Twice the size jet?

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Oct 28, 2003
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#1
I just pulled my carb apart to adjust the float height because it was dumping out fuel from the carb overflow while riding. I thought it was a float height issue.

But when i opened it up, I saw the jets were 85 & 165. Stock jetting is 42 & 165. ('91 kdx 250).

The bike is completely stock so why was the jetting changed. The wrong jet makes sense because it spooges a lot. I thought that maybe the float letting in too much fuel caused some spooge but it must be the jet.

I know the wrong jet will cause spooge, but will it cause the carb to overflow while running????

The weird thing is that it actually ran good.
 

Zerotact

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#2
you can run a larger pilot, the bike will run rich on the idle... I.E. Start easy, and spooge while idleing. Then feed in extra fuel througout the rpm range....
A richer pilot het will make things richer even at WOT....
In a nutshell you can run a bigger pilot to compensate for a small main jet, but you cannot run a bigger main jet to compensate for a small pilot
 
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#3
sooo...should I leave in that 85 in place of the 42?
I think that it may be the reason i'm dumping fuel out of the overflow tubes.

Or is it the float level that is causing the overflowing??

Maybe I'm having 2 issues here?:
1. The oversize slow jet is causing loads of spooge.
2. The float level is causing the carb to dump fuel.

Can one of these factors (wrong jet, float level) be causing both issues (spooge, loss of fuel), or are they seperate problems???

I tried to make this make sense, but i'm tired so sorry
 
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#4
is my main jet kinda small? (165)
would I lose much power if I put the stock jet back in?
I'm not a fan of all the spooge so i'd like to.

All opinions are welcome
 
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#5
Originally posted by s.d.duner
is my main jet kinda small? (165)
would I lose much power if I put the stock jet back in?
I'm not a fan of all the spooge so i'd like to.

All opinions are welcome

Your jetting is way off with a KDX250! End of story.

Get a #6 slide (leaner), The next leaner Kawi jet R1367H and then a 38/155-158 jets.

That will clean up the carburation on the bike and make some of the power you are missing. Be sure to remove the air snorkle and also get a .26" thick headgasket installed.
 
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#6
Duner I really think you need to learn how the circuits on a carb work.
My 92 250 will spooge if someone is just putting around on it, wind it out and it runs clean. It is a 2 stroke if you don't ride in the powerband, the pipe and port timing can't work together and you get a lot of unburned fuel left in the pipe. You posted this very thread a couple of weeks ago and got pretty much the same answers. You need to independantly tune each circuit of the carb, begin with the air screw, then do pilot, then main. Tuning the main you'll need to do both the jet and needle. After doing the main & needle you'll have to go back and recheck all the circuits again, Do lots of plug chops to make sure you don't burn it up.
Check out the tech tips for a very comprehensive article on carb tuning and operation.
Maby you should take it to a shop if your really not sure what your doing. A couple hours shop labour to set up your carb is a H**L of a lot cheaper than doing a complete top end cause you screwed up the jetting.
If you think you can do it start by tossing in a 40 pilot, fire it up tune the airscrew, go for a short ride and see how the idle to 'bout half throttle reacts, If it better but still rich go for a 38, then smaller if you have to. ONLY CHANGE ONE CIRCUIT AT A TIME, you can't tell which change helps if you make three at once!. Now tune the main remembering the needle controls things to about 3/4 throttle, and just the main from there up. Of course changes to the needle will effect the upper range of the pilot circuit.
Everything effects everything else in a carb.
This is all asuming your reeds are in good shape and you compression is within spec. It's almost impossible to tune a worn out engine!.
 

tedkxkdx

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#7
If your float valve is old it can be causing the fuel dump you are experiencing. The rubber gets harder and also forms a dent. This may not be very evident by the look and feel of the rubber even when worn. The piece is not expensive and if you don't have some particles inside your carb that is blocking the mating surface of the rubber to the metal I would replace the piece anyway. I think they are to be changed out every year but many of us wait until it just fails to do its job.