If you do plug chops

A reference for the PWK carbs...
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Re: If you do plug chops

Post by KDXGarage »

Awesome pics!
Thank you for participating on kdxrider.net. :bravo:
To post pictures from a device: viewtopic.php?f=88&t=24128
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Re: If you do plug chops

Post by John_S »

Here are some more pictures of main jet plug chops. Making multiple runs on one plug first started as a necessity because I don't have a long trail to hit 6th wide open. I found later that I like having a couple runs on it for better color. I start with a fully warmed up engine then put a new plug in and would take off from the truck 1st - 4th wide open, pull in the clutch but not kill the engine, turn around while idling then 1st - 4th wide open back to the truck this time pulling the clutch and killing the engine. That's what I'm calling 2 runs below in the description. It was a long enough run that I could hold wide open for at least 4-5 seconds after the bike is no longer revving any higher. It's weird at first because your brain is screaming at you to shift when your engine has fully flattened out. My instinct says it's gonna blow but it takes it like a champ. Start too rich and bring it down.

The first picture is a 160 main with 2 runs and shows why you can't just pull the plug and glance at it to see how your overall jetting is. This plug only has a minute on it and all three circuits look jet black from the overly rich main.
160.jpg
160.jpg (37.31 KiB) Viewed 6353 times
The second pic is a 155 main with 2 runs and it gained 640 max rpms over the 160
155.jpg
155.jpg (31.14 KiB) Viewed 6353 times
The third pic is a 150 main with 2 runs and it gained another 680 max rpm over the 155, 1320 over the 160.
150.jpg
150.jpg (34 KiB) Viewed 6353 times
The fourth one (which had something wrong with the pic and won't load) is a 145 with 4 runs on it. It looks pretty much just like the 150 picture. It gained another 430 max rpm over the 150, 1110 over the 155, and 1750 over the 160.

The seat of the pants horsepower gauge says it gained a bunch of power from 160 to 150 and the 145 feels amazing, especially with the addition of the FMF Rev pipe. The occasional full throttle, 2 foot high, long pull wheelie from the 3-4 shift makes all that messing around worth it. It won't do that nearly as easy with a 150.

My bike has a trail tech with rpm readings but one of those $20 ebay or amazon hour meters that also record max rpms are a great thing to have. I have one on another bike and its been good for years.

Edit: These 3 plug pictures are from an Honda 250R but all the notes were from the KDX. The KDX plug chops looked exactly like these. Both bikes used the same 4 jets, starting at 160 and both ending up at 145.
Last edited by John_S on 12:22 pm Jun 29 2020, edited 1 time in total.
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Re: If you do plug chops

Post by SS109 »

Thanks for the additional pics.

It's funny to me that so many people think their jetting is "good enough" without ever checking or realizing how much power and fuel mileage they are leaving untapped. With posts like yours, John, they have no excuse to not get it right.
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Re: If you do plug chops

Post by John_S »

Yeah it’s a trip. The differences in these jets or needles could be what seems like thousandths of an inch difference make a big change in power. The KDX isn’t known as a screamer but the right main jet makes a huge difference in power down at the 3, 4, 5,000 rpm at full throttle.

SS I’ve seen you on a few occasions talk about the 18mm float height. I have a clear water bottle looking “gas tank” that hooks on the handlebars if you’re working on the bike so you can start it without putting the tank on. When my float was at 15 I started it one time and it was drinking the gas at idle. We’re talking full guzzle where you could watch it go down quickly but the bike still idled and didn’t run horrible. Then with the 18mm float and the right pilot jet it seems like it would idle on that little bottle for a 1/2 hour. It’ll now get 5+ hours of ride time before it needs gas. Go on a 1/2 hour ride and it still looks damn near full. It sips gas. I put a KX85 petcock on it and don’t even worry that it doesn’t have reserve. The wrong pilot, needle, or main and it would be a gas guzzler. It’s really worth the effort.
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Re: If you do plug chops

Post by ericr »

Thanks for the post, John! This really is one of the best tuning tips I've seen.
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Re: If you do plug chops

Post by SS109 »

John_S wrote: 10:23 pm Jun 23 2020 Yeah it’s a trip. The differences in these jets or needles could be what seems like thousandths of an inch difference make a big change in power. The KDX isn’t known as a screamer but the right main jet makes a huge difference in power down at the 3, 4, 5,000 rpm at full throttle.

SS I’ve seen you on a few occasions talk about the 18mm float height. I have a clear water bottle looking “gas tank” that hooks on the handlebars if you’re working on the bike so you can start it without putting the tank on. When my float was at 15 I started it one time and it was drinking the gas at idle. We’re talking full guzzle where you could watch it go down quickly but the bike still idled and didn’t run horrible. Then with the 18mm float and the right pilot jet it seems like it would idle on that little bottle for a 1/2 hour. It’ll now get 5+ hours of ride time before it needs gas. Go on a 1/2 hour ride and it still looks damn near full. It sips gas. I put a KX85 petcock on it and don’t even worry that it doesn’t have reserve. The wrong pilot, needle, or main and it would be a gas guzzler. It’s really worth the effort.
Yep, little things do make a difference. Glad you tried the 18mm float height. I picked that up from smarter people than I am. I was just smart enough to listen! :mrgreen:

Oh, BTW, because this info is so important to jetting, it is now a sticky here in the Jets and Needles sub-forum. :supz:
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