Plug chop

[globe]

OK so time for the plug chop. My bike runs good at all ranges except WOT now. I would like to find out if lean or rich. Question is how can I do a plug chop if it doesn’t hold consistent power at WOT, or do I not need to? All the instructions on the web talk about holding it at WOT but this feels dangerous given it’s running condition

Cheers

[Akzle]

OK so time for the plug chop. My bike runs good at all ranges except WOT now. I would like to find out if lean or rich. Question is how can I do a plug chop if it doesn’t hold consistent power at WOT, or do I not need to? All the instructions on the web talk about holding it at WOT but this feels dangerous given it’s running condition

Cheers

the rear doesn't *have* to be on the ground.
reading won't be hunnits as it's not under load. but should be close.

does it bog or cut out? smoke? backfire? did you put a bigger main in?

[globe]

the rear doesn't *have* to be on the ground.
reading won't be hunnits as it's not under load. but should be close.

does it bog or cut out? smoke? backfire? did you put a bigger main in?

I moved the needle up so the clip was on the bottom groove. What happens is I go to WOT then it loses power for a couple of seconds or so then shoots off as though it is kicking in. Or I back off the throttle and it kicks in again. Hope that makes sense?

Maybe flat spot is a better description?

[Akzle]

I moved the needle up so the clip was on the bottom groove. What happens is I go to WOT then it loses power for a couple of seconds or so then shoots off as though it is kicking in. Or I back off the throttle and it kicks in again. Hope that makes sense?

so it's hesitation/ stumble, (likely fuel starving) rather than it wont go WOT?

pretty sure i said in the last thread, you'll probly be looking at going up on jet size. float one too.

check again your tank vent, petcock. make sure fuel not getting held up there.

[Crasherfromwayback]

I moved the needle up so the clip was on the bottom groove. What happens is I go to WOT then it loses power for a couple of seconds or so then shoots off as though it is kicking in. Or I back off the throttle and it kicks in again. Hope that makes sense?

Maybe flat spot is a better description?

What bike are we talking about here Bro?

[globe]

What bike are we talking about here Bro?

GN250 mate

[globe]

Haven’t done the chop yet but this is the plug with only about 20-30kms under load.

[Crasherfromwayback]

GN250 mate


Haven’t done the chop yet but this is the plug with only about 20-30kms under load.

Yeah but a plug chop is only accurate if it's been pulled from the engine right away after a full noise run, as soon as the engine runs even for a couple of seconds on anything else it's void.

Sounds a lil rich to me. Have you got an airbox in place?

[T.W.R]

Yeah but a plug chop is only accurate if it's been pulled from the engine right away after a full noise run, as soon as the engine runs even for a couple of seconds on anything else it's void.

Sounds a lil rich to me. Have you got an airbox in place?

Exactly :yes: and it has to be a brand new plug to give a accurate indication of what's going on.
get the bike up to operating temp, fit new plug & do the chop, remove plug immediately to get a true reading

[Crasherfromwayback]

Exactly :yes: and it has to be a brand new plug to give a accurate indication of what's going on.


Yep. When I had my RS250, at $280.00 a plug from HRC, it wasn't something I wanted to do too often. Pity you had to though. :facepalm:

[T.W.R]

Yep. When I had my RS250, at $280.00 a plug from HRC, it wasn't something I wanted to do too often. Pity you had to though. :facepalm:

Ouch! that's worse than a plug for an RE5 :crazy:

back to the OP though,

All this is well & good, but importantly how many kms has the bike? when were the valve clearances done last? etc
Doing a plug chop is really only truly any help as a accurate indication on freshly dialed-in (tuned) engine; you'll be chasing your tail for ever if other items are adrift elsewhere.
Higher kms the more worn the cam chain is and if so the whole timing advances slightly and GNs haven't got the gruntiest of ignition systems stock anyhow. Plug heat range? is the stock plug etc

Realistically to accurately get it as close to spec as possible you have to go back to base settings, carb, valves etc

A quick look at that plug in the pic & the symptoms you say it's showing ....a simple change in grade of plug may be the only thing needed and go to a slightly hotter grade plug ie: if the in it is a stock 8 go one temp range hotter to a 7 and vise versa if it was showing signs of blistering you'd go to a colder plug up to a 9.

[globe]

Ouch! that's worse than a plug for an RE5 :crazy:

back to the OP though,

All this is well & good, but importantly how many kms has the bike? when were the valve clearances done last? etc
Doing a plug chop is really only truly any help as a accurate indication on freshly dialed-in (tuned) engine; you'll be chasing your tail for ever if other items are adrift elsewhere.
Higher kms the more worn the cam chain is and if so the whole timing advances slightly and GNs haven't got the gruntiest of ignition systems stock anyhow. Plug heat range? is the stock plug etc

Realistically to accurately get it as close to spec as possible you have to go back to base settings, carb, valves etc

A quick look at that plug in the pic & the symptoms you say it's showing ....a simple change in grade of plug may be the only thing needed and go to a slightly hotter grade plug ie: if the in it is a stock 8 go one temp range hotter to a 7 and vise versa if it was showing signs of blistering you'd go to a colder plug up to a 9.

Cheers going to check timings tomorrow. Clearances about 4 weeks ago. Popped a new plug in and took it for a spin. That’s it after about 10min riding about. No chop etc

[Akzle]

Cheers going to check timings tomorrow. Clearances about 4 weeks ago. Popped a new plug in and took it for a spin. That’s it after about 10min riding about. No chop etc

i mean. obviously.

http://www.bmwclassicmotorcycles.com/parts/wp-content/uploads/2014/07/Bosch-Spark-Plug-reading.jpg

[pete376403]

Now that lead has been removed from fuel does the plug still show the range of colour? ie from scary bone white through to sooty black with the optimum being a nice light chocolate tan? Exhaust pipes now look black no matter what the F/A ratio.

[T.W.R]

Cheers going to check timings tomorrow. Clearances about 4 weeks ago. Popped a new plug in and took it for a spin. That’s it after about 10min riding about. No chop etc


<_< Let me guess you've got a cheapy pop-gun aftermarket muffler & pod filter on this thing huh?

[Voltaire]

Now that lead has been removed from fuel does the plug still show the range of colour? ie from scary bone white through to sooty black with the optimum being a nice light chocolate tan? Exhaust pipes now look black no matter what the F/A ratio.

On my old race BMW tending to be looking at plug base ring color to determine mixture and electrode arm to determine heat range.

Once a plug fouls its bin time.

[jellywrestler]

Once a plug fouls its bin time. have you tried an ultrasonic cleaner?

[Voltaire]

have you tried an ultrasonic cleaner?

👍that’s a good idea.

[Cosmik de Bris]

the rear doesn't *have* to be on the ground.
reading won't be hunnits as it's not under load. but should be close.


Plug problems usually occur under load so revving it up on the paddock stand isn't going to tell you much.

Cheers