1972 mercury 402, wont run longer than 3 seconds.

Hey everyone, first mercury, I bought it in poor running condition. Had a pretty bad fuel leak but couldn't determine from where. Decided to pick up a carb kit and disassemble & clean the carb. Only ended up having a few parts left from the kit(throttle plate assembly and a mini plug no bigger than a pinhead.) Reinstalled everything, prime it fires up instantly. But only for 3 seconds. even if I keep constant pressure on my primer I cannot get it to stay running. I'm not super familiar with 2 stokes period. I would think if the fuel pump was bad, me on the primer should keep it running. I've read that if the choke is slightly warped it wont seal proper, but I've already ruled that out.
Any help would be appreciated.

Does it run longer if you keep the choke on ?

Not at all.

Check that it still is sparking when it stops to eliminate that problem. I would look at the fuel pump too because of the age and unknown service record. Did you follow the manual procedure for setting the lever heights?

When you did your carbs did you check float height and float drop? Did you test if the needle and seat are working properly? You check that with float bowl off. You blow into fuel inlet. With carb upside down should be no flow. With it upright. Should be flow. Mixture screws should be pre set at 1.5 turns out from seated. Do not over tighten mixture screws just set them in till they stop. Then one and a half turns out. If you over tighten them you will damage the mixture screw.

Unfortunatly No manual . But mixture screws are backed off. Ive got good spark. Replaced the float. I basically removed and replaced and reinstalled. Boat is at the lake and had no service. I'll be heading up tomorrow again and needing some ideas.

Follow these instructions:

Try checking the fuel line and squeeze bulb for a restriction. Ethanol wreaks havoc with rubber. The line could be swollen or deteriorated inside allowing you to create enough pressure to get fuel to the carb(s) but the fuel pump won't be strong enough to pull the fuel through continuously Also check the tube and or filter in the tank if you have one. Good luck

Hey there so I managed to get this thing to run. I found the issue being the throttle plate assembly. The reason the previous owner sold this unit was because he could not get it into gear without it bogging out. Is there a proper procedure to set this throttle shutter/plate. Because currently at base idle or high idle it is still completely closed. I found that if I use a screwdriver to manually open the throttle it fires up & runs great.



I really didnt want to have to buy the repair manual..