Model 402 stalls at low idle

[slamb478]

I have a late 70 early 80 model 402 that will not idle well and stalls when I put it in gear. I have to start it with the high idle lever up and manipulate the main throttle and idle throttle to keep it from stalling when putting it in gear. Once past the initial desire to stall it runs great at a little above "no wake" through wide open speeds. Once it is warm it idles high but if it cools down for 15 minutes it is hell to start (idle lever full up) and get in gear without stalling. Seems that the spark plugs have a good bit off build up/carbon as well and when ever I take them out there is fuel on the threads. It has good compression >120psi. I have good fuel (non ethanol with sea foam), good fuel lines, filter, and the mixture screw is out 1.25-1.5 turns. Any help would be greatly appreciated.

[boats.net]

Have you completely cleaned and repaired the carburetor?

[slamb478]

I have had the motor "repaired" by a local guy, he replaced the carb with one he had lying around, i assumed he cleaned/overhauled it. I am going to remove the carb and take it apart and clean it myself as well as check all gaskets. When I got it back from him two of the crank case bolts we loose (about 1/8 inch backed out), I assumed tightening these two bolts would fix it. Any suggestions on other things I might need to look for. Not sure how easy it would be to check the reed valves without removing the powerhead. Thanks in advance for any help, rode the boat this past weekend on the local river/lake and it is like a slice of heaven on earth so it would be nice to have the motor reliable.

[boats.net]

Check the timing too.

[slamb478]

i have taken the carb apart, cleaned really good, shot carb cleaner through all the jets and passageways, all it perfectly clean. I tried to set the timing but cannot get the engine to idle, I have to start it with the high idle lever all the way up which makes putting it in gear to set the timing per the SELOC manual very difficult. At the lowest possible speed I can get it to idle in gear or in neutral is with the cam barely touching the primary pickup arm and the timing at about 8-10degrees BTDC. I have adjusted the idle screw the best I can but can still only get it to run at about half high idle. A shade tree mechanic worked on it last and the carb that he put on it does not match the description in the seloc manual. The carb installed has a clear tube attached to the top of the bowl to the idle mixture area on the arb. The clear tube at the top looks to be a fuel air tube as it's attached to the top of the bowl and the brass fitting where it connects to the bowl allows air in as well. I have read on some of the forums of people having problems with exhaust at idle speeds. Once in gear the boat runs fine at high "no wake" speed all the way to WOT so it has me very stumped. Any help would be greatly apperciated.
Thanks,

[boats.net]

Definately sound like it could have the incorrect carburetor. Unfortunately I cannot think of anything else to tell you to try.

[slamb478]

after some looking on several of the websites that have parts break downs and schematics I have determined that the man that worked on the motor took a model 402 lower unit and mounted a Mercury Model 40 power head on it, hence the different looking carb. Still cannot figure out the idle problem, the procedures per the SELOC manual are the same for both models.

Thanks in advance for any help

[boats.net]

On the motor there is a freeze plug with that motors serial number. What is the motor serial number?

[slamb478]

Sir, i am not sure if i found the freeze plug you are referring to but on the top of what the Model 40 parts lists show is the thermostatv cover right forward of the coils on the top of the engine the number stamped on it is 3801 66844 around the top of the cover. Also on the right side of the cylinders is the number 351-6662, the head has 1024-6651 and the exhaust plate on the left side of the engine has 55157. Where would this freeze plug be? does is resemble a car engine freeze plug?

Thanks,

[slamb478]

also when I cleaned the carb I made sure that the idle air mixture screw had a good seat by using a sharpie to coat the needle portion of the screw, inserted it and screwed it all the way in then with light torque to verify it was not worn or off center with the passageway, there was a perfect ring where the needle made contact with the seat.

Thanks again.

[boats.net]

Yes the freeze plug is similar to an automotive plug, however this plug would have a number stamped in it. Be sure the the Idle air mixture screw is turned out about 1.5 turns.

[slamb478]

sir, where on the powerhead would this freeze plug be, for some reason i do not see it

I have the idle air mixture screw backed out 1.25, it seems to run best there

Thanks,

[boats.net]

I am uncertain of the precise location.

[slamb478]

I took the boat to a local guy and he changed the main jet, apparently the one in it was too big and flooding the engine at low speed. Now the motor will idle great but I am still having trouble setting the timing per the seloc manual which states to put it in a test tank of the boat in the water, place the motor in gear and set the timing to 6 degrees BTDC and the cam barely touching the throttle. I placed the boat in the water still on the trailor and attempted to do this but the engine would stall as I placed it in gear and attempted to advance the throttle. Any advice or guidance on factory setting for the throttle and timing and any help would be greatly appreciated, I cannot seem to find the serial number, if I could i would purchase a Mercury service manual. Thanks

[boats.net]

You don't have to put in gear to set idle timing, just let engine idle and throttle up to set pickup timing.