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60hp 2 stroke idle & WOT issues

B

boardhauler

Contributing Member
I have a 1997 MM 60hp 2 stroke. It was in storage for 4-6 years after I bought it, without anything drained/prepped. So I......

rebuilt carbs
new pre carb fuel filter & hoses
rebuilt the fuel pump (main gaskets/diaphragms only not the valves)
drained the fuel tank, cleaned
new water separating fuel filter
new plugs
new water pump impeller, housing, gasket
new gear oil
fogged the cylinders with seafoam
put 50:1 oil in the fuel tank, just in case the oil injection had an issue

I ran it out on the water 2 times over 2 days. Overall it ran like a scalded dog, hit 39 mph in my 16' aluminum flats boat. Maybe it was not perfect, as I had not run it before or had any experience with older 2 strokes. The only issue was when I first started it and idled out of the canal, the overheat buzzer went off, but stopped once I gave it some throttle and water flow. It never came on again.

After that it sat for a few days, issues started. It was harder to start, would not idle well, and stalled every time I put it in gear. I found that the crap fuel filter I put in before the carbs had started to disintegrate. I think there was some glue in there that got pushed into the carbs. I found a translucent white goo in the bowls.

So I tore down the carbs and put them in the ultrasonic cleaner. But, the issues persisted.

I had not changed the float levels/adjustment to this time. They looked close to factory spec, I have the service manual. So I started to look at it closer. I could not adjust the float level to 9/16" as in the manual. The float would touch or come very very close to touching the top of the carb.

I picked up some MM carb gaskets and needle valves from a local dealer. And I noticed that the needle valves that I put in had a rubber tip/seat. The OEM MM ones were all metal. This change allowed me to get the float adjustment very close to the 9/16", probably closer to 5/8", but not perfect. I did have one needle seat that was not sealing well, so I polished it a bit with a wooden dowel and a sliver of 1000 grit paper. The carbs are 30 years old, so maybe the seats are worn enough to keep me from setting the float level perfect?

It is running better now, but still has issues idling. The only way I can get it to 1/2 way behave is to adjust the idle/timing screw when it is in the water to increase the idle speed.

There are a few things I have done along the way, multiple times to make sure everything was adjusted correctly......

link/sync the carbs
adjust roller cam clearance
check linkage and stop settings
set the timing in neutral, idling on the water muffs
checked the flywheel key and TDC on #1 vs the timing marks
adj. the idle screws/mix (I do get a lean stumble and back off 1/8-1/4 turn only as I adjust to get the highest rpm I can)

Here are some issues that I have noticed and can not figure out.....

I can set the timing to the factory spec at idle of 2 degrees ATDC (after top dead center), but it does not like it. I am setting this out of the water while on the ear muffs. The best I have gotten it to run, is after this initial setting, put the boat in the water, warm it up and open the cowl and turn the idle/timing screws until I get the highest idle that I can. I think it is ending up around 2 degrees BTDC. This does not match what I am reading in the manual???

After doing the above, I pulled the boat and when I was flushing the motor, I trimmed it all the way down (negative trim, back/aft of motor tilted down) and the idle sounded way better, stronger. Tilted it back up, and it bogged a bit. Still an issue with the carb float level OR idle circuit???

At WOT I am only hitting 4700 rpm. Over propped??? Is this also causing my stall when going into gear???
 
Be careful when setting idle timing.---Only set/ check maximum advance.----Idle timing is when throttle plates OPEN.-----Actual idle timing controls idle speed and is NOT a set value.----Also known as a link / synchronizing procedure.
 
racerone said:
Be careful when setting idle timing.---Only set/ check maximum advance.----Idle timing is when throttle plates OPEN.-----Actual idle timing controls idle speed and is NOT a set value.----Also known as a link / synchronizing procedure.
Click to expand...
Thanks, Could you elaborate?

I see a maximum WOT advance (BTDC) setting for 28, which is set at full WOT/carbs open at cranking speed, plugs out. I have not set this.

What do you mean by "idle timing is when throttle plates OPEN". The service manual shows 2-4 degrees ATDC while at idle. I had tried to set this on the muffs, at idle, neutral. Does it need to be set in the water, while in forward gear, idle speed?
 
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These adjustments rarely change from factory new.----Be careful when guessing.-----Best to visit your local shop to set this motor up.
 
racerone said:
These adjustments rarely change from factory new.----Be careful when guessing.-----Best to visit your local shop to set this motor up.
Click to expand...
Thanks. I understand how to time an engine. I'm just not experienced with a 2 stroke of this nature. And the service manual does not specify when 2-4 degrees ATDC should be checked. It's my understanding that this should be done at idle in neutral. I know that idle speed should be set when in the water and in forward gear. Is the idle timing (2-4 ATDC) referencing at idle, in forward also? If that is correct, that would be my issue as I have not taken the timing light to the dock yet. Or is 2-4 ATDC for idle timing at cranking speed (plugs removed)?
 
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1st off, in this last post you said 4 stroke.
On a 2 stroke, final carb mixture is set idling in the water. Adjusting on a trailer will never work well because of lack of back pressure.
Set timing to WOT as specified.
Idle speed should happen with throttle plates fully closed, proper mixture setting & then adjust idle timing stop for desired RPM. Actual idle timing is not important.
 
Idle timing on this motor is Not the same as it is on "granpa's 283 chevy"-----So investigate what is meant by " throttle pickup " timing on a 2 stroke.------And actual timing at smooth idle does NOT matter !!!
 
Droid said:
1st off, in this last post you said 4 stroke.
On a 2 stroke, final carb mixture is set idling in the water. Adjusting on a trailer will never work well because of lack of back pressure.
Set timing to WOT as specified.
Idle speed should happen with throttle plates fully closed, proper mixture setting & then adjust idle timing stop for desired RPM. Actual idle timing is not important.
Click to expand...
Thanks. I have set the final carb idle screws/mix in the water. I understand that WOT timing is set with the plugs out, throttle all the way open, at cranking speed. And I understand that idle speed is set in the water, in forward gear. Do you know what Mercury intended with the 2-4 BTDC spec? Is it at cranking speed, plugs out?
 
racerone said:
Idle timing on this motor is Not the same as it is on "granpa's 283 chevy"-----So investigate what is meant by " throttle pickup " timing on a 2 stroke.------And actual timing at smooth idle does NOT matter !!!
Click to expand...
Got it. It seems like there is a bit of different info on when to check idle timing. But, if I understand correctly. It should initially be 2-4 BTDC at cranking speed, plugs out. This ensures that timing passes TDC just as the carbs start to open. Then this idle timing would change once the carb idle circuits and idle speed in forward gear are set in the water. I think I need to check the timing with it in the water, so that I understand correctly and to double check that all is good.

Do you have any thoughts on setting the float height (9/16")? Is it measured at the exact point illustrated in the manual? With the engine picking up a little speed and idling smoother as the engine goes into negative tilt, it seems like a little more fuel in the bowls is helping.
 
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I found the back washer to fit my 4 blade prop on (same diameter, -2 pitch), which is original from my boat when it was built. This should increase RPM at WOT and be less stress when shifting into gear.

Now that I know that idle timing does not need to be 2-4 ATDC, adjusting idle and the carbs in the water should be straightforward.

My local mech said that the float bowls are not too particular and dead level should be good. But the difference between level and factory 9/16" does not jive with me.

If anyone else has any other suggestions, please send em'.
 
I went to the dock today and adjusted the idle timing and carb idle screws today. 1/8 turn more out on each carb and loosened/turned out the idle timing screw until I got 900 rpm in neutral and 675-690 rpm in forward. I checked the idle timing in neutral and it is sitting near 3 degrees BTDC.

I took it out and it is running much better now, with regard to idling and going in and out of gear. Forward or Reverse. No stalling.

I am still not getting over 4500-4600 rpm at WOT. My top speed is just over 30mph, around 8-9mph slower than my initial runs.

Back at the dock, I disconnected the throttle cable, and connecting rod between the timing arm(?) and carbs. With it in neutral, idling at 900 rpm, I pushed the advance to max (no butterfly movement). It read over 24 degrees, near 26 or 28 degrees. From what I understand this is too high.
 
Does anyone have any ideas/suggestions? I find the advanced timing at idle and WOT odd. I have NOT adjusted WOT timing at all/ever. Is it possible that my trigger, stator, or switch box has gone bad and is causing this and the failure to rear max RPM?
 
Is there anyone out there with solid experience with older 2 strokes? I would appreciate some tips.

I checked compression. 80,80,90 psi. Then sprayed a small amount of T9 oil in each cylinder and all three read near 90 psi.
Visual inspection of the cylinder walls looks the same as when I recommissioned the motor a few months ago. Cylinder 1 lightly scratched.
I checked timing at cranking speed. Idle is approx. 4-5 BTDC. WOT/full advance is 28+ BTDC!?!
My spark box shows good arc on all 3 with 1/4" or so gap.
The linkage between the max advance arm/throttle and the trigger are loose, but not horrible.
Flywheel key is perfect
The trigger looks in tact and good for an older motor.

It still seems like timing is advanced across the board 4-5 degrees more than it should be. From idle to WOT.
 
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