1998 9.9 2 stroke mercury troubles

Ian045

Cadet
Joined
Jul 12, 2025
Messages
13
Okay people I’m back again unfortunately, so now I’ve got a brand new carb, fuel filter, and fuel connector. I’m still have extreme trouble getting it to start, again only getting it to run at full throttle. I’ve tried factory carb settings I seen on a video on YouTube and I felt like it wanted to start in neutral but I couldn’t get it to, I tried turning my cam all the way up to get more throttle in neutral. Just trying to get some new ideas and figure something out, thank you.
 

airshot

Admiral
Joined
Jul 22, 2008
Messages
6,312
" new" carb... Factory or Chinese copy ? Factory specs come from a factory service manual, not youtube. If compression is up to specs and spark meets factory specs, you have a fuel issue. Is the carb getting the fuel from the tank and hose ? Many things could be the problem, throwing parts at it won't solve anything. Tests need done to find the problem or we are all just guessing.
 

Ian045

Cadet
Joined
Jul 12, 2025
Messages
13
Is the carb base gasket on correctly?
I believe so, all the holes lined up for the passageways
" new" carb... Factory or Chinese copy ? Factory specs come from a factory service manual, not youtube. If compression is up to specs and spark meets factory specs, you have a fuel issue. Is the carb getting the fuel from the tank and hose ? Many things could be the problem, throwing parts at it won't solve anything. Tests need done to find the problem or we are all just guessing.
It’s is a Factory carb, the guy on YouTube went over the factory specs from the manual (I looked them up to be sure) how do I go about checking compression? And the bulb on my tank will stay tight and I can see the fuel in the filter.
 

airshot

Admiral
Joined
Jul 22, 2008
Messages
6,312
I believe so, all the holes lined up for the passageways

It’s is a Factory carb, the guy on YouTube went over the factory specs from the manual (I looked them up to be sure) how do I go about checking compression? And the bulb on my tank will stay tight and I can see the fuel in the filter.
Get an engine compression tester, if you plan on working on engines you will need one so get a good one. Check fuel flow from the fuel pump. The carb settings are a starting point, once the engine is running, final fine tuning needs to be done while under way in the water. Get a spark tester, they are cheap and be sure the spark will jump a quarter inch gap. Glad to see you confirmed the adjustments from the manual. Post your test results when you get them.
 

Ian045

Cadet
Joined
Jul 12, 2025
Messages
13
Get an engine compression tester, if you plan on working on engines you will need one so get a good one. Check fuel flow from the fuel pump. The carb settings are a starting point, once the engine is running, final fine tuning needs to be done while under way in the water. Get a spark tester, they are cheap and be sure the spark will jump a quarter inch gap. Glad to see you confirmed the adjustments from the manual. Post your test results when you get them.
I’m going to pick up both testers today, so I’ll hopefully have the numbers this evening. And also how do I go about checking fuel flow?
 

airshot

Admiral
Joined
Jul 22, 2008
Messages
6,312
I’m going to pick up both testers today, so I’ll hopefully have the numbers this evening. And also how do I go about checking fuel flow?
They make gages, but a simple way is to get out at WOT then squeeze the ball and see if any improvement in engine running. Not very precise, but it will let you know if there is a major issue.
 

Ian045

Cadet
Joined
Jul 12, 2025
Messages
13
They make gages, but a simple way is to get out at WOT then squeeze the ball and see if any improvement in engine running. Not very precise, but it will let you know if there is a major issue.
Okay so I had 95PSI on top and bottom but I wasn’t getting good spark on the bottom plug, I used a drill to keep the engine turning so I could see and it would light up when I first got it going, but it wouldn’t stay lit for longer than a second, if you know how to properly check an Ignition coil I would appreciate the help. I know I have to check inside the coil but I don’t know what to use on the multimeter to check if the coil is bad.
 

airshot

Admiral
Joined
Jul 22, 2008
Messages
6,312
Spark gap tells how hot the spark is, the tool has an adjustable gap so you can see how far the spark will jump. Not sure on how to test the coil, but it sounds like low compression and weak spark could be part of your problem.
 
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