1977 Johnson 115 v4 backfire when tries to start

[mississippisportsman81]

I have a 1985 Performance Thruster 16 ft fiberglass boat that had a 1976 70hp that I locked up, bought a 1977 Johnson 115. When I got it mounted on the boat it cranked right up then I hooked the cables throttle cables to it and it wouldnt crank. Ive adjusted them back and forth but nothing. Whenever it tries to crank it backfires but will not start. I have been told it could be out of time or the spark advance be off but no on has been able to give me a definite answer. Any suggestion on what I should do?

 

[WillyBWright]

Re: 1977 Johnson 115 v4 backfire when tries to start

Timing was my first thought too. The flywheel key may be sheared. Make certain the plug wires are going to the right cylinder Two might be swapped.

 

[JB]

Re: 1977 Johnson 115 v4 backfire when tries to start

The problem here is that different people call very different behavior by the same term.

"backfire" could be a spit out the carbs, a cough or a very loud bang out the exhaust.

Could you describe what you call a backfire?

 

[DJ]

Re: 1977 Johnson 115 v4 backfire when tries to start

If you get a truly loud "BANG" or pop through the exhaust, you have a plug wire crossed.

 

[F_R]

Re: 1977 Johnson 115 v4 backfire when tries to start

Has anybody been monkeying with the wires at the power pack? But it sounds like a sheared flywheel key to me.

 

[OBJ]

Re: 1977 Johnson 115 v4 backfire when tries to start

I'm kinda' with JB here....would like to know a little more about the "backfire".

Does the engine turn over fast when cranking or is it a little slow? You need a good battery on these V4's to get them to crank over and start.

 

[mississippisportsman81]

Re: 1977 Johnson 115 v4 backfire when tries to start

The backfire i am referring to is a loud pop coming out of the exhaust which is usually accompained by a flame coming from the exhaust. I just bought this engine and when I mounted it , it cranked and then i hooked my throttle cables to it this is when my problem started dunno maybe its just coinciednce, I dont know. It was running tho before I hooked the throttle cables to it. I havent actually run my boat with this motor on it yet since Ive run into this problems with the installation of the motor. Thanks for any help you can give me.

 

[F_R]

Re: 1977 Johnson 115 v4 backfire when tries to start

That cannon shot fire coming out the exhaust says it is firing at the wrong time. It's already been suggested that some wires are crossed or that the flywheel key is sheared. Both will cause the problem. Since it was running and then didn't run, my money is still on the key.

 

[Walker]

Re: 1977 Johnson 115 v4 backfire when tries to start

Pull the darn cables back off and see what she does!

 

[R.Johnson]

Re: 1977 Johnson 115 v4 backfire when tries to start

I'm not sure when OMC started glueing the sensor magnet to the flywheel hub. Pull the flywheel, and see if that sensor magnet ring has slipped.

 

[mississippisportsman81]

Re: 1977 Johnson 115 v4 backfire when tries to start

Im gonna check those cables in the morning and make sure they are right, like i say I havent had em off but I guess they coulda been wrong when i got the motor, and Im gonna pull the flywheel and check the key and all , Ill let you guys know what I find and I do appreciate the help thus far. Thanks.

 

[OBJ]

Re: 1977 Johnson 115 v4 backfire when tries to start

You could check the leads from the power pack to the ignition coils. On the cover of the power pack there should be a diagram of where the leads go. Take a minute and check it out.

 

[mississippisportsman81]

Re: 1977 Johnson 115 v4 backfire when tries to start

I want to thank you guys for your help, I checked my motor out today the wires were not crossed but the flywheel key was sheared. I picked up one from work, I work at a tractor dealership in the parts department. It did not last tho sheared it right off, dunno maybe the metal was too soft anyway I got online and ordered the OEM replacement key that way I know Im putting the right thing in there so maybe that will work for me.

 

[OBJ]

Re: 1977 Johnson 115 v4 backfire when tries to start

Gotta make sure the mating surfaces are clean metal to metal matches 81. And did you use the correct torque spec?

EDIT: I'm hedging on the spec cause I can't remember what it is....LOL!!

 

[F_R]

Re: 1977 Johnson 115 v4 backfire when tries to start

The key is really not to be depended on to keep the flywheel and shaft oriented, but to align them till the nut is tightened. After that, the stress on the key is minimal. The tapers on the parts and nut torque is what holds them.

The tapers on both parts must be undamaged, clean and dry. NO oil, grease, anti-sieze or anything else. And the key slots must be undamaged. I think the torque spec is 100-105 ft/lbs, but double-check that before you proceed. That is vitally important.

If the parts are damaged, you'll never get it to hold.

 

[Dhadley]

Re: 1977 Johnson 115 v4 backfire when tries to start

After the key sheared, was the nut loose?

 

[DJ]

Re: 1977 Johnson 115 v4 backfire when tries to start

Let's go back to basics here.

1. Since you hooked up new (to that engine) cables do they fully retract? Look at the timing arm (Right-starboard) side. Does it go back to full rest at idle?

2. Did anyone mess with the spark plugs? Putting the wrong lead on the wrong cylinder will certainly cause a backfire. (Been there-done that) It's simple. You have four coils 1.2.3.4 from top to bottom on each side. The top coil on side one corresponds to the top spark plug on the same side-ditto for the other side..

Check the simple stuff first. OBJ and Dhadley made me do it and I fixed one that I thought was really messed up-doh! I took my jears and kept my wallet loaded.
d