1972 Mercury 650 65 hp 3 cylinder thunderbolt (Power/Throttle/Spark)

[dremd911]

I have a 1972 mercury 650 65 hp thunderbolt 3 cylinder outboard...phewww

now that the title is out of the way, i took the boat out as motor ran great out of the water. When I put her in the water it was almost as though power was not there anymore.

So when i put her in neutral and lift the starting throttle engine screams and responds well...

when i first put it in forward, throttle responds to me pushing forward but when i reach a certain point in throttle pressure, the engine would start to putter out, but i could return it to former position and it will continue to run fine but slow....well i continued to chase the fish at the speed motor would allow and all of a sudden, engine started to pickup and run full throttle and even faster if i pushed down, no longer did i have a loss of power and the chance of puttering out?????

so then i kept driving around with all that great power and after putting engine in neutral and trying again, power was not there again???

Do I have a fuel problem, should i change my spark plugs, tune up, timing, carb clean, etc... i have no clue what to try first

Any help would be great and if anyone has similar engine and experiences similar problem, please let me know

The engine starts everytime no problem, i think i have a fuel problem, any tips would be great..

P.s...i used fresh gas, so thats not an issue

 

[avenger79]

Re: 1972 Mercury 650 65 hp 3 cylinder thunderbolt (Power/Throttle/Spark)

I have a 1968 650 with similar issues. it seems to be a fuel issue. mine will run good out of the chute. when i first put her in the water we're good to go. if however I stop for anything and go to start again motor runs sluggish at best. throw the shifter forward and it dies immed. in N raise the idle lever it will scream. I think it is a fuel issue with the pump starving out or not being properly synched with throttle levers and motor.
was reading in the manual how to time and synch everything. I hope to try it soon, if it works I'll let you know.

forgot to add I have had carbs and fuel pumps rebuilt, has new plugs, new fuel tank, new lines etc.

 

[dremd911]

Re: 1972 Mercury 650 65 hp 3 cylinder thunderbolt (Power/Throttle/Spark)

did you end up trying out the timing?

I just got some new plugs in it, and i put the fuel line off the tank directly to fuel pump, a buddy of mine told me this helped his engine.

I am also going to clean all screens and filters and see if that helps at all but I think I need to bite the bullet and get all the timing and a tune up done by an outboard mechanic, just dont have the cashola right now

 

[Faztbullet]

Re: 1972 Mercury 650 65 hp 3 cylinder thunderbolt (Power/Throttle/Spark)

Check your sync and link set up, replace the fuel pump diaphram(water cooled) and if it has set up more than 6 months clean the carbs and replace the fuel lines as these can look good on the outside and swelled shut internally...

 

[dremd911]

Re: 1972 Mercury 650 65 hp 3 cylinder thunderbolt (Power/Throttle/Spark)

Check your sync and link set up, replace the fuel pump diaphram(water cooled) and if it has set up more than 6 months clean the carbs and replace the fuel lines as these can look good on the outside and swelled shut internally...

I dont have much mechanical skill, is there a good post on how to replace the fuel pump diaphram or how to replace and clean fuel lines?

 

[torontotony]

Re: 1972 Mercury 650 65 hp 3 cylinder thunderbolt (Power/Throttle/Spark)

Dremd. I have a 1975 650 65hp motor and I have exact problem 100% I have replaced the hoses and no change on mine. I replaced right to the tank with no positive results, but I have a new tank changed the plugs and wires , cleaned the carbs still no change! I have good compression in all 3 plugs ,now im stuck ,awaiting some advice along with you on this problem cheers! Tony

 

[dremd911]

Re: 1972 Mercury 650 65 hp 3 cylinder thunderbolt (Power/Throttle/Spark)

glad its not just me...but sad there is no solution. on a different note, i put the line from the gas tank directly to fuel pump and put three new spark plugs in, i started her up and she was wonderful. I felt like i could take the boat for a flight, but after going to neutral, i lost the full power again and only had half throttle. Then I turned off engine, started up again and had fullllll power again, so spark plugs definately helped, time for a fresh gas tank with oil. Best part was, I ended up towing in another guy who was telling me i had no compression in my motor hahahah

 

[avenger79]

Re: 1972 Mercury 650 65 hp 3 cylinder thunderbolt (Power/Throttle/Spark)

did you end up trying out the timing?

I just got some new plugs in it, and i put the fuel line off the tank directly to fuel pump, a buddy of mine told me this helped his engine.

I am also going to clean all screens and filters and see if that helps at all but I think I need to bite the bullet and get all the timing and a tune up done by an outboard mechanic, just dont have the cashola right now

hey dremd911 i haven't had a chance to look at it yet. house decided I needed to work on a water softener instead. LOL hoping to get to it in the next week or two.
do you have the manual on the engine? it is very thorough with it's descriptions of how to do things. I would recommend getting one if you plan to keep that engine.

 

[dremd911]

Re: 1972 Mercury 650 65 hp 3 cylinder thunderbolt (Power/Throttle/Spark)

hey dremd911 i haven't had a chance to look at it yet. house decided I needed to work on a water softener instead. LOL hoping to get to it in the next week or two.
do you have the manual on the engine? it is very thorough with it's descriptions of how to do things. I would recommend getting one if you plan to keep that engine.

Ya, I have the manual, and I have been troubleshooting with it...i just need to learn the lingo and parts so i can master the engine. Seems like a great little engine, minus this fuel issue it has "sometimes"

 

[avenger79]

Re: 1972 Mercury 650 65 hp 3 cylinder thunderbolt (Power/Throttle/Spark)

i know that feeling. I can work on cars, trucks, motorcycles, you name it. but this outboard engine configuration completely baffles me. it's probably more an issue of feaar of a new thing but still I shudder at the thought of actually digging in there too deep. LOL

 

[torontotony]

Re: 1972 Mercury 650 65 hp 3 cylinder thunderbolt (Power/Throttle/Spark)

glad its not just me...but sad there is no solution. on a different note, i put the line from the gas tank directly to fuel pump and put three new spark plugs in, i started her up and she was wonderful. I felt like i could take the boat for a flight, but after going to neutral, i lost the full power again and only had half throttle. Then I turned off engine, started up again and had fullllll power again, so spark plugs definately helped, time for a fresh gas tank with oil. Best part was, I ended up towing in another guy who was telling me i had no compression in my motor hahahah

hey dremd I took my carbs off today and found 1 spring on lower carb was not attached correctly so I cleaned the carbs and fixed the spring ,changed plugs and away I went .I rode around like mad for 20 min. starting and stoping no problem after mabe 1 hr my motor bogged down again and wouldnt start !! after pulling plugs I noticed they were very dirty(fowled Im thinkin } so I will change plugs and try again . good luck

 

[dremd911]

Re: 1972 Mercury 650 65 hp 3 cylinder thunderbolt (Power/Throttle/Spark)

So i think i finally figured out the engine, i changed the spark plugs and I put some fresh gas in with the CORRECT amount of oil mixture. On my previous tank, I put double the oil ...so now it runs great, i took the boat out three different occassions and everytime it ran great. Except the last time when I went out and it didnt start, i think its the solenoid, i need to check it but it will wait until after this dam hurricane

 

[torontotony]

Re: 1972 Mercury 650 65 hp 3 cylinder thunderbolt (Power/Throttle/Spark)

great you got it goin

 

[dremd911]

Re: 1972 Mercury 650 65 hp 3 cylinder thunderbolt (Power/Throttle/Spark)

I ended up having to replace rectifier after i got stuck out in the water, and while i was there i changed up some wires that looked frayed. Motor runs great now, just have to let it fire slowly, still cant slam throttle down and expect full power.

Anyone know if a tilt and trim can be added to a 650 1972 65 hp 3 cylinder thunderbolt. From my research there was not one made. If i could get a cheap one on ebay, could i add it to this motor, what kind of work am i looking at?

 

[ETS Relic Runner]

Re: 1972 Mercury 650 65 hp 3 cylinder thunderbolt (Power/Throttle/Spark)

And yet another member here with the same problem(s).My motor is a '73 Mercury 650 65 hp 3 cylinder with rebuilt carbs,new fuel line, new fuel pump diaphram,new plugs.Even compression and spark on all three!! Motor winds up,and idles well in water.Runs at half speed,no plane off.Then turn it off,start it,and no wind up at all! Idled in gear back to the dock.New plug wires needed? An air leak? Will soon change primer bulb.May need to be timed.Any advice is much appreciated.

 

[R_Woj]

Re: 1972 Mercury 650 65 hp 3 cylinder thunderbolt (Power/Throttle/Spark)

Hey guys, I just inherited this motor from my Dad... he had the boat buried with crap in the garage for the last 20 years so it's got pretty low hrs (he in turn got it off a guy who bought it new and wrecked the boat in the 1st year of ownership and thereafter kept the motor in the basement). I remember he had us out water-skiing when we were kids and we had the problem you were describing. I seem to remember it would always perform better after he had a mechanic "make adjustments". My Dad was adamant that the mechanic insisted that we only use 'Quicksilver' 2-stroke oil.. and maybe it was the placebo effect... but this problem seemed to be minimal when he sprang for the cost of it. Maybe using it would help you?

I just put the 650 on a 14.5 glastron skiflite (T-152) and the guy who did the switch-over (took off the dead evinrude 70) said that the 3-cyl Merc 650 is more like a 50HP motor. I guess marine mechanics don't like the 3-cyl mercs of this era. He said the evinrude was way better motor. Anyway, I was wondering if this problem might be the result of the motor being 'bogged-down' or under powered? I guess that wouldn't explain why the problem goes away when you re-start.... hmm...

Oh, btw.. does anyone know what the max RPM or the optimal RPM for this motor is? I plan on installing a tach so I can figure out the best prop pitch... I used the 'prop-wizard' at <http://www.watercraftservices.com/Propwiz.php?pageID=> it's suggesting maybe a 13P... I had 4 in the boat last weekend with a 15P and it had trouble planing unless someone sat in the bow....

Regards,
Rob

 

[ETS Relic Runner]

Re: 1972 Mercury 650 65 hp 3 cylinder thunderbolt (Power/Throttle/Spark)

I'll run the Quicksilver oil after this tank,thanks.My current problem is when I shift the gears into forward,motor bogs and dies.Seems to shift a bit hard,so I must check lower unit oil.Also bogs comming out of idle.
About your prop pitch.I run a stock 14 P and that is original.There is a complete chart for all the Mercs on MasterTech marine.com.Go to that site,click on props,and you'll find it.Has all the speeds and RPMs.

 

[pyro-1955]

Re: 1972 Mercury 650 65 hp 3 cylinder thunderbolt (Power/Throttle/Spark)

So i think i finally figured out the engine, i changed the spark plugs and I put some fresh gas in with the CORRECT amount of oil mixture. On my previous tank, I put double the oil ...so now it runs great, i took the boat out three different occassions and everytime it ran great. Except the last time when I went out and it didnt start, i think its the solenoid, i need to check it but it will wait until after this dam hurricane

Ok, I have a similar issue, and was wondering what the CORRECT mix ratio is??? I'm guessing I made the wrong mix, I believe my mix in the current tank is 50:1 is this correct? I know I looked it up somewhere and that was the recommendation, definately would like the correct one.

 

[R_Woj]

Re: 1972 Mercury 650 65 hp 3 cylinder thunderbolt (Power/Throttle/Spark)

I run 50:1. I've heard people say that with newer/higher quality oils (TCIII) you can run a little leaner; which makes some sense... my strategy is to err on the lean side. Have you guys tried running high-test? Just recently I got some crappy 87 octane gas and had lots of problems with bogging... last time for that.. I'm going to stick with 91 minimum... not worth the $avings to deal with that crap. I wonder if it's a fuel quality thing. These motors would have been designed for leaded fuel no?

 

[R_Woj]

Re: 1972 Mercury 650 65 hp 3 cylinder thunderbolt (Power/Throttle/Spark)

dremd911 I think I might be having solenoid issues too... I'm finding that sometimes she does not want to turn over and just 'clicks'. I'm going to try taking the leads of the solenoid and cleaning them... I know it's not the battery... brand new! Did you end up replacing your solenoid?