or replace....
BH:
BH:
Last edited by BAD-HABIT; 05-19-2003 at 04:57 PM.
05-19-2003, 04:57 PM
#35
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My take is the reason plugs are showing lean is the leak, air is bypassing the carb thus the lower air/fuel ratio. Leanness can also cause surging. I would try taking silicone & put along where the air is leaking. The longer you run motor lean the shorter the motor will live. Could be you got the motor hot one time & caused the heads to warp. I really could not see this happen but I have seen stranger things.
As for the motor dropping RPM, only reason I can think is you are reducing air volume & idle jetting is on rich side to start out with.
As for the motor dropping RPM, only reason I can think is you are reducing air volume & idle jetting is on rich side to start out with.
05-19-2003, 10:16 PM
#36
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Steady reading between 15-21inches at idle RPM -normal.Extremely low reading but steady at idle RPM-vacuum leak,incorrect timming.Fluctuates between high and low at idle RPM-blown head gasket between two adjacent cyl.Fluctuates 4-5 inches very slowley at idle RPM-spark plug gap to narrow,valves are sticking.Fluctuates rapidly at idle steadies as rpm is increased.-valve guides are worn.Continuously fluctuates between low and normal reading at regular intervals at idle RPM -burned or leaking valve.I don't think you have a vacuum leak 
Also I would not spray Starting fluid or W-D 40 on those type of gaskets as it might dammage the rubber.
Also I would not spray Starting fluid or W-D 40 on those type of gaskets as it might dammage the rubber.
05-20-2003, 03:31 AM
#37
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Bad-Habit, if you have a fuel supply problem , there could be a number of reasons behind that , eg the fuelpump and fuel pressure valve, the cam lobe that is driving the pump, clogged fuel lines, antisiphon valve in the tank, the fuel filter or that the system is sucking air somewhere before the pump. You may have done this already but I would carefully observe the pressure at the carburator all the way from idle to WOT and under hard acceleration ,to see if there are any fluctuations in order to get a clue of what is actually not working.
05-20-2003, 05:33 AM
#38
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Bad Habit
I would try the orange high temp silicone, it will handle the temperature and maybe temporarily segregate the problem. Test it after you let the stuff dry, the same way you tested it to get the rpms to drop, if they do not drop and idle stays the same, then do anothe plug read.
Post what you find.
Good Luck
Brian
I would try the orange high temp silicone, it will handle the temperature and maybe temporarily segregate the problem. Test it after you let the stuff dry, the same way you tested it to get the rpms to drop, if they do not drop and idle stays the same, then do anothe plug read.
Post what you find.
Good Luck
Brian
05-20-2003, 11:40 AM
#39
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If the fuel pressure dropped as the engine rpm increased I was going to say check the anti syphon valve, tank screen or fuel tank venting. Could be the fuel pump pressure control valve as well. Let's hope that is it!!
Good luck,
BT
Good luck,
BT
05-20-2003, 01:19 PM
#40
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Here's something else, that hasn't been brought up. Have you checked your water pressure at WOT? If all plugs are white, like new. You can be getting some water in the cylinders. Just a thought.
