Axiom Home Page Forums General Discussion The Water Cooler mechanics or spark plug change experienced???

Jay (or others) something I have always wondered, how important is setting the gap when you put the new plugs in. I always do it out of habit but how perfect does it have to be to noticeably effect performance. I know others who don't bother and seem to get along fine.

Well actually, my good ol' reliable 4.0 ltr inline 6 seems to work best when I avoid fancy plugs and stick with your basic Champion model and it comes preset at a 'correct for me' .035 so I don't have to touch them. But I still wonder how much difference a tenth of a millimeter can make.

Murph, a couple of winters ago my neighbour couldn't get his snowmobile started, which had been in storage for the summer in his garage. He had mentioned that his fuel mileage had dropped off somewhat the year before as well. Anyway, after several minutes of attempts, I told him to check the gap on the plugs...he was reluctant, thinking that it had run the previous year and he hadn't changed the gap. Well, we tried and tried to start it, figuring that maybe it just needed to burn off the fogging oil, but it just wouldn't catch. We took out the plugs finally and checked the gap...If I recall(couple of years ago) it had measured somewhere around .030" so I checked his engine (700 cc Skidoo) online and I believe the required gap was around .024". We tried cranking the motor with the plugs out to check for a spark at .030 to no avail, so I suggested we gap both plugs down at .002" increments to see where the motor would start. At .028" nothing, wouldn't catch, at .026" it was catching but only just...hard to start, but started non-the-less with a rough idle. So we took it down to the recommended .024" and it started much easier and ran better, although there was still a touch of roughness in the idle so we actually took it down to a gap of .022-.023 and it ran/started easily and smoothly. That could have easily explained why he was using so much fuel before and also would have made his sled run rough with much less power. I know this is a TWO stroke motor and may well be more succeptable to gap changes but I was amazed that such a small adjustment was the difference between not starting and running well(literally a few thous)...after that, it started on the first crank, every time.

Jay, the problem is that this plastic piece is to recessed in the spark plug hole to be able to twist it free. I tried needle nose, but pieces kept breaking off. My guess is that since I've never changed the plugs/cables they have become one.

Anyway, I was able to get it loose eventually. I may see what one of those removal pullers would cost. This would help eliminate dropping pieces down the cylinder.

Jay, the problem is that this plastic piece is to recessed in the spark plug hole to be able to twist it free. I tried needle nose, but pieces kept breaking off. My guess is that since I've never changed the plugs/cables they have become one.

Anyway, I was able to get it loose eventually. I may see what one of those removal pullers would cost. This would help eliminate dropping pieces down the cylinder.

I meant the twisting part before it breaks off. Once it is broken off then anything is fair game. I have used pry bars down beside the plug and a quick snap of the porcelain to break that section free. I am all too familiar with this scenario, it is not fun.

Murph, the plug gap is quite critical as Adrian pointed out. The older style non-HEI ignition systems were only good for ~20,000V and would only jump a much smaller gap. This is more or less the case Adrian had with that skidoo. The coil just didn't have enough power in it to jump the larger gap and Chrysler products are reknown for weak ignition coils. I can remember.035" as a standard and Champion is the OEM plug of choice by Chrysler, amazingly set to .035" from the factory. It seems to me the early to mid 90s is when almost all manufacturers had coils strong enough to jump larger gaps for increased fuel mixture burn in a bid to increase fuel mileage. I could get into the theories of flame fronts and ignition timing and how all of that relates to the plug gaps but I won't. I will say that if the top fuel dragsters and funny car guys get as anal as to have all the electrodes on their spark plugs lined up in the exact same position, say 6 oclock in when installed in the head, not to mention the plug gap on all cyliders, just to coax an extra tenth or thousandth of a second there must be something to it.

Cool Thanks guys. My question is well answered.
Another one of those things I did religiously but never knew why, is now better explained.

update: don't have time to tell you about all the rediculous problems I had, but the plugs/cables are in and the Rodeo is running like brand new again, not slugish anymore. Must not have been the transmission.

I do plan to get the tranny fluid/filter changed anyway someday.

thanks for all the help.

I don't exactly remember the miles you mentioned and am too lazy to click my way back to the top but I remember thinking it would be a good idea anyways.

Glad to hear things are running smooth again. Nothing more frustrating than a car that's not quit performing. Sometimes it's how I feel about getting a cold. Instead of weeks of trying hopeless remedies, sometimes I'd rather just have a bad flu for a couple of days and get it over with

Glad to hear it worked out, I figured it would once I heard you still the original wires and plugs in it. Almost always, a tune up is the first place to start, you did very well getting that much mileage out of the originals. I highly doubt you will get that much out of this set. I would be pulling the plugs out every 20K - 30K miles just to see how much the electrodes have worn down and to ensure the plug wires don't get as burned on as they were.

Yeah, I was suprised how much of the electrodes had been warn down compared to the recommended gap. Funny thing, these were Champian plugs in it, which I highly doubt are from the factory. I wonder if some mechanic in the past robbed my original ones and put in crap.

I still need to probably get the tranny fluid/filter changed. Just need to decide if I want to try to tackle it myself or pay to have it done.