plug chops

[camel]

numpty question i know but ive never done a proper plug chop
ive just built a bike with an iron stage 4 200 italian barrel..
30mm phbh with breathe sweet filter
ads 3 exhaust
jetting.55 pilot,av264 atom.x7 needle on 2nd clip and a 120 main
trying to set up from zero throttle to mid range
so how long would you advise to hold the revs at a given point before you cut the engine?
sound iffy to do that when riding but is that how its done?
im not miles away with how it rides but obviously i dont want it running weak.
any tips on doing the plug chop would be appreciated
thanks in advance

[ArmandTanzarian]

Actually that's a really good question. I've always assumed that I know how to do one but no one has actually told me the definitive method to get the best results.

[Andy Pickering]

From Goggle:

Usually, a person performs a plug chop to see the effects that a recent tuning has had on the engine. The plug can be interpreted to give information about the fuel/air ratio. It is important to realize that other factors (such as compression, weather, and carbon buildup) can affect plug readings and that chopping is only a glimpse of the goings-on inside the engine. All the same, it is a useful tool for analyzing the condition of an engine.

Performing the Plug chop

First, buy a new spark plug (used plugs won't give a good reading), but don't install it yet. Drive around for a few miles to bring the engine to full operating temperature and install the new plug. Now find a good straightaway with low traffic and run WOT for half a mile or so. Note: Some sources recommend running 5 miles or more to get a good reading. While still at WOT, hit the kill switch and coast to a stop. Do not allow the engine to idle before turning it off. The reason for this is that you want the plug to show the conditions of your engine at its hottest temperature and greatest amount of fuel/air mixture. Remove the spark plug and put the old one back in and ride home. Now you can carefully examine your plug

Look at the spark plug under a good light, paying attention to the area deep in the plug around the base of the center ceramic (you can cut the plug with a hacksaw if it helps). A nice chocolate brown color should be about right. Death white or gray is too lean (too much air, not enough fuel), black is too rich (too much fuel, not enough air). When adjusting the fuel/air mixture of your engine, you always want to start out rich and work your way down. Running a little rich won't hurt as long as it rev's out well and isn't fouling plugs but you should avoid running lean as it leads to poor lubrication and high temperatures, which can lead to engine seizure, piston holes, and loads of other bad stuff.

[Andy Pickering]

Another thing to add to this would be to put masking tape on both your throttle housing and grip, this way you can measure out your throttle positions etc..1/4..1/2..3/4..full, you can then do plug chops for the full rev range and adjust idle/needle-clip position/main jet..to ensure correct settings throughout the rev range

If this is a new bore you might want to up the main to 125 to ensure its rich then work down to 120..also you will find av266 richer again if its a new bore and piston..

[fred]

i tend to put a dot with tippex,or similar on the twistgrip,then 3 marks on switch housing at 1/4 , 1/2 , 3/4 throttle. I ride for a few miles till plug colours,or use an old plug.i normally do my plug chops in 3rd,especially at 3/4,and full throttle,as it revs higher than 4th.
ride for as far as i dare at each marking,ie ride at 1/4 throttle in 3rd for as far as i dare then turn ignition off,clutch in. plug check. then 1/2 throttle,3/4,and full.
I also tend to jet carb with a b8,w24,n3. then use a b9,w27,n2 for peace of mind.
this isn't definative,but it's served me well for over 20 years.
hope this helps
fred

[camel]

good advice thanks
Andy i just replaced the av266 for the 264 as it was a very slightly boggy from zero throttle(which mite be down to the filter),but i may put it back,i also have a 125 main at hand.
so its kill the ignition and clutch in the coast to a stop......sounds easy lol

[warts]

The engine should be under load too. You wouldn't consider doing a plug chop by just revving on the stand. A longish slow incline works well.

[tony]

The engine should be under load too. You wouldn't consider doing a plug chop by just revving on the stand. A longish slow incline works well.

Best advice ever. Get the motor under load midrange or low down where you will drive most going to rallies etc. You cant replicate that on an inertia dyno. And this is what Ralph was getting at with his famous 'saying'.

[Minority]

The engine should be under load too. You wouldn't consider doing a plug chop by just revving on the stand. A longish slow incline works well.

Best advice ever. Get the motor under load midrange or low down where you will drive most going to rallies etc. You cant replicate that on an inertia dyno. And this is what Ralph was getting at with his famous 'saying'.

OK, I'll ask, what famous saying?

[Andy Pickering]

The engine should be under load too. You wouldn't consider doing a plug chop by just revving on the stand. A longish slow incline works well.

Best advice ever. Get the motor under load midrange or low down where you will drive most going to rallies etc. You cant replicate that on an inertia dyno. And this is what Ralph was getting at with his famous 'saying'.

OK, I'll ask, what famous saying?

It rimes with swallocks..

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