Loss of Power at WOT 165hp inline 6

[lakebound&down]

I am losing power after running at WOT for longer periods of time and pulling a tube for only 10-15min. I have recently changed plugs/plug wires, distributor cap, points, condenser, rotor, coil. I have good fuel flow to the carb but can hear what sounds like a suction noise coming from inside the carburetor, while at idle, have yet to check if same noise exists while running but assume it does. All fuel filters are clean as well and WOT on the TACH reads around 4300-4500, if it is accurate. Little by little I am getting this old boat running better, any guidance would be greatly appreciated.

 

[ziggy]

Re: Loss of Power at WOT 165hp inline 6

maybe feel the coil. if it's real hot, it could be the culprit. my '72 trisonic did about what your describing and coil replacement fixed it.
as for the suction noise. a vacuum leak maybe?
if your tach is right. @ 4300-4500 your at or above wot spec. which is 3900-4300.

 

[lakebound&down]

Re: Loss of Power at WOT 165hp inline 6

I just replaced the coil yesterday, but just read in another post to check voltage at the positive side of coil and if I have 12v when key is in run position I might need a ballist resistor? Does that sound right? I know prior to replacing the coil I was getting 12v on the positive side when the key was in run position. I did not check it after replacing the coil, daughter was ready to go, but will check it prior to going out today and report back with my findings. I also read to try and loosen the gas fill cap when experiencing this issue and will try that today as well. Thanks for your help!!

 

[lakebound&down]

Re: Loss of Power at WOT 165hp inline 6

Still reading 12v with key in run position, brand new coil installed yesterday. Does the wire coming out of the distributer goto the positive or negative side of the coil? Just reaching for straws at this point. Stalled to the point of not wanting to start today. Coil was hot, as it is mounted to the side of the engine, so not sure if that matters or how to tell if it is too hot or not. I am going to pull the boat off the water tomorrow and spend the week troubleshooting and hopefully be up and running by next weekend. Tach running right at 4300 all day today. Ran great early on then slowly turned to nothing but "No Wake Speed"

 

[ziggy]

Re: Loss of Power at WOT 165hp inline 6

but just read in another post to check voltage at the positive side of coil and if I have 12v when key is in run position I might need a ballist resistor?

ya don't say what vintage 165? for my '75 L6 there is a resistance wire involved. the way i understand it is. when the starter is engaged the coil see's 12v. to give it a good spark to start it. then after start and yer in run. the current is supplied by the white wire that has a resistance wire in line with it. the resistance wire drops the voltage to the points. thus increasing their live span. weather that makes the coil hot, i dunno if it gets 12v. ya might also check the coil number. all coils are not equal imho. be sure ya got the right one.
the wire dia. attached is pretty much what i got on mine. granted the wire colors are hard to tell. they've faded away over time. i've not checked my voltage when in run. my suspicion is that it'd be less than 12v due to i think i have the resister wire. i'd think yours would need to be the same.
edit. oh,

Does the wire coming out of the distributer goto the positive or negative side of the coil?

negitive side per the wiring dia.

 

[lakebound&down]

Re: Loss of Power at WOT 165hp inline 6

Thanks for the wiring diagram. How can i check and see if my coil is the right one, 76' Mark Twain L6 165hp. I got it from my local boat mechanic at the marina. I also need clarification on how to test the coil. Should the engine be running with the key in run position or just the key in run position boat not running. I assumed, yes bad for assuming, just key in run position should produce a smaller voltage, 6-8v on positive side of coil and 12v when running. I had 12v on the positive side of the coil with the boat not running and the key in the run position. I am pulling the boat off the water tonight, if it starts and runs, and am going to begin my trouble shooting. I will pull the tank vent tube, and begin checking for the resistance wire as well. Please help as the summer is slowly fading away and i dont want to miss one weekend on the water and thanks for your previous/continuing help.

 

[Bondo]

Re: Loss of Power at WOT 165hp inline 6

Thanks for the wiring diagram. How can i check and see if my coil is the right one, 76' Mark Twain L6 165hp. I got it from my local boat mechanic at the marina. I also need clarification on how to test the coil. Should the engine be running with the key in run position or just the key in run position boat not running. I assumed, yes bad for assuming, just key in run position should produce a smaller voltage, 6-8v on positive side of coil and 12v when running. I had 12v on the positive side of the coil with the boat not running and the key in the run position. I am pulling the boat off the water tonight, if it starts and runs, and am going to begin my trouble shooting. I will pull the tank vent tube, and begin checking for the resistance wire as well. Please help as the summer is slowly fading away and i dont want to miss one weekend on the water and thanks for your previous/continuing help.

Ayuh,.... Welcome Aboard,... The 1st thing ya oughta do is go up to the Adults Only section at the top of this forum,....
'n Read up on How yer ignition works, 'n How to check yer fuel system,...

 

[lakebound&down]

Re: Loss of Power at WOT 165hp inline 6

Thanks for the help Bond-o. I have printed off both sections and hope to begin troubleshooting tonight. However, i did go up to my boat last night and i started right up. I removed a spark plug, no water in block. I began checking my fuel filters and when i removed the filter bowl on top of the fuel pump, there was no fuel in there. The spring seemd completely dry and had signs of rust on it. I then started the boat with the cap and filter off. Should this happen?? No fuel shot anywhere, so why is that fuel filter there? the boat sat at an idle with the bowl and filter completely removed. Does this tell anything?

 

[lakebound&down]

Re: Loss of Power at WOT 165hp inline 6

Oh, i checked voltage at the coil with the boat running and there was 12v. I have pictures on my computer at home i will post later of the coil and wires leading into it. I am starting to believe, with 12v at the coil while running my resistance wire is shot??? Y/N??

 

[lakebound&down]

1976 Mercruiser Coil 165hp merc I6

1976 Mercruiser Coil 165hp merc I6

I had a post a month or so ago dealing with loss of power @WOT. I have checked the wires going into the coil and am getting 12v with the boat running and have replaced the coil already. Does the resistance wire need replaced? Can i just use a similar wire or does it have to be something special? Thanks for any assistance

 

[Bondo]

Re: Loss of Power at WOT 165hp inline 6

I had a post a month or so ago dealing with loss of power @WOT. I have checked the wires going into the coil and am getting 12v with the boat running and have replaced the coil already. Does the resistance wire need replaced? Can i just use a similar wire or does it have to be something special? Thanks for any assistance

Ayuh,.... So keep postin' in this thread, so's the previous Info isn't lost,....

I moved yer New thread here, as it's the same topic, 'n you provided NO info 'bout yer motor, in yer New thread,...

 

[hivoltg]

Re: Loss of Power at WOT 165hp inline 6

The only thing that ballast resistor does is increase the total resistance on the coil to .7 ohms or more. Which drops voltage and keeps it cool (ohms law). If you have an internal resisted coil then you don't need an external resistor. I don't think that's your issue tho with the motor.

Do and ohm test on the primary and secondary side to rule it out and verify you have a good coil.

The resistance with nothing hooked up will tell you weather you need that external ballast or not. Less than .7, it needs a ballast. At or over .7, it doesn't. Your contact breaker points will most likely be pitted if this is really the issue.

I agree it kind of adds to the problem here that we are either working with a 9 volt coil or 12 volt coil and we dont know which it is. Put the old coil back in, how it was hooked up before, and eliminate this as the issue.

This problem was happening before you replaced those parts tho correct? So its not the coil causing it.

 

[lakebound&down]

Re: Loss of Power at WOT 165hp inline 6

Yes this problem was there prior to changing my coil out, but i will check resistance on the coil later tonight or tomorrow. i will also take a quick look at the points to check for pits. I am trying to get it up and running and am running out of options. Definately don't want to take it to a shop but if i cant figure it out through here i guess thats what i will have to do. From the thread above the last thing i havent checked is the fuel vent tube.
Lastly, when i was last looking at my boat i took the fuel filter bowl housing off the pump and tried to start the boat. 1) there was no gas in the bowl and my filter wasnt very moist, 2) boat fired up with filter and bowl off with no fuel spraying anywhere, is this common or correct to happen this way?
I'm guessing i should have posted a new thread for this one and will probably be scolded for it but there it is anyway.

 

[lakebound&down]

Re: Loss of Power at WOT 165hp inline 6

This new thread as you call it had the motor size, year and type in the subject so how did i not post any info on it? or maybe i should check the adults only section or read all the other posts on here about my situation. That always helps

 

[hivoltg]

Re: Loss of Power at WOT 165hp inline 6

I would check all the fuel fittings from the tank to the carb.
Make sure no hoses have a crack in them and are sucking air.
I would check the brass 90 fitting going into the tank (its an anti siphon valve with a ball and spring in it) they stick sometimes.

A boat will run for awhile with no gas going to it. Until the carb float bowl empties.

 

[Bondo]

Re: Loss of Power at WOT 165hp inline 6

This new thread as you call it had the motor size, year and type in the subject so how did i not post any info on it? or maybe i should check the adults only section or read all the other posts on here about my situation. That always helps

Ayuh,... You posted post #10 as a thread, mentionin' little of the history in this thread, other than Ziggy's comment,...

Everything that been said in this thread, woulda had to have been said again, as you didn't link to the old thread, which Has All of the history of yer issue, insteada just abit of yer problem,...

If you'd just posted in this thread, about the Same issue, just another question, it all wouda come to the top,...
instead, I merged 'em together,...

Less confusion, All the way 'round,...
Diagnosis is an On-goin' thing, history is continuity,...

Sorry, 'n thank you,...

 

[Bondo]

Re: Loss of Power at WOT 165hp inline 6

Yes this problem was there prior to changing my coil out, but i will check resistance on the coil later tonight or tomorrow. i will also take a quick look at the points to check for pits. I am trying to get it up and running and am running out of options. Definately don't want to take it to a shop but if i cant figure it out through here i guess thats what i will have to do. From the thread above the last thing i havent checked is the fuel vent tube.
Lastly, when i was last looking at my boat i took the fuel filter bowl housing off the pump and tried to start the boat. 1) there was no gas in the bowl and my filter wasnt very moist, 2) boat fired up with filter and bowl off with no fuel spraying anywhere, is this common or correct to happen this way?
I'm guessing i should have posted a new thread for this one and will probably be scolded for it but there it is anyway.

Ayuh,... The fuel filter housin' on yer fuel pump is on the Vacuum side, Not the push side,....
So, ya, that's normal,...

Did you ever read the articles I pointed out,..??

The "How to check yer Fuel system" will lead you to the fix,...