Rebuilt 70hp Will Not Start

I have rebuilt a 1984 Johnson 70, but now I cannot seem to get the thing to fire. I have tested the spark, easily jumps 7/16 open air gap with new spark plug wires. Compression is 140 psi on all cylinders so that is good. Which leads me to believe a fuel problem. I have tried spraying premix into the cylinders with the spark plugs out then turning the motor over after putting the plugs back in and nothing happens. Tried to spray premix into the carbs while starting and nothing happens. I took the fuel pump off and rebuilt it and it appears to be working fine. When I squeeze the bulb it gets hard and the carb bowls sound like they fill up with fuel. I am not sure what else the problem is, too much air getting into the system through leaky hoses (only one of the hoses from the fuel pump had a clamp on it), sticking floats in the carbs (I rebuilt them while working on the motor and put in new jets), a sheered flywheel key, or a blown primer solenoid? Any help would be appreciated. Thanks.

Plugs look dry when I take them out.

Re: Rebuilt 70hp Will Not Start

Hi Socak,

Check if you have the timing right, i.e. have the spark for the right cylinder at the right time.

Good luck, Peter

Re: Rebuilt 70hp Will Not Start

orbanp said:

Hi Socak,

Check if you have the timing right, i.e. have the spark for the right cylinder at the right time.

Good luck, Peter

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Not sure how the timing would be off unless I sheered the flywheel key.

Re: Rebuilt 70hp Will Not Start

Neighbor had 79 70 Johnny with same problem; he had good fuel, pump, spark, compression and carbs; turned out the starter need new brushes and bearings greased, wasn't turning the engine over fast enough. Just a thought.

Re: Rebuilt 70hp Will Not Start

Will Bark said:

Neighbor had 79 70 Johnny with same problem; he had good fuel, pump, spark, compression and carbs; turned out the starter need new brushes and bearings greased, wasn't turning the engine over fast enough. Just a thought.

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Sounds like a possibility, I hooked the tach up last night while starting but could not get a reading. Could this also cause fuel not to be drawn into the cylinders?

Re: Rebuilt 70hp Will Not Start

In his case wasn't turning fast enough to throw a real good spark under compression. Mechanic told him that engine has to spin 250/300 RPMS to generate a real good spark. One of the gurus will probably chime in to confirm. Good luck

Re: Rebuilt 70hp Will Not Start

Socak said:

Not sure how the timing would be off unless I sheered the flywheel key.

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I agree with you.
On the other hand, if the motor has compression, fuel, and ignition, it should show some life, and it does not.
I still would double check the timing.

Good luck, Peter

Re: Rebuilt 70hp Will Not Start

Even if the carburetors were off the engine, spraying premixed fuel into the intake manifold... OR... removing the spark plugs and spraying directly into the cylinders, replacing the spark plugs of course, then cranking the engine over... the engine would surely fire.

However, you say the engine does nothing. With the compression you state on all cylinders (140 psi), having proper spark, and fuel obviously present as you sprayed it in there... the engine would have to fire UNLESS the flywheel key is sheared, in which case the engine should at least backfire... OR... the engine is not cranking over fast enough for the stator to energize the powerpack.

The engine must crank over at least 300 rpms in order to have the stator function properly. You would be extremely lucky if a slow cranking engine ever starts.

Also... visually and closely inspect that stator to see if it is cracked in various places and/or dripping a sticky looking substance down on the powerhead area. This would cause a voltage drop to the powerpack which would result in weak, erratic and eventually no ignition (spark).

If slow cranking, make sure you have a known good battery and good cables. Remove and clean all cable ends and also the components they attach to which includes the battery terminals themselves and the ground cable at the powerhead.

Run good known cables directly from a good known fully charged battery directly to the electric starter. If the engine cranks over okay when jumped in this manner but not when wired the proper way, then obviously a cable/wiring problem exists. If however, the engine still cranks over slowly when jumped with a good fully charged battery, the starter needs reworking or replacing.

Let us know what you find.

Re: Rebuilt 70hp Will Not Start

I thought he posted that the spark was good. From post #1.
If spark jumps 7/16", he has enough RPM.
I think he obvoiusly has the spark timed wrong. I bet you have mis-wired the pack to coil wires, OR the timer base to pack.
On this engine, I don't know if that is possible or not with the polarized plugs, etc.

If it were me, I would mark TDC on the flywheel for all three cylinders, attach a timing light, and look for the timing light to illuminate the TDC marks you just made. All three cyls. It doesn't have to be exact right now, just look to see if the mark is visible at or near the timing pointer when the light flashes.

I feel that you will find them illuminated to the flashing elsewhere around the wheel than where they are supposed to be.....

Re: Rebuilt 70hp Will Not Start

If during the rebuild something was not done properly on the bottom end (seals leaking for example) fuel cannot get to the cylinders. After spraying stuff into the carbs and directly into the plug holes, what do the plugs look like. Are they wet? If so the engine is getting fuel. If bone dry it is not. If wet it is likely a spark or timing problem. If dry -- it is a fuel problem.

Re: Rebuilt 70hp Will Not Start

Does the engine fire at all and just not start? Or does it not even fire or sputter when cranking over?

I'm sure you've checked but is the kill switch lanyard connected properly? It must have been during the spark test but is it connected now?

Re: Rebuilt 70hp Will Not Start

He said he tried spraying into plug holes and carbs while cranking.
Tested 7/16 spark. I agree The timing must be off or plug wires on the wrong cylinders
maybe the flywheel key.

Re: Rebuilt 70hp Will Not Start

steelespike said:

He said he tried spraying into plug holes and carbs while cranking. Tested 7/16 spark. I agree The timing must be off or plug wires on the wrong cylinders, maybe the flywheel key.

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BUT he says "nothing happens", indicating no backfire, puff, pow, nothing! Even if the flywheel key was sheared, the plugs would still fire if the engine had compression, fuel, and spark, but it would fire out of time. This leads me to believe that with the plugs installed, there is no spark due to slow cranking speed, hence my previous explanation of the needed 300+ rpm cranking speed.

Socak.... Remove the flywheel and double check that flywheel key to put all our minds at ease. Note that it must be installed with the straight edge of it aligned with the vertical position of the engine (straight up and down), NOT with the crankshaft taper. Also the flywheel nut must be torqued to 105 foot pounds.

Daselbee... Yes, I saw that statement about having spark jump a 7/16" gap but that was with the s/plugs removed which of course is the normal test procedure BUT he did not mention if a strong drop in rpms existed when the plugs were installed. His mention of fuel sprayed directly into the cylinders... and still nothing! Compression, spark, fuel.... I would think an explosion of some kind would take place.

If cranking slow, rope starting would bypass that problem if all else is as it should be.

This has me wondering if the engine has low cranking rpms with the plugs installed (spark?), plus all of the starting attempts has the cylinders loaded with fuel?

Re: Rebuilt 70hp Will Not Start

Good points, Joe, especially regarding the crank speed with plugs installed vs without.

And you are right, it should backfire, pop, or something.

We will see.......

Re: Rebuilt 70hp Will Not Start

Ok so check list for today
-Remove flywheel to check for sheared woodruff key and make sure no black goop around stator
-Fully charged battery and different cables
-Torque back the flywheel nut to 105 ftlbs
-Replace existing fuel line
-Check lanyard to make sure its snug
-Check TDC for each cylinder
-Attempt to determine drop in rpms between plugs in and out

In regards to coils wired wrong, the top coil goes in the A pin location off the power pack, middle coil in the B location, bottom coil in the C location is this not correct?

Someone mentioned seals leaking, which would cause fuel not to get into the cylinders. Which seals, powerhead gasket or crankcase to cylinder head gasket?

I understand the process of finding top dead center, but I dont have a pointer on the motor. Do you just pick any point on the motor as your pointer and just keep it constant for each cylinder?

How much of a pain in the *** is it to pull start a 70?

Let me know if I forgot anything? I will report back with my findings with some pics and maybe video.

Re: Rebuilt 70hp Will Not Start

look under the sticky..Top Secret Files...the second posting has links to the color coded wiring diagrams for your motor...may be of help

Re: Rebuilt 70hp Will Not Start

UPDATE:

Sheared flywheel key, off to get a new one.

Re: Rebuilt 70hp Will Not Start

The flywheel key must be specific... NOT one you'll find in a hardware store. Part number 307480.

Re: Rebuilt 70hp Will Not Start

Joe Reeves said:

The flywheel key must be specific... NOT one you'll find in a hardware store. Part number 307480.

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Thanks. I went to a marine place anyways

Re: Rebuilt 70hp Will Not Start

And it runs. I can't believe it, I got a motor that is older than me running right again. I hope it will last another thirty years. Now I just need help setting the idle right. Is it pointless to set the idle on the muffs cause there is no load on the motor therefore it will idle way higher out of the water than in? In the top secret files when it talks about adjusting the carburetor, what are you supposed to turn? The screws on the outside for the high speed and low speed jets? Thank you everyone for you help, i could not have done it with out you. And all the great tips on here made this rebuild happen. ill have to post a video of it running later on when the Internet at the house gets fixed.

-York