Box Stock

how big is a stock 6.5 clone jet?

A

aaron78viper

Member
did some port work, going to do a cam soon, higher ratio rockers, and i bumped the timing. plug looks a little dry as it was and i dont want to cook it. what size is stock? I want to get some to try out. anyone have a couple pics of how to do a jet swap? never done it before
 
Stock jets are usually .72mm #72 or .029" remove the float bowl one bolt, turn jet out with screwdriver cannot get simpler.
 
Kart43 said:
Stock jets are usually .72mm #72 or .029" remove the float bowl one bolt, turn jet out with screwdriver cannot get simpler.
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okay, I did some calculations on cross section area of the jetting. on a website i found, they sell drilled jets. the smallest one is .83mm which is substantially larger than a stock jet. I do not know what is in the motor now, and I don't want to waste money on smaller jets. any recommendations?
 
well, I finally had a chance to run the kart on track with the jetting the way it was, and a brand new spark plug. the mods now are a little port work, timing key filed down, and throttle butterfly thinned. The plug looked like it was running a little lean to me, so I dropped the jet out and looked at it. it was already drilled out. I found a .85mm, and it was too small of a bit. I found a 1.02mm bit and brought it home to check.. at first, it seemed like it was bigger than the previous guy drilled. as I tried to slide it through it stopped at the top. so I was going to open it up with that bit, I put the jet in visegrips and the bit slid through easily! I gave it a turn and it cleared out a small burr. barely even visible and I have good eyes. once the tiny material was removed, the bit had wiggle room. It seems the jet was large to begin with. I think the burr might have had a small effect on the flow, so once I saw a clean jet, I reinstalled it. I think it is a touch bigger than 1.02 mm now(or .04inches) I will try it like that next race day. I also think I fixed the oil leak I had going on, it was getting on the right rear tire and had me sliding off every corner. hope to place better this time
 
Fuel is about 700 times denser than air. This should show you that the very smallest imperfection in a jet can affect your fuel flow.

People talk about drilling jets, but trust me, drilling a jet is not something you want to do. MSC has reamers in their catalog in .001 steps and some inbetween. They're expensive compared to drills, but well worth it.

Oh, and holding a jet in a vice grip while drilling, is a double no-no. And if you're using a hand drill motor, it's a triple no-no.

When you consider that the difference between a .039" and a .040" is something like 5.2% difference in flow, it should give you a better understanding of the importance of what you're doing and talking about.

From the desk of Al Nunley
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory. (Al Nunley)
 
I had read on here that it is extremely important to not screw up the jets. I did not use a drill. what part of the vise grip is an issue? the threads? or just squishing the jet? I did it lightly, and avoided the threads. I thought that would be okay. I didn't have to actually drill it out, but some burr in there was cleaned up. I inspected it closely before deciding I should just out it back in
 
aaron78viper said:
I had read on here that it is extremely important to not screw up the jets. I did not use a drill. what part of the vise grip is an issue? the threads? or just squishing the jet? I did it lightly, and avoided the threads. I thought that would be okay. I didn't have to actually drill it but some burr in there was cleaned up. I inspected it closely before deciding I should just out it back in
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the more you tell us, the more it seems like you did it right. Still, did you check the jet with a pin gauge? You can buy pin gauge sets on eBay & Craig's list. They have one with pins from .011" to .060". They're not real expensive, they're Chinese, but good enough. Pin gauge sets come in different tolerances. They might be a .0002" plus set or a .0002" minus set. Be sure you know which set you have. If you want to spend a little extra money, you can get an American set +/-.0001".

From the desk of Al Nunley
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory. (Al Nunley)
 
alvin l nunley said:
the more you tell us, the more it seems like you did it right. Still, did you check the jet with a pin gauge? You can buy pin gauge sets on eBay & Craig's list. They have one with pins from .011" to .060". They're not real expensive, they're Chinese, but good enough. Pin gauge sets come in different tolerances. They might be a .0002" plus set or a .0002" minus set. Be sure you know which set you have. If you want to spend a little extra money, you can get an American set +/-.0001".

From the desk of Al Nunley
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory. (Al Nunley)
Click to expand...

i dont have anything to accurately check the diameter, i just started karting again very recently. thanks for the help i do appreciate it
 
Get yourself a pin vice set at the local hardware store or maybe auto parts. This is a small pen shaped vice that will hold very tiny drill bits like we use for jets. Every pin vice I have bought came with bits, like sizes #40 thru #100
 
Weddle Racing said:
Get yourself a pin vice set at the local hardware store or maybe auto parts. This is a small pen shaped vice that will hold very tiny drill bits like we use for jets. Every pin vice I have bought came with bits, like sizes #40 thru #100
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I bought a pin vice at a hobby shop, which came with a .85mm bit in the package, but no other sizes. i had to go to the hardware store to get a bigger bit, which was 1.02mm... still smaller than the hole in the jet, but i cleaned out the jet from a burr inside. I'm still looking for other bit sets, but for now i will just see how the plug looks net time i run.
 
Your jet is drilled too large if you are passing a 1.02mm bit through it. As stated in your other thread by someone else you need to go down in jet size. Did the previous owner run it on Alcohol?
 
Kart43 said:
Your jet is drilled too large if you are passing a 1.02mm bit through it. As stated in your other thread by someone else you need to go down in jet size. Did the previous owner run it on Alcohol?
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I don't know much about these engines or carburetors but isn't .040" pretty close? It's hardly an alcohol jet.

From the desk of Al Nunley
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory. (Al Nunley)
 
AAron, what is done to the engine, what are the mods? Big pipe or small pipe, stock or aftermarket air filter, stock or builder carb? Give me an idea what you have, and what class you will be running and I can tell you about what size jets or bit you will need to get pretty close. If what you have now is letting the engine run good now but plug just looks a little lean, then the burr you cleaned up might let just enough more fuel in to richen it up some, or you may need to go up just one size bigger, maybe even half size bigger. If 1.02mm will pass thru it, id say you have close to a .041 or .042 jet, with the main being that big I'd guess the pilot jet is bigger also
 
Weddle Racing said:
AAron, what is done to the engine, what are the mods? Big pipe or small pipe, stock or aftermarket air filter, stock or builder carb? Give me an idea what you have, and what class you will be running and I can tell you about what size jets or bit you will need to get pretty close. If what you have now is letting the engine run good now but plug just looks a little lean, then the burr you cleaned up might let just enough more fuel in to richen it up some, or you may need to go up just one size bigger, maybe even half size bigger. If 1.02mm will pass thru it, id say you have close to a .041 or .042 jet, with the main being that big I'd guess the pilot jet is bigger also
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motor has an air filter kit, i dont know what pipe(it is a racing pipe), i did a little port work on the head, the head gasket looked quite thin, i did a timing key, and i thinned the throttle shaft, shortened the butterfly screw and thinned the butterfly at the edges. a lot of stuff i could do cheap basically
 
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