DT9.9C fuel problem

[bjw444mar]

I have an 89 DT9.9C that I bought used and it would stall after about 10 minutes of running. If I caught it in time I can keep it running by squeezing the primer bulb a few times and it would stay running as long as I squeezed the bulb every 5 or 10 minutes. I did a little research and some testing with some clear hose to check for air bubbles and found no air leaks on the boat side of the fuel system. I took the carb off and took apart the fuel pump to inspect it but couldn't see much anything wrong with it by looking at it. So I put it back together and I also cleaned out the fuel filter which didn't look dirty either.

I put it all back together and restarted it and it ran a little bit longer but then stalled again. I restarted it and this time ran it at about half throttle this time it kept running I still have the clear hoses on it and could see that the fuel pump was sucking fuel much better I then lowered the rpms back to idle and the fuel pump didn't suck as good. I'm assuming my problem could be that I need to put a new diaphragm kit in it since it doesn't want to suck at lower rpms. This is my first outboard kicker that I've worked on so can someone let me know if I'm on the right track or if there is something else I can check that might be causing it to not suck fuel at low rpm's.

Brian

[Solarman]

dt9.9, running issues

Does your fuel pump have 2 small plastic discs (check valves) in the base under the diaphragms? Am not familiar with your pump, and parts page doesn't show them. If so, they have been found to crack and fall apart. If that is the case here, then often the pieces lodge on the backside of the needle valve seat in the float chamber. This could cause fuel flow problems at any speed.
Before you buy a rebuild kit check this out. The only way to get the check valves replaced is with new pump (if it has them).
If your pump is working fine, there might be a small blockage in your low speed/idle mixture passage, or may need to adjust it a little.
Let us know what you find

[bjw444mar]

From what I could see the two discs looked ok. I couldn't see any cracks or missing pieces...also I forgot to mention before that is surges when it runs at low speed. It will run ok then it will speed up a few hundred rpm's for 10 seconds or so then it will slow back down then speed up etc...

Do you know what the carb settings are on the mixture screws and which screws are which because the picture doesn't show up on the parts site.

Thank you for your reply Solarman

Brian

[Solarman]

dt9.9, carb settings

There should only be one mixture screw. The high speed mixture is inside the float bowl, according to the parts page. Have you checked the float level in the bowl? This should be checked/ adjusted to make sure you're not running out of gas, also that the needle valve is working properly (not sticking shut).
Count the turns on your mixture screw clockwise until it lightly seats. This should be your base setting (it is running at this setting). Adjust the mixture screw in (CW) about 1/8 turn, no more than 1/4. If motor runs worse, try the opposite direction (CCW).
If someone else has been in the carb, then you should check all the jets, and blow air through the passages, basically soak it and clean it well, and check float setting.
if you don't have a manual, you might be able to download one some where on the internet? Try googling it?
Good luck, let us know.