Assess my Spark Plug

Assess my Spark Plug

Author
Discussion

PH lurker

Original Poster:

1,301 posts

164 months

Sunday 2nd September 2012
quotequote all
I have just changed the spark plug on a small single cylinder 4-stroke motorbike I have recently aquired. I don't know how many miles or months it is since it was last done. I would appreciate any opinions (my own isn't anything like expert) on how my engine might be running if possible from a picture of it. It is very 'dry'.

Thanks. smile

HustleRussell

25,204 posts

167 months

Sunday 2nd September 2012
quotequote all
It looks about right. I assume it's a carburated engine?
It is not excessively sooty and it's not burnt or oily.

PH lurker

Original Poster:

1,301 posts

164 months

Sunday 2nd September 2012
quotequote all
HustleRussell said:
It looks about right. I assume it's a carburated engine?
It is not excessively sooty and it's not burnt or oily.
You assume correctly; it's a carburated engine.

Cheers.

ch427

9,742 posts

240 months

Sunday 2nd September 2012
quotequote all
not too bad, maybe a tad rich

trickywoo

12,305 posts

237 months

Tuesday 4th September 2012
quotequote all
ch427 said:
maybe a tad rich
yes

HustleRussell

25,204 posts

167 months

Wednesday 5th September 2012
quotequote all
trickywoo said:
ch427 said:
maybe a tad rich
yes
I would certainly agree with this were it an injected engine, but given that it's carburated I'd say it was normal (although I am assuming that the plug has done several thousand miles or a lot of cold starts on the choke).
In my experience, a carburated engine which appears to run rich can often be running lean at some points in the rev range, so I tend to leave well alone if the engine is running correctly and not fouling plugs up very quickly.

PH lurker

Original Poster:

1,301 posts

164 months

Wednesday 5th September 2012
quotequote all
HustleRussell said:
I would certainly agree with this were it an injected engine, but given that it's carburated I'd say it was normal (although I am assuming that the plug has done several thousand miles or a lot of cold starts on the choke).
In my experience, a carburated engine which appears to run rich can often be running lean at some points in the rev range, so I tend to leave well alone if the engine is running correctly and not fouling plugs up very quickly.
Thanks. This makes sense. The previous owner probably did use a lot of choke and commuted over hills through the winters. I expected it to have done a lot of miles on this plug too.

hman

7,487 posts

201 months

Wednesday 5th September 2012
quotequote all
clean it up, pop it back in, take it for a ride for 5 mins or so to warm up and after holding a constant 40 or so in 4th, kill the engine with the stop switch and whip out the ha ha ha hot plug.

If it looks fairly clean and the tip is a sort of straw colour then you are pretty much fine.

ian_uk1975

1,189 posts

209 months

Thursday 6th September 2012
quotequote all
Looks fine. Plug reading is tough to do with unleaded fuel anyway, so don't get bogged-down trying to fine tune your carb jetting from reading the plugs! Most important thing to note is no oil or heavy carbon fouling. For carb jetting (I'm talking about fine tuning here for max power), nothing beats a rolling road with an exhaust gas analyser. Looks like you're in the ball park though, so ride on smile

PH lurker

Original Poster:

1,301 posts

164 months

Sunday 9th September 2012
quotequote all
ian_uk1975 said:
Looks fine. Plug reading is tough to do with unleaded fuel anyway, so don't get bogged-down trying to fine tune your carb jetting from reading the plugs! Most important thing to note is no oil or heavy carbon fouling. For carb jetting (I'm talking about fine tuning here for max power), nothing beats a rolling road with an exhaust gas analyser. Looks like you're in the ball park though, so ride on smile
Thanks, very helpful. smile

I'd just like to say that this plug is not from the bike I'm selling, it's the from the bike I've just bought.


Athlon

5,169 posts

213 months

Sunday 9th September 2012
quotequote all
hman said:
clean it up, pop it back in, take it for a ride for 5 mins or so to warm up and after holding a constant 40 or so in 4th, kill the engine with the stop switch and whip out the ha ha ha hot plug.

If it looks fairly clean and the tip is a sort of straw colour then you are pretty much fine.
This is correct, How can you 'read' that plug in the pic? has it just started? been on a run, new/old gapped right for the engine etc etc

You can only get a decent read if the plug is correct for the engine, gapped correctly and the pulled when the engine is warm and been run at a constant, dyno best, drag strip good for full power runs, good road with lay by where you can kill the engine and coast in easiest.