'83 Mercury Tower of Power Curious Issue

Danny C

Petty Officer 2nd Class
Joined
Dec 3, 2010
Messages
124
Took the boat out yesterday, started it up and ran across the lake with no issues except a bit of surging on its way up to WOT. Once it got there, ran great. On the other side of the lake, I idled around for a bit then when I went to throttle up again and it bogged down and died. I could idle up in neutral bet every time I put load on it bogged and died. I was finally able to ease the throttle up and get cylinders 1 and 2 to run enough to limp home (other 4 not firing). If I tried to throttle too high it bogged and died again. Halfway across the lake while limping I tried a little more gas and all of a sudden the other cylinders kicked in one at a time and started running great again. Once they all started running, I could keep going but if I throttle down to idle and throttle up again same issue, I would have to bably it through the lower end of the throttle until all cylinders would catch. It seemed to get better the more I ran it through idle to full throttle cycles.

I am thinking it is a carb issue but really am trying not to have to rip the carbs apart. I rebuilt them last year and went out several times with no issues. Fogged them for the winter and now this. Could the fogging oil have gummed up the system? No tach so cannot give specific rpms. Tried adjusting air screws with no results. Couldn't pull and check plugs while on the water. Left tank as low as possible for winter and drained even further before topping off with fresh gas this year. Maybe bad gas??? bad carbs???

Thanks,
Dan
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,047
Plugged carburetors can lead to major engine damage from a lack of oil.---Test spark as it must jump a gap of 7/16" on all 6 leads.---Compression test does not hurt either.
 

mr 88

Commander
Joined
Nov 3, 2010
Messages
2,115
Classic symptom of the idle screws needing adjustment.Turn one idle screw at a time out about the thickness [or a tad more ]of the screwdriver blade. Do the top one and then test. Then move down to the next carb and test,then the bottom. Repeat untill it works,you may lose some of your smoothness at idle but thats the price you pay to go fast. These carbs have basicaly no transition circuit from low speed to high,except for the gas from the low speed circuit.Been there done that.....
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Since it happened after it was running well, I would suspect some dirt was sucked into the carbs. First check compression to make sure no damage, Next clean all fuel filters and change the water separator if you have one. If it doesn't get better, you probably should check the spark and finally, clean the carbs.
 

Danny C

Petty Officer 2nd Class
Joined
Dec 3, 2010
Messages
124
Thanks for the responses. I had spark on all plugs before I went out. Can too much fogging oil cause carb clogging? I know I was excessive last year when winterizing. I have never done a compression check. I assume I need to buy a plug gauge of some sort, install it and turn over the motor for each cylinder. Am I on the right track? What about the fact that it seems to run well at idle but not under load. That is one thing that made me suspect compression until all cylinder started running again.
 

mr 88

Commander
Joined
Nov 3, 2010
Messages
2,115
Read my 1st reply again.Your problem is not compression,its the idle screws. If it makes you feel better go do a compression test. ME,I would start out with the idle screws. You stated it runs good once you get past the no accelertion zone,so why do a compression test and dig any further than you have to if it runs okay except for the acceleration.YOUR problem is the transistion from slow to fast speed and again as I already stated , the carbs on the Towers are not very good at doing that.Do a search on this forum for your issue and you will get the same answer...No over fogging it with oil or whatever will not clog up your carb,the gas will wash everything away.
 

Danny C

Petty Officer 2nd Class
Joined
Dec 3, 2010
Messages
124
Thanks again Mr 88. I did not really think compression either but wouldn't hurt to check them if for no other reason than I never have. I was probably less than clear but once I get all cylinders running, I can work up and down the throttle range without issue. But after idling for awhile, as you said, it is that little spot from idle to getting going that is bogging on me. When I had the motor running on 2 cylinders, with the wife driving, I adjusted the air/fuel mix screws while under way. I felt no change. I did adjust them a lot at a time and not finely as you recommended. Just to be clear, when you say idle screw, you are talking about the adjustment screw on the carbs and not the idle stop screw for the throttle correct? Additional info, I rebuilt the fuel pump before going out (looked clean) and emptied the fuel filter (also clean).
 

mr 88

Commander
Joined
Nov 3, 2010
Messages
2,115
Yes I am talking about the screws on the carbs. To verify they all are working when at idle turn each one of them in until motor starts to die then back off a 1/8 of a turn.Now when you go out you have a base to work with. Take the face plate off and use the hole in the front bracket to access the idle screws.Start with the top screw and turn it out 1/8 of a turn,try acceleration. Still the same move on to the middle and repeat,then to the bottom.If still the same start at the top and repeat until it accelerates crisply.
 

Georgesalmon

Lieutenant Commander
Joined
Apr 14, 2012
Messages
1,793
Good ideas. I would turn all the screws in to just stop lightly, then back out 1.5 turns for a starting place since you monkeyed with them a lot. Then adjust as explained above. They will have little effect at running speed, just at idle and when you punch i.
 

Danny C

Petty Officer 2nd Class
Joined
Dec 3, 2010
Messages
124
Just wanted to stop back in with an update. I was able to get out on the water after work this week. I was a little skeptical that the screws were the issue only because it had run so good before and I have changed nothing. I do not know why I doubted. I dialed in the carbs by going through the range of the screws and the engine ended up purring like a kitten. Still curious as to why it became out of tune out of nowhere but bottom line is it worked. I will find out if it sticks tomorrow on the water. Thank you all for your help.
 
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