kdx bogging

[kaosroolz]

I have a 1995 kdx200 with a fmf pipe, no air box lid and boysen reeds and ever since I've started running it on avgas (108+ octane rating) it has started bogging when the throttle is snapped open, if u just roll it on itll go ok, it was fine when running normal pump gas, its running a 45 main jet. Any ideas??

thanks

 

[Jtown]

Try raising your needle a notch (drop the clip 1 notch) and see what it does. My bike had the same problem with pump gas and raising the needle eliminated the problem. It was running a little lean off idle. If it helps but doesn't fix the problem, you may have to go with a bigger pilot jet.

 

[canyncarvr]

What does 108+ avgas do for you?

That rating (octane) is a number assigned to a fuel to compare it to, well...OCTANE. The higher the octane#, the slower it burns.

In a low compression engine, that isn't necessarily a good thing.

Anyway, it's a jetting issue. Probably resolved by adjusting the air screw, although your pilot is a bit on the fat side.

Which is opposite of what jtown said, I realize. It depends on what type of 'bog' it is. I'll bet it's too rich on the pilot @ 45.

But you NEVER listen to what someone says is THE way to jet. You have to figure out your own setup.

...but you're probably too rich;)

BTW...you don't say what pipe, but a -35 runs richer (needs a leaner jet set) than a -30 does.

Another BTW...I'm assuming the 45 is a pilot jet. It its a main jet, you've seized it already.

 

[D36-108A]

...or he left the "1" off 145. hehe, for some of us, our pilot is our main jet.

 

[kaosroolz]

Thanks for the input, it has a 155 jet and a 45 jet (not to sure which 1 is which), as for the pipe number I cant find 1, it was on the bike when I got it all I can see what it says is fmf gold series, the needle is on the middle clip. Would advancing the timing help it at all??

Thanks fo the advice

 

[D36-108A]

The FMF part number may be on the high mounting tab. You've got the same setup and jetting I do, but I have a RAD valve. I'm not sure about aviation fuel but race gas often makes bikes run richer. I'd lower that needle.

 

[G. Gearloose]

Hope you come up with a good reason to use avgas before Rich finds this... :eek:
Why would you want all that plug-fouling lead on your plug, anyway?
No, don't touch the timing, you really gotta sort out the jetting and gas thang before you can properly evaluate the effect of altering timing.

 

[canyncarvr]

Aw c'mon!! Mr. rich never has anything but nice to say about ANYthing or anybody.

It would be fun to read his take on 108 av-gas in a kdx..........

 

[kaosroolz]

I use avgas because the pump gas here is such poor quality its not worth buying and race gas is hard to come by and very expensive, it seems to make the engine run cooler for the tight woods riding and gives a small power increase, it also smells good but thats just a bonus. I put it all back together today only to find I was outa gas so I couldnt find out if it was running any better, I'm hoping for good results.

 

[Michelle]

They sell avgas here as racegas, but you can also buy proper race gas (hard to find) at $6-7 a litre (so US$3-3.50 or so a LITRE, not a gallon). If you talk to pretty much any Kiwi and they mention race gas, they will be meaning avgas.
It is not unusual and goes in all sorts of bikes for MX, enduros, trails, harescrambles, whatever (except I doubt it goes in trials bikes somehow lol). As for smelling good, I much prefer pump gas with motul 800 to avgas with it, but don't notice it anymore anyway ;)

I run a 50/50 mix of 96 & avgas, which was recommended to me by the previous owner (Chris Birch), as the KDX didn't like straight avgas or straight 96. I'm not sure if you're in Auckland or where. My jetting's not 100%, but is okay - it just suffers spooge. I've got a PC pipe, FMF muffler, pretty much no airbox, radvalve, boyeseen reeds and think that's about it. Had to run premium the other week as left it too late to get avgas. It was slightly harder to start, but it's a good standby.

BTW, your pipe is probably a rev pipe as they're the most common FMF pipes over here. I'm one of the few I know of that's got a torque pipe - it's a lot fatter to look at & kept being asked what the hell pipe I had on my bike when I was running with it. If it looks very similar to the PC, it's definitely a rev.
Hope that helps some.