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#1
10-23-2011, 04:14 PM
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performance update
Hi guys the motor is getting spark on all six cylinders.
The compression test with all plugs removed and a cold motor were #2 85 #4 85 #6 85 #1 85 #3 80 #5 85 I then took boat out in the bay and tested compression in one cylinder with all plugs still in the compression was between 95 and 100 on cylinder #2. I can't understand why I was getting 5200 rpm last weekend and then such a huge drop in rpm's. I'm sure the compression was the same last week. Could a failing fuel pump be the cause? Again Thanks everyone for you're help. 
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#2
10-23-2011, 05:08 PM
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Did it sputter or have trouble starting or just fail to reach rpm?
You mentioned moving the throttle cables - could they been moved or adjusted enough restrict full range of their movement, say not open enough or be able to "floor it" on the gas? If your butterflies are restricting air flow you wont reach your rpms.
__________________
there's no such thing as normal anymore...
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#3
10-23-2011, 06:20 PM
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Hi Mcgilli thanks for responding to my thread. What I meant by moving the linkage cables was I slid some of the slack under the floor to make room for more storage. I opened the cowling when I was out on the wAter today and adjust the throttle a little bit I was able to get another 200 rpm's. The engine cranks up no problem no sputtering at all. Also when I moved the battery I swapped the engines power cables with the ones that were going the battery to the console when the battery was located in the stern. The cables from the motor were not long enough to reach console anyway both cables seem to be the same gauge. I just figured I threw that out there also. Does anyone know if there is any adjust on the shifter handle itself? It seems I have to push shifter handle pretty far forward before I get any response from motor. I'll probably pick up a service manual to find out how to adjust linkage. Thanks again!!
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#4
10-23-2011, 06:49 PM
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Quote:
The throttle cable adjustment is at the motor end of the cable. To check if it's a throttle adjustment problem, remove the cowl, and then remove the front air box cover. With the air box cover off, you'll be able to see the carb butterflies. With the engine off, push your throttle all the way forward. If the butterflies aren't wide open, that's your problem. It could be a simple matter of adjusting the throttle linkage, or the throttle cam could have slipped out of adjustment. The manual will tell you how to fix either problem. Or you can check it out and post questions here. Dave
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Blue Heron Boat Works Reinventing the wheel, one spoke at a time.
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#5
10-23-2011, 08:16 PM
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Quote:
This will allow for strech. You may have to come back and micro manage it. Cheers, GFS
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#6
10-23-2011, 09:40 PM
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On a V6 it could be a coil dropping out, stator or trigger...
It's hard to tell when you are running if you are dropping a cyclinder. Also your bottom carb may have trash in it as it is the first to get junk in it.. Do a spark check first, then head for the fuel system. Old fuel line will break down with the crap we have for gas now. The liner in some fuel lines just breaks apart and clogs everything!! Just my 2¢ worth... 
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See ya, Ken ©
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#7
10-24-2011, 08:17 AM
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I'm with Ken on this one....go straight to the carbs. There are very tiny jets and fuel pathways in the carb that can get clogged up very easily, especially the high speed jets and it's then a "no go" on high RPM.
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#8
10-24-2011, 10:59 AM
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I suspect your compression gauge is off . . . A healthy 2.0L merc is generally 115 - 120psi. B/c all the cylinders are even and the motor starts easily and runs . . . sounds like a bad compression gauge.
A bad stator will cause the motor to run rough/misfire above 2500 - 3000 rpm (high speed coil). A bad switch boxes will cause one side of the motor not to fire. A bad trigger can cause one or more cylinders not to fire, but they almost never fail (unless it's the sheathing on one of the wires). Coils can fail . . . check grounds and make sure plug wires are snug. If you have the idle stabilizer connected . . . you might consider removing it. Read why on screamandfly.com. Also . . . oil injection is problematic on these motors (2.0, 2.4 and 2.5L mercs). Merc makes a plug you can buy specifically for folks that want to remove the oil injection. If you are concerned about high speed jets on the carbs being clogged . . . you can pull the cowling and the air box cover off the carbs and have someone else drive. Get on a plane (faster the better) and look down the throats of the carbs . . . you will see a nice fan spray of fuel. If one differs significantly from the other 5 . . . you likely have some crud blocking the high speed jet. If the spray is very different on one cylinder . . . back off and drive home at low speed and pull apart the carb with the issue (you may want to do all of them). Is there a strong smell of fuel or any noticeable fuel leak? when you remove the cowling? Did the motor get HOT? Are there any wires that look like they melted? a bad fuel pump usually causes surging at higher speeds . . . if you pump the bulb while running it will usually overcome problems with low fuel pressure or a weak pump . . . then you know you need to rebuild it. online merc manuals http://1manual.com/Mercury%20manuals/intro.html unfortunately they don't have anything back to 1988 . . . just 1992 and newer. There will be some relevant information in that manual. http://1manual.com/Mercury%20manuals...52r3/cover.pdf Last edited by Bigshrimpin; 10-24-2011 at 11:40 AM.
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