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mercruiser 3.0l stalls and backfires through carb HELP!!!

J

jmiles8701

New member
I have an 87 glasstream with 3.0L mercruiser and alphaone outdrive. my issues started with the boat having trouble starting, it would turn over but not fire. then came after it would start and you attempt to accelerate the boat would skip and miss and back fire out of the carb, same when decelerating, but once able to get going the motor ran great from about 1/4 throttle to WOT. now its gotten worse. the motor wont start at all unless you give it a bunch of gas. once it does start you have to keep it near about 1/2 throttle to keep it running, any change and the motor will instantly start missing and backfiring out of the carb and stall. today I removed the carb and gave it a good cleaning. put it back on and don't see any improvements. obviously I will do a tune up on it asap (plugs, wires, cap, rotor,) but I wanted to post on here to see if I could get any help. my thoughts are to add a water separator, and drain the fuel tank to eliminate the possibility of water in the fuel. any other ideas?
 
If you have a points ignition consider a new set of points and condenser and make sure the dwell is set to specs and the timing is correct. Look under the points plate in the distributor and make sure the mechanical advance is working properly. Back firing comes from improper timing, cross firing plug wires, a lean mixture or a burnt exhaust valve. Check the compression.
 
Help me more!!!!!!!

:confused:update: still need help...... I performed a full tune up. ...plugs, wires, cap, rotor, cleaned the carb, cleaned and set points gap to .22, added a fuel/ water separator, did a full fuel system flush and messed with the timing. I found that the points in the distributer had come loose and was all out of whack, thanks everybody for your help! now, I have a new problem, after doing all of this its developed a new issue, it will start and idle great but when I put anything over 1/4 throttle to it, it falls flat and just doesn't go anywhere, doesn't stall, just doesn't continue to accelerate and acts like im still at 1/4 throttle the whole time. it only does this when its in the water, when on the trailer hooked to the hose pipe it runs flawlessly! I assumed that the water separator was starving it of fuel when under load so I switched that back out, but it didn't help. could it be a timing issue? I only set the timing by ear and feel (don't have a light) so I have no idea if its right at 6* like the motor sticker says.:mad:
 
Under the plate the points are mounted to should be two counter wieghts with springs, they need to move freely.
these are your mechanical timing advance wieghts(system).

If they do not move freely that may be your issue.

Also you should buy NEW points, rotor and condensor.

Cleaning only lasts so long as the surface of the points now has lost its hardened coating.......

Also if you are going to guess on timing that may not be a good thing.... You MUST know someone with a timing light...........
 
what about converting it to electronic ignition? just get rid of the points all together, ive heard there is a kit out there to do that. anyones thoughts?
 
guyjg said:
Pertronix electronic ignition conversion kit.
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wow those are more expensive then I was thinking. Update: ive set the time properly with a light and still no better. ill replace the points today and remove all the inline fuel filters to eliminate any fuel restriction issues and see what happens then.
 
Inspect the timing advance under the points plate! Also replace the condenser w/the points. Beg, borrow a dwell meter to set the points' dwell...more accurate than a feeler gauge.
 
i inspected everything under the points plate and it all looks good, I didn't replace the condenser but I did replace the points and now im not getting any spark. ive tried everything I can think of.:mad: when I put my test light on the coil I get light at the positive side when turning the key but not on the negative side that goes to the point (I think that's how it should be?) at first I thought maybe I got a bad set of points so I switched back to the old one that worked fine before removing... still no spark.
 
I didn't replace the condenser
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It is an electrolytic capacitor that can short out or change its farad value. Disconnect it and see if you get spark. Also look very closely at all wires that may have been pinched by a screw or plate.
 
guyjg said:
It is an electrolytic capacitor that can short out or change its farad value. Disconnect it and see if you get spark. Also look very closely at all wires that may have been pinched by a screw or plate.
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so do you think not replacing the condenser is the problem? (no broken wires found, although the wire out of the condenser was pinched)
 
replaced the condenser and still nothing. let me add that just prior to changing the points I added a second battery and rerouted all my batter cables. is there anything I could have messed up in doing that? I tested that the batteries were hooked properly by just hitting the key switch real quick, I never actually fired it up before I dove into the distributer to change out the points. could maybe by moving the main ground change something? I feel like an idiot that I cant figure this out, ive changed everything but the coil.
 
is there anything I could have messed up in doing that?
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Reset the main circuit breaker on the engine...big red button on it. Still not working then you have a wire off the + or - terminals on the battery.
 
When you installed the points did you install the properly? You should put them in on the flat spot of the cam and bring it up to the high spot to gap them. Does your dwell meter have a point checker on it. You could check to see if they are open and closing. Did you install the rotor? Wouldn't be the first time I forgot to put it back.
 
I may have an answer for you. I have a 3.0 liter mercruiser that is having the same problem. I replaced everything you could think of. Finally I decided to check compression. Everything was fine when the engine was cold . Once it ran and got to temp it would spit and sputter cough and choke then it would die. Only after it cooled it would start again. I decided then to check compression when it was hot and found 120 lbs in #1 and only 60lbs in 2,3,4 cylinder. Two conclusions. Cracked head or blown head gasket. I pulled the head and sure enough the head gasket was blown between 2&3 and 3&4. I will be replacing it next week and let you know how it turns out. It ran great in the driveway but not in the water just like you say yours does.
 
ive officially changed EVERYTHING!!! coil, cap, rotor, plugs, wires, points, wire from coil to points...etc. still no spark. its had plenty of spark until I changed the points and added the second battery/ re-routed the cables.
 
You made a mistake somewhere or you may have a bad condenser...check it for a pinched wire ro disconnect it to see if there is spark.
 
guyjg said:
You made a mistake somewhere or you may have a bad condenser...check it for a pinched wire ro disconnect it to see if there is spark.
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...I forgot to mention, ive also already changed the condenser! ugh!!!!:mad: its obviously something I did wrong or messed up, ive just gone through the whole thing tracing wires and checking connectors trying to find something. I have the feeling its something small.... just don't know what!!!!!!! I appreciate everyones help a lot, keep it coming!!!!
 
ive also already changed the condenser!
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They are known to be bad right out of the box...disconnect it and try again! Beg, borrow a dwell meter to set the points' dwell...more accurate than a feeler gauge.
could maybe by moving the main ground change something?
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What exactly did you do?
 
Make sure that you are not grounding the points or the condenser out. I'm not familiar with your setup but I have seen some where they come through the distributor and there is a plastic isolator. Make sure that your on that. Make sure that any bare wires coming from the points are not touching the distributor. If you can take a picture of what you have that may help.
 
its very possible that moving the main ground changed something.... ill look at that! ..ill also take a pic of what everything looks like and post it, maybe one of you guys will see something im missing!!!!! the wire coming from the coil goes into the distributer and joins the condenser wire at the points, is that correct?
 
you may want to check the control box for a kill switch...also, remove the grey wire from the "-" terminal of the coil going to the tach...leave the one going to the points connected...test light on the "-" terminal should flash on when the points open...
 
makomark said:
you may want to check the control box for a kill switch...also, remove the grey wire from the "-" terminal of the coil going to the tach...leave the one going to the points connected...test light on the "-" terminal should flash on when the points open...
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your not the first one to mention a "control box", I have no idea where one would be on my boat. best I can find is the big red main breaker button.(of course ive made sure it hadn't been tripped)
 
points don't line up real good....primary lead, from points to coil, is missing the grommet at the breaker plate.

Looks like a good deal of rust around the spark plug holes but it looks fresh...
 
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