Wont run, I quit.

Larson70 · Jul 25, 2012

I have a 1990 70 hp Mercury motor, I have changed the starter and plugs, cleaned the carbs, checked the compression which is 115, 113, 114. I have tried every proper starting with choke, start, wait, try again. Every combination of choke and none. Im at the point of lighting the motor on fire (which will not solve anything). Please give me as many things as you can think of to try. Im about to try draining the gas tank, cleaning it and trying new fuel. The fuel housing containing the filter fully fills when using the primer bulb (which also gets hard and isn't loosing suction). Please HELP!!!

coolbri70 · Jul 25, 2012

Re: Wont run, I quit.

check for spark

oldman570 · Jul 25, 2012

Re: Wont run, I quit.

Make sure the emergency man overboard switch on the control is in the correct position. If it has been triped the motor will not start untill it has been reset with the clip and lanyard correctly. The plastic clips will break after sometime. You can also disconect the yellow/ black wire from the switchbox and see if it will start. If the motor starts you will need to hook the wire back up, and if the motor dies as soon as you touch the wire back on the switchbox an kills the motor, you have a problem with the wiring. JMO
Oldman570

Larson70 · Jul 25, 2012

Re: Wont run, I quit.

oldman570 where is this switch? What is it directly connected to? I have a bilge pump switch, lights, fuel gauge and the ignition box. Its a 1970's set-up. I know how it works on jet skis, its essentially a dead man switch but I have not found anything similar on my unit. It did fire up last week before the new plugs (which are the right ones and are tightened) but keep the new ideas coming.

coolbri70 · Jul 25, 2012

Re: Wont run, I quit.

it ran before replacing the plugs? did you set the gaps right on the plugs? put the old plugs back in if it runs it's the plugs, new or not

Timestep · Jul 26, 2012

Re: Wont run, I quit.

check for spark

+1

BonairII · Jul 26, 2012

Re: Wont run, I quit.

Def check spark......with an adjustable spark checker. Spark needs to jump 7/16" air gap.

If you have good quality spark, good compression(you do), good fuel flow.....then you might want to check timing(sheared flywheel key?)

Use a portable fuel tank(if you have one), to rule out problems with your current tank.

oldman570 · Jul 26, 2012

Re: Wont run, I quit.

Conrols of the 1970 Mercontro; do not have a dead man switch. The newer Comander and Camander 200 do have the dead man switch. If the motor was turned over without the plugs or plug wires being grounded to the block when testing the compression, chances are that eaither the switchbox, trigger, or stator is now burnt up. Time to breake out the ohm meter and test the stator, trigger, and coils. How to test directions are in the OME manual for that motor and are a cheap investment when compaired to most all electrical componits for the motor. Manuals can be bought online and at dealers. OME manuals are the best as others will have one scratching their head trying to figure things out. My bet is that the switchbox is gone or the wires are not on the correct plugs as they should be.
Oldman570

Charlie61 · Jul 26, 2012

Re: Wont run, I quit.

time to test for voltage comming from stator to rect, when to switch boxs is the first thing to .do. if no voltage comming of stator , next ohms from stator, then to trigger and so www.maxrules hads a wiriing di , it will show you color and where wirng going . you may need and could have a service manual

Larson70 · Jul 26, 2012

Re: Wont run, I quit.

I am going to get a spark tester today (will post details soon) but just wanted to post details of the situation to keep other ideas flowing. Purchased the boat after it had sat for 11 months and got it for a steal because it was "loosing compression", i brought it home and tested it and it was near perfect in all three cylinders. So changed the lower unit oil and took it out on the water after some choking it fired and idled for 5 min. After leaving it on the trailer in the water (making sure it was pulling water to cool) gave it half throttle with no problem. So took it off trailer, put it in reverse and it stalled. Went to start again and found out starter failed. Took it out and while waiting for the starter to be shipped i cleaned the carbs (careful not to touch any adjustment screws) and replaced the spark plugs (which don't need to be gapped). Now can't get it started. Also it did have under a quarter of a tank of old fuel in it so i tried to get as much out as possible and filled it with fresh new fuel. Keep the ideas coming...

The_Kid · Jul 26, 2012

Re: Wont run, I quit.

A quick way to see if it's fuel, or no spark is to grab a can of WD40 and spray into each carb for a second, then try to start it. If it runs for a second or two you have a fuel problem. If it still doesn't fire you have a spark problem.

tipitina · Jul 26, 2012

Re: Wont run, I quit.

Is it tryin to start? Flywheel turning? If not, do you have enough charge on batteries? Is the engine in neutral? Kill switch? All plugs and cables seated properly?

Larson70 · Jul 26, 2012

Re: Wont run, I quit.

tipitina said:
Is it tryin to start? Flywheel turning? If not, do you have enough charge on batteries? Is the engine in neutral? Kill switch? All plugs and cables seated properly?

The bendix on the starter engages the flywheel. Spins it for a second- two and drops back as it should. It sounds as if it wants to start, just doesn't

coolbri70 · Jul 26, 2012

Re: Wont run, I quit.

Never heard of a sparkplug that didn't need gapped just put plugs in mine they must have been bounced around during shipping as most the gaps were closed when I took them from the pacaging if I hadn't gapped them it wouldn't have run

Larson70 · Jul 26, 2012

Re: Wont run, I quit.

....Ive only gapped plugs that have the lip that drops down, this is more of a glow plug for a two stroke. otherwise let me know

Moody Blue · Jul 26, 2012

Re: Wont run, I quit.

They are called surface gap plugs. A common marine type plug. Have you checked the plug surfaces after trying to start the motor? They should be wet with fuel if the carbs are operating properly. If they are dry, you have a carb problem.

How did you "clean" the carbs? The ONLY way to clean the 2 cycle carbs is to remove them, take them apart, soak them in a carb cleaner, blow them out with compressed air, replace the inlet needle and seat, check idle adjusting screws for wear (replace as required), check the floats for cracks etc (replace as required) and then rebuild the whole thing. The float height adjustment is critical to the operation of the motor.

Larson70 · Jul 26, 2012

Re: Wont run, I quit.

I took them out sprayed threw everything possible. Replaced the needle and put it back together. The float was in good shape. I didn't play with the adjustment because it ran nicely previously....

Larson70 · Jul 26, 2012

Re: Wont run, I quit.

Ok so I took the top plug out and put it right off of a ground bolt and there was no spark and the new plugs still look unfired. This motor did fire before the break down of the starter/carbs. Where to go from here?

Dave1027 · Jul 26, 2012

Re: Wont run, I quit.

Larson70 said:
Ok so I took the top plug out and put it right off of a ground bolt and there was no spark and the new plugs still look unfired. This motor did fire before the break down of the starter/carbs. Where to go from here?

Probably disturbed a wire that was ready to lose connectivity. The proverbial straw that broke the camel's back.

Is the kill switch grounded? That would be the first thing to check. Get a wiring diagram.

Larson70 · Jul 26, 2012

Re: Wont run, I quit.

Here is the problematic piece. One of the ground pins is snapped and just spins so i cut the wire, going to strip it and put a new connector on but need this piece. What do i call it?

Wont run, I quit.

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