What the F&@$ is Wrong with My Bike?

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Mayor Brap Brap
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What the F&@$ is Wrong with My Bike?

Post by Mayor Brap Brap »

As some of you may know, I have been through hell trying to get my KDX to run right. I was experiencing bad low-end stuttering and burbling in power. I went through the entire process of inspecting and cleaning my KIPS system, which now works just about the way it should. I replaced the floats, jetblock gasket, and nearly everything else in my carb, and cleaned it thoroughly. The air filter is new and oiled, and every part down to the crank has been inspected.

I recently went on an enduro trip in NH, riding some fast and sometimes technical trails. In order to get any sort of power, I had to shift up and pin it to reach mid to high power, as there was almost nothing down low. On the trip I experimented by putting in a larger pilot and main. After that, low end was completely unusable. When I changed back to the smaller pilot and dropped the needle, the low end got a lot better, but nowhere near great.

Thing is, it's jetted with a 42 pilot and 155 main. It seems like going down to a 40 or 38 pilot is crazy lean, but has anyone else gone that low? My friend, who has an H-series with identical mods, is at almost stock jetting (160 main, 45 pilot) and his bike runs perfectly.

What's going on here?
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Re: What the F&@$ is Wrong with My Bike?

Post by Tedh98 »

Would your friend let you try his carb? That would be an easy/quick way to rule out jetting and anything internal to the carb.

I run a 40 pilot in my 200.
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Re: What the F&@$ is Wrong with My Bike?

Post by Mayor Brap Brap »

Tedh98 wrote:Would your friend let you try his carb? That would be an easy/quick way to rule out jetting and anything internal to the carb.

I run a 40 pilot in my 200.
We threw his carb on my bike, but that was before I cleaned and inspected the KIPS system. So, there was no real way to tell if that was the issue. I guess some bikes like to be jetted leaner? I also have a #6 slide and 1173 needle.

Maybe I'll try his carb again now that everything else has been checked...
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Re: What the F&@$ is Wrong with My Bike?

Post by royadams »

Ive got a kdx 250 I run a 35 pilot. Thats just what it wants, I jet the pilot to the air screw. You cannot go by what someone else uses.
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Re: What the F&@$ is Wrong with My Bike?

Post by Mayor Brap Brap »

royadams wrote:Ive got a kdx 250 I run a 35 pilot. Thats just what it wants, I jet the pilot to the air screw. You cannot go by what someone else uses.
Interesting--I didn't know jetting could differ so much between model to model. On my old CRF230 I followed jetting recommended by a CRF specialist that many other riders were using with awesome results. On my ZRX, Ivan gives almost standard recommendations and it runs like a charm. Are two strokes that much different than four strokes when it comes to jetting?
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Re: What the F&@$ is Wrong with My Bike?

Post by Postigo »

It depends of your riding conditions, altitude, humidity and temperature. I'm in Puerto Rico here the humidity is always hight, the temperature is between 80 to 90 degrees with near sea level altitude my 220 Kdx is running 30/138 with a 1mm overbore piston and stock 33mm carb. She runs strong and crisp with this setup. Hope this helps. :supz:
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What the F&@$ is Wrong with My Bike?

Post by TrickyRic »

I have 2 identical ’98 and ’99 KDX’s here in Michigan both with Boysen reeds and modified air box lids, one with a fmf desert pipe and a stock silencer and one with a fmf woods pipe and a turbine core silencer. The jetting is way different. The one with the woods pipe runs great with a 38 pilot, BGQ needle 4th clip and a 152 main. The one with the desert pipe needed a 45 pilot, BEP needle 3rd clip and a 155 main. As you can see the woods set-up is way leaner across the board. There is no easy way to jet a bike, just ONE change and ride it to see if it gets better or worse. Just be careful! especially with the main.

p.s. The black frame is awesome!
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What the F&@$ is Wrong with My Bike?

Post by Mayor Brap Brap »

TrickyRic wrote:I have 2 identical ’98 and ’99 KDX’s here in Michigan both with Boysen reeds and modified air box lids, one with a fmf desert pipe and a stock silencer and one with a fmf woods pipe and a turbine core silencer. The jetting is way different. The one with the woods pipe runs great with a 38 pilot, BGQ needle 4th clip and a 152 main. The one with the desert pipe needed a 45 pilot, BEP needle 3rd clip and a 155 main. As you can see the woods set-up is way leaner across the board. There is no easy way to jet a bike, just ONE change and ride it to see if it gets better or worse. Just be careful! especially with the main.

p.s. The black frame is awesome!
Thank you! This is the information I'm after! I'll try smaller pilots and go from there... :supz:
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What the F&@$ is Wrong with My Bike?

Post by scheckaet »

have you read the jetting guide?
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What the F&@$ is Wrong with My Bike?

Post by Mayor Brap Brap »

scheckaet wrote:have you read the jetting guide?
Yeah, I know, I know. I've never had to jet via that method with any other bike in the past, and I'm really reluctant to do it because of the number of plugs I'll burn through and amount of time it will take.
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What the F&@$ is Wrong with My Bike?

Post by scheckaet »

i only burnt 2 plugs doing mine, in 1 afternoon...
if you're not gonna do the work then don't be surprised if it doesn't run right...just sayin.
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Re: What the F&@$ is Wrong with My Bike?

Post by Tedh98 »

Plug chops are for WOT.

If your problems are down low, then you won't be going through plugs. That is unless you are so rich you are fouling them.
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Re: What the F&@$ is Wrong with My Bike?

Post by Mayor Brap Brap »

I'll try to figure out the pilot with that method. How do I know I have the right idle before I start turning the air screw?
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Re: What the F&@$ is Wrong with My Bike?

Post by Tedh98 »

I always kicked my idle up a little higher from what I normally run. It seemed like it was easier for me to tell when the RPMs peaked.
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What the F&@$ is Wrong with My Bike?

Post by bufftester »

Mayor Brap Brap wrote:
scheckaet wrote:have you read the jetting guide?
Yeah, I know, I know. I've never had to jet via that method with any other bike in the past, and I'm really reluctant to do it because of the number of plugs I'll burn through and amount of time it will take.
You can lead a horse to water......

The jetting guide is the result of years of tried and true testing,and ALWAYS works for power valve 2Ts. It won't help with a 4T, or with someone with a 4T mentality...

There's a reason so many threads on here start with that advice, go weeks with every complaint about this and that not helping, only to end with "finally went through the jetting guide and it runs like a raped ape/scalded dog/select your euphemism...
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Re: What the F&@$ is Wrong with My Bike?

Post by Mayor Brap Brap »

Okay, I did the pilot test by setting the idle slightly high after being warmed up and starting with the mixture screw at 1.5. When turning it in, the idle lowered and bogged. Turning it out made little to no difference, maybe the slightest bit of an increase in idle speed. So, I went down to a 40 pilot. Took it out, and the bottom end was really nice. It still had a bit of a burble, but the front end was picking up nicely and quickly, quite responsive.

However, as I kept riding, gradually the problems reverted back, and my low end was extremely stuttery and crappy. Low end was usable, but far from enjoyable. So at this point, it looks like a gradual degradation of low end power as I ride. What the hell is going on?
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Re: What the F&@$ is Wrong with My Bike?

Post by ICRage42 »

ok maybe this helps you some.

Done the same thing as you. Cleaned my kips....didn't need it. Cleaned my carb and replaced jetblock. I had done a lot already and it had me stumped just didn't post about it because I found out what the deal was.....well for me. Plug chops fuel from the gods needles to make a necklace. You name it.

I had a very weird like crease in my air box boot to carb. You really couldn't see it ......I was able tho after a bit of clean riding and heat from engine to see just a little bit too. Seems with heat it got worse.

I couldn't get anything thing to really change wise with carb settings just ran. Kdx will do that tho hahaha.

Fixed the leak and whalla brap brap brap. I couldn't power over a 1x6 board in the yard without revin it to get the front off the ground. Drove me nuts went out to the garage and opened a beer leaned over and hugged the kdx and looked down at tear in boot. Gotta love how you inspect everything but yet you didn't see something right in front of you.

Take a good look and flex your boot to inspect. Hope it helps!
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Re: What the F&@$ is Wrong with My Bike?

Post by Mayor Brap Brap »

Inspecting my reed block and I found a gasket here:

Image

Should that even be there, or does the carb boot bolt directly to the reed cage? Also, what do stock reeds look like and how do I know if I'm having a problem with them?
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Re: What the F&@$ is Wrong with My Bike?

Post by Julien D »

If you'll flip that cage over we can have a look at the reeds. I think I see a peek of a stock reed stop on the other side. As for the gasket, it would not hurt to have one on both sides.
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Re: What the F&@$ is Wrong with My Bike?

Post by Putter »

An air leak from not having the gasket in from of the read block would not give "running rich" symptoms down low. In fact it would mask them.

Take your reed block and look through from the carb side while holding it up to the light. If you see daylight, replace the reeds. Reeds are a low rpm system that prevents air from pulsing back through the carb backwards (and picking up fuel) and then coming back through the next cycle picking up even more fuel.

Good luck your honor.
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