Grinded out header, now runs bad

[Kyle T.]

Hey guys, I heard about grinding down the welds on the stock header for a little better flow. So today I went ahead and gave it a go. Grinded them down and gave it a nice smooth transition inside the header.

Heres what it looks like:
http://i48.photobucket.com/albums/f206/optionboarder81/IMG_3285.jpg

After that I bolted the header back on, put everything back together. Go to start the atv and when I try to rev it up, it sputters and sort of backfires/pops. Tried getting it warm and it still does it. Could grinding the welds affect how it runs that much?
Also I didnt see any crush gasket on the header, but it didnt really seem like there was an exhaust leak there.


Id also like to mention I have a pro circuit t4 slip on and some small vents in the air box. This was done by the previous owner. He was unsure whether the atv was rejetted or not. Could it be running so bad because its super lean with the slip on and ported header now? :confused:

[Zakradu398]

Whats your jetting specs/ Elevation

[xtreme762]

Sounds like jetting.

[Kyle T.]

Originally posted by Zakradu398
Whats your jetting specs/ Elevation

Near milwaukee, wi. which google says is about 680ft.

Im not sure about jets. I just bought this about 2 weeks ago. Previous owner was unsure about rejetting. Before I did this it would always die idleing when it was cold. But idle fine when warm. I noticed that it would backfire alot on decel. So Im guessing its probably still stock jet. Atv has t4 slip on and 2 small vents in the air box.



Originally posted by xtreme762
Sounds like jetting.

Anyway I can check what size jet it have? Im guessing Ill have to open up the carb.

[xtreme762]

Yeah, you'll have to open the carb. up and take a look. I'm betting it's stock. For that elevation, I would try the 42 pilot jet and a 165, or 170 main. With 2.5t on the pilot screw.

I'm at 550ft. and use stock pilot, and 155 main, with a stock filter w/o air box top, and stock muffler. With 2.5t on the pilot screw.

The jets are clearly marked as to what size they are. Just have to get to them.

[Kyle T.]

Originally posted by xtreme762
Yeah, you'll have to open the carb. up and take a look. I'm betting it's stock. For that elevation, I would try the 42 pilot jet and a 165, or 170 main. With 2.5t on the pilot screw.

I'm at 550ft. and use stock pilot, and 155 main, with a stock filter w/o air box top, and stock muffler. With 2.5t on the pilot screw.

The jets are clearly marked as to what size they are. Just have to get to them.

Thanks for the info :) , Ill open it up either tonight or tomorrow.

What has me confused, is that it ran great when I was warm but could grinding out the welds make that much of an impact on how it ran? What about the exhaust gaskets?

Also, do I need a special socket for the spark plug? It says in my manual that its an 18mm but theres no way my 18 fits in there.

[CJM]

Yea the gaskets usually should be replaced when you remove the header. Make sure the nuts are snug too, could be loose. To check for exhaust leaks, start it up and put your hand over the tailpipe to seal it. Any hissing its leaking somewhere.

Its a special socket, look on ebay for an entire kit as the socket alone is like 12 bucks form honda. Or you can buy a motion pro one for like 20.

[2001400exrida]

the easy way to check the mainjet is to simply turn the carb and take the large cap screw out of the bottom of the bowl. the mainjet will be right there and accessible. It's always a good idea to check your jets anytime you get a new machine, especially when there's mods done.

[Kyle T.]

Thanks for the help guys. I checked for leaks by holding my hand over the exhaust and it doesnt seem like I have any. Although the atv doesnt even idle for 5 seconds when cold. Just keeps dying on me.

Also jeez $20 for a spark plug socket. Good thinking on buying the tool kit because mine didnt come with one.


Originally posted by 2001400exrida
the easy way to check the mainjet is to simply turn the carb and take the large cap screw out of the bottom of the bowl. the mainjet will be right there and accessible. It's always a good idea to check your jets anytime you get a new machine, especially when there's mods done.

Good idea, will I still have to disconnect all the lines to be able to turn it? And will I be able to check the pilot too?

[Nrgy]

I wouldn't have thought grinding the welds would have done enough to require a jetting change, but obviously your quad is telling you otherwise.

An easy place to start would be to adjust your pilot screw. You'll need to be able to access the bottom of your carb with a small flat head though. Turn it in all the way, counting the number of turns until it is lightly seated, then back it out the same number of turns + 1/2 turn. I'm guessing this would put you around 2-3/4 turns out.

If you have to go much more over than 3 turns on the pilot screw then it's best to go up a size on the pilot jet.

My quad had a lot of trouble starting during a cold start after doing a filter and vented lid. My pilot screw was only 1-1/2 turns out...I increased it to 2-1/2 turns out and it started SO MUCH easier. Didn't even need to really use the choke after that.

[Kyle T.]

Originally posted by Nrgy
I wouldn't have thought grinding the welds would have done enough to require a jetting change, but obviously your quad is telling you otherwise.

An easy place to start would be to adjust your pilot screw. You'll need to be able to access the bottom of your carb with a small flat head though. Turn it in all the way, counting the number of turns until it is lightly seated, then back it out the same number of turns + 1/2 turn. I'm guessing this would put you around 2-3/4 turns out.

If you have to go much more over than 3 turns on the pilot screw then it's best to go up a size on the pilot jet.

My quad had a lot of trouble starting during a cold start after doing a filter and vented lid. My pilot screw was only 1-1/2 turns out...I increased it to 2-1/2 turns out and it started SO MUCH easier. Didn't even need to really use the choke after that.

Thanks, I will try that.


If its a jetting issue, and I put the stock silencer back on, it should run correctly, right? I was thinking about trying that to narrow it down.

[Zakradu398]

Originally posted by Kyle T.
Thanks, I will try that.


If its a jetting issue, and I put the stock silencer back on, it should run correctly, right? I was thinking about trying that to narrow it down.

If your doing it that way I think it would be easier to plug up the holes in the airbox you cut and see if it runs better.

[Kyle T.]

Originally posted by Zakradu398
If your doing it that way I think it would be easier to plug up the holes in the airbox you cut and see if it runs better.

I didnt cut them, I bought it like that. And theyre just the small uni airbox vents.

heres a picture
http://i48.photobucket.com/albums/f206/optionboarder81/IMG_3288.jpg

I think I will try and plug them, and put on the stock silencer and see. Then Ill open up the carb and check out the jets.

[Nrgy]

Yeah I would just put some tape over the holes, and throw on the stock silencer if you want and see how it runs. If that solves your issues, then just adjust your pilot screw a bit, and as others said you might want to bump your main jet up a size if it stumbles past 3/4 throttle.

Also, I would recommend getting a few more of those Uni vents and putting them in the lid. I put on all 6 that came in the package. If you gotta be making adjustments to your jetting anyway, may as well let the engine breathe a little more.

[pmg8134]

you can grind the the outside of a standard 18mm plug socket and it`ll work out just fine keep the change for a bigger main jet and some crush gaskets

[Kyle T.]

Put on the stock exhaust and covered the airbox vents and it ran alot better.

I opened up the carb and took a look at the jets and what do you know, theyre stock!

http://i48.photobucket.com/albums/f206/optionboarder81/IMG_3293.jpg

http://i48.photobucket.com/albums/f206/optionboarder81/IMG_3292.jpg

I guess that would explain why it was backfiring and running bad.

Now the question is what size jet should I go with?

Mods:
T-4 slip on
Grinded down/ported header
Foam filter with 2 1" airbox vents. (I have been thinking about adding the 2 more I have or possibly removing the lid)

I ride in anywhere from 20*-90* outside. Im near Milwaukee, WI which has an elevation of about 580ft.

Im pretty set with a 42 pilot but not sure on the main size. And also should I stick with keihin jets? I read that dyno jets are a different size.

[Stickman400]

Deff. stick with Keihin jets. I would recommend a 155 with your current setup and a 160 if you remove the lid, and the 42 pilot jet is good. Also you can take the actual main out of the holder that you have laying there. The piece with the nut on it is just a holder, don't need to remove that when swapping the main.

[Kyle T.]

Originally posted by Stickman400
Deff. stick with Keihin jets. I would recommend a 155 with your current setup and a 160 if you remove the lid, and the 42 pilot jet is good. Also you can take the actual main out of the holder that you have laying there. The piece with the nut on it is just a holder, don't need to remove that when swapping the main.

155 main. You think that will be big enough? On the last page someone told me to run a 165 or even a 170

Do you think most dealers stock an assortment of jets or will they probably have to be ordered?

[AtvKid4Eva]

ive always ran a 165 with a slip on on a 400ex and they run perfect. Some say a 155 too..youll have to do some plug checks to find out whats best for your elevation. And yes the dealer should sell single Keihn jets and stock most sizes.

[Kyle T.]

Hmm ok. Ill see what some others have to say on the size and ill go pick up a couple jets.

Will I have to adjust the needle? and what about the air/fuel screw?

[Kyle T.]

Originally posted by Kyle T.
Hmm ok. Ill see what some others have to say on the size and ill go pick up a couple jets.

Will I have to adjust the needle? and what about the air/fuel screw?

Thinking about a 165 main. anyone care to chime in? Also still not sure on the questions posted above

[jgar]

Iam at 1500', foam filter, welds ground out, stock motor and pipe. Running a 155 with the f/a screw 2 1/4 turns out.
If you are close to a shop that sells jets start with a 160 and go from there.

[dxcody]

I would say you need between a 158-160...


Somewhere in there.

[Kyle T.]

Hm. So Ill get a 42 pilot and then I think either a 160 and 165 main or 165 and 170. Will I need to rejet if I run it in the winter?

[dxcody]

Only if you are picky.

Do you have the choke removed?

A 42 pilot will be too rich on take off if you have your choke.

A 40 pilot would probably be better.

[Kyle T.]

Yes I still have the choke.

[Kyle T.]

So 40 or 42 pilot? Its about 50-60* outside and before I grinded out the header the atv would not stay idling when cold. It would just die and I would have to rev it up a couple or times or go for a quick ride to warm it up otherwise it would just die idleing. Now that I ported the header it idles even worse that when cold.

[dxcody]

Idk, Mine personally, and my buddies (Bornconfused) both run really rich on the low end, with a 42 pilot.

But i'm not expert at jetting.

Most of the guys that run a 42 Pilot, remove the choke.

The choke removed is OK in the summer but in 50-60 degree weather it sucks, and I don't want to see how it will be in the 20-30 degree weather.

[Kyle T.]

What are your mods?

[xtreme762]

Originally posted by dxcody
Idk, Mine personally, and my buddies (Bornconfused) both run really rich on the low end, with a 42 pilot.


This is what I have found with mine also. But mine was all stock, so with mods it might be different. We'll see in a few weeks after it's put back together.

[Kyle T.]

Yea I think Im gonna go with the 42. If its a little rich I can always at 2 more vents in the airbox or even remove the lid.

Still a little unsure on the main. Thanks for all the help guys and feel free to chime in with your opinions :)

[CJM]

Dump the airbox lid, its really restrictive. Your worried about water getting in there I suggest the EHS outwears lid. The kit is cheaper than the lid already done up, but it aint cheap.

However its worth it.

[dxcody]

Originally posted by Kyle T.
What are your mods?

Pro Circut ground down header welds, (not as cut as yours) and open airbox.

[Kyle T.]

Dealer didnt have the right jets instock so I had them order some. Only $6 for all 3 jets! I got the 42, 155 & 160. The guy working there said that those 2 should be good and the 170 would make it rich even with the airbox open. Should have them in tomorrow and Ill see.

[Zakradu398]

Originally posted by Kyle T.
Dealer didnt have the right jets instock so I had them order some. Only $6 for all 3 jets! I got the 42, 155 & 160. The guy working there said that those 2 should be good and the 170 would make it rich even with the airbox open. Should have them in tomorrow and Ill see.

yea, I haven't broke 170 yet with an 11:1 piston, open airbox and full exhaust.

EDIT: Just went down and threw a 170 in it and its runnin gooooodd

[Kyle T.]

Just went and picked up the main jets. They wont have the pilot in until monday.

Do you think I can get it running ok with the 155 main and the stock pilot? I was hoping to go riding this weekend :ermm:

[Nrgy]

Yeah I think so. Just adjust the pilot screw. Find out where it's at now by turning it clockwise counting the number of turns until it lightly seats, then back it out and add another 1/2 turn.

See how it runs, if it's still hard to start or won't idle very well, try again in 1/4 turn increments.

Also, you will want to adjust your air screw to help get a nice smooth idle after you mess with your pilot screw. I just start the bike up and adjust it by ear until the idle is nice and smooth.

It's all still fresh in my head because I had to do some rejetting after installing a full exhaust lol.

[Kyle T.]

I ran it for a little bit with just the 155 jet. Taped over the airbox vents. Its still pretty cold blooded but not as bad as it used to be.

I didnt change the air/fuel screw at all. Once warm seemed to idle ok, when driving it didnt bog or anything, ran good. Just on decel and coming back down in the revs it still backfires alot. Im guessing the pilot jet should fix this.

Once I put the 42 pilot in I will peel the tape off the 2 airbox vents and possibly add the 2 more I have laying around. I havent had the chance to check out the plug since I dont have the socket for it but I will soon.

[Kyle T.]

Went riding for a little bit today. With the stock pilot and 155 main. Covered the airbox vents. Still dies when idling cold, but once warm its fine. Runs good at wide open throttle, no bogging or anything. Still backfires alot on decel. Once I get the 42 pilot, I will uncover the 2 airbox vents and possibly add 2 more and hopefully it will idle better cold and not backfire as much. Might throw in the 160 main also depending on how the plug looks. Still gotta get that dang socket for it. I havent touched the air/fuel screw or the needle.

[pmg8134]

open up the fuel screw- turn it counter clockwise. you`re running lean. more vents more air more lean. more lean equals more heat equals burnt piston

[Kyle T.]

Got the 42 pilot. And I switched out the 155 for the 160 main. Didnt run it yet. Ordered that dang socket for the spark plug so Ill be able to take a look at that soon.

[Kyle T.]

What are you guys using for the spark plug socket? Should I just spend the $20 for the nice motion pro socket? Or go and get a cheap socket and grind it down? How much grinding do you have to do to get a regular socket to fit?

[Thumpin440ex]

I ground down a metric deep socket when i was in a pinch, but have since found my orig one that came with the bike.


John

[Kyle T.]

How much did you have to grind down the socket?

I dont have the original tool kit so thats not an option :ermm:

[Thumpin440ex]

Best and easiest way to do it is by putting it in a vise an use a hand held grinder to do it. I just kept taking material off untill it fit down in the head. Then used a 1" extension and a ratchet.

John

[Stickman400]

I use to use the stock one also and it was good. But I decided to get one of the Motion Pro sockets and it's pretty dang nice. You can use a 3/8" ratchet right on the top of it and it's the perfect height so you don't need any extension, just the socket and ratchet. It also has holes if you want/need to use a straight blade screwdriver or something, also can use a socket over the top of it if you want, but idk why. It also has a rubber insulator in the socket to grab and hold the plug for when you take it out or put it in so you don't burn your hand if your motor is hot. Idk if it's worth $20 but it is a very nice piece.

[Kyle T.]

So I put the 42 pilot it and switched the 155 out for a 160 main. It started instantly and idles perfect cold without even using the choke. Never dies, idles great.

But I dont know if it has to do with the pilot or switching from the 155 to 160 main, but it seems like I lost a little low end power. I took off the airbox lid and it doesnt seem as torquey, but it really screams with the lid off. Lifts the wheels through all the gears, but low end seems a little lacking. I dont know if this has to do with my jetting or something.

As far as checking the plug, to check the main I run it wide open then shut it off, let it cool down and check the plug right?

Then to check the pilot should I just let it idle for a bit then check the plug?


Im still really confused about the needle and air/fuel screw. How do I know if it needs to be adjusted or not?

[pmg8134]

air screw- 2 stroke
fuel screw- 4 stroke

the fuel screw(you have) is like a mini adjust between main jet changes when figuring out your jetting. it lets you have a fine tune for temp/ elev/ humidity changes. it`s not always enough for all seasons but can make the difference between running perfect or not. hop on the search feature of the site and type in 400ex carb jetting and you`ll get hours of info and you won`t be confused about that carb at all.

[Kyle T.]

Ah ok, that makes sense.

Ive read a couple of the big jetting threads on here and I still dont know how to tell if the needle should be adjusted.

And still confused why I lost a little low end after jetting. I guess Ill have to check the plug.

[Kyle T.]

Originally posted by Kyle T.
So I put the 42 pilot it and switched the 155 out for a 160 main. It started instantly and idles perfect cold without even using the choke. Never dies, idles great.

But I dont know if it has to do with the pilot or switching from the 155 to 160 main, but it seems like I lost a little low end power. I took off the airbox lid and it doesnt seem as torquey, but it really screams with the lid off. Lifts the wheels through all the gears, but low end seems a little lacking. I dont know if this has to do with my jetting or something.

As far as checking the plug, to check the main I run it wide open then shut it off, let it cool down and check the plug right?

Then to check the pilot should I just let it idle for a bit then check the plug?


Anyone have any input on this?

[CJM]

new plug. Go for a good ride, check plug. Plug should be tan to brown. Slightly black is ok but rich, white is lean.

Ive done the whole run it then shut it off wide open throttle and it doesnt work for me.

[Kyle T.]

Originally posted by CJM
new plug. Go for a good ride, check plug. Plug should be tan to brown. Slightly black is ok but rich, white is lean.

Ive done the whole run it then shut it off wide open throttle and it doesnt work for me.

Sounds good. I guess all I need is that spark plug socket.

[Zakradu398]

Originally posted by Kyle T.
Sounds good. I guess all I need is that spark plug socket.

I can fit a normal 18mm socket in mine. Silicon spray can help get it in (thats what she said)

[Kyle T.]

Originally posted by Zakradu398
I can fit a normal 18mm socket in mine. Silicon spray can help get it in (thats what she said)

Really? I tried a craftsmen 18mm deep socket and it didnt no matter how it tried to wedge it in. The 17mm does but obviously wont fit the plug. Damn you honda! :cuss:

[CJM]

Depends on the brand. The tool is better anyways. Stupid design but hey way it goes.

[Kyle T.]

I did some searching and found that some people have been having luck with the gearwrench 18mm socket from advance auto. So I figured Id give it a try. And it fits! Just barely but it worked.
http://i48.photobucket.com/albums/f206/optionboarder81/IMG_3317-2.jpg

It was still sorta a pain to get it out but oh well. So heres the plug thats been in it before I bought it. Looks pretty good to me.

http://i48.photobucket.com/albums/f206/optionboarder81/IMG_3315-2.jpg

Im gonna go to the dealer and get a couple plugs and then do a true plug chop.

[Kyle T.]

Anyone? Color seems to be ok, right?

[CJM]

The color is ok but it has deposits from fuel. Id say you should check it after you throw a new one in and see what it looks like.

[Kyle T.]

Yea I was going to get some new plugs this week and Ill do a plug chop.

[Kyle T.]

Got a new plug, gapped to .025. Ran it through 1st, hit the rev limiter in 2nd for a tiny bit and then all the way through 3rd and quickly shut it off. Heres what the plug looks like

http://i48.photobucket.com/albums/f206/optionboarder81/IMG_3324.jpg
http://i48.photobucket.com/albums/f206/optionboarder81/IMG_3325.jpg
http://i48.photobucket.com/albums/f206/optionboarder81/IMG_3327.jpg

Stock motor
t-4 slip on
grinded welds in header
foam filter
no airbox lid

Currently have 42 pilot and 160 main jets

[CJM]

Doesnt have enough time on it to really get color on the plug.

Ride it more then check it.

[Kyle T.]

Ok Ill ride it for a little longer and post the results.

[Kyle T.]

Ok here is what the new plug looks like after riding a little bit with the airbox lid on. I still plan on removing the lid and ordered some larger jets for that but heres the specs as of right now.

42 pilot
160 main
3 turns out on the fuel screw

http://i48.photobucket.com/albums/f206/optionboarder81/IMG_3343-1.jpg

The tip still looks a little lean, but why does the lower ring part look so black?

[atvrider13]

That looks like oil. It might be burning a little oil. Where u located in WI. I live near GB

[Kyle T.]

No smoke out of the exhaust, I dont smell burning out at all, and Im not loosing any oil either. And Im about 20mi southwest of milwaukee.

[duneslider]

I think the plug looks pretty good jetting wise. I wouldn't worry about that color.

It does look a little oily on the end of the threads but it could just be wet from fuel too.

[Kyle T.]

I think the oil youre talking about might be the anti-seize I put on the threads. Might of accidentally got a little on top part

[Kyle T.]

Anyone? Think Im too rich? Seems like alot of carbon build up for only riding for about 20 minutes.

[CJM]

The carbon build up is mostly your pilot. Might be too rich slightly with the 42 pilot and 3 turns of the fuel/air screw.

Cut the threads off the plug without damaging the inner porcelain and then show us what it looks like. Should be tan-brown.

[Kyle T.]

Will I be fine to ride it like that this weekend? Or should I turn the fuel screw in a little?

I still have the airbox lid on because the 160 is the largest main jet I have. I ordered some bigger ones and will be ditching the lid once they come in. So hopefully the 42 will be fine without the lid.

[CJM]

Id turn it in a 1/4 or 1/2 of a turn, 3 turns out and it can possibly fall out.

Id leave the lid on for now as well.

[dxcody]

Your fine dude. As long as it doesn't cut out any.

Even if it cuts out and goes on, you wont hurt anything, just annoying.

You have to ride for a good solid 3-4 hours to get a true plug read too.

A quick 30- an hour minute ride around the house wont give you a good plug reading.

[Kyle T.]

Cool, yea it runs good. Starts right up when cold, never bogs or really cuts out.

I might turn it in a little if I can get in there without taking the carb off haha :rolleyes:

[CJM]

Loosen the boots on the carb, turn it towards you and use a small screwdriver. Might have to remove the idle screw bracket tho.

[Kyle T.]

I tried rotating it, but couldnt get it enough for a screwdriver to line up. I might have a tiny one that I can get at it without removing it though.

[CJM]

I use a small 4inch screwdriver and I usually remove the idle screw bracket.

[Kyle T.]

I was able to get in there with a long skinny flathead. I turned it in a full turn, do you think that was too much? It now should be at 2 turns out.

[Kyle T.]

Heres the lid I made. Got the outerwears pre filter sheets from denniskirk.

http://i48.photobucket.com/albums/f206/optionboarder81/p_00782.jpg

http://i48.photobucket.com/albums/f206/optionboarder81/p_00783.jpg

Currently have the rear carrier all apart, but Im going to put the 180 main in and as soon as everything is back together Ill be able to test it.

[Stickman400]

Put some button head allen bolts on there and paint it your favorite color and that will look legit man. Looks really good.

[CJM]

Looks very nice. 400ex lid is all nice and flat, unliek the 450r lid..what a total pita but I made my own for it!

[Kyle T.]

Thanks guys, and I was going to paint it black but I kinda like the polished look more.

[Kyle T.]

Now that I have the outerwears airbox lid. Should I just plug the stock airbox snorkel thing? Or just leave it? Judging by my air filter it seems the stock snorkel lets in alot of dust. (talking about the clear tube that goes up under the gas tank)

Also got it looking nice and clean with some eagle 1 mag cleaner!

http://i48.photobucket.com/albums/f206/optionboarder81/8206631706_79559febba_c.jpg

[CJM]

Yea block it off with a spraypaint can lid.

[Kyle T.]

Ah cool, good idea.

[Stickman400]

What kind of camera did you use to take that pic anyway? I know it's kinda off topic but that is a really clear high res. picture. I'm looking to buy a nice camera to take pictures of the quad and stuff but I don't want to waste time buying something and finding out it's junk.

[Kyle T.]

Originally posted by Stickman400
What kind of camera did you use to take that pic anyway? I know it's kinda off topic but that is a really clear high res. picture. I'm looking to buy a nice camera to take pictures of the quad and stuff but I don't want to waste time buying something and finding out it's junk.

Canon rebel t2i. Awesome camera, I love mine.

[Stickman400]

Thanks, I see alot of people using those in other threads also so I think that is what I'm lookin' to get. Back on topic, 400 looks nice. That Eagle 1 does really good at cleaning these things up.

[Kyle T.]

Finally got everything back together and got a chance to ride it for a little bit. I just left the same plug that I did the previous jet tuning with, still a pretty new plug. Just rode it around my yard for a little trying to rev out as many gears as I could.

And heres how the plug looks.
http://i48.photobucket.com/albums/f206/optionboarder81/IMG_3365-1_zps273d5777.jpg

Looks pretty good, right?

[JOHNDOE83]

Actually, you cant tell anything by looking at the plug.

You have to physically cut it open to see anything to do with main jet.

What your looking at now is only from pilot and needle jet and timing, because of e85 in fuel you will not be able to read the plug properly.

You absolutly cannot ride around and look at a plug to determine jetting.

There is a much easier way.

www.jetsrus.com go to the faq section and look up jetting, make sure you read the whole thing.

[CJM]

Cant reuse same plug either.

John is right in that if you do that method you find the richest jet you can run but it takes time.

My way is to throw a size I know will be richer and work my way down. IE Most people will run approx a 165-175 main so start at 175ish and work way down.

Only other way to really do it besides what John is saying is a plug chop.