idle issues

[circuttracer1]

i have a 1979 larson manta 17.02 foot 140 mercruiser i/o. have replaced lifters, pushrods, and rockers. installed pertronix ign. after rebuilding dist. dist spring towers for the mechanical advance weight had worn out the dist plate. so i tig welded the spring towers in place at 90 deg angle. had to play with different springs to find correct spring to make total adv. of 28 deg at 2200 rpms. i want more adv. but will mess with it later. When i fire it up cold with a little throttle, she fires instantly. after warmup on pucks, 145 degs, i bring idle down and is set at 750 rpm. NOW LETS GO TO THE LAKE!!!! put her in, fire her up, and everthing is good. O.K. lets go wide open throttle for a couple of miles and shut her down to unload a skiier. When i come to a stop the motor is lding at around 11 00 to 1200 rpm and slowly creeps down to set idle, maybe in 30 to 45 seconds. i shut her off, unload skiier, and when i try to restart motor, i usually have to give her a little throttle for a few seconds and hurry to put her in gear so she wont die. choke is set and works perfect. just seems like after shut down, she just does not want to idle correctly in any situation after normal start up and running her. checked for vacuum leaks, she has NONE. TIMING IS SET AT A STEADY 6 DEG BTD, AND I MEAN STEADY. I HAVE BUILT TO MANY SMALL BLOCKS TO COUNT AND I HAVE NEVER SEEN A TIMING MARK AS SOLID AS THIS ONE IS. IT HAS NO MOVEMENT WHAT SO EVER. and as set, i get 22 deg of adv plus initial 6 for a total of 28 deg. I just do not understand how the idle can fluctuate over such a broad range of rpms. Home on pucks after warm up,,,700 to 750 rmp. then to lake and idle after using her just seems to have a mind of her own. any where from 1200 down to almost no idle at all. plugs look great, compression is just OK. 125 to 130 psi in all cyliders, but even across the board. can someone please give me a direction to go to. i am really up for suggestions. i have a good idea what it is but just want to be reassured before i spend money that i really do not have. my wife is starting to say sell this d### thing , take the loss,and move on. but she is in such good shape for a 3rd owner boat that i really want to keep her,. advice needed

 

[NHGuy]

Re: idle issues

Take your tools out on the boat and run it as you did the day she misbehaved. Drop your anchor.
Do a rev up and see if it slowly returns to idle. Check your timing during this rev down to see if the advance is too high and returning to base too slowly, holding up the engine speed. If yes you might recheck your distributor work. Maybe the advance is sticky or weak on the returns.
After that, shut it down, remove the throttle cable from the carb and restart it, rev it to whatever rpm is your problem point and allow it to idle without the throttle cable attached. See if it still does the slow drop to idle. If it does you have eliminated the linkage as a culprit.
And if it's not the distributor or the throttle maybe you have an internal carb issue.

 

[circuttracer1]

Re: idle issues

Take your tools out on the boat and run it as you did the day she misbehaved. Drop your anchor.
Do a rev up and see if it slowly returns to idle. Check your timing during this rev down to see if the advance is too high and returning to base too slowly, holding up the engine speed. If yes you might recheck your distributor work. Maybe the advance is sticky or weak on the returns.
After that, shut it down, remove the throttle cable from the carb and restart it, rev it to whatever rpm is your problem point and allow it to idle without the throttle cable attached. See if it still does the slow drop to idle. If it does you have eliminated the linkage as a culprit.
And if it's not the distributor or the throttle maybe you have an internal carb issue.

iwill give it a shot. ido know that the timing drops back to 6 degs even at 1200 rpms. already checked that