Major bogging - - Help

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#1
I recently purchased a '90 kdx200 that came with a pipe,silencer,reeds,air box cover removed and had been jetted accordingly..the bike ran great.
I decided to clean the carbon out of the pipe and repack the silencer with household insulation..After preforming this mantainance the boging problem started.
Now the bike bogs whenever I quickly snap the throttle wide open.The lower the rpms the more the bog. I'm talking total lack of power...as if someone turned off the power switch.
It will bog,then stutter,, then it will finall build rpms as it should.The bog will happen for about 2 to 3 secs.
If I roll into the throttle the problem does not exist.
Help,,,,did I repack the silencer too tight/loose. Do I need to rejet.
Does it seem to now be running too rich or too lean....
Doh!!
Thanks in advance :)
 
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#2
Since the problem started right after you performed these two tasks, it seemingly should be related. How did you clean the pipe out? Could something be in the pipe, restricting it? Are these the only things that you did? Very loose packing in a silencer can cause a lot of turbulence in the exhaust, effectively restricting it. The problem you describe does sound like a possible restriction in the exhaust. I had a Yamaha DT 250 once, and when i purchased it, it ran much as you describe. When you opened the throttle, it would sputter and break up for a few seconds, then clean itself out and begin revving correctly. The problem turned out to be a carboned up silencer. As for the jetting, if it ran correctly before, then the jetting is probably fine.
 
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#3
Yeah they have a perforated core in the pipe which might have fallen in, but unlikely as it is a real fight to get it out when you want to. Pull the muffler apart & check the packing is in the right place if it is standard muffler. Only over the perforated tube.

Try winding the idle mixture screw in if it gets better off idle it was lean (only off idle), maybe someone adjusted it with a dirty airfilter & the ungungeing of the pipe made it worse.
 
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#4
Thanks for the speedy replies.

Both the pipe and silencer are after market FMF bolt-ons.
Oven cleaner was used to clean both then a propane torch was used on the pipe. I cleaned out all the small holes in the silencer with a small drill bit. Man what a long task that was. As I mentioned I used standard insulation to pack the silencer. I tried to match the amount of insulation that was orginally stuffed in the unit. The orginal packing was drenched with spooge and the majority of the holes were plugged. My thoughts - - - there may be better exhaust flow now and I figured jetting my be a solution( just a guess there, I have read tons about jetting btw).
I think the key to finding the solution may lay in the fact that this only happens when I'm aggressive with the throttle opeining. Slowing rolling into the juice does not produce this prob.

I'm going to take apart the Silencer again. I'm absolutely positive there is not a blockage in the pipe.
talk soon.Thanks again:)
 
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#5
Here's a though/question.

If an exhaust gasket is missing or badly dried out will this cause my problem.
Just remembered that I only have one exhaust gasket as one broke while I was taking the pipe off..
I know, I know ( ..... I'll go buy one tomorrow....hehee :)
thanks.
Bucket
 
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#6
ok,,I've figured out what the problem is......

Here it is

.....ME !
Here's what I did/found.
I sealed up the exhaust at the header section of the pipe and where it enters the cylinder.. I repacked the silencer as recommend by the form.
Today was test day...In the morning it was cool > around 15'C < and the bike ran great.. No bog at all...yeehaa!!
As the day and the bike warmed the problem got progressively worse..
I know,,,colder air = more dense air = leaner mixture.(you'll understand ,,,read on)
Sooooo,,,I played around with the air screw and had no change what-so-ever. In/out it just did not make a difference.still bogged
I then pulled the choke out, went for a whrill and....TA-DA...no more bog.
And here I was going on about my jetting knowledge...oh well.
Now all I need to do is replaced my pilot jet with a larger one.right???

Any recommendations????(see above for current jetting specs)

Please keep in mind that adjusting the air screw to 1/2 turn out had the best affect..I chose not to turn it in any more for fear of the unknown...I'm sure a fully closed air screw would no be a good thing..I guess I'll buy 45,46,47 and just try them all.....

Thanks again...

Bucket-in training-
 
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#7
And again,,,an update..
I've been reading this form alot...everthing from jetting to the kips exhaust system....
and behold...yet another problem was found.
I found the the gears on the left exhaust valve stripped....If I manually operated the exhaust valve operating rod,,the right and main exhaust vavles would work. The left would only operate sometimes.. Parts on order.
I think I still have a lean pilot jet as the engine has a ton more power when the choke is operated and the air screw is almost all the way in..
later.
Bucket
 
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#8
Yeah that left one is a pilock id-in-tit?

Just out of interest look at your carb slide to check for wear. Mine is so badly grooved that I believe it is letting air past in the idle position.

I’m just trying to psych myself up for the cost of a new one, which costs about the same as 2 powervalves. It’s only a slide dammit!
 
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#9
Hello all.
Sorry for taking soo long getting back to the form. (too much overtime I guess)
Here's the latest.
I did indeed find the jets I was looking for.
I replaced the exhaust valves,replaced the #45 pilot with a new 48 pilot jet...buttoned the engine up and went for a ride..
Wow!! what a difference..especially after I dialed in the pilot circuit using the air screw..
I still feel I'm a little lean at WOT...The power really flattens out at the top.
I'm going to install a new 152 main and test...I also have a 155 main if the weather gets cooler...currently we are at about 15-20'c.
When I say wow,,I really mean WOW.. I near scared myself a few times last ride..
The bike pulls amazingly well right from the bottom, through the mid and the unfortunetly flattens out at the very top.
The sound this little monster makes is incredible. It really growls now.
I hope the main will clean the wot problem...if not I'll look at the timing.
thanks and I will keep all posted.
Bucket - in the dirt -:D


P.S. It'd be nice to have someone experienced riding the KDX200 take my bike for a spin...An experienced opion on how my unit is performing would be very advantagous.. I live in the Toronto Canada area and ride maining in the Ganaraski Forest.
Thanks again
 
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#10
Glad you are happy.

I’ve just received my new carb slide not an hour ago so look forward to some sensible results without it leaking.

$170 even in NZ Rupees is still a lot of dosh for something so small.

Nice & shiny though.