I see Fire (or spark) in one carburetor

[Ira]

With my cover off the carburetors on my V6 1988 200 HP Evinrude, with the motor running at 2000 to 3000 RPM,, (not at idle) I notice that while the motor was running, that in one of the carburetor I could see it fire, (or spark) But in the rest of the carburetor everything seemed normal. What could cause this? For I know on a two cycle engine the piston is suppose to be up pass the intake ports before it fires, but this seems to fire at a delay or before top dead center. If timing was off, it looks like to me I would see fire in all of the carburetors. Does anyone have any suggestion? Thanks, Ira

 

[Scaaty]

Re: I see Fire (or spark) in one carburetor

Weird, probably blown Reeds...

 

[F_R]

Re: I see Fire (or spark) in one carburetor

Weird, probably blown Reeds...

Wierd, indeed!! I hope we get a feedback when he finds the problem. I don't have a clue, but am thinking blown piston. A compression test certainly is a good starting point.

 

[Barnacle_Bill]

Re: I see Fire (or spark) in one carburetor

Reflection from a light?

 

[JoLin]

Re: I see Fire (or spark) in one carburetor

Being a newbie to 2-cycle engines, I immediately equated it to a sticking valve on a 4-cycle, which would cause backfire and potentially, flames through the carb. The valve is all that stands between the spark in the cylinder, and the fuel intake via the carb.

If the reeds on a 2-cycle are what stand between the spark and the carb, then I'd also guess a problem there. My (uninformed) 2 cents.

 

[F_R]

Re: I see Fire (or spark) in one carburetor

Pondering on the problem a bit more and considering what JoLin said, I can see where a reed could be involved. In the first place, that cylinder can't be "running" with fire in the crankcase. So the fire has to come from somewhere else, probably back pressure from the exhaust. The piston and cylinder ports act as the rest of the valving on a two-stroke. That is where my pot-shot guess came from. But taking it a step further, even if the exhaust were blowing back into the crankcase, you wouldn't be able to see it through the carburetor because the reeds would block it.

So, logical conclusion would be reeds. And possibly piston involvement. Heck, maybe the whole thing is wiped out for that cylinder. It could have tossed a rod, wiping out the reeds and everything else in it's path. Back to square one: a compression test.

 

[Dhadley]

Re: I see Fire (or spark) in one carburetor

It's not unusual to have fire in the crankcase, especially at idle. If you're actually seeing it, it's most likely because of a reed issue. The reed could be hanging open or be broken.

The fire in the crankcase can be aggravated by a lean condition - which running it under a load with the airbox cover off will certianly do - or by a "double firing" or shadow firing ignition component on that cylinder. That cylinder may be getting spark when the intake port is open.

If you've run it very long (it can happen in seconds) without the airbox under a load you may already have a damaged piston.

 

[TerryMSU]

Re: I see Fire (or spark) in one carburetor

Quoted from DHadley...

"If you've run it very long (it can happen in seconds) without the airbox under a load you may already have a damaged piston."

What are you talking about? The plastic box over the carb input or the overall cowling that covers the entire motor? How would that damage a piston? I don't doubt your word, I just want to understand what the issue is here.

Thanks,
TerryMSU

 

[Dhadley]

Re: I see Fire (or spark) in one carburetor

On an 1988 OMC looper the carb assemblies are calibrated with air flow coming in from behind and around and then into the venturi. Removing the airbox cover changes that pattern and therefore changes the calibration. It'll lean out, usually about 12 to 15 numbers. Running it that lean at speed under a load can result in a damaged piston rather quickly.

 

[Ira]

Re: I see Fire (or spark) in one carburetor

Hi, Thanks for your response. I checked the reed valves and they seemed to look find, I even held them up to the light and they seem to be sealing good. But I did notice that in that one carburetor on the reed valve housing that it looked a little burnt, not on the valve itself, but a burnt residue on the housing. The others looked find,, I checked the compression and all cylinders were the same 90-95 lbs. I Change the coil, wire, and plug, and still it's firing it that carburetor you can even hear it pop. It does not do it at idle, just when it's rev up a little. Runs find at crusing speed, but ragged at idle to the point that it cut off. Thanks, Ira

 

[Dhadley]

Re: I see Fire (or spark) in one carburetor

I think you're back to the double fire or shadow fire. Which carb is it?

 

[Ira]

Re: I see Fire (or spark) in one carburetor

Middle carb on starboard side.

 

[Dhadley]

Re: I see Fire (or spark) in one carburetor

OK, that feeds the middle port cylinder which is #4.

Does it do this with the air box cover on and off or just off?

 

[Ira]

Re: I see Fire (or spark) in one carburetor

I don't know,, I'll try it tomorrow and let you know. I probably won't be able to see it spark,, but with the carb cover off, I can see it, and hear it pop. So what I'll do is with the cover on I'll listen for the popping noise. (I do want to thank you, for your help) I'll let you know tomorrow. Thanks, Ira

 

[Dhadley]

Re: I see Fire (or spark) in one carburetor

Cool, keep us posted. Just don't run it anymore without the cover.

 

[Ira]

Re: I see Fire (or spark) in one carburetor

I tried running it with the air cover on, and motor cover on it. And it's still doing it, it's not backfiring, it sound like a sparkplug when it fires, (a sharp tick) it does not do it at idle, only when the motor is rev up a little. I'm wandering if the stator is shorting out and jumping fire somewhere. I've put a new Rectifier, and powerpack on it, the only thing left to change is the stator and timing plate. I tell you what I'm going to do: I'm going to find me some deep water somewhere and take my shotgun and blow a hole in the bottom of the boat and sink it!

 

[clemsonfor]

Re: I see Fire (or spark) in one carburetor

Just to clear things up for the guys that can help, you said "It does not do it at idle, just when it's rev up a little. Runs find at crusing speed, but ragged at idle to the point that it cut off" Then you said "it does not do it at idle, only when the motor is rev up a little". Does it run fine at idle of not? You should not need the covor off to see it just feel if the motor is surging/missing, etc. Not trying to question you, this maybe a mistype, just want to help clear things up!

-NAte

 

[CharlieB]

Re: I see Fire (or spark) in one carburetor

Early Force Prestolite ignitions would go bad, sometime cross-fireing, hitting one cyl a 2nd time during the intake, causing a flash in the intake, also made that cyl lean at speed and burnt the piston/cyl.

Prove it, use a timing light, bring it to the speed it occurs, check the timing mark, then look all around the flywheel again with the timing light, if the timing mark appears again in another spot, you just proved it's crossfiring and change the ignition module.

 

[Ira]

Re: I see Fire (or spark) in one carburetor

Okay, I see, Let me try to explain: It does not spark in the carb at idle, only when you rev it up a little to 2000-3000 rpms. then you can see it spark in only one carb. #4 (only now a then, it's not a constant spark). Now on the water at crusing speed or wide open it seems to runs find. But at idle it does cut off.
One mechanic said this spark in the carb, is normal, and it will do this sometimes and not to worry about it. I Don't know maybe he's right. Maybe the reason my motor won't idle could be dirty carbs. It idles find out of the water and yes it does seem the shake and sounds ruff at idle, but in the water it cuts off at idle.
If he's right about the spark in the carb, is normal, then my next step is rebuild the carbs. then maybe it will idle smooth.
Do you think this spark in the carb is normal? Anyone?

 

[Dhadley]

Re: I see Fire (or spark) in one carburetor

Without reprinting my answer above let's do this -- if you even think the carbs are dirty, clean them. That may be the issue but lets not take the chance of leaning out a cylinder from lack of fuel and/or oil.

We may still be looking at a double firing ignitio but lets get the basics out of the way first and clean the carbs.

While you're doing that, look up under the flywheel. Are any of the 6 outer magnets loose?