So dis guy sez

How can some outrageous driving trick reveal the true state of your car's spark plugs/fuel mixture? That's a bit like taking cocaine and holding your breath before checking your blood pressure, isn't it?

On Fri, 21 May 2004 17:30:43 -0700, "Mike Rocket J. Squirrel Elliott" ran around screaming and yelling:

you should listen to him, he knows what he is talking about....it is common practice to do a highway "plugcheck" when dealing with carburetion issues.. JT

That's about _exactly_ how you are supposed to do a plug check. Better to get up to highway speed for 20 minutes, push in the clutch, kill the engine and brake to a stop. It's even better if you can coast into a spot where you can kick back and let the engine cool. It's a b*ch doing a plug check on an ACVW. #1 and #3, you see.

It works. It's the right thing to do. What's your problem? Cocaine?

I concur with JT. I have heard the same advice from more than one source, including someone who works at Gene Berg. The problem is, because of thermal expansion, taking the plugs out when the engine is still warm can result in the aluminum threads in the head coming out wedged in the steel threads of the plug. And who wants to wait an hour or more for the engine to cool off? I was lucky to make a 75 mile drive home from the Mojave Desert after performing such an operation without a spark plug popping out.

Randall

No, that is a metaphor.

My point is if you never go around driving on the highway with your engine turned off, how can that possibly show you the state of your engine's normal driving condition? (Just as artificially stressing your heart can't show your normal blood pressure.)

It was sound advice.

Jan

*Mental note to self - Next time I go to the doctor, do not, I repeat do NOT snort cocaine and hold my breath just before they check my blood pressure like I did last time. :-) *munches on early-morning pork rind*

A while back I was gonna tell you about how I used to do plug checks on my race bikes. I figured you weren't "ready for it" yet! :o) It involved a mile long blacktopped test track with banked corners and a really long straightaway. It also involved locking up the rear wheeel and sliding to a stop from around

60-70mph (small dirt bikes!) It also involved a broken crankshaft and a couple wasted pistons and some bent rods, so I decided maybe it wouldn't go over real good here!

If you are testing the jetting of the mainjet circuit, the last thing the plugs should be exposed to is the mixture you are testing - that is, on the mainjet only with good flow through the running engine at proper operating temperature. In a perfect scenario, you would pull the plug while the engine was pushing you down the road at 60mph and read it then. I haven't figured out a way to do that just yet! Years ago I had a gadget that screwed into the plug hole that had a mica window so you could see the color of the combustion. I don't think I ever got it to work. I most probably didn't comprehend the complexity of the issue (much younger and smarter back then!)

Oh yeah, my comment above about "on the mainjet only" - there is, AFIK no time at which a carb is "running" solely on one jet circuit. All the jets influence and need to balance out with each other. Compromise is reality. -BH

house, cooling down

20-mile bike

of all things

we swap stories

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turn off, kill

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been wondering if

automobile

shorts. What do you

Uh, kill the engine and push in the clutch at the same time, then brake to a stop. Then check. I don't understand the problem.

The theory being that as you kill the ignition the engine continues turning and the resulting fuel entering the cyls and being compressed and exhausted will significantly change the coloration of the plug. If you stop the fuel and air or otherwise stop the engine too suddenly something is very likely to be damaged significantly. Your way is the best way until something better comes along - which it won't! I might recommend loosening the plug(s) - remove them and put your choice of high pressure / high temp lube on the threads and reinstall without tightening to the full torque spec before running it (stock engine). This is just for a very short term and if your threads are already marginal, you could blow a plug out. As soon as you've gotten up to test temp and speed do the reading then torque the plugs properly.

I suppose you should never torque the plugs when they're hot or even warm (or the head's hot or even warm) cuz as it cools, the plug could become too tight and strip threads.

Speaking of coloration, I have been clearing out my old engine parts and found a really neat wristpin - it must be a fancy hi perf model cuz it has two really bright blue stripes around it! I was amazed at how well the heat transfers at the conrod. The part of the pin that was in the piston is brown with spots of blue. The part that was in the bearing (rod) was still shiny silver like it's supposed to be. The little bands where it was not in contact with either and were totally exposed are brilliant blue from heat. Definitely a collectors item! (Must remember to check oil more often!) -BH

,

it

time, then brake to

[snip]

And I thank you guys for your advice. Don't know if I'll ever see those guys again, but if I do and if they have any other words of wisdom, I'll be sure to listen.

Do all the theory you like, but that's not what happens. I've done plug checks for twenty years. No problem. Good results.

Which brings up another facet of checking the plugs. Over on the Type2.com forum, it was suggested that the good ol' color photos that illustrate plugs, their various and wondrous colors, and the causes thereof*, are out of date. According to the poster, those charts date from leaded fuel days, and today's fuel formulations give more subtle results.

*For example:

The chart in question is still valid, although I'll bet hardly anyone sees all conditions in their life. I've never seen ash fouling, and the only glaze fowling I've seen was from my primitive British motorcycle runining

12:1 compression with, ah, "creative" additives to supress pre-ignition. (What a freaking mistake that whole setup was.)

IMHO the perfect plug reading is either a very light tan or very light grey - depending upon the fuel.

So what are you saying? You can't read? Try the second sentence after the one you quoted. Of COURSE it works fine. Of COURSE it's the way to do it. SHEESH! -BH

,

engine

cyls

change

I've done plug

Sorry, I can't understand what you are saying. I can't read. I can only write.

Considering that, yer doing pretty damned well. BTW - I've got 34 years of plug reading. So THERE! -BH

,

read. I can only write.

Well, I kilt a bear when I was only three. So there! (Is that too obscure?)