70 hp mercury refuses to start

[FordDoc]

I bought an 1983 mercury 70 hp outboard according to owner had just been rebuilt. Got it home will not start unless you spray carb cleaner. will not start on gas or gas mix sprayed into carb. ck'd spark all 3 plugs appear to have good blue spark, check'd bowls both carbs have fuel in the bowls, ck'd compression cyl1 has 150psi, cylinder2 has 150psi and cylinder 3 has 147psi. the spark plugs are new, I rebuilt the fuel pump, I checked the timing if if the marks are correct and i am checking properly the timing is right. I can spray enough gas into carbs to hydrolock the motor. I've tried changing choke & throttle while crancking it only seems to start on carb cleaner which I know not to use in a 2 stroke. What am i overlooking it appears i have fire, fuel and compression.....any help, thoughts, ideas or suggestions would be greatly appreciated

 

[Maxz695]

Re: 70 hp mercury refuses to start

Are you 100% positive this is a 2 stroke engine ? also maybe oil has settled and not well mixed could be old gas

I bought an 1983 mercury 70 hp outboard according to owner had just been rebuilt. Got it home will not start unless you spray carb cleaner. will not start on gas or gas mix sprayed into carb. ck'd spark all 3 plugs appear to have good blue spark, check'd bowls both carbs have fuel in the bowls, ck'd compression cyl1 has 150psi, cylinder2 has 150psi and cylinder 3 has 147psi. the spark plugs are new, I rebuilt the fuel pump, I checked the timing if if the marks are correct and i am checking properly the timing is right. I can spray enough gas into carbs to hydrolock the motor. I've tried changing choke & throttle while crancking it only seems to start on carb cleaner which I know not to use in a 2 stroke. What am i overlooking it appears i have fire, fuel and compression.....any help, thoughts, ideas or suggestions would be greatly appreciated

 

[Maxz695]

Re: 70 hp mercury refuses to start

Starting fluid has a lower flashpoint and will ignite must faster than gas like you said do not use continuosly on a 2 stroke engine did you try to elavate the throttle to full throttle in neutral to get it to fire. If it is getting to much gas this will be the best way to clear it and get it to fire up. If it fires rebuild the carburetoror fuel pump . The fact that the engine does start shows a fuel supply problem not limited to the carb or just the fuel pump which you can easily test by removing the fuel line from the carb and turning it over but also a fuel fiter may be clogged ,cracked fuel line allowing air and even the bulb syphon

 

[jeffersondodson561]

Re: 70 hp mercury refuses to start

You need to verify tdc and check timing with a timing light, what do the reeds look like? Are the throttle plates synced correctly? Idle timing should be in neighborhood of 0-4 degrees after top dead center as far a wot timing refers to manual or airbox...refer to manual since rebuilt. Hydrlocked motor with starter engaged? Uh oh.

 

[Moody Blue]

Re: 70 hp mercury refuses to start

I bought an 1983 mercury 70 hp outboard according to owner had just been rebuilt. Got it home will not start unless you spray carb cleaner. will not start on gas or gas mix sprayed into carb. ck'd spark all 3 plugs appear to have good blue spark, check'd bowls both carbs have fuel in the bowls, ck'd compression cyl1 has 150psi, cylinder2 has 150psi and cylinder 3 has 147psi. the spark plugs are new, I rebuilt the fuel pump, I checked the timing if if the marks are correct and i am checking properly the timing is right. I can spray enough gas into carbs to hydrolock the motor. I've tried changing choke & throttle while crancking it only seems to start on carb cleaner which I know not to use in a 2 stroke. What am i overlooking it appears i have fire, fuel and compression.....any help, thoughts, ideas or suggestions would be greatly appreciated

Couple of thoughts. Check spark with a spark gap tester set to about 3/8" gap. Could be your not producing a "hot" enough spark. If you're checking spark just at the plugs, it may not be a valid test because it requires more energy to jump the gap under high compression.

As mentioned, you need to mechanically verify TDC and compare it with the timing decal. Could be the motor was not reassembled properly after the rebuild and ignition timing is WAY off. You are checking timing at #1 cyl, correct?

Put in a fresh/new set of plugs and without "spray enough gas into carbs to hydrolock the motor", try to start the motor normally. Choke ON, fast idle advanced, primer bulb pumped. Crank the motor for 10 seconds and repeat if it doesn't fire. Try this three or four times. Pull the plugs and inspect them. Are they wet or dry?

 

[FordDoc]

Re: 70 hp mercury refuses to start

Thanks for the input i'll update any findings later today

 

[CharlieB]

Re: 70 hp mercury refuses to start

Just for goo dmeasure, test compression. Broken rings, etc., can cause serious starting issues.

 

[FordDoc]

Re: 70 hp mercury refuses to start

well went to check motor today after thinking about some of the suggestions decided i would clean timing marks on flywheel to make sure i was reading things correctly. so i cleaned flywheel and painted it let it dry. brought #1 to tdc verified tmark on 0 put plug back in hit key and it fired its never done that so i verified primer bulb was still firm gave it a shot of gas mix into both carbs blew a 12 flame out the hub & spuutered out now it starts briefly sputters & stalls out...also appears oil? is running out of prop hub. gonna go get another set of plugs this week & recheck it

 

[Maxz695]

Re: 70 hp mercury refuses to start

check to see you have the right firing order reverse the plug wires try again this same thing happened to me last week and I still for the life of me cannot figure how the wires got switched I was fine for 2 hrs died in a instant got towed in checked all night next day after coming here to iBoats I took information checked TDC watched the spark at a 7 / 16 gap bright blue and noticed #2 was firing on #1 scratched my head switched the wired and fired it up Still in aww on how this happened Confused switchbox?