Eoughphilly
Cadet
- Joined
- Jul 13, 2019
- Messages
- 28
I have a new to me boat I purchased with a 1991 mercury 90hp outboard. When I start it up, it seems to be misfiring and will not idle. Once it gets below 1200 rms it starts to shutdown. I cannot get it to idle long enough to put in gear when in the water or under load. But I can when I have the hose hooked up. I started troubleshooting and have exhausted the possibilites of what is causing this. Below is a list of things I have done so far.
Current idler screw adjustment
Top - 1 1/4
Middle - 1 1/4
Bottom - 1 1/4
Seated idler adjustment screws and pulled out 1 1/2.
No change, still misfiring at low rpms and not idling.
Checked compression.
Top - 95
Middle - 95
Bottom - 100
Ignition coil resistance test
Top - posts .4 and wire to post .951
Middle - posts .5 and wire to post .917
Bottom - posts .3 and wire to posts .918
Attached in line spark tester on each plug and all are lighting up good.
Performed 1/4" spark gap test - has spark
Replaced fuel hose between inline filter and carburetor. There are no air bubbles. Fuel pump should be good.
Rebuilt carburetors, no gunk or anything found to be causing any problems.
Inspected read valves through inlet while carbs were off. Also examined carbs with air vents removed for any blow back. None seen, also air vents were clean.
Replaced spark plugs even though they looked ok.
Here is a video of it running.
Misfire?
Replaced inline fuel filter with a clear view glass filter. In the video you can see it looks like the fuel filter doesnt fill up and doesnt keep up very well. I don't know if this is normal or not because i didnt see any bubbles when i had the clear hose on.
At this point I am unsure if this is fuel or spark related. I havent done a cdi test with a dva adapter yet because I dont have one. Any thoughts or ideas to help point me in the right direction would be so much appreciated. Thank you in advance.
Current idler screw adjustment
Top - 1 1/4
Middle - 1 1/4
Bottom - 1 1/4
Seated idler adjustment screws and pulled out 1 1/2.
No change, still misfiring at low rpms and not idling.
Checked compression.
Top - 95
Middle - 95
Bottom - 100
Ignition coil resistance test
Top - posts .4 and wire to post .951
Middle - posts .5 and wire to post .917
Bottom - posts .3 and wire to posts .918
Attached in line spark tester on each plug and all are lighting up good.
Performed 1/4" spark gap test - has spark
Replaced fuel hose between inline filter and carburetor. There are no air bubbles. Fuel pump should be good.
Rebuilt carburetors, no gunk or anything found to be causing any problems.
Inspected read valves through inlet while carbs were off. Also examined carbs with air vents removed for any blow back. None seen, also air vents were clean.
Replaced spark plugs even though they looked ok.
Here is a video of it running.
Misfire?
Replaced inline fuel filter with a clear view glass filter. In the video you can see it looks like the fuel filter doesnt fill up and doesnt keep up very well. I don't know if this is normal or not because i didnt see any bubbles when i had the clear hose on.
At this point I am unsure if this is fuel or spark related. I havent done a cdi test with a dva adapter yet because I dont have one. Any thoughts or ideas to help point me in the right direction would be so much appreciated. Thank you in advance.