1978 Johnson 115 hp won't fire on all cylinders

[pltrkt]

My husband wanted me to post this and ask if anyone would know where to start checking when my motor is not firing on all cylinders. The motor will start but it back fires. If there is someone on tonight and reads this, then I will get my husband and he can detail the problem.

 

[rabidfish]

Re: 1978 Johnson 115 hp won't fire on all cylinders

Let's have a looksee...

 

[pltrkt]

Re: 1978 Johnson 115 hp won't fire on all cylinders

well I start the motor and it misses like three or four times and then backfires through the exhaust<br />the rythm it has tells me that it is only one cylinder.<br />the motor was ran 12 times this year and 3 times the year before with no trouble. it was rebuilt 2 years ago. so i dont thing it is machanical but might be

 

[rabidfish]

Re: 1978 Johnson 115 hp won't fire on all cylinders

If you remove the spark plugs, do all four cylinders have spark?<br /><br />That kinda sounds like you have crossed a couple of plug wires... Have you changed the plugs recently?

 

[pltrkt]

Re: 1978 Johnson 115 hp won't fire on all cylinders

yes they do but i don't know if they might have a weak spark the flame seems strong and is blue in color

 

[rabidfish]

Re: 1978 Johnson 115 hp won't fire on all cylinders

blue spark is good... will it keep running if the rpms are higher?

 

[pltrkt]

Re: 1978 Johnson 115 hp won't fire on all cylinders

i don't understand the series of misses between backfires if it were a stuck exhast valve wouldn't it fire through the exhaust every time

 

[rabidfish]

Re: 1978 Johnson 115 hp won't fire on all cylinders

There is no exhaust valve... to speak of. The piston opens and closes the exhaust port.<br /><br />Ok, answer this question... Have you recently changed the spark plugs?

 

[pltrkt]

Re: 1978 Johnson 115 hp won't fire on all cylinders

yeah that was the first thing i did when this started happening figuring one was fouled. they didn't look bad when i pulled the old ones but i took them out and replaced them anyway. so if the piston is opening the exhaust port is there some way to change the spark timing on just that cylinder?????

 

[rabidfish]

Re: 1978 Johnson 115 hp won't fire on all cylinders

Yes. but only if you switch wires.<br /><br />(either a spark plug wire, or a power pack wire)<br /><br />Verify the plug wires are reattached to the proper plug, then get back to me here.

 

[pltrkt]

Re: 1978 Johnson 115 hp won't fire on all cylinders

each cylinder has it's own little coil on the cylinder head and the plug wires are only about 4 inches or 4 1/2 inches long. long enough to reach its own plug

 

[rabidfish]

Re: 1978 Johnson 115 hp won't fire on all cylinders

OK, when it runs, is there exhaust(smoke) coming from someplace inside the cowling? <br />Or... is there a wet area on the side of the engine block? Indicating a gasket leaking?<br /><br />Is it possible that the coils have been removed and put back on the other(opposite) coil mount..

 

[pltrkt]

Re: 1978 Johnson 115 hp won't fire on all cylinders

they coils have not been removed since the rebuild and it ran fine until recently. however i am not sure what a cowling is this is my first boat not all of the water goes out the little hole from the impeller though. the impeller has a good hard stream coming out the hole but i do notice ALOT of water coming from right below the motor shooting out the back of the lower part of the motor housing

 

[rabidfish]

Re: 1978 Johnson 115 hp won't fire on all cylinders

Is this inside the engine compartment, or underneath... (there's two holes in the exhaust housing about 1/2 inch in diameter)<br /><br />The "cowling" is the hood that covers the actual engine(what we call "powerhead")

 

[pltrkt]

Re: 1978 Johnson 115 hp won't fire on all cylinders

Ok my exhaust goes out through the propeller but there are the 2 holes you spoke of and yes that is where this extra water seems to spit out of

 

[rabidfish]

Re: 1978 Johnson 115 hp won't fire on all cylinders

how about compression.. It's possible that you have a head gasket leaking into another cylinder...

 

[pltrkt]

Re: 1978 Johnson 115 hp won't fire on all cylinders

yes i do have compression. although i don't have a compression tester i can blow a rag out of the heads. that is not to say that i have that right now but i did have at least before the problem.

 

[rabidfish]

Re: 1978 Johnson 115 hp won't fire on all cylinders

Well... this is it for me tonight...<br /><br />You need a real compression reading to verify it.<br />Then, I would suggest a run to a repair shop...<br /><br />Good luck, let us know what you find.

 

[pltrkt]

Re: 1978 Johnson 115 hp won't fire on all cylinders

ok hey thanks a lot for all the help though i did learn alot and i appreciate it.

 

[reeldutch]

Re: 1978 Johnson 115 hp won't fire on all cylinders

i think your moter is sneezing and might be running lean.<br />do you have a water fuel seperator?