Mercury throttle issues

[Aquamaniac]

Need some help from the Merc experts out there.....
Noticed that the throttle response on my Merc 150 V6  (yep....the Frankenmerc I had to extend to 25") was not at all smooth. Seemed to run poorly in a couple areas of the 'throttle curve' for lack of a better term.
In fact there were a few times it really seemed to have no power at all when throttle advanced, but would then act right after throttle backed off, then on again.

Does this seem to be a throttle cable issue, carbs, fuel, or ??????
Where should I start? I know this motor is a dinosaur......but it is what I have and sure would like it to serve for a good long while (particularly with just dropping $500 on the extension!)
Thanks guys!

[fitz73222]

Too much to write at the moment...We can discuss after work today...

[fitz73222]

No silver bullet here...It's going to be process of elimination. Sounds like an intermittent issue which leads into an ignition malfunction. Does the engine start to miss fire in a certain throttle position but then recovers pulling back to idle or  advancing to high RPM but runs poorly in the midrange? When you push the throttle down the engine just falls flat on its face, does it shut off? Two courses of action; first determine if this is a fueling issue or ignition issue. Pull the plugs and see if any are excessively wet or dry, indicating flooding or lean. See if there is a pattern to how the plugs look. An example would be that all the plugs look wet on the left bank, we may be looking at a bad switchbox; your engine as two, one for each bank. If two to four cylinders across each bank look wet; maybe a bad trigger or broken trigger wire (common) and when you advance the throttle the trigger rotates to advance the timing and the wire opens causing the loss of fire. Your engine had stator issues (very common) which can cause a host of issues from no fire to random fire. Has the under cowl filter been changed? Run the engine on a 6 gallon tank with fresh fuel and a different fuel hose to isolate the boat's fuel system as potential root cause. The goal here is to change how the engine is running by eliminating basic systems. Instead of guessing at this point lets start with fueling and work back into the engine. The good news is your engine is very simple in its design and parts are easily sourced.

[Aquamaniac]

Thanks Farley .....will take her out today/tomorrow and see if issue recurs. If so....then try to work through some of this using your guidance. Dividing up systems sure makes sense. Thanks again!

[GoneFission]

Sounds like a bad switchbox to me.  They can be intermittent and the mota will only run on 3 cylinders, then come back at times.  You can try to isolate which bank of cylinders are affected and change out that switchbox, or just change both of them.  They are about $100 each online:
http://www.ebay.com/itm/Switchbox-Mercu ... 77&vxp=mtr

[Aquamaniac]

Took her out yesterday for a short run. Did not notice any of the 'almost dying' with throttling up. Still seemed to have some transition zone 'notchiness' .....but that might just take me getting used to moving above or below those low/mid/high zones.
Maybe symptom was just some trash/water in line or tank....although fuel separator looks good and had no water in bowl when drained.
Remember....this is all new to me!
Overall, yesterday the motor seemed to idle well, cruised comfortably, and had more get up and go than I could want  

Looking at the prices of used newer motors in 115 to 150 HP range, I sure am keeping my fingers crossed that this old beast will do me right for a good long while.
Will try to digest all the advise and begin to tweak it into reliably performing well. Have been studying shop manual as well.......LOTS of info to make use of.  

Reliable is a keyword. I run an old Harley and hold to 'chrome don't getcha home'. Sure am fond of getting out AND back!  8)  Not to mention 'my captain' is a bit gun shy after steering loss on maiden voyage. Go figure   :P  But my fishing time is directly related to her cruising time....so keeping her confidence level up is a good thing.

Thanks again for the guidance.

[GoneFission]

 Not to mention 'my captain' is a bit gun shy after steering loss on maiden voyage. Go figure   :P  But my fishing time is directly related to her cruising time....so keeping her confidence level up is a good thing.
Thanks again for the guidance.

Good to hear she's running better!    Sometimes just using the motor helps - clearing the carbs, combustion chambers, etc.  

BTW - you are the "Captain" - she is the "Admiral"  

See ya on the water!

[Aquamaniac]

HAHAHA....I stand corrected.

GF : I see you are NC. We call NC home as well. Farm in SE NC.....although the Admiral is doing a lot of arm twisting to sell farm and be in SW FL permanently. Would be big change for this old dog. But the fishing here sure is hard to argue with and pretty enticing. Not to mention I would miss all that freezing cold, snow and ice.

[slvrlng]

Admiral is definitely the right term!!!!  LOL!!!

Aquamaniac, try the canal just north of Blind Pass park on Manasota key early in the morning. Deep natural canal, my great uncle had the seawall put in back in the early 70s. Big trout, sometimes even a tarpon shows later in the year. Pretty skinny water getting from the intercoastal to there but it can be done!

https://www.google.com/maps/@26.9683567,-82.3870817,17z

https://www.google.com/maps/@26.968829, ... jiF2ug!2e0

[seabob4]

Now if only Lewis could convince Bridget to be a State Farm guru in, oh, let's say Venice, he'd be a happy boy!!  

[GoneFission]

Now if only Lewis could convince Bridget to be a State Farm guru in, oh, let's say Venice, he'd be a happy boy!!  

Lew's an ATL guy to da core.  First name basis at Bass Pro, got the vineyard there, knows everybody within 200 miles, etc.  I don't think he's leaving anytime soon...  

[seabob4]

JJ, everytime we chat, somehow, Englewood creeps into the conversation.  Makes me wonder... 8)

[fitz73222]

Took her out yesterday for a short run. Did not notice any of the 'almost dying' with throttling up. Still seemed to have some transition zone 'notchiness' .....but that might just take me getting used to moving above or below those low/mid/high zones.
Maybe symptom was just some trash/water in line or tank....although fuel separator looks good and had no water in bowl when drained.
Remember....this is all new to me!
Overall, yesterday the motor seemed to idle well, cruised comfortably, and had more get up and go than I could want  

Looking at the prices of used newer motors in 115 to 150 HP range, I sure am keeping my fingers crossed that this old beast will do me right for a good long while.
Will try to digest all the advise and begin to tweak it into reliably performing well. Have been studying shop manual as well.......LOTS of info to make use of.  

Reliable is a keyword. I run an old Harley and hold to 'chrome don't getcha home'. Sure am fond of getting out AND back!  8)  Not to mention 'my captain' is a bit gun shy after steering loss on maiden voyage. Go figure   :P  But my fishing time is directly related to her cruising time....so keeping her confidence level up is a good thing.

Thanks again for the guidance.

If you own and maintain an old Harley, you'll do fine with keeping an old Merc running! Try to get in the habit before you put her on trailer after crusing all day is to open her up at least above 5000 rpm for 1/2-1 mile and let it breathe. This exercizes the rings, cleans out some carbon, gets purged of internal puddled fuel and gets it at max operating temp. It's very beneficial for the engine to do this and you'll add life to the engine. If there was ever an engine that didn't mind being twisted hard, it's a V6 Merc.

[Aquamaniac]

Farley: will do. These are the things I need to know.

Bob: we love Englewood. Will hate to leave this coming month, but will be back next year as well if the creek don't rise.

Lewis : now THAT is the place I need! Guess I am a day late and a dollar short as usual
Thanks for the tip. I have been working the mangrove islands and holes north of Rag alley and all down through Rag with pretty good success.

[seabob4]

Bob: we love Englewood. Will hate to leave this coming month, but will be back next year as well if the creek don't rise.

You're not gonna hate that when you see August temps in the 90s...and it's been that way since May!!! :x