High speed jet carb adjustment on 1987 70 HP 3cyl merc

[skipper123]

I had a ignition issue on the motor and in the process tried to adjust the carb screws on the side of the carbs on the port side of the engine beside what looks like jet screws. After I found my switchbox was bad and had a rotten wire from the trigger and got thoes two items replaced my motor now starts and idles great. Then went out for a test run to find out when I gave it some throttle it ran rough and had no power so I adjusted thoes same three screws one on each carb out two turns and got my power back but some what of a bog at a certain speed as well as a little rough at WOT. My question is where to set the high speed screws from the get go that will be close and what to look for to let me know where to fine tune them. When the engine bogs at a certain speed does that mean not enough fuel or to much. And if I go out to far will the engine flood and run rough. I turned the screws out to gain more power. I have to think that means more fuel ? I turned each screw the same amount but one screw seems like it is a couple rounds different than the other two. I am good at rebuilding and cleaning carbs but always have trouble adjusting them.

 

[skipper123]

Re: High speed jet carb adjustment on 1987 70 HP 3cyl merc

While on the carb issue is their a low speed or idle adjustment on these carbs ?

 

[Faztbullet]

Re: High speed jet carb adjustment on 1987 70 HP 3cyl merc

The high speeds are non adjustable as they are fixed jets, what you are adjusting is the idle mixtures. A good starting point for for adjusting is to turn in till they just seat and CW out 1-1/2 turn. Start engine and start on bottom carb and work you way up to top. turn in screw in 1/8 turns till engine misses/spits/looses rpm (lean point) and back out till it smooths out then add 1/2 turn CW. Make sure you adjust in a barrel or backed in lake on trailer as you cannot do it on hose due to engine has no back-pressure. Also did you reset timing after changing the bad trigger????

 

[skipper123]

Re: High speed jet carb adjustment on 1987 70 HP 3cyl merc

Thanks for the help. And no I have not adjusted timing yet. I did adjust carbs at the lake today and got her running pretty good other than a little rough at 1/4 throttle. I guess I still get her a lttle lean. Im researching now on how to set timing. I will pick up a timing light tomorrow.

 

[quicktach]

Re: High speed jet carb adjustment on 1987 70 HP 3cyl merc

Have you cleaned out the carbs and is fuel filtering all clean?