Merc 650 idle issues when IN water

[sutor623]

So check it out guys. Two weeks ago I made a post about my motor starting fine on muffs, and then when I took 'er to the lake she would not start. When I got home I could barely get it to start, but it didnt idle until I ran 1 gallon of seafoam and gas through the motor at partial throttle. Changed the main power wire to starter, installed fuel/water separator, and treated the gas with water removing iso-heet. Motor then ran again on muffs, and in a small bucket (didn't sit in the water as much as it would on the lake) and did very well.

I took the boat out today, and it had a little bit of a tough time starting in the morning. (Took about three or four key cranks.) Once she started, she would run well, but ALMOST idle. If I tried to get her to idle, she would die out. But I ran her on the lake all day, and if I kept the revs up just a bit, no problem. Now, if the motor was warm, it would idle, and start up immediately, but after idling for a few, it would die out.

It was suggested to do a leak down test, but the motor pushed the 600lb. boat 34mph with 4 200lb. people, and few hundred pounds of gear. The compression is great, and I doubt highly that it would fail a leak down. Should I invest in a leak-down tester and rule that out, or should I point my finger directly at 45 year old carbs with original fuel lines that probably has some varnish in the low speed jet?

 

[aussieflash]

Re: Merc 650 idle issues when IN water

You may just be idling too low.Adjust idle on lake in forward gear to around 750rpm,or on muffs at aroung 950rpm.
Checking carbs cant hurt.

 

[sutor623]

Re: Merc 650 idle issues when IN water

You may just be idling too low.Adjust idle on lake in forward gear to around 750rpm,or on muffs at aroung 950rpm.
Checking carbs cant hurt.

Cool, thanks man Ill give that I try, although I think that the idle speed is okay. I dont exactly have a tach right now. Would a spark plug change be in order

 

[Gomer50]

Re: Merc 650 idle issues when IN water

These motors are cold hearted.But when warmed up run like a bat out of hell.As I see it pushing that kind of weight and going 34mph not too shabby.These motors have bleed restrictors that over age get sucked up into the motor and can affect idle (nothing to worry about).As stated above adjust your motor in the water and in gear to achieve the best lowest idle in gear.The best I ever got with an old 80hp was around 750RPM and would idle in neutral about 800RPM.Idle set screws should be around 1 1/2 turns out from being slightly seated.If the hole shot suffers give each one 1/8 of a turn out until you get a good hole shot.One thing for sure if trying to adjust your motor on the muffs (This does not work because there is no back pressure to give you positive results)..Happy Boating

 

[sutor623]

Re: Merc 650 idle issues when IN water

These motors are cold hearted.But when warmed up run like a bat out of hell.As I see it pushing that kind of weight and going 34mph not too shabby.These motors have bleed restrictors that over age get sucked up into the motor and can affect idle (nothing to worry about).As stated above adjust your motor in the water and in gear to achieve the best lowest idle in gear.The best I ever got with an old 80hp was around 750RPM and would idle in neutral about 800RPM.Idle set screws should be around 1 1/2 turns out from being slightly seated.If the hole shot suffers give each one 1/8 of a turn out until you get a good hole shot.One thing for sure if trying to adjust your motor on the muffs (This does not work because there is no back pressure to give you positive results)..Happy Boating

Cool, thanks for your input! And yes this motor sure does run like a bat outta hell! What exactly is this bleed restrictor? Where is the idle screw? My carbs are leaking fuel through and it is running down the midsection of the motor, and also out of the port side above water exhaust outlet. It seems as if the float chambers are just draining the fuel out. Is this normal or do I need to tighten up the float screws? And lastly, why do you think the motor is a bit hard to start, is it because like you said it is cold hearted?

 

[Mi duckdown]

Re: Merc 650 idle issues when IN water

serial number. ??

 

[sutor623]

Re: Merc 650 idle issues when IN water

It is a 1967 4 cylinder. Serial number is 2200000ish.

 

[jbjennings]

Re: Merc 650 idle issues when IN water

So check it out guys. Two weeks ago I made a post about my motor starting fine on muffs, and then when I took 'er to the lake she would not start. When I got home I could barely get it to start, but it didnt idle until I ran 1 gallon of seafoam and gas through the motor at partial throttle. Changed the main power wire to starter, installed fuel/water separator, and treated the gas with water removing iso-heet. Motor then ran again on muffs, and in a small bucket (didn't sit in the water as much as it would on the lake) and did very well.

I took the boat out today, and it had a little bit of a tough time starting in the morning. (Took about three or four key cranks.) Once she started, she would run well, but ALMOST idle. If I tried to get her to idle, she would die out. But I ran her on the lake all day, and if I kept the revs up just a bit, no problem. Now, if the motor was warm, it would idle, and start up immediately, but after idling for a few, it would die out.

It was suggested to do a leak down test, but the motor pushed the 600lb. boat 34mph with 4 200lb. people, and few hundred pounds of gear. The compression is great, and I doubt highly that it would fail a leak down. Should I invest in a leak-down tester and rule that out, or should I point my finger directly at 45 year old carbs with original fuel lines that probably has some varnish in the low speed jet?

I would follow your own suggestion. You shouldn't have fuel leaking out of your bowls. If it's been more than a couple of years since the carbs were cleaned, and you still are using original fuel lines......... You're asking for more trouble than an idle problem. If your high speed jets are just a little lean, it could spell disaster for your pistons.
Stop worrying about it and bite the bullet and clean your carbs.
JBJ

 

[sutor623]

Re: Merc 650 idle issues when IN water

If your high speed jets are just a little lean, it could spell disaster for your pistons.

Yeah man, makes sense to me....

 

[Texasmark]

Re: Merc 650 idle issues when IN water

I have a 90 3 cyl and have a similar issue. It is extremely cold natured, but once lit off for the day it performs flawlessly. My manual says 675 +/- 25 in F gear in the water at idle throttle setting. Number is set by the idle screw which controls the movement of the throttle lever in the engine. On my engine it advances/retards the timing from the starting point of 5 BTDC. Course it sits in the garage for 2-3 months at a time and I know that is part of it.

HTH,

Mark

 

[brandon110]

Re: Merc 650 idle issues when IN water

clean the carbs. and replace the fuel lines even if they look ok from the outside the inside of them will fall apart. if you pinch to fuel lines and you find a soft spot that is a sign that there erroded on the inside. you may find the black pieces of fuel line in the carbs. that may be your issue. they get stuck in the seat of the needle and seat. Also i highly reccomend that you do not add iso heat to the gas expecially in a 2 stroke. reason is your gas is already 10% alcohol by you adding more alcohol to it you can dilute your oil. chances are you didnt put a whole bottle in a small amout of gas but there has been blown up powerheads due to this issue so be careful with it.

 

[sutor623]

Re: Merc 650 idle issues when IN water

Word. Well guys I just went ahead and did it. They sure do tuck the carbs of these motors in deep, but I pulled the carbs and fuel pumps out. I am also going to change the distributor cap, wires, plugs and timing belt. While I'm in there I want to take care of everything that I can. Some of my wires in the internal wiring harness are corroded to the point of extreme fragility, so I am going to change those out. Should be a pretty ready-to-go motor when I'm done with her....