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Unread 09-28-2014, 04:03 PM   #1
turbogus
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Motor 'spits' once in a while

Well, a couple of weeks back I went and visited my good friend Craig formerly of the late great Macs Jeeparts (We lost a 'beard of knowledge' God Bless you Mac) a couple of years ago.
Anyway, Craig had to move up the Freeway to Jefferson and on the way back Black Betty ('78 CJ5) was getting pushed by maniacal traffic on I-5. In the process I broke loose some carbon and closed the gap on one of my plugs, shorting it out and causing a miss, with that the exhaust tune changed and I changed out all of the plugs. This took care of the miss, but now I have a new issue. Randomly and only once or twice in my 12 mile commute the motor (AMC 360) 'spits', (like a small backfire through the carburator) note that this is random and normally only once a day. The exhaust note has not yet returned. This occurs when the motor is at operating temp and cruising on the Highway, this 'spit' has yet to occur during slower, stop and go city driving.
Since, I've run a tank of Premium fuel through her and reved up the rpm's shifting at 3800 rather than my usual 3000.
I'm leaning toward a fuel issue and if I have time I'm going to check my fuel connections tonight, and perhaps change out the fuel filter - one of the few items I have'nt touched since first buying 'BB'.

I welcome any other opinions as after my 11 hour work day my mind is on wind down and I'm zombie'n pretty hard.

Thanks and a lift of the lynch lid.
Gus

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Unread 09-28-2014, 04:05 PM   #2
Matt1981CJ7
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Spits what, where?

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Unread 09-28-2014, 04:12 PM   #3
turbogus
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The spit I refer to is like a small backfire through the carb. It's almost as though there's a momentary lean condition.
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Unread 09-28-2014, 04:24 PM   #4
rah2eq
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I'm fairly certain that the only way for an engine to backfire through the carb is due to a timing issue where the intake valve is open at the same time as the plug fires. Given the fact that fuel is always flowing through the carb, there has to be a source of ignition in the case of a backfire. It could be related to a timing chain issue, distributor issue, or even a camshaft/valvetrain issue. I'd lean towards something with your timing chain or distributor for a backfire as infrequent as you describe.
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Unread 09-28-2014, 04:46 PM   #5
Matt1981CJ7
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Quote:
Originally Posted by turbogus View Post
The spit I refer to is like a small backfire through the carb. It's almost as though there's a momentary lean condition.
rah2eq hit on the most likely culprits above.

I'd start by checking the rotor and cab. Look for carbon trails in the cap, indicating any cross-firing. Make sure none of your plug wires cross or touch each other. If everything looks OK, I'd check timing.

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Unread 09-28-2014, 06:46 PM   #6
turbogus
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The Cap and Rotor are recent Standard and Blue Streak and the plugs are brand new. I'll check the timing and the cap tonight if I have time

The odd thing is this single spit only happens at the most once per day, yesterday not at all.
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Unread 09-29-2014, 08:59 AM   #7
turbogus
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Going to search for my timing light tonight, haven't seen it since the move two years ago.
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Unread 09-29-2014, 10:01 AM   #8
JeepHammer
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Quote:
Originally Posted by rah2eq View Post
I'm fairly certain that the only way for an engine to backfire through the carb is due to a timing issue where the intake valve is open at the same time as the plug fires. Given the fact that fuel is always flowing through the carb, there has to be a source of ignition in the case of a backfire. It could be related to a timing chain issue, distributor issue, or even a camshaft/valvetrain issue. I'd lean towards something with your timing chain or distributor for a backfire as infrequent as you describe.
I don't agree...

USUALLY the 'Sneeze' through the intake is a camshaft or valve issue.
For fire to make it into the intake and up through the carb, the intake valve has to be open.

Most vacuum leaks, momentary lean out conditions happen and cause a misfire, not a sneeze through the intake.

Cross fire in the distributor will sometimes cause this, but that would mean one plug is firing 90 to 180 degrees too soon, while the intake valve is still open.

I would suspect a broken valve spring not keeping the intake valve closed,
Something in the valve seat keeping the intake valve open, Ect.
A compression test would tell you if you have a valve/valve seat issue.

You will also get a sneeze through the intake if you have a lifter keeping the valve open too long.
Again, a comprehensive compression test should show this issue.

Lean out conditions usually don't lead to a backfire through the intake,
It's usually more of a 'Pop' when the super lean cylinder detonates,
And the 'Pop' rattles EVERYTHING which a lot of people misinterpret as a 'Mild Backfire', but it's hardest on the valves/piston/rings/rod/crank.

The tell of the tale is to check your compression,
Remove the air cleaner top, look for carbon on the top of the air cleaner and inside the air fliter.
Backfires leave carbon residue in the intake tract, so if you find carbon you KNOW FOR A FACT the intake valve didn't close...

*IF*... You are correct about something getting loose and hammering a plug gap closed...
Then you have more serious issues than you think.

Anything large enough to hammer a plug gap closed is large enough to bend a valve if it got caught between valve and seat.
It's also big enough to have damaged the valve seat surfaces allowing FIRE to get into the intake tract...
Again, a compression or leak down test will show you this in short order...
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Unread 09-29-2014, 10:36 AM   #9
Mike Romain
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If your pistons are kicking off big enough carbon chunks to close a spark plug gap, my first suspicion would be a chunk occasionally holding a valve from sealing tight.

If you want yo get all the carbon out at once, find a place where smoke won't be an issue and slowly pour a pint of ATF down the running carb while keeping the revs up high enough so it doesn't stall. This will create a huge cloud of smoke and make your combustion chamber clean like new. Back when I worked in garages this was part of a fall tune up for city driven carb engines or before tearing down an engine for a valve job. I have heard of others using a pint of water this way, but have only seen and done the ATF way.
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Unread 09-29-2014, 02:02 PM   #10
turbogus
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Thanks JH and Mike, I was hoping you guys would chime in. Lacking time and tools this may be a while before I can do a compression test. Indeed it was flaky carbon that bridged the gap on one of the plugs. Sorry for my mis text "closed the gap" in my earlier post. Once I have results I'll post 'em here.
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The parts shop that stocks part for Skylab II will not have parts for our year/model of Jeep
We cannot accurately judge the trajectory of a speeding critter (cat, dog, sasquatch)
Record heat waves and floods only occur when we visit that area
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Unread 09-29-2014, 06:21 PM   #11
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I normally agree with Mike Romain, but on this we differ GREATLY!

I wouldn't use ATF unless you want to change the muffler when you are done.
ATF will also kill a cat converter, for anyone reading that is thinking of doing this...

A tall pop bottle of water will work fine, something between a pint & quart,
Have a HOT engine, run the throttle up to about 2,000-2,500 RPM and TRICKLE the water down the carb.

First off, the water will IMMEDIATELY turn to steam when it hits the combustion chamber,
Where oil of any kind will start making carbon, the water will steam clean pistons, ring lands, combustion chambers, and in most cases will remove a good deal of crud off the back side of the exhaust valves on the way out.

Not only don't you piss the neighbors off with a bunch of smoke,
But the steam will clean out all SOFT carbon on the way out, and a good deal of hard carbon also.

The draw back here is, you will make STEAM, and what ever your exhaust pipe is pointed at will turn black!
Momma will kick your butt if you coat the side of the house with black soot that WILL NOT wash off!
And you can PERMANENTLY stain concrete with this exhaust, so keep that in mind, this stuff will NOT wash out no mater what you do!

The second thing is,
Depending on the muffler you have, you can actually plug up that muffler with carbon out of the engine.
most mufflers won't, but those super quiet types can plug up... Just a risk you take.

I also wouldn't do this until I was ready to change oil.
Steam WILL migrate past the rings, into the oil pan/engine and the moisture WILL condense in the oil and turn the oil brown.
So an oil change isn't a bad idea afterwards...
Some of this depends on your rings, older, leaky rings will allow more moisture into the oil pan,
And if you use a lot of water, quart opposed to just a pint, you will get moisture in the engine.

Think about it this way,
Transmission fluid is HYDRAULIC OIL,
Pouring a high temp hydraulic fluid down the intake is a REALLY good way to hydraulic the engine to death.
Nothing like sending a piston through a cylinder wall, or wadding a connecting rod up like a pretzel.

Water turns to steam as soon as it hits the chamber. Steam can compress, so you reduce the chances of a hydraulic lock.
Steam cleans MUCH better than something that will burn, adhere to the cylinder and make more carbon.

My dad and his friends STILL swear by kerosene or ATF, and I hear guys repeat that all the time...
There is NO WAY I would pour a hydraulic fluid into a rotating engine!
I've seen head gasket leaks fill cylinders over night, and just the starter motor pushed the piston right through the cylinder wall,
So there is no way I'm going to use a high temp hydraulic oil when water/coolant will blow a cylinder out with nothing but the starter motor!

I hear them say that water will wash off the cylinder walls...
Maybe so, but ABOVE the rings.
Below the rings at 2,000 to 2,500 RPM there is PLENTY of oil being sloshed onto the cylinder walls off the crank and rods.
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Unread 09-29-2014, 07:23 PM   #12
Mike Romain
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Jeephammer has a good point about the cat. The engines that used to get done where I worked didn't have such a thing. And no matter what you use, just trickle it in or as said, bad things can happen....

My CJ doesn't have a cat and when I changed my head gasket I used ATF first. When I opened it, it was clean like new and really easy to inspect the head for cracks, etc. Mine did blow out big chunks too, there were a couple left.

The smoke can stop traffic though, it is seriously thick stuff. Had a neighbour almost call the fire dept.
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Unread 09-30-2014, 08:33 AM   #13
turbogus
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I reckon I've got to figure out a strategem on where/when to do this with water. I remeber 30 years ago running a product called 'Carb-Out' in the 350 that what in my '66 Malibu ~ made one heckofa smoke plume for about 30 minutes but in that case it was something else that was the culprit.
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The parts shop that stocks part for Skylab II will not have parts for our year/model of Jeep
We cannot accurately judge the trajectory of a speeding critter (cat, dog, sasquatch)
Record heat waves and floods only occur when we visit that area
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Unread 09-30-2014, 03:45 PM   #14
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It's a case of what will do the best job with the least side effects.

Since water will IMMEDATELY turn to steam in a hot running engine,
And will only condense into water if it remains in the cat converter/muffler,
And since steam is a wonderful cleaning agent while leaving behind zero residue,
And the thermal shock of water to steam will pop loose more of the carbon you are trying to get rid of,
Water is best to NOT smoke up the neighborhood! Steam usually disapates quickly, usually within about 10 feet or so, good for NOT having the fire department show up!
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Unread 10-01-2014, 08:23 AM   #15
turbogus
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Thanks JH, despite your disclaimer " 'Free' internet information is worth EXACTLY what you paid for it!" Your posts are one of a short list that I've come to rely on over the last few years. I may try this on the dock at work this week depending on whom is present at the time.
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The parts shop that stocks part for Skylab II will not have parts for our year/model of Jeep
We cannot accurately judge the trajectory of a speeding critter (cat, dog, sasquatch)
Record heat waves and floods only occur when we visit that area
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