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Discussion Starter #1
I bought this 1998 KLR about a month and a half ago. From the first time I tried to really wrap it out, it starts missing in 3rd, 4th and 5th between 4500 and 5500. It has a jet kit with a Supertrapp exhaust and an aftermarket filter. I've tried replacing the petcock, fuel lines, vacuum lines and I even replace the coil. I can't get it to run smoothly under hard acceleration. It still coughs at 4500 to 5500 RPM in 3rd,4th, and 5th. I can accelerate hard from 1st to 2nd and it will be smooth up to 7500 rpm. I took off the carburetor and cleaned it with carb cleaner. Nothing has worked so far. I would appreciate some insight. Thanks.
 

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I bought this 1998 KLR about a month and a half ago. From the first time I tried to really wrap it out, it starts missing in 3rd, 4th and 5th between 4500 and 5500. It has a jet kit with a Supertrapp exhaust and an aftermarket filter. I've tried replacing the petcock, fuel lines, vacuum lines and I even replace the coil. I can't get it to run smoothly under hard acceleration. It still coughs at 4500 to 5500 RPM in 3rd,4th, and 5th. I can accelerate hard from 1st to 2nd and it will be smooth up to 7500 rpm. I took off the carburetor and cleaned it with carb cleaner. Nothing has worked so far. I would appreciate some insight. Thanks.

Hmm...

I'm thinking that you do have a carb problem. Where is the throttle postion when you get the missing? Probably in 1st and 2nd you are going through the spot so fast you don't notice the problem.

Motorcycle carbs work on throttle postion not RPM. You'll be in the needle to main jet transtion at 1/2-3/4 throttle. Look at the sizes of the main and needle jet. Check the needle itself be sure it's seated right and not damaged. Usually it's better to put everthing back to stock and go from there. How's the plug look, it will give you an overall indication of mixture.
 

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Discussion Starter #3
It happens at full throttle. The carb has been jetted. It is on the medium jet that comes with the kit. Could I be reaching a lean situation at this area? Should I try the bigger jet?
 

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It happens at full throttle. The carb has been jetted. It is on the medium jet that comes with the kit. Could I be reaching a lean situation at this area? Should I try the bigger jet?

It's hard to diagnose virtually... when you say it coughs what do you mean? If it feels like the motor can't keep up with the throttle, "bogs" is the term I would use it's too rich. If the motor suddenly surges in a certain area that would indicate a lean condition.

In the rpm range you mentioned 4500-5500 my bike is at 3/4 throttle (4th and 5th gear) right where it transtions onto the main jet. If the needle taper/height is too aburpt the transtion won't be right. Does it have the stock needle in it? if so does it have any washers on it (for the .22 mod)? Is it seated right on the slide's plastic deal (technical term!)? Bike Bandit 1998 KLR fiche look at the carb section make sure your sis put together right.

You need to research the jet kit you have and see how it compares to stock. Maybe the last owner put the wrong kit in it? What does the plug look like?
 

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Throw a new spark plug in 'er an see what happens.

NGK DPR8EA-9. Kind of important to get that one. Around 3 bucks. We can hold a bake sale if you need an assist. You may very well have carburetor problems, yet I have an inkling the wrong or fouled plug may be an issue. A weak or colder plug may not be strong enough to burn the full load at higher rpm
 

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Discussion Starter #6
It surges and everyone has told me that it feels like a lean condition. The needle did come with the kit and has different heights. If I adjust the needle what direction do you suggest I go? I am assuming I need to pull it up a notch to allow more fuel. I have done minimal work on carburetors and could use all the help I can get. And I replaced the plug early on and the plug that was in it was perfectly fine with normal wear.
 

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Discussion Starter #7
No need for the bake sale. The spark plug was one of the first things I replaced. The plug that was in it was perfectly fine with normal wear. I think I may have to tear into the carburetor.
 

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No need for the bake sale. The spark plug was one of the first things I replaced. The plug that was in it was perfectly fine with normal wear. I think I may have to tear into the carburetor.
Good to know about the plug. You hadn't mentioned that you replaced it. You did specify a miss at high RPM's. Now you describe a surge. They are different, and can have different origins. Surging implies carburetor issues to me. A dead miss at high RPM's does not.

The perfectly good plug you removed should answer your questions in a general way as to whether the bike is running rich or lean by the coloration.

Surging can be attributed to any of a number of things.....how long has that SuperTrapp muffler been on there, and what is the condition of the packing? Have you thoroughly inspected your drive chain for wear? Chain problems will surface in higher gears and at higher speeds more than in low gears at higher RPM's. Some aftermarket air cleaners do not seal well, creating intermittent lean conditions. Restricted exhaust can cause rich conditions.

Did this bike ever run well in it's current exhaust / air cleaner / carburetor jetted state? What I mean is, did the bike run well, and develop these surging issues, or did someone mess it up, and you are trying to straighten it out?

The spark plug you took out has a story to tell you may not be able to put into words.
 

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I will try that, but isn't there something that is drilled out when you install a jet kit? Won't this have an effect if I put in the stock jet and needle?


Part of the 22 cent modification, drilling the slide allows a quicker response of the slide. It will not affect jetting.

You need to keep in mind that with an aftermarket exhaust and an aftermarket air filter system, stock jets may not be appropriate to achieve a stable running engine, should you decide to go back stock.


*****
 

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Discussion Starter #12
I just bought this bike a month and half ago and it was already jetted, with the supertrapp and the aftermarket foam filter. It has never run right. I guess what I am trying to say is the kit probably was not put in correctly and I am trying to fix what someone messed up before I aquired this bike. The chain probably does need replacing. It seems to have some hard spots even though I keep it lubed. I am pretty sure I am encountering a lean condition at this RPM. I think I need to adjust that needle or try a different jet. What do you think? I will check the air filter and possibly replace it.
 

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Discussion Starter #14
I just bought this bike a month and half ago and it was already jetted, with the supertrapp and the aftermarket foam filter. It has never run right. I guess what I am trying to say is the kit probably was not put in correctly and I am trying to fix what someone messed up before I aquired this bike. The chain probably does need replacing. It seems to have some hard spots even though I keep it lubed. I am pretty sure I am encountering a lean condition at this RPM. I think I need to adjust that needle or try a different jet. What do you think? I will check the air filter and possibly replace it.
 

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Look at the spark plug you took out and replaced, and the replacement new spark plug you put in. They should indicate if you are running lean or running rich.

It's your bike, and I do not want to seem critical of your suspicions or direction of problem solving. But. We do have indicators available to us to help diagnose a problem and select a path for a solution.
Going into a carburetor and swapping jets on a WAG rarely produces positive results. YMMV. I would become fully informed of what I had going on externally [exhaust, air cleaner, fuel, elevation, ambient temperatures, possible air leaks in the intake and exhaust] before I got too wild about re-jetting.

If your drive chain has tight spots in it, you could very well have surging with a perfectly tuned motorcycle. And if that chain decides to give up the ghost and come loose, jetting will be the least of your problems. You state the bike performs well in first and second gear, and acts up in higher gears at higher RPM's. Exactly where the symptoms of a bad chain will appear.
 

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I just bought this bike a month and half ago and it was already jetted, with the supertrapp and the aftermarket foam filter. It has never run right. I guess what I am trying to say is the kit probably was not put in correctly and I am trying to fix what someone messed up before I aquired this bike. The chain probably does need replacing. It seems to have some hard spots even though I keep it lubed. I am pretty sure I am encountering a lean condition at this RPM. I think I need to adjust that needle or try a different jet. What do you think? I will check the air filter and possibly replace it.

Raising the needle will richen the mixture.

The carb's jetting circuits overlap somewhat so your main jet might be lean also. To really know what's going on (short of a dyno and an air/fuel sensor) you can do plug checks. To do them right you have to ride in the circuit you're interested in. Just riding around like normal and then checking the plug won't help much.

It's called a plug chop. You put in a new plug and ride at least a mile or so in the circuit you're interested in. As level a road as possible and at a steady throttle. Then you kill the motor, pull in the clutch and coast to a stop. Pull the plug and see what it looks like.

In your case looking at the needle jet circuit you would want to be somewhere between 1/2-3/4 throttle. Takes awhile to dial in a carb like this!

Just noticed that you have a SuperTrapp exhaust. Does it have a lot of disks in it? More disks = less restriction (= NOISE) and a leaner mixture. Is the airbox modified (= leaner mixture)?
 

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Discussion Starter #17
Look at the spark plug you took out and replaced, and the replacement new spark plug you put in. They should indicate if you are running lean or running rich.

It's your bike, and I do not want to seem critical of your suspicions or direction of problem solving. But. We do have indicators available to us to help diagnose a problem and select a path for a solution.
Going into a carburetor and swapping jets on a WAG rarely produces positive results. YMMV. I would become fully informed of what I had going on externally [exhaust, air cleaner, fuel, elevation, ambient temperatures, possible air leaks in the intake and exhaust] before I got too wild about re-jetting.

If your drive chain has tight spots in it, you could very well have surging with a perfectly tuned motorcycle. And if that chain decides to give up the ghost and come loose, jetting will be the least of your problems. You state the bike performs well in first and second gear, and acts up in higher gears at higher RPM's. Exactly where the symptoms of a bad chain will appear.
Well, you're not going to hurt my feelings. I appreciate the input. I suspect the chain is the original. When it's parked I can see where it is kinked a little. I really should replace it. I am also going to check everything you suggested. This is my second KLR and I was skeptical about buying one that was jetted but I got a great deal on it. My first one was a stock 2000 KLR and it ran like a scalded ape. Again I appreciate all the input.
 

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Discussion Starter #18
Raising the needle will richen the mixture.

The carb's jetting circuits overlap somewhat so your main jet might be lean also. To really know what's going on (short of a dyno and an air/fuel sensor) you can do plug checks. To do them right you have to ride in the circuit you're interested in. Just riding around like normal and then checking the plug won't help much.

It's called a plug chop. You put in a new plug and ride at least a mile or so in the circuit you're interested in. As level a road as possible and at a steady throttle. Then you kill the motor, pull in the clutch and coast to a stop. Pull the plug and see what it looks like.

In your case looking at the needle jet circuit you would want to be somewhere between 1/2-3/4 throttle. Takes awhile to dial in a carb like this!

Just noticed that you have a SuperTrapp exhaust. Does it have a lot of disks in it? More disks = less restriction (= NOISE) and a leaner mixture. Is the airbox modified (= leaner mixture)?
The SuperTrapp has all but 5 disks.
 

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Discussion Starter #19
Look at the spark plug you took out and replaced, and the replacement new spark plug you put in. They should indicate if you are running lean or running rich.

It's your bike, and I do not want to seem critical of your suspicions or direction of problem solving. But. We do have indicators available to us to help diagnose a problem and select a path for a solution.
Going into a carburetor and swapping jets on a WAG rarely produces positive results. YMMV. I would become fully informed of what I had going on externally [exhaust, air cleaner, fuel, elevation, ambient temperatures, possible air leaks in the intake and exhaust] before I got too wild about re-jetting.

If your drive chain has tight spots in it, you could very well have surging with a perfectly tuned motorcycle. And if that chain decides to give up the ghost and come loose, jetting will be the least of your problems. You state the bike performs well in first and second gear, and acts up in higher gears at higher RPM's. Exactly where the symptoms of a bad chain will appear.
Well I finally got myself a new chain for my bike and I still have the same problem. I am getting very frustrated. I guess it's time to dive into that carburetor. What do you think?
 
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