The XT350 thread

[Calkins]

Originally Posted by Brypoint

Ok thx for this, I'm ok with a little rub. Does that tire look bigger/better then stock? If you can remember lol.

This is the only photo I have right now. It looks SO MUCH better with these tires on it! I thought it look like a kid's bike with the stock size on it!

[Calkins]

Originally Posted by Brypoint

These problems showed up after you cleaned the carbs? Could you have possibly bent the float at all? Seems like it may be allowing too much fuel in at the higher rpms (hence the fouled plug) and when your buddy starved it, it began to run better. How's the plug? maybe its not firing properly at high r's and that would cause a rich enviorment too due to not burning all the fuel.

I thought about the float too, but since the last time I messed with the carb and had the bowl off, it has ran 'ok' I was starting to consider ignition, until we started killing the fuel to it. I am really lost now. I think I am going to order all NEW stock jets and start there.

[Brypoint]

Originally Posted by Calkins

This is the only photo I have right now. It looks SO MUCH better with these tires on it! I thought it look like a kid's bike with the stock size on it!

Yah that's a nice looking bike, I might go with the Kenda's K270 rear130 as they are about half the price of the Dunlop's. They got some pretty good review's.

[Brypoint]

Originally Posted by Calkins

I am really lost now. I think I am going to order all NEW stock jets and start there.

Well if your going to replace jets why not go up a size? Everyone here says they are too lean and need to be up a size or two. I'm also seeing people try to get their primary and secondary main jets as close as possible. (stock 125&1106 respectively) So I might try 130's on both. Then try a 45 on the pilot jet seeing its 42 stock.

[Calkins]

Originally Posted by Brypoint

Well if your going to replace jets why not go up a size? Everyone here says they are too lean and need to be up a size or two. I'm also seeing people try to get their primary and secondary main jets as close as possible. (stock 122&125 respectively) So I might try 130's on both. Then try a 45 on the pilot jet seeing its 40 stock.

Ok. The reason I am thinking of replacing them, is I think I might have reamed out my pilot jet when I drilled the crap out of it. I think I was using a #63 bit, and I did see a tiny bit of brass on the bit when I was finished.

[Brypoint]

Originally Posted by Calkins

Ok. The reason I am thinking of replacing them, is I think I might have reamed out my pilot jet when I drilled the crap out of it. I think I was using a #63 bit, and I did see a tiny bit of brass on the bit when I was finished.

Well someone correct if I'm wrong but I believe the pilot jet is only for idle and low rpm's. So while this may give you trouble at low RPM's you may have a different high rpm problem. I just thought of something else how are the hoses and connections to your secoundary carb doing? Is the diaphram in good shape? Maybe the trouble is in their. If the secondary isn't working properly this would give you high rpm issues. But the rich enviroment is troubling me too.

[Calkins]

Originally Posted by Brypoint

Well someone correct if I'm wrong but I believe the pilot jet is only for idle and low rpm's. So while this may give you trouble at low RPM's you may have a different high rpm problem. I just thought of something else how are the hoses and connections to your secoundary carb doing? Is the diaphram in good shape? Maybe the trouble is in their. If the secondary isn't working properly this would give you high rpm issues. But the rich enviroment is troubling me too.

I just replaced at the hoses and recleaned the carbs. Put about half a tank worth of riding on it then filled the tank. That's when I had problems. That is the same pump I filled at the last two or three times, without major problems.

The way my Honda guy (Small engines tech at my work) and I thought about the pilot is that it is low RPM. BUT! If it's rich and idle and low RPM (mine is) it can get worse on the top end. SO, I am thinking I need to fix the low end to have a better top end, then fix that.

Does that make sense, or are we tarded?

[Brypoint]

I found this on the web and though it might be useful to some.

Jetting!

Carburetor jetting can be easily understood if we understand the basic principles of carburetor and engine operation. A carburetor mixes fuel with air before it goes into the engine. When the mixture is correct the engine runs well. The bottom line is a carburetor must be adjusted to deliver fuel and air to the engine at a precise ratio. This precise ratio can be affected by a number of outside and inside influences. If you are aware of these influences you can re-jet your carburetor to compensate for the changes. I'm going to show you some examples of how you can change your jetting for better performance and in some cases increased engine life. As with any engine work be sure you have good tools the correct parts and a good manual before you get your hands dirty!

Altitude Compensation
For our first example let's say we find a new riding area WAY up in the mountains. Our jetting is dialed in for our usual riding area which ranges from sea level to 1500 feet. Our NEW riding area starts at 4000 feet and goes up from there. Going to a higher elevation will require will require a jetting change but which way? Like our fuel density, air density can also change. Higher elevations have less air density then lower ones. At high elevations our engines are getting less air, so they need less fuel to maintain the proper air/fuel ratio. Generally you would go down one main jet size for every 1750 to 2000 feet of elevation you go up (info for Mikuni carbs). If you normally run a 160 main jet at sea level you would drop down to a 140 at 4000 feet. Something else goes down as you go up in elevation is horsepower. You can figure on losing about 3% or your power for every 1000 feet you go up. At 4000 feet your power will be down about 12%-even though you rejetted! For our second example let's say we are still at our new 4000-feet elevation riding area and a storm comes in. We head back to camp and ride it out overnight. The next day there's a foot of snow on the ground the skies are clear and it's COLD! Aside from getting the campfire going and making some coffee you should be thinking about jetting again! Cold air is dense air and dense air requires bigger jets. If the 140 jet ran good the day before you will need a bigger jet to run properly today. If the temperature is 50 degrees colder than it was the day before you can actually go back to your sea level jetting, a 160 main jet! If you don't rejet you can kiss your assets goodbye when you rebuild the seized engine. Air temperature makes that much difference!


Our final example will deal with something often overlooked. We are still up in the hills enjoying our NEW riding area when we notice the old fuel supply getting shorter. No biggie; there's a little store/gas station just down the road. A short trip a few bucks change hands and we are ready to go again. Out on the trail the bikes are running funny, sometimes "pinging" and running HOT. What happened?! When we changed jets to compensate for altitude and temperature we were still using SEA LEVEL gasoline. Gasoline sold at higher elevations have a different blend of additives to compensate for the altitude. Generally high elevation gasoline is less dense to compensate for less available air going into the engine and to aid starting. The lighter specific gravity of the high elevation fuel actually "leaned out" our mixture! One to two sizes bigger main jet will get us back into the hunt. If you ride in vastly different areas try to bring enough or your normal fuel along to last the entire ride. It will save you hassles and gray hair in the long run!

Pilots, Needles & Mains
So far we have only talked about main jet changes to compensate for altitude, temperature and fuel density. As most of you know there is a pile of jets in a carburetor. While main jets are the most critical for ensuring full power operation and engine longevity, the other jets are equally as important for a good running engine. Let's run through them quickly.

Pilot Jets: Pilot jets control the low-speed and idle mixtures. Many times an adjustable jet is used in conjunction with the pilot jet. The adjustable jet allows a precise setting of the idle mixture. If the adjustable jet is located to the rear of the carburetor and usually on one side it is a AIR adjustment. It controls the amount of air that mixes with the fuel coming from the pilot jet. If the adjustable jet is to the front of the carburetor, on the side or bottom, it controls the amount of air/fuel mixture going into the engine. In either case if adjusting the mixture screw won't improve the low-end running speed it's time for a different pilot jet.

Slide: Throttle valves (the slide) control the off idle, to one-quarter open, mixture. Some aftermarket carbs have replacement slides available with different "cutaways". Changing the cutaway changes the mixture. More cutaway is lean, less cutaway is rich. Some carbs do not have different slides available, so you have to compensate by changing the mixture on the idle circuit or needle circuit. Partial throttle hesitation or rough running can be caused by the slide cutaway.

Needle Jets: Needle jets control the amount of fuel going by the needle and into the engine at low to mid throttle. There are 2 types of needle jets used in a carburetor. One is a primary type that has a very precise hole hole drilled through the middle of it, along it's length. The size of the hole relative to the size of the needle determines how much fuel goes into the engine. The other type of needle jet is constructed essentially the same except for a bunch of holes drilled into the side of the jet. These holes allow air to mix with the fuel before it's metered into the engine. Either type of needle jet works well in most cases but there is power to be gained on high performance four-strokes by going to the needle with the holes in the side. These are called "bleed" type needle jets and produce more midrange power in a four-stroke. In any engine going to a leaner (smaller) needle jet is the easiest way to rejet the midrange running when going to higher elevations. Changing the needle jet leans out the mixture evenly at all the midrange throttle settings moving the needle clip doesn't.

Needle: Jet needles more commonly know as the "needle" control the fuel mixture throughout the midrange. The shape or taper of the needle dictates how much fuel goes into the engine at a given throttle opening. The needle must work in conjunction with the fueling requirements of the engine relative to slide position. If you have an engine with a strong hit in the midrange the needle will probable have a noticeable reduction in size the the slide is half open. Remember it takes fuel to make power and when the engine makes power it needs fuel NOW! If it doesn't get the right amount of fuel it pings or misses. You many have cleared up a little midrange pinging by moving the needle up a notch but at the same time you may have over richened some other areas. If the problem isn't too bad you won't even notice the rich condition. If the machine stutters before it comes on the power that part of the needle's taper is too small and the only way to cure it is to get a needle with a different taper. Finding the right needle can be difficult so hopefully moving the clip will do the job.

Main Jet: Finally the good old main jet comes into play at three-quarters open to full throttle conditions. Most of you already know a bigger main jet has a bigger hole so it lets more gas into the engine! Pretty simple! As simple as it is the minuet is absolutely CRITICAL to high-speed engine operation. Not only does it meter the gas into the engine, it can aid in cooling the engine as well. A properly sized main jet will let the engine make good power for a long time. One size smaller main jet may make greater power for awhile. A slightly rich mixture burns cooler than a lean one so be sure the main jet is big enough!

One final note on jets. All of them and the carburetion functions then perform tend to overlap into some other jet's territory. If you mess with one jet, you may have to mess with a few of the others. My best advice is to not change more than one jet at a time. Slowly work out the correct jetting and keep notes on what you are doing. If you get totally fouled up at least you can go back to where you started.

Sign, Symptoms & Causes
How would you know if there was something wrong with your jetting? If you listen, your engine will tell you! All you need is an interpreter. Since I speak and understand several different engine dialects, I will give you a hand. Let's start with lean conditions because they can cause the most damage. In a lean condition the engine will surge and sometimes ping under acceleration. The engine will also be "cold-blooded" (hard to start and keep running) but will run better when hot. The spark plug will look bone white or burned in extreme cases. The engine may spit back or sneeze through the carburetor once in awhile too.. If the engine is running rich the throttle response will be fuzzy and not too quick. The engine will burble, miss and blow black smoke. It will start easy but will run funny when fully warmed up. The plug will be dark, wet or fouled (possible all three!).

Ok so what do you do first to cure the problem? The very first thing is to check and adjust the float level. If it's off one way or another it can throw the jetting off too. Set the float to the specs and retest the running. The next item is to determine a rich or lean condition. Let's say the engine gets hot and doesn't pull well. This is a lean condition so the engine wants more fuel. Stick in at least a two size bigger main jet and try it again. If it's better but still not right go even bigger on the jet. and try it again. Bear in mind that drastic or sudden changes in jetting usually mean an air leak has developed somewhere in the engine. Find it and FIX IT! When the engine burbles on the top end come down one jet size at a time until it winds all the way down. Don't drop and more sizes! If the engine seems sluggish and lumpy or want to load up on the bottom end the mixture is TOO RICH. Adjusting the low speed mixture screw helps a little but doesn't cure the problem completely. What you need now is a new pilot jet. Go one size smaller and try the adjustment again. When the engine runs smooth with the adjustment screw about one and a half turns out from the seat you have it!

Final Thought
There's a lot more to jetting than just stuffing jets in holes and hoping the problem goes away. If you can understand what your engine is trying to tell you when it runs funny you will have a better chance or correcting the problem than someone who doesn't have a clue. When you rejet, go slowly and carefully until the problem is solved. As a final thought let me remind you that jetting is a lot like life, if you have a choice it's always better to be a little rich!

[Brypoint]

Originally Posted by Calkins

Does that make sense, or are we tarded?

This article wasn't a cut at you or anything just thought it might help understand carbs better for both of us lol. Your top-end troubles might have to do with the coil, but I'm totally lost when it comes to electrical. I'm from the school of find whats wrong and slap a new part on.

[Brypoint]

Another informative article

4Strokes.com Technical: How to Read Your Spark Plug

You can tell a lot by reading your spark plug. Here's how to check your jetting by reading the plug. Always start with a new plug that is of proper heat range and reach. Using a plug with an improper heat range or incorrect reach can cause engine damage or poor performance. Proper torque is essential as an improperly tightened plug can damage the engine. Before removing any plug, clean the area around it thoroughly to prevent debris from entering the cylinder. A dry acid brush and an air compressor work great. Run the engine at least 10 minutes, as a new plug will not color immediately.

To obtain an accurate reading from a new spark plug:
Accelerate at full throttle on a straight
Push the engine stop button and pull the clutch lever in to release the clutch
Coast to a stop
Remove the spark plug
It is best to use a magnifying glass to inspect the spark plug. The porcelain insulator (1) around the center electrode (2) should appear clean and colorless with a gray ring around the center electrode where it exits the porcelain. Metallic specks indicate lean jetting that is removing metal from the piston. Black sooty streaks on the porcelain indicate rich jetting.

What does a spark plug look like for different carburetor mixture conditions:
Optimal - White or no color change with light gray ring
Lean - Extreme white with aluminum specs (overheating)
Rich - Wet or sooty
In addition to improper jetting:
A lean condition can be caused by air leaks in the inlet tract or exhaust system, passing of too much air because of the use of the wrong air filter, use of a less-restrictive aftermarket exhaust system, or leaks in the air box.
A rich condition can be caused by a plugged or dirty air filter, use of a more-restrictive aftermarket exhaust system, a clogged spark arrester, or excessive oil on the air cleaner. Excessive smoking may occur with this condition.
Spark Plug Related Article from Forums

Reading spark plugs isn't too hard to do, but I've read various understandings of how to read spark plugs and it seems there's different schools of thought on this. I always use a lighted magnifying glass of 5X to 10X to better see the tiny deposits. When checking your spark plug, always use a good used spark plug, making sure it's not worn out. A worn out spark plug will have a worn or rounded center electrode and or side electrode. New spark plugs are hard to read accurately for mixture checks, but if you have to use a new spark plug, then make sure to put at least 15 to 20 hard minutes on it before attempting to get a reading. I do my spark plug readings from the base ring at the bottom of the threaded body. The 'L' shaped grounded side electrode that's welded to the base ring will clue you into the heat range as this is the closest part to the piston. The porcelain will clue you into timing and preignition/detonation issues while the base ring will clue you into the mixture. Many people I've talked to and some of the articles I've read simply look at the porcelain color and use that as their sole guide for a proper air/fuel mixture, but I don't agree with that all together and would not recommend basing your jetting decisions solely on the color of your spark plugs porcelain.

Spark Plug Center/Ground Electrode
You want to first carefully look at the grounded side electrode to determine if you've got the proper heat range for your spark plug and this is done by closely examining the color change of the side electrode. If the color of the electrode changes near its end where it sits over the center electrode, then the spark plug heat range is too cold and what you're seeing is the color changing due to the heat transferring too quickly. If the color of the side electrode changes color near where it's welded to the base ring, then your spark plug is too hot and what you're seeing is a slower heat transfer from the side electrode to the base ring, resulting in preignition/detonation issues and most of the deposits will be burned off. Ideally, you want the side electrode of your spark plug to change color at about the half way point, about where it makes it's 'L' shaped bend.

Spark Plug Base Ring
The second thing you want to check is your spark plugs base ring and this will clue you into how your bike is jetted. The color of the base ring itself is close in color to the crown of the piston and what you're looking for here is a nice light to medium brown color all the way around the base ring. If you're seeing a chalky whitish or light grayish color or the color doesn't uniformly go all the way around the ring, then you are running too lean. If the color does go all the way around the ring, but you see dark colored soft dry soot that's heavily spotted on top of the base ring color, then you're running too rich and or possibly have a spark plug with too cold of a heat range. The presence of wet oil or ash deposits is a tell tale sign of possible engine problems such as valve stem or valve guide wear or worn out piston rings, etc, so don't confuse this with a rich mixture that leaves your spark plug carbon fouled.

Spark Plug Porcelain Color
The third thing to check is the porcelain color and this will clue you into preignition/detonation issues. What you're looking for are tiny specs of aluminum on the porcelain, which can be either black or shiny. If the tip of the insulator appears melted, then this is yet another clue to a pre-ignition/detonation problem. The detonation is caused by the air/fuel mixture exploding instead of burning and you may hear the resulting knocking sound from this, particularly when the engine is under a load. The knocking sound heard is actually a shock wave that's disrupting the boundary layer of cooler gasses that cover the internal parts of the combustion chamber, resulting in incomplete combustion. This rapid rise in pressure and temperature exerts extreme force on engine components and can do very bad things such as crack your engines head, crack or put holes in your piston, blow head gaskets, break your connecting rod, damage bearings, seals, etc. This is why you should not base all your jetting decisions on just the porcelain color alone because the porcelain color doesn't tell the whole story. Although the porcelain and base ring colors are similar, the porcelain usually appears lighter in color when compared to the base ring.

[Zecatfish]

My parts came in today and I got the new timing chain on the crank.
Side cover back on no problems and even cleaned the oil level sight glass.
Now the bad side, I get to take it back apart.
I forgot to fold the tabs over on the nut on the clutch spindle.
So the side cover and clutch gets to come back off.

[Calkins]

Originally Posted by Zecatfish

My parts came in today and I got the new timing chain on the crank.
Side cover back on no problems and even cleaned the oil level sight glass.
Now the bad side, I get to take it back apart.
I forgot to fold the tabs over on the nut on the clutch spindle.
So the side cover and clutch gets to come back off.

I just finished tightening the last cam cover bolt and looked into my parts box when I figured out my screw up! You know that big O ring on the lower part of the sleeve, under the cylinder? Yea, it's still not leaking, so it's not coming back apart!

[SkidMarx]

Originally Posted by Calkins

I have some crap going on with mine today. Went for a ride and 5k stumble came back, and won't let the bike rev past. I was at WOT on the highway for a bit, and it was slowly losing power, and about 4k was the max I could get, in 4th on up. Came home and found that it's rich as heck, black plug, and inside muffler. Tore out the end of the pipe/spark arrestor. No change. My buddy got on and slowly turned the petcock closed at WOT and got it to run much better, when it's lean. It was turned to about 8:00. At that point I had tons of power and it would freely rev to 8-9k under load.

SO? What's up?

As we rode, I was thinking about what I have done. Then it hit me! When I douched out my carb, I had a jet that was oacked full of crap, and I had to use a finger drill on it. That was the Pilot Jet. What RPM range does that cover?

Pilot is 0 to 1/4ish throttle.
I'd just pull it apart again and see if there is anything obviously wrong.

[klaviator]

Originally Posted by Grreatdog;16362034.......

And, yes, it is pretty difficult to adjust the valves. It is easy enough to check the clearances. Do that just like any other bike. But XT350's are shim and bucket which means you need a shim chart and the correct shims plus a tool to compress the valve spring or you can remove the cams. But it is a good idea to check the valve clearances. If you aren't sure how to do it then it is worth paying for. It has to be done cold though so it is usually an overnight service.
.....

The valves can be adjusted without the special tool (which is no longer available) and without removing the cams. It really isn't that difficult. My valves didn't need adjustment until over 16k miles.

[Zecatfish]

Originally Posted by Calkins

I just finished tightening the last cam cover bolt and looked into my parts box when I figured out my screw up! You know that big O ring on the lower part of the sleeve, under the cylinder? Yea, it's still not leaking, so it's not coming back apart!

This is the second time.
That lock on the nut for counter balancer shaft, I forgot it too, but I was still looking at it so no need to remove stuff to fix it.

At least I remembered it, so it doesn't back off 100 miles from home.

If yours isn't leaking I wouldn't tear it down either.
Did you leave the old on the cylinder maybe? IT might need needed replacing.