Greetings from finland to all TT-Forum gods and everyone blessed with knowledge around my probem..

 

Introducing myself as a noobie here, but not usually with these things  :jawdrop:

Im beginning to be pretty pissed and fed up with this bike(-97 XR400R), since it never really has worked on me. I've owned it 3 years and only driven about 100miles with it. Even though ive spent thousands of hours building it, i never seem to get it right or then a new error occures.

 

Right now im having problem with losing the spark, after the bike has ran for a minute, and even that time im having a struggle to keep it running with the choke on. It spits and coughs and misfires untill it wont run at all, no matter how much you spin the idle screw or try to rev it..

 

I have eliminated the first issues with carbs, by trying 3 different ones. Now theres BST40 Mikuni, which worked fine before spark issue, if it would start.

 

At this point i have installed a new spark plug and a new ign coil, but seems that its running even worse than before..

 

Today i opened the flywheel case, to see if there is some damage in the stator or its friend next to the flywheel picking up ign signal( couldn't remember the name of the component) But they look fine to me.

 

Have any of you had any issues with CDI on these or do you have any idea what the hell is wrong with it?

I could borrow a multimeter from my pal, to try measure some components, if i just knew what readings to expect and from where?

 

I suppose a few pics would be nice along with the apology of my bad english  ;)

 

2hgdz55.jpg

 

33vog2o.jpg

 

xpwy00.jpg

 

f09a90.jpg

With all that new paint, check your ground wires to frame and engine ground to frame.  Paint is an insulator.

Get rid of that stupid stubby fuel tank vent and valve. Those things are nothing but problems. The fuel delivery issues that they cause can easily come across as being electrical in nature.

In picture #4, whats that loose strand of wire on the 2 ignition windings?

With all that new paint, check your ground wires to frame and engine ground to frame.  Paint is an insulator.

 

Wouldnt it be strange that the paint isnt an insulator when the bike starts, but starts insulating after minute of running? And the bike has ran just fine with the paint on.

 

 

Get rid of that stupid stubby fuel tank vent and valve. Those things are nothing but problems. The fuel delivery issues that they cause can easily come across as being electrical in nature.

In picture #4, whats that loose strand of wire on the 2 ignition windings?

 

I've tried to run the bike without the tank cap, and usually without the tank at all, so that i didnt have to disassemble them all the time..

 

I think youre looking at the casting on the case.

Have you tried narrowing he plug gap. Nock it down some.

Have you tried narrowing he plug gap. Nock it down some.

 

I honesty cant believe that would solve the problem, but i guess ill try that next..

 

btw is that thingy inside the plug cap some sort of ceramic resistor? Could it cause trouble?

btw is that thingy inside the plug cap some sort of ceramic resistor? Could it cause trouble?

I was going to suggest that, but you said you replaced the coil, which the spark plug cap and wire are attached to, unless your new coil didn't come with a wire and cap.

I replaced the resistor with an equal length and size of copper wire.

Edited by Trailryder42

 

Right now im having problem with losing the spark, after the bike has ran for a minute, and even that time im having a struggle to keep it running with the choke on. It spits and coughs and misfires untill it wont run at all, no matter how much you spin the idle screw or try to rev it..

 

I have eliminated the first issues with carbs, by trying 3 different ones. Now theres BST40 Mikuni, which worked fine before spark issue, if it would start.

This is a bit confusing to me when you say "I have eliminated the first issues...".  Do you mean you eliminated the no spark issue or ruled out the carb being the problem?

 

Are you really losing spark or are you just suspecting this because of the behavior of the engine?  If it is a spark issue, we can rule out any fuel related causes.

 

I've tried to run the bike without the tank cap, and usually without the tank at all, so that i didnt have to disassemble them all the time..

If not a spark issue, did the bike run fine with the tank off?  Did you use a separate source of fuel, or just the existing tank with a hose extension?

 

I honesty cant believe that would solve the problem, but i guess ill try that next..

 

btw is that thingy inside the plug cap some sort of ceramic resistor? Could it cause trouble?

I doubt the plug gap is an issue as well unless it's WAY off, but then it likely wouldn't start either.  The resister is also an unlikely culprit.  I still have them on my 250 and 400 with no issues.  And the resistor wouldn't care if the bike was running for 5 seconds or 5 hours, it would still produce the same output.

I was going to suggest that, but you said you replaced the coil, which the spark plug cap and wire are attached to, unless your new coil didn't come with a wire and cap.

I replaced the resistor with an equal length and size of copper wire.

The new coil did not have plug cap within, i had to screw the old one back in with the resistor.

 

 

This is a bit confusing to me when you say "I have eliminated the first issues...".  Do you mean you eliminated the no spark issue or ruled out the carb being the problem?

 

Are you really losing spark or are you just suspecting this because of the behavior of the engine?  If it is a spark issue, we can rule out any fuel related causes.

 

If not a spark issue, did the bike run fine with the tank off?  Did you use a separate source of fuel, or just the existing tank with a hose extension?

 

I doubt the plug gap is an issue as well unless it's WAY off, but then it likely wouldn't start either.  The resister is also an unlikely culprit.  I still have them on my 250 and 400 with no issues.  And the resistor wouldn't care if the bike was running for 5 seconds or 5 hours, it would still produce the same output.

I did have carb issues at first, and still have with the stock keihin. The bike starts and picks up normally with it, but wont rev past ~5,5k on stand and on load it wont rev past ~4krpm. The next move was to try the BST40 and it worked great and revved to the limiter, just didnt want to start as easy but i made a patent on the choke and now it starts with ease.

Next symptom occured after the bike had ran for about a minute or atleast warmed up barely. I immediately suspected the spark, since it spat fire and refused to rev, just popping that unignited fuel in the crazy hot exhaust. Then it revved more low and more low and more low, untill it wouldnt even run at idle, no matter how much i tried to screw the idle or feed it with choke. Then it just dies.

 

When cold, it starts fine and continues with the same pattern.

 

Of course i had hose connector and bigger diameter hose filled with gas, when used without tank.

With the stock carb, Are you using the choke correctly. Lever all the way up is full choke, all the way down is choke off.

Have you ever had the cam out or cam chain off? Wondering if it could be a timing issue. Any engine work you've done that you haven't mentioned yet?

Edited by Trailryder42

With the stock carb, Are you using the choke correctly. Lever all the way up is full choke, all the way down is choke off.

Have you ever had the cam out or cam chain off? Wondering if it could be a timing issue. Any engine work you've done that you haven't mentioned yet?

 

Yes i do know how the choke works, the engine is so bone stock that all bolts that i have opened make that special cracking noise when opened the first time.

The complete engine has never been apart. I havent done any engine work to it yet, hence i planned to work on it next winter.

 

Only the timing chain tensioner has been checked by me when i first bought the XR and an oil change..

 

Now that i have the flywheel case off, i suppose i could check the timing too.

The new coil did not have plug cap within, i had to screw the old one back in with the resistor.

 

 

I did have carb issues at first, and still have with the stock keihin. The bike starts and picks up normally with it, but wont rev past ~5,5k on stand and on load it wont rev past ~4krpm. The next move was to try the BST40 and it worked great and revved to the limiter, just didnt want to start as easy but i made a patent on the choke and now it starts with ease.

Next symptom occured after the bike had ran for about a minute or atleast warmed up barely. I immediately suspected the spark, since it spat fire and refused to rev, just popping that unignited fuel in the crazy hot exhaust. Then it revved more low and more low and more low, untill it wouldnt even run at idle, no matter how much i tried to screw the idle or feed it with choke. Then it just dies.

 

When cold, it starts fine and continues with the same pattern.

 

Of course i had hose connector and bigger diameter hose filled with gas, when used without tank.

This sounds like either a fuel delivery issue or your ignition coil heating up.  To test the coil, have a spare spark plug handy.  Run the engine until it quits, then quickly pull the spark plug wire and install the spare plug.  Test for spark.  If you get good spark, the coil is fine and you can eliminate that as a cause.

 

For fuel delivery, I suspect the tank itself, since you say the same thing happens with different carbs.  That leaves the supply - i.e. tank.  If there is a minor blockage in the tank, it will allow the float bowl to fill over a long period of time.  When you run the bike for a minute or so, the flow bowl empties and the flow from the tank isn't sufficient to re-fill the float bowl.  To test, run the fuel line from the tank to a gas can and set the petcock to 'On'.  If there is good flow, you can eliminate the tank/petcock as a cause.

 

I'd start with easy tests like this to eliminate possible causes before trying to fix things that may not be broken or misaligned/not to spec.

Timing has now been checked, it was dead on.

2mmalc2.jpg

 

v43y9s.jpg

 

Spark plug gap was really thin, but i sorted it out.

343qgcx.jpg

 

&%$#@!!? I immediately tried the tank petcock thingy since i had it at hands right now, and it really does not feed on "ON" position  :lol:

 

Is it dirt and soil that causes it?  Meaning if it can be cleaned?

Edited by TuGeTu

This sounds like either a fuel delivery issue or your ignition coil heating up.  To test the coil, have a spare spark plug handy.  Run the engine until it quits, then quickly pull the spark plug wire and install the spare plug.  Test for spark.  If you get good spark, the coil is fine and you can eliminate that as a cause.

 

For fuel delivery, I suspect the tank itself, since you say the same thing happens with different carbs.  That leaves the supply - i.e. tank.  If there is a minor blockage in the tank, it will allow the float bowl to fill over a long period of time.  When you run the bike for a minute or so, the flow bowl empties and the flow from the tank isn't sufficient to re-fill the float bowl.  To test, run the fuel line from the tank to a gas can and set the petcock to 'On'.  If there is good flow, you can eliminate the tank/petcock as a cause.

 

I'd start with easy tests like this to eliminate possible causes before trying to fix things that may not be broken or misaligned/not to spec.

 

As i mentioned earlier, i just replaced the coil with a new one and it does not get hot determined by touch, neither did the old one..  

 

And even though the petcock seems to not work properly, it does the same thing without the tank on. :thinking:

Edited by TuGeTu

There is a screen attached to the petcock inside the tank, and it can get clogged if you're not careful with filling the tank and introduce debris.

 

Empty the tank, then remove the petcock (two small screws).  Check the bottom of the tank for debris.  Slosh some clean fuel around the tank, then dispose of it. Clean the screen and run some compressed air through the petcock to clean it out.  Retest flow.

 

 

Though it does seem odd that you get the same behaviour with the tank not in the system.  Unless you're fuel hose is also restricted or you have a limited amount of gas on the supply side.

Edited by Redpoint

There is a screen attached to the petcock inside the tank, and it can get clogged if you're not careful with filling the tank and introduce debris.

 

Empty the tank, then remove the petcock (two small screws).  Check the bottom of the tank for debris.  Slosh some clean fuel around the tank, then dispose of it. Clean the screen and run some compressed air through the petcock to clean it out.  Retest flow.

 

 

Though it does seem odd that you get the same behaviour with the tank not in the system.  Unless you're fuel hose is also restricted or you have a limited amount of gas on the supply side.

 

I've sorted the supply without the tank, by lenghtening the fuel hose with a really enormous tube and then filling it up. It should not restrict..

This is how i feed it.

5vy974.jpg

 

I know it wont last for long, but long enough for me to determine if its working or not :)

Sounds like your ignition problem was not much of a problem. I never read where you pulled the plug and laid it along side the cylinder to verify that you were getting spark.

 

With a stock engine the stock carburetor should have been able to make the bike go quite well. At worst some adjustment in jetting would make so. Seems like throwing new carbs on the bike without making sure that they are tuned to the engine (a presumption on my part) is an expensive solution. Having it spit flames because it rich (or very lean) does not really imply the carb.

 

Maybe you jetted the carb richer because it seemed like it needed it as it was not getting fuel.

 

I have cleared up poorly running machines by narrowing the spark plug gap. It can help if the mixture is wrong or the plug is a bit wet too. A wider gap takes higher voltage.

 

Timing has now been checked, it was dead on.

2mmalc2.jpg

 

v43y9s.jpg

 

Spark plug gap was really thin, but i sorted it out.

343qgcx.jpg

 

&%$#@!!? I immediately tried the tank petcock thingy since i had it at hands right now, and it really does not feed on "ON" position  :lol:

 

Is it dirt and soil that causes it?  Meaning if it can be cleaned?

Sounds like your ignition problem was not much of a problem. I never read where you pulled the plug and laid it along side the cylinder to verify that you were getting spark.

 

With a stock engine the stock carburetor should have been able to make the bike go quite well. At worst some adjustment in jetting would make so. Seems like throwing new carbs on the bike without making sure that they are tuned to the engine (a presumption on my part) is an expensive solution. Having it spit flames because it rich (or very lean) does not really imply the carb.

 

Maybe you jetted the carb richer because it seemed like it needed it as it was not getting fuel.

 

I have cleared up poorly running machines by narrowing the spark plug gap. It can help if the mixture is wrong or the plug is a bit wet too. A wider gap takes higher voltage.

I have tested the spark when cold, but it looks pretty poor to me.

 

The stock carb worked last summer but this year it wont work, even though there is no modifications made to it. I've cleaned it 5 times and did not find anything wrong with it..

I had all these carbs laying in the shed, so it really hasn't gone from my wallet  :lol:  I jetted the bst with the settings ive read that work.

 

And i STILL do have the same issue without tank..

Did you test for spark after it shuts down yet?

This is what happens when you do a whole bunch of modifications at one time.  Many people blame the mysterious CDI but it ends up being lousy carburetion.

 

I think the problem is air/fuel and perhaps exhaust, not electrical.  What air cleaner?   Is the fuel old?  What jets are in the stock carb?  Is the muffler too restrictive?  Are all the passages in the carb clear?  Does the fuel screw cause adjustment or have no affect?  Does it run better with the choke closed or partially closed?

 

 Another thing I should mention is that the spark on these bikes is tiny and difficult to see outdoors.  It's not a lawnmower.

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