Low rpm bogging

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Derepic
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Low rpm bogging

Post by Derepic »

On my 1993 Kdx200 its bogging really bad in the low and lower middle rpm ranges. It pulls decently once you get on the pipe.

FUEL:
I don't think it is jetting as I have tried everything from 155-140 main and 48-36 pilot with every step in between. I've landed on 35 pilot and 150 main 3rd clip position and the air screw about 2.5 turns out. It also idles really bad. The air screw seemingly does nothing and it will only stay alive if you have the idle adjust turned all the way in.
With the carb out it looked really clean inside and the guy who had it before me had ultrasonically cleaned it, I also adjusted the floats. So again I don't think its a fuel issue. (32:1 oil ratio)

SPARK:
I checked the timing and it was right on the arrow and the spark on the head while my buddy kicked it over looked maybe a little dim but it was definitely sparking.

COMPRESSION:
It passed a compression check with flying colors showing strong numbers right off rip

AIR:
The intake tract has no cracks on the inside of the boots and I just put in the Boyesen Power reeds thinking it was that. it idled really well one time when we tried it with no air filter but once it warmed up some it went back to crappy.

Here is a video where I ride it in 1st gear on my street. I was about 3/4-7/8 throttle there and it barley accelerates.
Before we changed the jetting a bunch it would surge and die really fast in that range almost like you were spamming the kill button. its a little better than that now but it still feels messed up.

Any advice appreciated I'm really at a loss for what to do here
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SS109
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Re: Low rpm bogging

Post by SS109 »

Your vid is set to private. Change your settings so we can actually view it.

There are lots of factors that can still be in play. Air leaks, weak ignition coil, failing plug wire, weak source coil, failing CDI, bad ground connections, etc., etc. Have you tested the jet block gasket? Also, is it a genuine Keihin carb and not a knock off? Have you done a leak down test?
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Current KDX: '98 KDX220
Old KDX: '90 KDX200 -White/Blue
'11 GasGas EC250R
Derepic
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Re: Low rpm bogging

Post by Derepic »

Sorry about that the video should be good to go now!

I plan on doing a leak down test tomorrow but I don't have a tester. I think the spark should be good enough to where it shouldn't bog like that especially since it pulls good in the higher rpms.

I have not checked the jet block gasket but I will do that tomorrow also.

I should mention that I found a significant amount of oil behind the stator cover.

Its the genuine stock Keihin carb.

I do want to replace the plug wire and other stuff since its relatively cheap to do also.
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SS109
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Re: Low rpm bogging

Post by SS109 »

Derepic wrote: 08:33 pm Mar 31 2024 I should mention that I found a significant amount of oil behind the stator cover.
That is concerning. There should be no oil there and that normally indicates a bad crank seal. A leak down test will confirm this.
Youtube Channel: WildAzzRacing
AZ State Parks & Trails OHV Ambassador - Trail Riders of Southern AZ
Current KDX: '98 KDX220
Old KDX: '90 KDX200 -White/Blue
'11 GasGas EC250R
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Re: Low rpm bogging

Post by KDXGarage »

It may be weeping from the steel inserts area. https://www.eric-gorr.com/files/pdfs/mo ... wasaki.pdf
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bufftester
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Re: Low rpm bogging

Post by bufftester »

Air screw at 2.5 and makes no difference when you adjust it tells me its either jetting or an air leak, the jet block gasket is a huge suspect in these types of issues.
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Trackdog
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Re: Low rpm bogging

Post by Trackdog »

SS109 wrote: 07:54 pm Mar 31 2024 Your vid is set to private. Change your settings so we can actually view it.

There are lots of factors that can still be in play. Air leaks, weak ignition coil, failing plug wire, weak source coil, failing CDI, bad ground connections, etc., etc. Have you tested the jet block gasket? Also, is it a genuine Keihin carb and not a knock off? Have you done a leak down test?
Totally agree. Could be any or a combination.
But a leak down would be a good place to start.
https://www.motionpro.com/product/08-0071
I have the Motion Pro kit. I was having trouble jetting a bike and found a leak at the manifold. Yet I still had people telling, try this, try that.
You have an air leak, your done.
My KX was giving me trouble until I replace the jet block gasket.
2004 KDX 200
2004 KX 125
1986 CR 125
1994 DR350
1998 VFR
2004 DUCATI S4R
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