Spark Plug

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, and others.
KevTrem

KevTrem

Well-Known Member
Messages
897
Location
Newcastle, UK
Morning all,

I have a question about spark plugs and what signs are given when they start to go bad. I'm running NGK CMR7H in both rigs and both have been running good so not pushing my luck, btw both are 29cc 30Degree North Engines running 997 Carbs.

On one of the rigs its becoming a pain to start, pulled the plug and it seemed OK, decided to preheat the plug with blow torch, banged it back in and engine fired straight up, I tested remote kill, then fired straight up again fine.
Left it for a day and a pain to start, wouldn't even crack on the choke, pulled plug, blow torch, cracked on second pull and fired up like nothing was wrong.
I'm gonna throw a fresh plug in anyways, but does this sound like a fouled plug or am I barking up wrong tree?
Thanks in advance for your knowledge and opinions
 
Last edited:
Seandonato73 said:
My motto with plugs is, when in doubt chuck it out. Your most likely I bit on the rich side, but not a huge deal if you don't mind tossing a plug in now and then.
Click to expand...
I'd rather replace the plug than keep rebuilding engines every 3rd bash. I think it was the original plug from when I bought the engine last August, so more than happy to swap it out.
I'll take a picture of it later and bang it on here.
 
As promised here is a picture. (Ps I'm highly impressed with the camera on Samsung S21 - new phone week lol)
Going by the video above this defo looks like a fouled plug to me, plus swapped it out for a new NGK CMR7H and it cracked straight into life. 20210415_153855.jpg
 
Cut the threads off, and repost if you feel like it. In general you rich, and your using plenty of oil judging by the amount left on the plug. Cant tell top end tune on an old plug super accurately. But you'll get a good idea by where the tan ring is on the top of the porcelain farthest away from the electrode. You'll also be able to see if the timing is good or not.
 
Seandonato73 said:
Cut the threads off, and repost if you feel like it. In general you rich, and your using plenty of oil judging by the amount left on the plug. Cant tell top end tune on an old plug super accurately. But you'll get a good idea by where the tan ring is on the top of the porcelain farthest away from the electrode. You'll also be able to see if the timing is good or not.
Click to expand...
That would mean diving into the bin to dig it out.
I run 25:1 fuel to oil ratio and have killed at least 3 top ends from running lean, so having someone like yourself tell me I'm running rich will suite me just fine for now while I gather experience and confidence to tune it a little leaner as I run it more.
 
Running lean is a separate issue from oil ratio. The higher ratio of oil you run will make you run leaner on fuel. (All needle settings staying the same) they should be treated as separate issues. Little extra lube and fuel doesn't hurt the engine per say, just doesn't achieve max power. I too try to er on the safe side as well. Just don't run near as much oil as some do.
 
You can't accurately tell if your tune is rich or lean by looking at the tip of the electrode. You really need a magnifying glass and look down inside the base of the porcelin insulator on a new plug to gage your tune. If you google "plug chop" theres some excellent reading on the subject. What you do NOT want to see is silvery speckles stuck to the electrode this means your getting detonation and thats not good.
 
Last edited:
Polar_Bus said:
You can't accurately tell if your tune is rich or lean by looking at the tip of the electrode. You really need a magnifying glass and look down inside the base of the porcelin insulator on a new plug to gage your tune. If you google "plug chop" theres some excellent reading on the subject. What you do NOT want to see is silvery speckes stuck to the electrode this means your getting detonation and thats not good.
Click to expand...
RIGHT HERE !!!
 
KevTrem said:
I may try changing my oil/fuel ratio a little, see if that helps stop fouling the plugs.
Click to expand...
It will not. Go back and read Seand's post #11. It speaks facts about oil ratio and plug fouling. Trying to lessen your oil content percentage in an attempt to "lean" your engine running condition is going about it wrong. Stick with whatever oil ration you prefer and tune your carb for best acceleration behaviors. I don't like suggesting "plug color" as i said its not the best way to accurately verify a tune, but if your plug insulator is a dark brown, and you don't hear any high rpm "crackle" (too lean), you have a decent tune for your average rpm operation. The "plug chop" test is the most accurrate method for verifying your peak and "loaded" engine rpm tune.
 
Polar_Bus said:
It will not. Go back and read Seand's post #11. It speaks facts about oil ratio and plug fouling. Trying to lessen your oil content percentage in an attempt to "lean" your engine running condition is going about it wrong. Stick with whatever oil ration you prefer and tune your carb for best acceleration behaviors. I don't like suggesting "plug color" as i said its not the best way to accurately verify a tune, but if your plug insulator is a dark brown, and you don't hear any high rpm "crackle" (too lean), you have a decent tune for your average rpm operation. The "plug chop" test is the most accurrate method for verifying your peak and "loaded" engine rpm tune.
Click to expand...
But also needs done on a fresh plug for accurate readings.
 
Back
Top
✖
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock    No Thanks