Trouble help with 1969 Tower of Power 1250 power issues. stumbling now.

Well my awesome boat is done. Spent lots of time running wires and mounting everything as clean and professional as I have ever done. Very proud of this boat that Mike and Mike Blessed me with.

Got out to test today and my big old Merc tower after 8 years of maintance free operation (pretty good for a motor made in 1970.) Well as you know I had rebuilt one of the carbs and cleaned the other 2 before I sank my old boat and motor was running fine until the boat started to sick. At that time it started missfiring and chugging upon acceleration. My thoughts at the time were water in gas from boat sinking before I knew it.

So I put cleaned dry plastic 14 gallon tempo tank with new fittings and new hoses in new boat. Drained all 3 carbs. Ran new gas with Stabil and Seafoam with my always used Quicksilver 2 stroke oil. Have new marine water seperator and extra see thru glass fuel in line filter after bulb. So I thought all would be good. NOTTTTTTTTTTTTTTT

Motor starts right up and idles smooth and accelerates smooth out of gear. However when put in gear the motor shakes and badly stumbles trying to get past 12mph. You can feel it like it wants to catch and take off but it seems to missfire and will not power up and shakes and grunts. Like and old man like me . Squeeze ball and no change. Ball solid. Its getting gas. When it dies smoke comes out of bottom carb. Like its not running right in gear. Then it would not run much at all. My thoughts are now fouled plugs. These plugs are 5 years old but I clean them. I can start it again and it idles fine. But under power it seems like it will blow up!

Do not have funds to rebuild so if it can not be fixed by me or friends it will have to sit until I can fix it or replace. The Honda 4stroke kicker does me good so I can still fish my close areas. Just kinda bites that I am having issues with this old motor that has treated me right for years. Any old merc guys with some troubleshooting tips for me?
Will check compression tomorrow.
Thanks

Tod

Its a Mercury 1970 model 1250hp 6 cyl tower of power.
Please note: although no board code and smiley buttons are shown, they are still usable.

Was the distributor under water ??------------Did you take it apart to clean all the bits.---------------Have you checked for strong spark ( jump a gap of 3/8" ) on all 6.----------------How long did the motor run when recovered from the " sinking ship " ---???

I would start with new plugs. 5 year old plugs, *though clean* on an engine that sank...
then do that spark test. Next would be to check your stator and trigger with an voltmeter. That might help isolate your problem.

Did you sink in salt or fresh water?

First off thank you so much for helping!

Next, To clarify the motor was never underwater. The transom split but I was able to get it to beach before totally submerged. No part of motor besides lower unit was exposed to water and it was in fresh water FYI.

I was going to try new plugs. However the Merc shop manual says that unless the center probe is less then a 16th from base do not replace. All still are past base. Should I still try and replace?

No I have not checked spark, need another person to crank motor so I can see.

The motor will power up to 5000 rpm without stumble with no load. Just stumbles in forward.

ANother thing I notice. I can get it to hold 9-10 mph as it stumbles and grunts and shakes in forward. If I quickly put out of gear and gas up to high rpm, then get back to idle and put in gear. It starts to run better to about 16mph for a few seconds before starting to run terrible again. Like it wants to go.

All motors will wind up in nuetral !!-------That is not a test and it means nothing.----------Test for proper spark on each cylinder !!-----------------------Do not run motor untill you verify that carburetors are absolutely clean !------Blockage in one carburetor on your motor means no fuel to 2 cylinders and no oil either.---------You risk ruining a fine motor !!

Thanks. I removed all 3 carbs and all were clear. I still cleaned them with cleaner and seafoam then blew them out. No obstructions. Put back on motor and still stumbling bad. I can shoot carb cleaner one at a time in each carb and idle goes down before picking back up. So all cylinders getting oil and gas. Did compression test and all fine. Very odd. I am about to try plugs as multiple people on forums have said they had same issue with bad plugs. Only thing is Merc manual says these plugs as long as probe is still long enough (measured and mine are) are not to be replaced as they are foul proofs. Ugg, pulling hair out of head.

Have you checked pick-up timing ????------------------Have you tried opening the low speed mixture adjustment ???--------------Have you used a timing light ( on each cylinder ) to see if the issue is spark related or fuel issues ???

Try this next time you're on the water: Just before opening the throttle, tap the choke ON. Don't mash the choke button (or key switch) and hold it--just tap it for a split second. If the motor responds and starts taking throttle, then it's bogging due to a lean condition (which is common).

Now, if the above trick lessens, or cures the bog, then you have two options: Reset the idle mixture screws (more on this below), or drill out the holes in the butterflies (as I have done with great success on triples, which are basicahalf an in-line six).

The Fastjeff Idle Adjustment Technique: Tie the boat to a dock so it can't move, warm the motor thoroughly, then put it in gear. Dial the best idle possible for the carbs, taking your time to let each adjustment settle out. Then add 1/4 turn CCW (richer).

Next, with the throttle up to the point just BEFORE the carbs start to open, slowly flip the carbs open via the lever on top. Did it bog and die on you, or did it respond? (Motor MUST be in gear.) If no, flip it open a it faster this time. Still good? If yes, go boating.

Now, if that sucker still bogs on you, especially when you slowly flipped the carbs open, then get out your drill. Remove the carbs (again!) and drill out the holes in the butterflies to at least a 1/16 inch drill size larger. (I used a 1/8" bit.) Most of these carbs have three vertical holes to the left side--them's the ones. I have done this on two triples and the results are superb! Instead of a bog (regardless of idle adjustments) the thing roars out of the hole like a drag boat!

Jeff

Thanks guys.> I adjusted the idle mixture screws on basice 2 to 2 and half turns from fullt engaged as per shop manual and then fooled based on in gear idle and still no love.

In fact new symptons have appeared. After pulling all 3 carbs and cleaning them again. PUt them on and adjusted I took boat for run. Motor was not shaking as much but still could not initially get over 12 mph on water and was still not powering up. As I went along it got less and less power. To the point of I could only start it and as soon as put in gear it would die. Sure seeming like something other then fuel issue. Going back to plugs. Could it be an electrical issue. This is very odd. Gas is new non ethanol and I have good fuel delivery to carbs.

No I have not touched timing ever and have not tested for proper spark.

Thanks friends.

Proper testing will get you somewhere !!!-------I hope you replaced the water pump impeller -----------It is an absolute MUST DO on that motor.---------Go ahead and test for proper spark , It needs to jump a gap of at least 3/8"--------------If it does not do that there is something wrong !!!