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Old 10-31-2019, 07:27 AM
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Cliff R Cliff R is offline
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Default Learned a good lesson yesterday, long read but worth it.

Not directly Pontiac related but the information sure applies to what we do here.

So I consider myself pretty good at working on engines, carburetors and see a lot of small power equipment in the shop. I own a hole host of older chainsaws, mostly Husqvarna models and use them a lot as I heat my house and shop with firewood.

Back in the Spring my pride and joy Husqvarna 268XP chainsaw starts running like crap. It got a complete "make-over" back in 2009. This included rebuilding the Tillotson carb, intake gaskets, new fuel line/filter, tank vent, crank seals, gas cap, and air filter.

It's been flawless since, then when I pulled it out after sitting most of the Winter is refuses to idle for more than 2-5 seconds after you come out of a cut. Flawless at WOT and making great power like it has for decades.

So I just figure the carb is gummed up or it's got at air leak in the intake system. I removed the spark plug and laid it against the jug and it's firing fine. Moved on to the carb and bought a new genuine Tillotson kit for it and no improvement. I ever removed the Welch plug in case there was some debris hiding under it, no better. Replaced the fuel line and tank vent, still woln't idle. Replaced the intake gaskets even though they looked perfect and same deal if not running a little worse at this point.

Then I started making tiny adjustments to the metering lever height as it was acting like it was running out of fuel at idle, it only gets worse and worse so I got frustrated and shelved it.

Last Sunday I'm getting all the saws ready for firewood cutting and take another stab at it. Now it refuses to run more than a few seconds. I go back thru EVERYTHING, spark is fine, fuel line good, tank venting fine, carb is spotless and correctly adjusted but it will not run.

Hum, right before I put it away I looked over at my 1980 Husqvarna 480CD and just for the heck of it stole the spark plug out of it and put it in the 268XP.....it roars to life and runs FLAWLESSLY.

Good lesson learned here with spark plugs. Just because they fire like crazy out of the engine doesn't mean they work when tightened in place. I was feeling pretty stupid about this entire ordeal after such a simple fix but though I'd put it up here so others could learn from it.......Cliff

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Old 10-31-2019, 08:11 AM
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HWYSTR455 HWYSTR455 is offline
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Yeah, have had similar experiences with plugs, guess the resistance in the ceramic tower starts going up with age/use. Since small engines use a mag, the idle rpm is usually lower on output.


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Old 10-31-2019, 08:17 AM
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So on performance cars, like what most here have, street/strip, if you're using regular plugs, like the AC ones, you should change them regardless of what they 'look' like at regular intervals. The factory recommends every 24k miles, and I suggest something more like 16k. If you run an MSD or other CD box, every 10-12k max.

Could probably add to that and say not only miles, but every like 3-5 years.


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Old 10-31-2019, 08:22 AM
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I feel your pain Cliff!
I had one of my motors on a dyno back in the early 80's and the plugs after the first 2 pulls where reading to hot, but the motor made the before hand estimated 525 hp pretty much.

I then installed a 1 set of one step colder Champs and the motor would hardly idle and was down 100 hp to boot, yet was not missing!

Along with the plug change we took the Holley apart to jet up 1 number so we had to work first had to work thru the Carb to confirm it was ok after the issue started.

In short it turned out to be a full 8 of the brand new Champ plugs that where bad!!

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Old 10-31-2019, 08:37 AM
mgarblik mgarblik is offline
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Cliff, I have been burned by that same situation a couple times. Interestingly, it always seems to be 2-cycle engines that get me. One was a Lawn Boy D-series. Had the same situation as your saw. It seems car engines with multiple cylinders don't have as much of a pronounced failure. The other properly running cylinders mask the problem spark plug. With a small engine, you are one and done.

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Old 10-31-2019, 09:17 AM
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Spark plugs is something I've had no trouble with on my chainsaws and the plug in the 480CD is the original from 1980 and it has at least a zillion hours on it.

Most of the better saws will use Bosch or NGK's that I've seen, and they typically last the life of the saw, or at least this is the very first time I've had a spark plug mimic idle fuel delivery issues. I suppose it was just going bad and at low RPM's there was just enough resistance and the spark weak enough it could not sustain idle speed.

If you were working with the saw you'd think for sure it was fuel related as it idled OK briefly, then started to slow down and die out like it was running out of fuel/going lean. Sure threw me off but it's important to know here that spark plugs can function sub-par and hurting engine power and performance the entire time. For sure we can figure out when they completely crap out as we get a steady misfire and on a V-8 engine it only takes a few minutes to isolate the culprit.

I've had next to zero problems with these Pontiac engines far as spark plugs go. My NGK's are over 10 years old and still the engine runs flawlessly everyplace, although I'm thinking about swapping them out just for good measure after this recent incident with the 268XP........Cliff

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Old 10-31-2019, 09:21 AM
65CatCoupe 65CatCoupe is offline
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Changing the plug seems too easy so I've always resisted the urge. If its clean dry and gapped its gotta be something else. Sounds like that's not always the case.

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Old 10-31-2019, 09:33 AM
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Quote:
Originally Posted by mgarblik View Post
Cliff, I have been burned by that same situation a couple times. Interestingly, it always seems to be 2-cycle engines that get me. One was a Lawn Boy D-series. Had the same situation as your saw. It seems car engines with multiple cylinders don't have as much of a pronounced failure. The other properly running cylinders mask the problem spark plug. With a small engine, you are one and done.
Yep. Got a 10550 Lawn Boy. Last of the 2 strokes. That thing has done that to me a couple of times. Course , it takes me 100 rope pulls to learn.

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Old 10-31-2019, 09:35 AM
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Had my 065 Husky do that a few times, thought the ignition system was going bad, then would take for ever to get
started. finally broke down and changed the plug, just like new. Plug looks ok, but wasn't. Now I keep a spare when we get firewood.

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Old 10-31-2019, 09:38 AM
69 Limelight 69 Limelight is offline
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Default Learned a Good Lesson

Maybe that's why "back in the day" (mid 60's) the Ford tractor dealer I worked at (and just about any tractor or car dealer around here as well as most independent shops around here) had a spark plug cleaning machine that also had a feature that you could put plug in, hook up air supply and keep increasing pressure and watch it spark through a little viewing window. Amazing how many used plugs would quit firing under compression.

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Old 10-31-2019, 10:03 AM
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FWIW, the company I worked for had bought a new wheelbarrow air compressor for my service truck to operate air tools and blow out radiators etc, when doing PM services.

It was doing some really weird things as far as running and stalling after about one hour of total running since new. I took it to a Briggs & Stratton repair shop and in about 10 minutes the guy diagnosed it as a bad plug, installed a new one, wrote up the paperwork, and I was on my way.

I never changed that plug the entire time I worked for that company, it ran flawlessly for years after that. That was a Champion plug, which I have probably installed thousands of over my years as a mechanic. I've only had 3 bad ones new, that wouldn't fire in all that time.

I realize that Champion isn't the most favored plug amongst many service techs, and over the years I've heard lots of negative stories about them. Truth is, when I worked in GM dealerships, (of course you have no choice in what brand plug you install) I've seen many more AC plugs defective right out of the boxes.

Anyone old enough to remember, or have read about Milt Schornack doing the supertunes out of Royal Pontiac will probably remember he used Champion spark plugs, there must be some reason why he preferred Champion over AC while working at a GM dealership. I've met the man in person several times over the years, but never had the presence of mind to ask him why he preferred Champions. Hopefully someone will ask him that question in the future, I'd really like to know the rational for the choice.

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Old 10-31-2019, 10:17 AM
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I rank Champion spark plugs right up there with Fram oil filters. They do good for many, I've had very poor results with them over the years so avoid them. For the most part I use AC Delco, NGK or Bosch. NGK preferred if they have one for what I'm working on.......Cliff

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Old 10-31-2019, 10:44 AM
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Argh, 2 strokes humble my azz every time!
I have a fleet of dirt bikes as well as a few Sthil tools around here. Sometimes I can’t get one of my dirt bikes going and will give up on that thing and walk away. One of my kids will go out there and be ripping around on it after a few kicks! I always keep a supply of plugs on hand as my 2 strokes (except the Sthils) seem to be a lot more sensitive to plugs going bad.

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Old 10-31-2019, 11:21 AM
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On 2 cycle I used to always have to heat the plug tip with a propane torch and quickly put it back in and pull the rope. Always had to do that the first start of the season or I would have to pull the rope forever and never get it to start. After that it wood start for the rest of the season. Can't explain that. And it seems like the newer 2 cycle stuff I own is not as bad as it used to be.

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Old 10-31-2019, 12:01 PM
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I always wanted to do a horror spoof where the villain jumps out, but can't get his chainsaw started (complete with pulling it 50 times and spraying starter fluid, the whole deal).

Midway through he would be chasing the now less than terrified virgin around and it still not running.

By the end she would be standing around bored, while the repair shop owner is telling the deflated monster: "oh-yah- I can fix dat, but dat dere's going to be expenshive…."

K

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Old 10-31-2019, 01:17 PM
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Let me guess Cliff, it was a Champion plug. Some plugs will spark with no pressure on them but then add cylinder pressure, and they just can't overcome the pressure to spark correctly.

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Old 10-31-2019, 01:30 PM
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Sort of related concerning hard to start garden and small outdoor equipment. Although it's expensive stuff many swear by the cans of ethanol-free gas sold at hardware stores.


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Old 10-31-2019, 01:30 PM
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Don't you just love a good challenge like that

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Old 10-31-2019, 01:41 PM
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Quote:
Originally Posted by gtofreek View Post
...Some plugs will spark with no pressure on them but then add cylinder pressure, and they just can't overcome the pressure to spark correctly.
wonderful. something else I did not know that could go wrong that does and won't show up on a bench test.

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Old 10-31-2019, 02:25 PM
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Add the spark arrestor screen to the list of things that will mess small engines up. Throw those away first thing. If they get clogged, they won't fire a lick no matter what.

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