Need help with micro drill bits and drilling out jet

[Super]

I been reading around and trying to get my NT carb tuned properly. What it's doing is bogging down at 3/4 to full throttle. It runs and idles fine, but whether I'm riding or siting still, if I try to rev the rpms up to full throttle it bogs and it's not getting to full rpms. I had a cns2 carb on it that I could never get fuly working.(I didn't try to drill the jets, I just got the bits in today.) This CNS carb, when I closed the clock would kick it in gear and it would then jump forward at full rpms. So I know what the motor is capable of. With this NT carb, if I try closing the choke it bogs it down and kills the engine. So the only thing the choke is good for with this carb is for cold starting. Which is what it is suppose to be for, really. I can't really tell but I think it might be 4 choking when it gets up to high rpms.

I found this site that has a great guide on the nt carb. NT Carb Tuning Basics - MotoredBikes.com: Motorized Bicycle Forum

Here is a video of me showing you how the rpms fluctuate when at full throttle while riding and sitting still. I know when I had the CNS carb on and was sitting still, it would rev up all the way and I would stop afraid of blowing something up it screamed so high. Now, I run at full throttle and can hold it there with no worries. I know it has lots more power to give.
Oct11_0001.3gp - YouTube

Heres what I've done so far.

1. I've check the the distance from the carb bottom(where the gasket goes) to the top of the float is 21mm. And it was.

2. I've sprayed starter fluid where the carb connects to the intake, to check for air leak. It didn't rev up but it did rev down. But this may be because some got pulled into the air filter.

3. The C-clip was originally set on the second from the top. After reading the above link, I realized the slide needle also controls the idle in a way. Well in the second notch my bike wouldn't idle even with the screw turned all the way in. I move the c-clip down one notch at a time until I realized moving it down was only making it worse. So I moved it to the very top notch and that is where it is at now. I am able to adjust the idle now with just the screw.

I was worried that I might run too lean with the c-clip all the way on the top notch. Well I have no spare plugs to test at the moment. (have 4 on order) But I have been riding it to work and back the last week. (only a half mile, round trip) I took the plug( Plug is a few months old) out today and the spark area is nice and dry but the rest of the plug is black and oily wet. I tried taking some pics but my phone would not capture a good res pic that close
Here is my blurry pics:

http://img94.imageshack.us/img94/664/oct110004.jpg
http://img822.imageshack.us/img822/9895/oct110005.jpg
http://img43.imageshack.us/img43/4852/oct110007.jpg
can only add 5 imgs, so I just posted a link to last 3

I did find a good quality pic on the net that I think looks close. Not so black on the spark tips

So where I'm at is I figure I needed to drill out my jets. Because in the above link it says the jets control the 3/4 to full throttle part. I think I need to go bigger, but I'm not sure and before I do anything I wanted to gets some advice on if I'm doing things right.

I bought the micro drill set on amazon. Here is the link; Amazon.com: 20pc MICRO-DRILL BITS INDEX 61-80 w/ Plastic Case: Home Improvement Everyone I read talks about sizes starting from like 70 to 76, or something like that. But the sizes on this set are from smallest to largest; 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.2, 1.3,1.4, 1.5,and 1.6. I tried looking at this conversion table I found, but I can't figure it out. Drill Size Conversion Table

Anyways, I'm not totally 100% I should even drill out my jets to a larger or smaller size. But it seems that everyone that has problems with theses carbs, that is what they end up doing.

What do you guys think? Thanks and if you you need any more info just let me know?

Btw this is my new bike from my crashed one. A thread I started a few weeks ago.

Here's my crash thread

 

[killercanuck]

Nice bike. Before you drill, you should do a "Plug Chop".

Run the engine at full throttle for a couple hundred feet, and kill the ignition and pull the clutch in. Don't let it fire. Once the engine has cooled some(never pull a plug from a hot head, the threads will come out with the plug!). Doing this will tell you where you are with your main jet.

It's best to do this on the way home, or a nice spot to chill while you wait.

Then you'll know where to go from there

 

[Venice Motor Bikes]

First question... What ratio are you mixing your gas & oil?

 

[wayne z]

That plug looks like it's running rich. If it's not from too much oil in the mix, drilling the jet will make it worse.

If you determine by plug chop that it is too lean, try your bits until you find one that fits snug. Then drill it out with the next size larger bit an try it.

Do you have a gasket or o-ring or silicone sealer in the carb socket? Dang air leak will have you chasing gremlins.

If it's too rich, the motor useualy stutters(4 stroking) at high rpm or low engine load.

If it's way too lean, it will bog out with no firing at all at full throttle or high load.

I like your bike.

Just my humble experience with These and many other 2 strokes over the years.

 

[Super]

Nice bike. Before you drill, you should do a "Plug Chop".

Run the engine at full throttle for a couple hundred feet, and kill the ignition and pull the clutch in. Don't let it fire. Once the engine has cooled some(never pull a plug from a hot head, the threads will come out with the plug!). Doing this will tell you where you are with your main jet.

It's best to do this on the way home, or a nice spot to chill while you wait.

Then you'll know where to go from there

Cool, thats what I plan to do when I get them Thursday, Thanks for the detailed explanation.

First question... What ratio are you mixing your gas & oil?

32:1, the plug is old and I think I was running rich with the CNS carb, that's probably why it's black. Gotta wait for stupid plugs. NAPA is the only parts store in town.

That plug looks like it's running rich. If it's not from too much oil in the mix, drilling the jet will make it worse.

If you determine by plug chop that it is too lean, try your bits until you find one that fits snug. Then drill it out with the next size larger bit an try it.

Do you have a gasket or o-ring or silicone sealer in the carb socket? Dang air leak will have you chasing gremlins.

If it's too rich, the motor useualy stutters(4 stroking) at high rpm or low engine load.

If it's way too lean, it will bog out with no firing at all at full throttle or high load.

I like your bike.

Just my humble experience with These and many other 2 strokes over the years.

Did you watch the video? What did it sound like to you? I don't have a good ear for sounds. I'm tone def or something. Plus I don't have much experience with 2 strokes. Trying to learn as I go.

Thanks for the replies.

 

[wayne z]

ok, I just watched the video. Definitly 4 stroking and too rich.

Most of these carbs come from the factory jetted on the rich side. I have had to solder them and drill smaller on a couple of kits, when the top notch was still too rich
Sweat just a little solder in the hole opposit of the threaded end. Backdrill the jet from the threaded end carefully with a larger bit, one that just fits the hole, until you drill thru the solder in there and see some brass in the bottom of the hole. Then drill your new hole thru from the bottom end of the jet.

Seems I rember a .023" hole worked in those cases. I started with
.018" and tried it. too lean then tried next size, .023 They are metric bits but I used a dial caliper to check diameters in inches.

Don't trust the sizes marked on the drill pouch. Lot of my Amazon bits didn't match the pouch numbers.

Be sure and use a hand driven pin vise to drill with and go easy with drill pressure.

 

[Super]

I check the size of the jet by fitting each bit in until one fit. I did the same thing for the CNS jet I have. The NT jet was at .75, the CNS jet is at .70. But this sould right, because the NT speed carb is supposed to have a bit bigger jet for the 66cc motors, i read somewhere. Well I soldered the jet and drilled it out 4 sizes down to .5. (Check my first post for my list of the sizes given on my drill bit set.) I went and bought a Champion CJ7Y Spark plug to test with. Gaped it with a knife using the other dirty spark plug as a guide. Can't find my gaper. lol.I ran it for a few mins and still did the same thing if not a little worse. Its bogged down under a heavy load and sounded like it was 4 stroking bad. It vibrates the bike like crazy when I rev it up.stood stil and reved it as high as it would go for a few mins and killed it. Waited a few more mins and took out the plug. It was wet and already turning black. Pic is below. I'm already at the very top notch on the c-clip, which to my understanding is the leanest setting. I went 4 drills sizes lower on my jet and I'm still running to rich, why? And remember I check the float already.

Seems I rember a .023" hole worked in those cases. I started with
.018" and tried it. too lean then tried next size, .023 They are metric bits but I used a dial caliper to check diameters in inches.

Don't trust the sizes marked on the drill pouch. Lot of my Amazon bits didn't match the pouch numbers.
pressure.

I'm sry but I don't know what those drill sizes mean. Most post I read ppl talk about their jets coming factory at the size "72" and going up from there; 73, 74, etc. My drill sizes list goes up by .05's. For example; 0.5, 0.55, 0.6, etc. And now you stating sizes at .023 and .018. I mean dam how many different bit standards are there? Only 2 for wrenches, metric and standard. Here in the USA, anyways. I do know that my drill sizes listed on my set are metric. I took the 1.0 bit and it is exactly 1mm. In this title "20pc MICRO-DRILL BITS INDEX 61-80", the "61-80", their not talking about "wire numbers", are they? Because that number goes down for bigger sizes and what I thought I've read in the past was ppl talking about making the hole bigger and the numbers going up as stated above. 72, 73, 74

For the second part, I can understand not trusting the sizes listed on such a cheap drill set, but it's all I have to work with at the moment. If it is off, it couldn't be more than a few atoms as small as the bits are lol. Would it really make a difference?

 

[wayne z]

Yeah I don't bother with all the guage wire # jet sizes and metric measurements too much. But that is the standard way to measure them. wi All my accurate measuring tools are in inches so that's what I work with. The measurements in my posts are in decimal fractions of inches.

Don't realy matter if you measure metric or inches or guage sizes ect as long as you are mesauring accuratly to determine where you are. There are conversion charts and data easily found on the web to convert from one type mearsurement to another.

Yes, the change from one minute bit size to another can make a dramatic difference in the way the motor runs.

Go to Harbor Freight and spend about $20 or less for a stainless steel dial caliper and you can get very easy , simple accurate measurements down to .0005 thousands if you want by splitting the difference between the marks. If yer a little more techno oriented, you can but an electronic digital caliper for about the same price but i like my trusty old dial calipers and micrometers for their easy simplicity .
Are you sure that yer choke's not vibrating closed? It's normal for these thingd to be able to vibrate yer fillings loose LOL.
Maybe yours vibes more than normal, maybe some harmonic vibes happening causing thr float valve to jiggle and not seal? Wouldn't be suprised .

Try setting the float slightly lower than normal and see what happens. Or try canting the carb some from vertical on the manifold and see what happens.

 

[Super]

I think I understand now. My bits (if they were 100% accurate) go up in size 0.05 mm at a time. The numbers I'm looking for are 72, right. What I was confused about was I thought those numbers were the wire size but really ppl were just leaving out the decimal. Really they were saying 0.72 mm. So I need bits that go up in size .01 mm at a time instead of .05 mm at a time. I did a search and I can't seem to find any bits that go up to that small of a degree. Even the really nice micro bit sets only go up 0.05 mm at a time.

But why am I still running so rich with the jet sized reduced so low. I dropped it to 0.5 from 0.75. Now I know you say .01 mm makes a big difference so shouldn't dropping my jet size .2 mm and having my c-clip all the way to top notch make my engine run too lean, if at all. Why am I still getting so much fule into the mixture?

 

[Super]

I soldered the jet again and this time doing a little experiment, I drilled it out at my lowest bit size, a 0.3 mm. I still runs I can even work it into high rpms. That is new. But If I try to put a load on it, it bogs no matter how carefully I try to work the throttle. How is gas getting through such a tiny hole? Well enough to keep it running anyways.

One thing I failed to tell yall. The motor sounds like it's running at a lower pitch. Before with the cns carb it ran at a higher pitch with a lot less vibration. Is this the 4 stroking I'm noticing? Cause I thought I would be able to tell by the firing sound. For example

2 stroking: bam..bam..bam..bam..bam..bam..bam
4 stroking: bam.........bam..........bam.........bam

But I'm having a hard time telling the diference in the firing and the rpm sound. Ahhh this is so frustrating. Even now with the jet at .3 mm it still sound really low pitched. And just in case; by pitch I mean a lawnmower has a lower pitch sound than a weedeater. Please guys help me fix this.

 

[Super]

Hellooo...ooo..ooo.oo, Anybody out there..here..ere..re?

 

[killercanuck]

I'd try doing a run without your air-cleaner on. (and/or) put some extra holes in the cover. If the cleaner is too restrictive, it'll pull extra gas due to the extra vacuum. Or it's like there's not enough air for the amount of fuel. I forget which. Try a run with the cleaner off to see if that's holding you back.

Making the jet that much smaller should've made some difference...

gl.

 

[Venice Motor Bikes]

It's been my personal experience with most carbs for these engines that they need to be jetted smaller to perform better.

 

[biknut]

I see the same as Venice Motor Bikes. My personal experience has been that all the NT carb bikes I've worked on were rich out of the box, and needed to be jetted leaner. The one CNS carb bike I have experience with was jetted way way too lean.

NT carbs come with a jet that's = to about a #70 or #71 jet size, not drill bit size, and end up needing a 68-66 jet. Even my 50 runs a 68, and it's a little rich, but I like it.

 

[Super]

I see the same as Venice Motor Bikes. My personal experience has been that all the NT carb bikes I've worked on were rich out of the box, and needed to be jetted leaner. The one CNS carb bike I have experience with was jetted way way too lean.

NT carbs come with a jet that's = to about a #70 or #71 jet size, not drill bit size, and end up needing a 68-66 jet. Even my 50 runs a 68, and it's a little rich, but I like it.

so, what exactly are the jet "sizes"? How do i know what bit to use if say I wanted a #72 jet size?

 

[biknut]

so, what exactly are the jet "sizes"? How do i know what bit to use if say I wanted a #72 jet size?

This is what I know about jets for an NT carb. The stock jet doesn't have a # stamped on it, but it's about the same size as a after market #70 but considering the poor quality some are closer to a #71. You can buy NT jets from SBP.

As far as machinist drill bits, the smaller the number, the bigger the dia. of the bit. I've never drilled a NT jet because they're readily available to buy, so I don't know what size to recommend, but if I guessed I'd say a #75, or 73 drill bit.

The biggest bit I have is a #71, and it's about the same as a #70 NT jet. Is that confusing enough for ya?

 

[killercanuck]

yea, that's confusing. Who came up with the 'bigger number is smaller size'? yeesh.

Did you try a run without the air cleaner Super?

I found this chart from here:

But yea. I had a similar problem today like your's Super. I won't get into details, but this is my setup now:
http://motorbicycling.com/members/k...2262-shorty-intake-clutch-cable-mount-mod.jpg

When I went back to this,(/\) I used the innards from a stock air cleaner, just the mesh and the circle of plastic. I went for a store run, and had the same symptoms. It didn't want to go past half-3/4 throttle, and was 4-stroking like mad. So I pulled over, took the mesh/circle off and it ran great.(always carry tools)

(That's nuts, that I posted here, then got the same symptoms, lol)

But anyway, do a run without your air cleaner and see how she runs.

gl.

 

[Super]

I will thx. I broke a window at my house and had to focus on that today after work. I'm tired and will try tomorrow. I will post my progress.

 

[Super]

Hello guys, sry, been busy with work. OK I took the air filter off and road it around a bit. I noticed it shooting gas out where the air filter goes. It did this in high rpms. BTW I think I got the jet where they needs to be. I been riding around the last few days on a new plug and when I pulled it today its was a nice grayish color. But whats with the gas coming out of the carb. Is this because my float bowl is getting too full? It is running alot better, but it still sounds funny when I rev it up high and goes to vibrating like crazy. I read they adjusting the spark gap could advance or decrease the timing of the spark and could fix this. What do you think of this?

Btw I ended up settling on a jet size around .45mm

 

[wayne z]

Gas fog at the carb intake is normal for a piston ported 2 stroke. A little gets pushed out before the piston closes the port.