15 hp Johnson has spark, fuel, air but not cranking...

Good morning,

OK, I have been trying to figure this out on my own but........ Here I am!

I have a 1977 15 hp Johnson- 15R77M...... I bought it about 2 weeks ago, it fired up and shut right back off when I looked at it the first time. Tried pulling it and no go.The negotiations begin and I wind up with this motor and a '72 16' Ouachita and trailer.... for $650.00....

Anyhow, Cant get it to crank so I removed the carb....looks like it was just rebuilt as the prev. owner told me. Sprayed it down, removed bowl and saw a few small gritty pieces in the bottom of the bowl. sprayed thru the port from bowl to chamber and all clear. Float appeared to be ok. Put factory speced plugs in (champion). Key way is in line so timeing should be good. New Power Pack yesterday spark looks blue now but still not cranking. Anyway, I have spark, I have fuel, I have air!!!!!!!!! Why would I not not have combustion.....could I be flooding? Not sure who rebuilt the carb or what else I should have checked on it for blockage or maybe even damage from being gauged out by someone else cleaning it.


The spark is enough to ignite the fuel outside the motor while checking for spark as the fuel sprays out of the plug port. Actually blazed right up for a second and I got it out immediatly. No damage. Mom wanted me to back it up to her house and work on it when she saw that!!!! lol

The plan is to leave work early and get two coils and put on it today. I dont mind putting money in it as the parts are all original (35 years old). I just want an understanding of how to check the power pack and diagnose one that is bad. I ohmed the coils out and they were fine or at least both reading the same.

Am I missing something with the carb? What should I check or replace under the flywheel. I have been reading up on the Capacitor Discharge Ignition but need a much better understanding. hard to find specs on the power pack and I dont have a peak reading multi meter, or at least I dont think I do. Who is out there that can lend a few ideas or instructions, the mechanic I talk to will not work on this old motor although he did show me a few things when the pull starter spring came apart. I got it wound back up and placed back in the housing but I wasnt sure about the clip that locks into the bar. He is very short with people so he is not always happiest person in the world but I still try to talk to him.

Man I love this site, I read stuf that doesnt even pertain to my situation. Ready for something new!

Anyway, thanks in advance for the help!

Have you done a compression check on the motor yet?

broken or sheered off crankshaft key perhaps????

Johny25 said:

Have you done a compression check on the motor yet?

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80# on bottom and 79# on top

shawnfish said:

broken or sheered off crankshaft key perhaps????

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If you are talking about the key way that is directly under the flywheel then its in there and in tact. Removed flywheel last night and checked that before I posted. Thanks though.

What else?

Replaced both coils today after lunch. I have a blue spark at both once again and no combustion!

What I am missing here? whats under the flywheel that may need to be updated?

I honestly thought I had a good thing here, My eleven yaer old is getting pissed about this. he wants me to take it to someone but I really want to get this myself and soon. I have about $200 more dollars before I take it to someone.

HELP:!:

When I removed the flywheel it seemed to me the keyway was down too far. It looks to me that a small potion of the keyway is sitting in the slot of the flywheel, but none the less its in the slot and turning. The prop turns when the motor is in gear and the rope is pulled on. ???? Is that ok?

pulled spark plugs, put em back in the boots, pulled rope just to take a look at the blue spark (confirmed), put it all back together, turned the idle alll the way in, walked the dog for potty (no phone) , came back, just reached and pulled--- she fired up!!!!!!!!!!

Kinda frantic and shocked I cut it off with the kill switch. NO WATER HOOKED UP! Ran around the house to turn water on and now she will not pop off again...... Fuel problem all along?

Are the plugs wet when you pull them out after trying a few times to start it?

Have you checked the low speed needle to see how far out it is? I had an issue with a 9.5 johnson when the needle was out too far. I turned it all the way in then out 1.5 turns and it fired right up.

Does the primer bulb stay firm after a few pumps?
If not pull fuel pump and make sure the diaphram isn't busted and pumping gas through the pulse port into the cylinder. Once you pull it the backside should be wet, you can also squeeze the primer bulb to check.

Also another thing to try is to unhook the gas tank and try spraying some mixed gas into the carb to see if it will fire? That sometimes will rule out a stuck or high float since there will be no gas in the bowl and it only has the gas you spray in it to fire on.

^^^^Yes spray some mix directly into the carb throat and see what happens. Oh and 79 and 80lbs is not great compression at all. Good compression is anything over 100 and with 10% of each other. So your engine does not sound healthy at all and may be in need of new rings, cylinder wall honing etc. #-o Basically a rebuild internally

sharrison said:

Are the plugs wet when you pull them out after trying a few times to start it?

Have you checked the low speed needle to see how far out it is? I had an issue with a 9.5 johnson when the needle was out too far. I turned it all the way in then out 1.5 turns and it fired right up.

Does the primer bulb stay firm after a few pumps?
If not pull fuel pump and make sure the diaphram isn't busted and pumping gas through the pulse port into the cylinder. Once you pull it the backside should be wet, you can also squeeze the primer bulb to check.

Also another thing to try is to unhook the gas tank and try spraying some mixed gas into the carb to see if it will fire? That sometimes will rule out a stuck or high float since there will be no gas in the bowl and it only has the gas you spray in it to fire on.

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They were wet before. I have seen the fuel in the plug port while checking for spark. I will check again later today

I have to do a little research to figure out where the low sppeed needle is located and what iti looks like.

The primer bulb appears to remain hard. The fuel npump looks like its new or at least been cleaned quite well recently. I will check though.

I will get a spray bottle and attempt this. The float looked used in the clean carb. It is the black plastic float. The float was not stuck and moved freely, It appeared to sit correctly while bowl would be empty as I held the carb up.

Johny25 said:

^^^^Yes spray some mix directly into the carb throat and see what happens. Oh and 79 and 80lbs is not great compression at all. Good compression is anything over 100 and with 10% of each other. So your engine does not sound healthy at all and may be in need of new rings, cylinder wall honing etc. #-o Basically a rebuild internally

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Yeah, I read where the compression was low but I also read that it should still run fine for a good while. I am using this motor to get educated mainly. I will more than likely do a complete rebuild in the future once I use it a while or until it last.
What I read was 60# on the cylinders would be to low, but 80# should be ok and that 100# is ideal. It's a gamble but this motor will be good for to troll in the 16' jon boat in the shallows of the Congaree River. It's a gamble and I may wind up finding a similar motor and having spare parts. I'm no outboard mechanic but doing hvac work gets old and I like tinkering with something new. thanks for the help and please feel free to offer more advice in the future as this may take a while.

She fired up! Only the spray bottle wasnt what did it, I bypassed the fuel pump and put the tank up on a ladder higher than the motor, she purrs like a kitten as long as you keep pumping the ball and shooting gas to it. Took the pump off this time instead of listening to the seller and found a complete circle crack in the diaphram around the center hole of the diaphram.

I'm still baffled as to why the motor wouldnt start by injecting the spray into the carb. Although spraying it into the spark plug port and putting the plugs back in it fired once. Thats when I decided to bypass the pump and go gravity fed.

I still may have carb issues but I;m going to rebuild the pump on Monday, then I'm going to buy a carb kit if need be.


thanks for the suggestions

Dear Gator,

Well at least you know the motor is capable of running now.

I'm glad you posted this thread and posted your troubleshooting process as you used the suggestions made by others to narrow the problem areas down. Luckily I don't need any repairs to my present motors but I welcome the chance to read and learn from others. I'm about as handy as a third testicle but I can usually figure things out and fix many things if I put my mind to them. This forum provides a lot of knowledge and experience for free and I appreciate that fact and want to say thanks.

Regards,

Tim Murphy

That was a good idea about bypassing the fuel pump. Glad ya got her going.

good job on the diagnosis. to rebuild those pumps, its not that hard. a little time a piece of ply wood and 4 long screws. check leeroys ramblings for some really good tips!
dino

I just bought a pump for it, OMC does not offer the rebuild kit and I wanted to get it on so I can continue with carb quickly. I will get a kit and rebuild the old pump or actually I thought about making the diaphram and having that as a spare or sell it on ebay to get a few bucks back. Either way I got it to crank but cant keep it running. I have spent enough money now that the guy at the marina says to bring the carb in and he will look at it and show me what I need to know. Awesome!

I figure $30 more and she will be cutting up and down the Congaree River with me and my youngest son.

Should get this done today and maybe take her out tomorrow afternoon.

dkonrai said:

good job on the diagnosis. to rebuild those pumps, its not that hard. a little time a piece of ply wood and 4 long screws. check leeroys ramblings for some really good tips!
dino

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Yeah man! My problem with Leeroysramblings is I cant stop reading. I always read everything, even what doesnt pertain to me. I have 4 more carbs I have to do on a 1992 V4 120 hp thats on another boat I acquired.

I cant wait to get these two going so I can start on the boats. The aluminum sheet metal is where I think I will excell. I hope anyway. Looking for a high frequency welder for the projects now.
thanks

92 V4 120 big bore looper? I am jealous now :mrgreen:

Johny25 said:

92 V4 120 big bore looper? I am jealous now :mrgreen:

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Yep! You speak as if you know this motor? I have already done a few things to it. Starting another thread on that in a few minutes. Please pop in!