Rad valve

[quote="queen of spodes":2dikr0v8][quote="CamP":2dikr0v8]The Rad Valve increases the vacuum signal on the carb so more fuel is pulled into the engine, which causes a richer condition. You need to lean the jetting to compensate for this.[/quote:2dikr0v8]

My top end was rebuild a few months ago (new piston & rings) and it still pings - more now than before. It pings when I'm on the gas, especially in mid & upper RPMs. It is even worse when the weather warms up. I've lived with the pinging since I bought the bike 2 years ago, but after installing the RAD valve it's much worse.

I use 93 pump gas, haven't tried race gas and don't have easy access to it.

I want to try going one size larger on my main jet but I don't want to damage anything.[/quote:2dikr0v8]

Going up 1 size on the main jet won't hurt anything. Detonation will.

The worst thing that will happen if you go too large on the main jet is you'll foul a plug. Too lean (like you are right now) will cause a blown motor.

When discussing jetting, remember it's throttle position you're thinking about, not rpm's.
The main jet controls the fuel from 3/4 throttle opening to full throttle.
Needle is 1/4 to 3/4
Pilot is 0 to 1/4.
Yes, there's more involved than that, but just trying to keep it simple.

Start out by getting the main jet correct, or at least closer. Pick up the next 3 sizes in main jets, probably 160, 165 and 170. Throw the 170 in there and see if the full throttle noise goes away. If it does, you'll know you're on the right track. You've got to start somewhere.

[quote="Knobbyjake":35zgnnj1]If you have an auto parts store or Walmart nearby you can buy octane booster there if you can't get race gas.[/quote:35zgnnj1]
I was always told NEVER use octane booster or fuel stabilizer or anything like that.

[quote="CamP":pui8z7lh]Most octane booster are nothing more than overpriced Toluene. The problem with Toluene is that when you add enough to make the bike quit pinging, you lose throttle response.[/quote:pui8z7lh]
And this is because when you start dumping stuff into gasoline products, you screw with the distillation curve. Automotive pump gas has a HORRIBLE distillation curve; the beginning, mid and endpoints are way undesireable. Not to mention pump gas is notorious for inconsistent blending specs. You can pull a sample from one tanker and it tests totally different than a tanker 2 day later. All those guys show is thier advertised RON+MON/2 data, and that is sketchy at best. Throw in RVP, specific gravity and the other specs, well its doesnt take long to see that pump gas is not too much better than pond water. And when you start mixing pump swill with other additives (or even 50/50 with decent race fuel) you end up with a witch's brew gasoline where who knows what the distillation curve actually is.

Its all about the distillation curve folks. Race fuel might be spendy, and no doubt most OEM dirt bike engines dont need the added detonation resistance - but race fuel DOES give you very predictable blending from batch-to-batch and a very favorable distillation curve that will allow your bike to get closer to stoichiometric combustion.

If all else fails stack 2 base gaskets, this will reduce static compression and decrease port timing. Cometic makes a thicker base gasket if this works. Does that year KX have the wire that goes to the carb for throttle position sensor, try unhooking it.

This bike should run on pump gas, shouldn't it????

[quote="Foster576":yzqp8hjc][quote="T-Fish123":yzqp8hjc]Posi-Trac is a GM term. Mopar used the term Sure Grip. So to answer your question, it doesn't.

Just an FYI.[/quote:yzqp8hjc]

So your gonna' tell me that you don't have no black cats, no roman candles, or screaming mimis? You're gonna stand there, owning a fireworks stand, and tell me you don't have no whistling bungholes, no spleen spliters, whisker biscuits, honkey lighters, hoosker doos, hoosker donts, cherry bombs, nipsy daisers, with or without the scooter stick, or one single whistling kitty chaser?[/quote:yzqp8hjc]

I use that line at Burger King all the time.

Unleaded is 3.49 a gallon race. fuel is 5.00. DO NOT MIX IT! just run some race gas and be happy with spot on jetting and no crap clogging your pilot jet.

It probably doesn't have anything to do with your problem but I will mention it anyways to save you some head ache. You didn't mention what year the KX250 was. If it is a fairly newer one, be sure you run the EIX plug like it says to. If you go running a BR8EG or BR8ES in that thing it will do all kinds of crazy shit. I run a B7 EIX. I like a hotter plug. One crazy thing about B7EIX plugs are that once you foul them they are toast. Very rarely can you take a piece of sandpaper and get it to work again. They also cost about twice as much as other plugs. So playing around with Jetting on a KX250 can get expensive.
I agree with Williamsmotowerx. I'd say you have a mechanical problem. One thing you might check that won't cost you any money is to check your clutch adjustment on the motor side of the cable. If it is not pulling enough slack out of the plates it can bind on the crank and actually stall the motor. It can also be just loose enough to make all kinds of noise. All the KX's that I have had are pretty finicky when it comes to this adjustment. 3 threads one way it to much and 3 the other are too loose. Something you might look at. Especially since you have a flywheel weight. I'd also just take the clutch cover off and check things out. You need to change your oil anyway. lol. Check for some metal frag.

Buy a four stroke.



















Just kidding. You'd hear a lot more pinging with one of those overweight hogs, just before it grenades.

Being it is a 99 I think an Es plug is fine. I don't think they started the EIX thing until about 2003.

[quote="queen of spodes":xg8b37bb]Is it legal to order race gas and have it delivered?[/quote:xg8b37bb]

You should be able to get race gas in Atlanta. Let your fingers do the walking and call the local 2 and 4 wheel performance shops. For your 2 stroke you want a leaded 108-110 octane race fuel, Preferably VP C12 or 110.

If you keep it sealed tight it will be good for months .

[quote="queen of spodes":1vmg5z18]

I found a site for a VP dealer in Atlanta. I haven't heard back from them yet, but wanted to know if there is a type of race gas that won't turn to gel if it sits for a few weeks at a time. I'd love to ride every few days but that rarely happens.[/quote:1vmg5z18]

The only fuel that does that is the old VP U4 four stroke fuel. If you get VP C12 or 110 you won't have that issue. Just keep it tightly sealed can, preferably a metal can, and if you use a plastic jug keep it out of the sun because the sun will oxidize the lead in the fuel.

I had the same problem with my 2000 KX 250. If you can get the VP Red that will fix the problem. If you can only get the C12 mix 50/50 with pump gas. The C12 was too much octane and would stop the pingging but give the bike poor throttle response. I spent a month trying to figure out what was wrong with my jetting and finnally fixed the problem by mixing the C12 50/50.

If you are concerned about storage. I need to run race fuel 50/50 in my trials bikes. When I buy race fuel I use a steel army style gas can with metal cap. I have stored race fuel for three years and it was still fine. If you can keep the fuel sealed from outside air it will last a long time. I just use a seperate can that I take ridding and mix my fuel in.