motor won't start

[ajl1275]

I have a 1997 Johnson 90 hp that has run great for years until last week. It got hard to start 2 or 3 times then would not start at all. I've got good spark on all 4 cylinders, plenty of gas at the fuel pump, any suggestions out there?

 

[rterrian]

Re: motor won't start

The gas at the fuel pump means nothing if it's no getting thru the carb(s) to the cylinder(s). To run, The motor needs three things, Air and Fuel Mixture, Spark and compression, all in the clyinder and at the right time. Check by squiting a small amount of fuel into the carb(s) throat while engaging the starter. Let us know.

 

[ajl1275]

Re: motor won't start

shot some fuel directly into carb throats, still no ignition. Is it possible that the plugs won't spark under pressure but will outside the cylinder? Al

 

[jim dozier]

Re: motor won't start

Have you done a compression test on the engine? <br /><br />If you have good spark and you squirt pre-mix into the carbs you will usually at least fire the engine although it may not run for more than a second or two, unless the engine is completely flooded with gas. <br /><br />How did you verify that you had good spark? Pull out the plugs and ground them on the engine and check for a strong blue spark. Better yet, get a spark tester, you should be able to jump a 1/2 inch stong blue spark. If you do indeed have good spark, disconnect the fuel hose, and crank the engine with the plugs out at full throttle to air the engine out. Go get a beer and let it set for 30 minutes and then reconnect the fuel hose and start from scratch. Pull off the airbox from the carb throats and watch what happens when you pump the fuel bulb, see any gas? If you do thats bad, your floats are sticking open. If not try and crank it up without the choke. If no go, squirt some more pre-mix in the carb throats. It should fire. If it won't run the carbs need cleaning. If it doesn't fire something is seriously wrong in there and we'll go from there.

 

[ajl1275]

Re: motor won't start

I'll try your ideas today and let you know. Thanks for this help. Al

 

[ajl1275]

Re: motor won't start

Took your advice, checked compression all cylinders are fine, spark test appears good, good fuel, turned the engine over to air it out, squirted some starting fluid into the throats..nothing! It has got to be no spark under compression, that situation would be rare but what else can it be? Al

 

[jim dozier]

Re: motor won't start

Don't use starting fluid (ether) its hard on the 2 stroke engines, use pre-mix in a squirt bottle.<br /><br />What exactly are the compression numbers?<br /><br />If you have a strong spark (not a weak one) it will spark under compression. So unless you're inaccurate in your description of a strong spark, I don't think that's it.<br /><br />Is there now, or was there when it was running last, any evidence of leakage from the crankshaft seals? That's about the only thing other than reed valves that I can think of that would stop it from firing when you squirt gas in there. Have you removed the airbox from the carb throats? If not do that and squirt the premix directly into the carbs and verify that its not firing. It might be worthwhile to get a spark tester to measure the length of your spark (should jump 1/2 inch) to accurately check the spark before you go any further. Hopefully someone with more experience will get in on this. I would guess after putting any spark issue to rest you would remove the carbs and visually check the reeds. Usually if you got fire and you squirt fuel it will at least run a moment.<br /><br />I had another thought. I have never had this happen to me but I have read it on other posts, check the flywheel key and see if you have sheared it which will upset the timing.