Strange 'backfiring' issue

[andrewdouv]

I'm by no means a boat mechanic but I've spent a lot of time wrenching on these V4's and have come across an unfamiliar issue.
Not sure what its called, but the gold port shown in the picture, (on the head, to the left of starter) shoots fire during the backfire. Also sprays some fuel at the same time.

What is this called? Is it an exhaust relief port or something like that? What do I do to fix this?
Also I have 2 weak coils on the motor currently. They're coils that went bad on another motor, and I epoxy'd them, got good resistance readings and stuck em on this motor just so I could start really working on it (I'm very cheap).

Will new coils fix this do you think?
This motor is new to me and didn't have this problem when I got her running the first day with new coils. Today is day2 and suddenly its sneezing and backfirin and shootin fire.

Really hoping I don't have to open up the head

 

[andrewdouv]

To clarify: When I say ran well first day with new coils, I meant ran well the first day I put my rebuilt crap coils on there. And day 2 with rebuilt crap coils I began getting backfire

 

[racerone]

What motor is this ??

 

[V153]

What year? Model? HP?

 

[andrewdouv]

Can't believe I forgot to mention--- It is a 1976 135 HP Johnson V4 (135EL76)

 

[boobie]

Put some decent coils on it. If that doesn't do it, check your flywheel key.

 

[andrewdouv]

Put some decent coils on it. If that doesn't do it, check your flywheel key.

Will pull good coils from my primary boat (same motor) to try. Anyone know what the gold oriface is from my original post? If I had a bad coil and was firing on three cylinders, why would the excess gas be shot out of here. Furthermore, why was it igniting on its way out the hole?

 

[emdsapmgr]

A sheared flywheel key will cause the engine to get out of time. Backfiring is a normal result. Any fire inside the engine can get transmitted back into the engine if the timing stroke is off. The only open crankcase port in that area is the small brass nipple for the airbox drain hose. It's right below the starter on the port front of the block. Normally that hole is plumbed direct into the block on the bottom cylinder. It will suck excess fuel/oil out of the airbox back into #4 cyl where it is burned normally as the engine runs. Sort of an environmental protection thing. So, it's a direct hole (port) into #4 cyl. Any back fire could exit that hole at the incorrect time. Further, it's possible that the brass nipple end is missing and all that's left in the hole is remnants of the brass nipple which would need to be drilled out and replaced. Fire would come out of there in that case. Do you see any sign of the airbox drain hose on that engine?

 

[andrewdouv]

So I found a hose draining airbox flooding into the front of the powerhead (2). I also found that the gold ring is long enough to be a nipple for a hose (3) though obviously not connected to anything. So am I right in thinking the purpose of this hole is an exhaust relief specifically designed to spit fuel/release pressure during a backfire?

In regards to a sheared flywheel key-
I don't have the tool for removing the flywheel. How expensive of a job is this? I have a second motor that if I swap all the coils, plugs, and starter from motor 1 to motor 2 I'll have another running motor. I am also pretty broke right now. I also have access to a tractor to swap the motors 'easily' (I've done this more times than I care to count). How much would it cost to get a shop to replace the key for me? How confident that this is solution? I rechecked my coils and I'm getting good resistance readings on all, so I don't really think they are the problem, but I'll be able to replace them with new coils this weekend from a third motor I have stored elsewhere.

 

[racerone]

????--------There is no exhaust near that nipple at all.-----And it is not a pressure relief either.-----There is something wrong in the engine if fire spits out of that hole !-------Start with a compression test on this motor and report the results.

 

[emdsapmgr]

Sound like that nipple is intact-is hard to see in the picture. That bottom intake manifold nipple connects a hose to the airbox drain nipple. Fire can come out if the engine backfires due to being out of time. A sheared key can be the culprit. Rent a 3 legged automotive harmonic balancer puller-it will pull the flywheel of the top of the crank once you've got the big nut removed. Replace the key with only a factory. It's special. Make sure you absolutely torque the flywheel nut to the proper torque, or it can shear again when cranking.

 

[Fed]

Shouldn't that #1 non connected hose go to the crankcase for the pulse?

 

[Bosunsmate]

You say that hole is on the head? Ive never come across anything like that

 

[Fed]

I think the nipple is on the crankcase Bosun?
I's still be worried about the backfire, isn't that why they invented pulse limiters.

 

[andrewdouv]

????-------Start with a compression test on this motor and report the results.

Compression is even on all cylinders between 125 and 130 psi.

That bottom intake manifold nipple connects a hose to the airbox drain nipple

That's correct, but that is a different nipple than the one that shoots fire.

Rent a 3 legged automotive harmonic balancer puller-it

Sounds much better than paying the boat mechanic. Thanks, will try this.

Shouldn't that #1 non connected hose go to the crankcase for the pulse?

I'm not sure where it goes, I don't have my other motor here to compare. Will need to wait til the weekend

You say that hole is on the head? Ive never come across anything like that

I'm using 'head' as a general term like 'engine block'. I'm still learning

Also what is the 'pulse' you guys are talking about? And is this really strange for fire to be coming out of here? If so I'll try to get a very clear video of it for the youtube in case other people get the same problem, I can link to the solution here (hopefully).

I am very curious as to why I didn't not have this problem on Day 1, although admittedly I only ran for 10 minutes on Day 1. It backfired once or twice and then ran fine the rest of Day 1. Then Day 2 and onward it happens very frequently. The next time I start the motor I am going to do everything the same as I did in day 1 (removing the plugs, draining the carbs, pumping gas through etc) to see if I can recreate the smooth running in case this has anything to do with the vacuum and fuel delivery.

 

[Fed]

Your fuel pump has 3 hoses, fuel in, fuel out & a pulse hose that should be connected to the crankcase to make it work.
The clever people here will be able to advise you if you should also install a pulse limiting gadget.

 

[V153]

That is the pulse fitting for the fuel pump. As your pump is not mounted onto a crankcase port, this is how it's driven. You say it runs without that line being connected? Hmm.

 

[andrewdouv]

That is the pulse fitting for the fuel pump. As your pump is not mounted onto a crankcase port, this is how it's driven. You say it runs without that line being connected? Hmm.

I never ran it for more than a minute or two. The backfiring and stalling made me weary of causing damage of running too long. Okay, it's too late at night to run the motor but I'll hook it up in the morning and report back.

 

[Fed]

The backfiring probably blew the hose right off, perhaps an early version of a pulse limiter. Better than damaging the fuel pump.

 

[racerone]

????---------Wrenched on these motors for some time ?----------All 3 hoses on that pump need to go somewhere !-------One is fuel in on the cover.------One is fuel out to the carburetors and one is the pulse hose.