# Gearing Help.

On my current bike I am running 13/51 gearing for mostly hillclimbing and super technical trail riding. I really like this gearing but I wish I could have the same gear ratio with smaller sprocket. On BMX bikes I know that for every 3 added on the front equals 1 in the back. So would the same be 12/49 or is it different because the small one is in the front?

On my current bike I am running 13/51 gearing for mostly hillclimbing and super technical trail riding. I really like this gearing but I wish I could have the same gear ratio with smaller sprocket. On BMX bikes I know that for every 3 added on the front equals 1 in the back. So would the same be 12/49 or is it different because the small one is in the front?

Just convert the ratio to a percentage by dividing the front into the rear 13/51 = 25.5%....try other gear combinations to get the same quotient.  12/49 = 24.5%...so not the same.  12/47 would be VERY close.....

At least this is how I understand it...

Edited by Fattonz

You are about correct that one tooth on the front equals 3 on the rear.  But to make 1nd gear feel like 2st gear, you'll have to go up probably two teeth in the front (or six in the rear, or one in front three in rear).

Do you have a close or wide ratio tranny?

try this another way.  Your gear ratio right now is 51/13 = 3.92.  So for every 3.92 rotations of the smaller countershaft sprocket, you have 1 turn of the rear sprocket or rear wheel.

With 49/12 your gear ratio is 49/12 =4.08..or the countershaft sprocket now turns 4.08 revolutions for every 1 revolution of the rear sprocket or rear wheel.  The 12/49 combo is 'lower geared" and requires more engine rpm to go the same speed as the 51/13 combo.

If you want the same gear ratio use 47/12 = 3.92.  Note that a smaller countershaft sprocket can increase the wear across the plastic slider on the top of the swingarm, increase wear on the chain due to tighter radius at the countershaft sprocket, and your chain may be too long requiring you to remove links (unless you have a lot of room to adjust the rear wheel further toward the back).

I had to think to remember this one from my Power Engineering classes but you can use the law of means and extremes.

So I'll a write a random ratio like this:

3 : 4  ::  6 : 8

In the above equation the 3 and the 8 are the "extremes", and the 4 and the 6 are the "means"

Now the rule states "the product of the two extremes divided by either mean will give the other mean"  and that "the product of the two means divided by either extreme will give the other extreme"

So in other words:

Using the two extremes:

3 x 8 = 24 then 24 / 6 = 4 or 24 / 6  = 6

Using the two means:

4 x 6 = 24 then 24 / 3 = 8 or 24 / 8 = 3

So knowing the rule we can now apply it to gear selection:

You are using 13/51 and let's say you want to go to a 12T front sprocket and maintain the same relationship:

We could write it as follows where there is one unknown variable:

13 : 51 :: 12 : _

Then we apply the rule:

51 x 12 = 612 then 612 / 13 = 47.08.....but since we can't have .08 teeth, the closest is a 47T sprocket.

So not identical gearing, but very close.  Clear as mud?

Edited by Fattonz

So 13/51 is actually pretty tall geared? How does it compare to a 12/49? Like the power delivery, does it pull better on the bottom with the 12/49 and pull better on the top with a 13/51?

A 12 tooth front is not often recommended, the chain sees quite a lot of wear.

So 13/51 is actually pretty tall geared? How does it compare to a 12/49? Like the power delivery, does it pull better on the bottom with the 12/49 and pull better on the top with a 13/51?

I definitely would not call 13/51 tall gearing...quite the opposite actually.  However it is taller than 12/49...  I could go all the way to 14/38 on my bike, now that's tall...

We've established that 13/51 is like 12/47....so going to a 49T rear sprocket is going to give you more low rpm torque and less top end.....it is "lower" gearing...as someone else put it, you'll need more engine speed to have the same rotation of the rear wheel....

Not sure why you would want to run the 12T though...

Edited by Fattonz

I would stay away from a 12 cs  , I run a 15/51

Edited by capt justin

So 13/51 is actually pretty tall geared? How does it compare to a 12/49? Like the power delivery, does it pull better on the bottom with the 12/49 and pull better on the top with a 13/51?

Didnt say 13/51 was 'tall geared', just that 12/49 is 'geared lower' than 13/51.  To be exact, the engine RPM would be 4% higher at a given rear wheel speed using 12/49 vs. 13/51.  This is strictly a mathematical exercise (4.08/3.92 = 104% or 4% higher rpm).  What bike are we talking about?...I dont know how it was equipped from the factory and cant say whether 13/51 is higher or lower geared than the stock configuration.

Ultimately, what determines how fast the rear wheel turns compared to the engine rpms are 3 different things:

• Gear ratio for the particular gear you are in
• The primary drive ratio (within the gearbox), and
• The secondary drive ratio (front countershaft sprocket & rear wheel sprocket).

The only thing we are talking about here is the 3rd item....secondary drive ratio.

Let me give you a concrete example:  WR450F.....1st gear ratio is 2.417.  Primary Drive ratio = 2.652 and Secondary Drive ratio = 3.846 (this is determined by a 50 tooth rear sprocket and 13 tooth front sprocket or 50/13 = 3.846).  So final driveline speed is ultimately reduced by 2.417 x 2.652 x 3.846 = 24.65.  This means for every 24.65 rotations of the engine crankshaft (e.g. rpms) the rear wheel will turn one revolution.  So at 2000 rpm....rear wheel will turn 81.13 times in a minute.

Let's turn those wheel revolutions into something we understand.  Let's say the outside wheel diameter is 22".  We know that circumference is Pi x Diameter or 3.14 x 22" = 69.08 inches traveled for every revolution of the rear tire.  Translating to feet we divide 69.08 inches by 12 which gives us 5.76 ft traveled per every rear wheel revolution.  We multiply by the 81.13 revolutions of the rear tire per minute we calculated above and we get 467.04 feet per minute traveled x 60 minutes to get 28,022 ft traveled per hour and then we divide by 5,280 ft per mi....and we get to something we can relate to....5.30 miles per hour at a constant 2,000 rpm engine speed when we are in first gear. (assuming absolutely no clutch slippage or rear tire slippage).

On your question of how it pulls etc.....you will have to try it out to see how that gearing/rpm work with your particular motor and the power curve of that motor.  Generally speaking, with 12/47, you will be able to ride it slower (a neglible amount) at the same RPM as you used to ride.  At the top end, you will be scrubbing off some top speed (e.g. it will go 4% slower at maximum RPM compared to 51/13).  These are fixed ratios....so there is no way to lower the gearing in 1st gear and up the gearing in 5th gear without changing the actual ratios in the gear box.

Here is a tool that might be useful for you:

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• By Kev_XR
If you own an XR250, many of these tips will apply, however, the carburator jet sizes will be different.
ALL OF THE LINKS ARE BROKEN!!!
I will fix them as time allows.
Until then the Search Feature and enter "kevin's xr400 mods".
The results will bring up most of the links.
The longer the straights, the taller the hills, the deeper the sand; the bigger XR you want. The tighter the trail, the smaller hills, firmer terrain; the smaller XR you want.
The XR400 has a great motor that will pull you almost anywhere. You can be sloppy on a hill climb on an XR400, where you have to keep the 250 singing. The XR400 weight is most noticable when you drop it or try to stop it going down a long downhill. (Moooomentum!)
The XR250 feels like a mtn bike compared to the XR400. My friend rode his XR250 for years before decided he needed more power. Even then you can add a 300 kit and get good power.
If you were heading to ride fireroads in Baja, I'd tell you to get the 600/650.
To the tight woods, get the 250.
A lot of both, the 400.
Dual-sporting? Go bigger for more freeway, but don't show up at the trailhead with too big of a bike.
All of the XR's are great. Pick the one that fits your needs.
Gordon's Mods for XR400 (Uncorking the bottle up performance)
Gordon's Mods for XR400
XR400 History
The changes to the XR400 have been listed here several times. This list appears to be complete.
In addition, HairyScary discusses how to tell if a part has been updated by the part number. Good tip!
XR400 history
Getting the Spark plug out
It seems the MotionPro spark plug socket does not work on the XR400R, but works on the XR250R.
There is an OEM tool kit being sold on eBay that seems to work.
717448 XR400 oil change
Here is a way to make changing the oil much cleaner.
This tips is really handy if you have a skid plate.
XR400 oil change
XR400 FAQ by Paul Gortmaker
Paul usually has very good info.
http://www.freewebs.com/hairyscary/XR400_FAQ.txt
Small bolts
BE CAREFULL with the bolts on the oil filter cover!
An oil covered bolt will not torque at the same rate as a dry bolt.
The friction doesn't build up, the force simply builds until the threads strip.
This is the reason many people strip out these bolts.
Here is an execllent website on bolts, oil, and misc values.
Did you ever wonder why a 8mm box wrench is half as long as a 18mm box wrench?
It is shorter as most 8mm bolts cannot take very much torque.
I highly recommend getting getting an 1/4" socket set.
I bought the Craftsman set at Orchard (owned by Sears), which tends to sell them for less.
What is the Snorkle?
http://www.4strokes.com/tech/honda/snorkel.asp
This place has a description and pic, it's easy after you pull the seat. I siliconed a piece of coarse screen (fiberglass) over mine to keep bugs and stuff out. - NORTEXT
717439 XR400/250 Pre-Filter
After pulling the snorkle, there is a big hole on the top of your XR400. My friend showed me this prefilter trick.
Pre-Filter
767409 XR400 Engine Bog, Pilot jet, and the Fuel Screw
On XR400's twisting the throttle from fully closed to wide open will cause the engine to "bog" or in some cases die.
Engine Bog, Pilot jet, and the Fuel Screw
831305 Valve adjustment (Am I retarded...)
Inspect and adjust valve clearance while the engine is cold (35C, 95F).
389095 bigger jets (Lists stock jet sizes.)
96-97 XR400's were jetted assuming you would remove the intake and exhaust snorkel.
98 and later XR's were jetted assuming you would leave them in.
bigger jets
739907 Cheap Tool for Setting the Fork Oil Height
There are some really nice tools out there for doing this job.
This tool costs \$4.49 at Kragen.
Cheap Tool
392932 high altitude jetting
There are two big factors for jetting, elevation and temperature.
high altitude jetting
Allen screws for the XR400 carb
This lists the screws you need to convert the XR400 carb to use allen screws.
Allen screws
Screws for the brake and clutch after removing the stock handguards
TBD - There is a post with the shorter screw part numbers for after the stock handguards are removed. Use search.
Very quick engine hop up
------------------------
This is a very minimal change that should take less than an hour.
Most of that time is removing the float bowl (3 screws).
If you decide to do the full "Gordon's Mods" later, you will need to replace the jets again.
o Pull the intake snorkle.
o Pilot jet to 55, main jet to 155. (Assuming sea level and moderate air temps.)
Source: Motocross Action magazine.
Quick engine hop up
--------------------
Gordon's mods
Baja Designs Baja Baffle with 96' spark arrestor.
Pull the intake snorkle, UniFilter, 60 pilot jet, 162 main jet.
(Depending on altitude and temp.)
What to add to a new XR400 or XR250?
------------------------------------
Acerbis wrap around style handguards (saves levers and bars as they don't dig in)
Baja Designs skid plate (Made by Utah Sports Cycle)
Acerbis fork/disc protector
Suspension
---------------
Spend you money on the suspension, not a pipe!
First get some stiffer fork springs (96-97, 98-99 years)
Fork revalve (cost: 2 qts of oil & time)
Shock revalve (cost: oil, nitrogen, shim stack, friend who knows shocks)
Jetting for Altitude (XR400)
----------------------------
Assuming at sea level and 68 degrees, you would use a 60 pilot and 162 main.
At 5000 feet and 68 degrees.
Jettting correction:
5000 feet and 68 degrees.
Main 0.96 * 162 = 155 -> 155 main
Pilot 0.92 * 60 = 50.6 -> 55 pilot
Due to your elevation, you have less air and less fuel.
Your bike will not behave the same as a bike at sealevel.
First, check the fuel screw. If it does not affect the idle speed, you have the wrong one.
------------------
kevin's xr400 mods
• By 230F
Jetting the 230F
By: Phil Vieira
This project takes no less than 2 hours if you have never done jetting to a bike before. It took me 1.5 hours, to take my bike apart, take out the needle, change my pilot jet and the main, and take pictures along the way, but I have seen the inside of my carb 3 times, so I know my way around it pretty well…
You should be jetting this bike right when you get it home. This bike comes lean from the factory. If you don’t know what that means, it means that the bike is getting too much air, in terms, a hotter engine, and your plugs will get hotter, and a decrease in HP. To make your engine last longer, do this.
These jetting combos are for a 2000 feet and below scenario. Any altitudes higher, you should do a search on the forum. If it cannot be found, post on the forum. Please don’t post on the forum “How do I do this…” You have all the answers here.
This project comes to a grand total of less than 30 dollars. The needle is 20, the main jet is about 3 dollars, and the pilot is 5 dollars. You may not need to do the pilot jet depending on your situation, but again, if you’re riding 2000 feet and below, it’s a good idea to get a pilot jet.
The jets I used consist of a 132 main, 45 pilot and the power up needle with the clip on the 4th position.
Part numbers:
16012-KPS-921 – Needle (Includes Power up needle, Clip, and needle jet)
99113-GHB-XXX0 – Main jet (Where XXX is the size)
99103-MT2-0XX0 – Pilot jet (Where XX is the size)
For the Jets, just tell them you need jets for a regular Keihn carb, (also known as a Keihn Long Hex) main jet size XXX, pilot jet size XX. They should know the part numbers. For the needle, bring the number along. If you are lazy, they should have a fiche and they can look up the numbers. Then again you can take in the old jets, and make sure they match up to the new ones.

Now, the tools you will need are as follows:

~A collecting cup of some sort. I used a peanut butter jar.
~Ratchets for the following sizes:
- 6mm, 8mm, 10mm, 12mm
- Extension for the sockets needed
~Phillips and Flathead screwdriver (Be sure these are in perfect condition. A badly worn screwdriver will strip the screws)
~Needle nose pliers
~”Vise grips” or known as locking pliers (Two)
~Open end wrench 7mm and 12mm
~ It’s a good idea to have a extra hand around
(Not needed, but I highly recommend tiny Phillips and flathead screwdrivers (Pictured next to the jar and the ¼” extension) I recommend these for removing a couple things since you can put pressure with your thumb on the end and unscrew it with the other hand. This insures that you will not over tighten any parts, and ensure that you will not strip the heads of the bolts.
Ok, now that you have the tools, let’s start by putting the bike on a bike stand. I put it on the stand rather than the kickstand because it’s more stable and sits higher. I hate working on my knees. Start by taking the number plates off. Yes, both of them. The right side, you take off one bolt and the top comes off of its rubber grommets, pull the top off, and the plate comes right off. The left hand side, use the 10mm socket to take the battery bolts off, and then take the Phillips bolt near the back. Again, rubber grommets are used to hold the top in place. Take the seat off. There are two mounting bolts on the back:

Those two bolts are both a 12mm socket. Use the open end wrench on the inside, and use the socket on the outside. You may need to use an extension if you don’t have a deep socket. Once you have the two bolts off, slide the seat back, and lift it up. This is what you have. Notice there is a hook in the middle and a knob on the tank. That is what you are sliding the seat off of.

Now that the seat is off, you must take the gas tank off. Don’t worry, you won’t spill any gas any where, I promise. On the left hand side of the bike where the valve is, slide down the metal clip holding the tube in place. Turn off the gas supply, and slip the tube off slowly. Now take off the two bolts in the front of the take. This is on the lowest part of the gas tank in the front, behind the tank shrouds. The socket you will use is an 8mm socket. Take the bolts all the way off and set them aside. Now look back at the last picture posted. On the back of the tank, there is a rubber piece connected to the knob and the frame. Slip that rubber piece off of the frame. Pull the vent tube out of the steering stem and lift the tank up. Don’t tip it, and lay the tank aside where you won’t trip on it. This is what you’ll end up with:

It may be a good idea to take a rag, and wipe all the dirt off the top of the bike if any. You don’t want anything dropping down into the carb. If you do, engine damage is the result. A clean bike is always a good thing! Now we must drain the gas out into that container. This is very easy. Make sure you open the garage door, windows, whatever, to let the fumes out. Breathing this crap is bad. Here is where the drain screw is:

(Don’t worry about removing the carb, that comes later) This is on the right side of the carb, on the float bowl. The vent tube that goes down to the bottom of the bike is where the gas drains to. Put the jar under that tube and start to unscrew that screw, enough so that the gas leaks into that jar. Once the gas doesn’t drip anymore, close the screw all the way. Now on to the top of the carb. We are going to take this cover off:

This cover comes off by removing the two screws. Once removed, the lid comes off as well as the gasket. Flip it over and set it aside. Do not set the gasket side down on the ground, as it will get contaminants! Here is what you are facing:

The angle of the camera cannot show the two screws. But one is visible. It has a red dot, and opposite of that side is a darker red dot. I made it darker because it’s not visible, but that is where it is. This is where I use the miniature screw drivers to get the screws. I magnetize the screwdrivers, and use care to make sure I don’t strip the heads. Metal pieces in a piston are not good! Remove the two screws. Put these screws on a clean surface so they do not get contaminants. Now get your vise grips and set it so that it will lock onto the throttle, not too tight, not too loose. Set the vise grips on the seat. Start to open the throttle slowly as you guide that “plunger holder” (as I call it) up to the top. Once you have the throttle all the way open, take the vise grips, and lock it so that the throttle does not go back any more. What I do is I hold it pinned and lock it up against the brake so it doesn’t rewind on me. If you don’t have locking grips, a friend will do, just have them hold the throttle open all the way until you are finished. How fold the plunger holder to the back of the carb and pull the piece up to the top. Take care not to remove it, as it is a pain to get back together! If it came apart on you, this is what it should be assembled to:

Once you get the holder out of the slider, set it back like this:

As you can see, the bar is back 45 degrees, while the holder is forward 45 degrees to make a S. Here is what you are faced with when you look down on the carb:

Where the red dot is where the needle lies. Grab needle nose pliers and carefully pull up the needle out of its slot. This is what the needle looks like once it is out.

Now we must move the carb to take the bowl off. Untie the two straps on the front and back of the carb. Don’t take them off; just loosen them until the threads are at the end. Take the front of the carb off the boot and twist the bowl as much as you can towards you. Tie the back tie down to that it does not rewind back on you. This is what you have:

Now we must take off the bowl. Some people take that hex nut off to change the main jet, which you can, but you cannot access the pilot jet, and you can’t take out the needle jet (a piece the needle slides into), so we need to take it off. It’s just three bolts. As we look at the underside of the carb, this is what you will see:

The bolts with the red square dots are the bolts you will be removing. These are Phillips head bolts, and the bolt with the blue dot is your fuel screw. This is what you will adjust when the time comes, but keep in mind where that bolt is. You need a small flat blade to adjust it.
Well, take those screws off, and you are faced with this:

The blue dot is for cross reference, which is the fuel screw once again. The green dot is the pilot jet. You can remove this using a flat blade screwdriver. Just unscrew it and pull it out. Once you pull it out, set it aside and put in the 45 pilot jet you got. The red dot is the main. You remove this by using a 6mm socket. Just unscrew it. If the whole thing turns, not just the jet, but the 7mm sized socket under it, don’t worry, that piece has to come out as well. If it doesn’t, use a 7mm to unscrew it off. Here is what the jets look like:

Pilot Jet

Main jet attached to the tube. Take the main jet off by using an open end wrench and a socket on the jet. Again, it screws right off.
Here is what you are faced with if you look form the bottom up.

From left to right: Main jet, Pilot Jet, Fuel screw. Now in the main jet’s hole, if you look closely, you see a bronze piece in the middle of that hole. We are going to take this off. Since I did not do this part (I only changed my pilot jet when I took these pictures) there are no pictures taken for this section but this is really simple to do if you’ve been a good student and know where things go. You should know anyways, you have to put the bike back together!
(Notice: There have been discussions about these needle jets being the same. Only change this needle jet if the one you have is worn out. If you do not have the old needle, a older drill bit bigger than 3/20ths (.150), and smaller than 11/100 (.11") Use the tapered side of the bit, set it down in the hole and tap it out carefully.)
Now take your OLD needle, I repeat, the OLD needle because what you are going to do next will ruin it. Pull the clip off with your needle nose pliers, or a tiny screwdriver to pry it off. Then put the needle back in the hole where it goes. That’s right, just to clarify, you took off the needle, and you put the needle back in the hole with no clip. Slide the point side first, just as it would go normally. Now if you look at the bottom of the carb, the needle is protruding past the main jets hole. Grab another pair of locking pliers (vise grips as I call them) and lock it as tight as you can on the needle. Pull with all your might on the needle. Use two hands. Have a friend hold the carb so you don’t pull it off the boot. Tell them to stick their fingers in the hole that goes to the engine, and pull up. After pulling hard, the needle jet should slip right off. Then notice which side goes towards the top of the carb. There is one side that is a smaller diameter than the other. Take the new needle jet, and push it up into the hole the way the old one was set. Just get it straight. Take the tube the main jet goes into, and start threading it in. Once you can’t tie it down anymore with a ratchet, unscrew it and look at the needle jet to make sure it’s set. That’s it for the needle jet. Now let’s start putting the carb back together.
(Notice: Many people have destroyed jets and such by overtighting them! Use the thumb on the head of the wrench and two fingers on the wrench to tighten it down.)
Thread the main jet into the tube it goes into, and then start putting it back on the carb. Thread the pilot jet in as well if you haven’t done so already. Remember these carburetor metals are soft as cheese, so don’t over tighten the jets very much. What I do is I put my thumb on the top of my ratchet, and use two fingers closest to the head of the ratchet to tighten the jet. That’s how tight I go when I tie them back in.
Now before we put the carb back together, let’s adjust the fuel screw. Take a small screwdriver, and start screwing in the fuel screw until it sets. Again, do not over tighten, just let it set. Then count back your turns. Count back 1.75 turns.
Now we must put the bowl back on. The white piece that came off with the bowl goes back as followed:

If you look directly under the carb, the round hole is aligned with the pilot jet. Take the float bowl, and put it back on.
Untie the rear clamp and the front clamp as well. Slip the carb back the way it used to. Make sure that it is straight up and down with the rest of the bike. The notch on the front boot should be aligned with the notch on the carburetor, and the notch on the carburetor should be in that slot. Tie the clamps down securely.
Let’s put the needle in. These are how the needle numbers go:

The top clip position is #1, the lowest one, closest to the bottom, is #5. (The picture says six but it is five in this case) For reference #1 is the leanest position, while 5 is the richest. I put the clip in the 4th position. Read at the bottom of the page and you can know what conditions I ride in, and you can adjust them to your preference.
Put the clip in the new needle, slip it in. Take the vise grips off your grips and start guiding the plunger holder down to the bottom. Remember not to let that assembly come apart because it is a pain in the ass to get it back together! Once you get it to the bottom, put the two screws on, and then put the cover on.
Now that you have done the carburetor mods, there is still one thing you want to do to complete the process. Don’t worry, this takes less than a minute! On the top of the air box there is a snorkel:

As you can see, you can slip your fingers in and pull it out. Do that. This lets more air in to the air box. Don’t worry about water getting in. There is a lip that is about 1/8” high that doesn’t let water in. When you wash, don’t spray a lot under the seat, but don’t worry about it too much.
The next thing you must do is remove the exhaust baffle. The screw is a torx type, or you can carefully use an allen wrench and take care not to strip it:

The screw is at the 5 o’clock position and all you do is unscrew it, reach in, and yank it out. This setup still passes the dB test. The bike runs 92 dB per AMA standards, which is acceptable. Just carry this baffle in your gear bag if the ranger is a jerk off. I’ve never had a problem, but don’t take chances.
That’s it! Start putting your tank on, seat, and covers. After you put the seat on, pull up on the front, and the middle of the seat to make sure the hooks set in place.
Turn on the bike, and take a can of WD-40. Spray the WD-40 around the boot where it meets the carburetor. If the RPM rises, you know you have a leak, and the leak must be stopped. You must do this to make sure there are no leaks!
Here is my configuration:
04’ 230F
Uni Air filter
132 Main Jet
45 Pilot Jet
Power up needle, 4th clip position
Fuel screw 1.75 turns out
Riding elevation: 2000ft - Sea level
Temperature – Around 60-90 degrees
Spark Plug Tips
When you jet your carb, a spark plug is a best friend. Make sure your spark plug is gapped correctly, (.035) but that’s not all that matters. You want to make sure the electrode is over the center, and you want the electrode to be parallel, not like a wave of a sea. Put in the plug, and run the bike for 15 mins, ride it around too then turn it off. Then take off the spark plug after letting the bike cool. The ceramic insulator should be tan, like a paper bag. If it is black, it is running rich, if it is white, it is running lean. The fuel screw should be turned out if it is running lean, and turned in if it is running rich. Go ¼ turns at a time until your plug is a nice tan color.
Making sure your bike is jetted correctly
While you are running the bike for those 15 mins to check the plug color, you want to make sure it’s jetted correctly now. Here is what the jets/needle/screw control:
0- 3/8 throttle – Pilot jet
¼ to ¾ throttle – Needle
5/8 – full throttle – Main jet
0-Full – Fuel screw
Pin the gas, does it bog much? Just put around, is it responsive? When you’re coming down a hill, the rpm’s are high and you have no hand on the throttle, does it pop? If it pops, it is lean and the pilot jet should be bigger. If it’s responsive your needle is set perfectly. You shouldn’t have to go any leaner than the 3rd position, but I put mine in the 4th position to get the most response. Your bike shouldn’t bog much when you have it pinned. If it does it is too rich of a main jet.
Determining the plug color, you will have to mess with the fuel screw.
That’s it, have fun jetting, and any questions, post on the forum, but remember to do a search first.
Also, if your bike requires different jets due to alititude, humidity, or temperature, please post the following so we can better assist you:
Average temperature
Altitude (If you do not know this, there is a link in the Jetting forum that you can look up your alititude)
Average Humidity
What jets you are currently running
What the problem is (If there is one)
Just do that and we'll help you out the best we can.
EDIT: The girl using this login name is my girlfriend. You can reach me on my new login name at 250Thumpher
Then again, you're more than welcome to say hi to her!
-Phill Vieira
• By kashlak
JUst curious of how many bikes,quads,trikes people owned over the years and what they were?
78 honda atc 70
85 honda atc 110
?? handa trail 70
78 yamaha mx 80
85 yamaha yz 60
82 yamaha it 125
85 kawasaki kxt 250 tecate
79 yamaha yz 400
86 yamaha yz 125
85 yamaha yz 80 (playbike)
92 kawasaki kx 250
93 yamaha xt 350
and last but not least a 99 kawasaki kx 250
• By Bosch232
Were the XL's the predecessor to the XR's?
I have a friend who's looking at an old XL350, and I don't know anything about these bikes.