idk wat my problem is i need help

[jordannelson96]

Ok so i just bought this yamaha bobber xs400 ive had it for about 6 weeks and the only thing ive done to the motor since i bought it was change the spark plus, now right before i changed these spark plugs i would drive it and i felt like i could only hear it out of one muffler and would bogg down so after the spark plugs (cause i figured they were fouled) were changed it ran great for 3 more days, then started to bogg on me again could the plug on the right be fouled again? That quick? Ignition coil? Tue only other thing is ive taken the mufflers off and painted them and thought my flanges were on backwards, could that affect the air/ fuel ratio?? Someone please help!

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[jmd_forest]

1) Make sure the plugs you are using are the right plugs.
2) Actually pull the plugs and look at them. What do they look like? Black and oily could mean either bad rings or valve seals or both or running very rich. Bad rings vrs rich require different fix. Do a compression test. Good compression generally will rule out bad rings.
3) Check the intake of the bad cylinder to make sure there are no air restrictions that could be causing a rich condition
4) Check the wires for arching. Run the bike while it is dark and jostle the ignition wire around a little with a wooden handle. Do you see any sparks arching between the wire and the engine? If so replace the wire.
5) Do you have gas leaking from the carbs or gas in the cranckcase oil. That is likely a sign of the float level being set too low (or high depending on which reference frame you are using) and causing a over rich condition.
6) I've read a number of threads on this site regarding recently purchased bikes where the PO rebuilt the carbs incorrectly or installed inappropriate jets. That could be another cause of over rich condition.

This is the easy stuff. I'm sure some more experienced XS400 gurus will jump in with even more suggestions.

 

[jordannelson96]

Ok so my plugs are ngk bp7es, how do i know if their right thats what the guy at the motorcycle store said, when i changed them the first time they looked dry and black like every other pair of plugs ive seen, and i just checked the one i replaced them with and they were dry and black so i dont think its a fouled plug, could the wire make it putter when driving, like i said it idles fine its just when im driving, how do i do a compression test the (kickstar works just fine), i took the carbs off and cleaned them, didnt mess with any screws it was just a wash and rince also this problem didnt occur until about 2 weeks after i bought it, and theres no gass leaking anywhere ugh these things are some work

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[jmd_forest]

Its a 30 year old motorcycle with an unknown ,maintenance history. Its bound to have some problems. From what I have read, NGK BP7ES is the right plug. A comppression test is done using a compression tester. You can buy one at ,most big box auto stores for around $20 or so. To do a compression test, remove BOTH spark plugs, screw in the tester into one spark plug hole, Open the throttle all the way, and hit the starter or have someone kick it over a few times. Write down the reading on a pience of paper. Remove the tester and repeat in the other spark plug hole. Readings should be around 130+ PSI (give or take a little).
Sooty black plugs indicate ignition and/or rich fuel. Plugs should be dry and tan to dark tan in color. Look around the web there are plenty of pictures of plugs with accompanying descriptions. In many cases, an extremely thorough cleaning of the carbs, and I mean EXTREMELY thorough, will resolve or greatly reduce the type of problems you describe. Make sure to insert an in line gas filter IMMEDIATELY after cleaning to catch any dirt in the tank or you will be right back where you started in a matter of days (speaking from experience here). Also, a bad wire or connector can cause sputtering under load.

 

[Daddio]

I am betting on carbs flooding one bank.

 

[jordannelson96]

What would cause the carbs to do that? Why would it flood on the side that the gas is not put in?? And i also just found out it probly happeneds about 20 mins into the ride

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[jmd_forest]

"What would cause the carbs to do that?": Items 5) and/or 6) from my initial post.
"Why would it flood on the side the gas is not put in?": Items 5) and/or 6) from my initial post.
"it probly happens about 20 minutes into the ride": If that is accurate it MIGHT be related to the an ignition component building up heat. Since you don't state the model or year it could be coil, condenser, or TCI.

Things to do:
1) Compression test, It will help identify or eliminate serious mechanical problems as the cause.
2) Clean the carbs EXTREMELY well and replace any worn rubber parts (o-rings, float needle and seat, throttle seals). Do a little research and do an EXTEMLY good job on them. Set the float height correctly. Check the jet sizes while you're in there.
3) If you have points and condenser, replace them. It will eliminate a few variables pretty cheaply.

 

[Daddio]

I would vote to clean, bench match and sync your carbs.
What makes you say the issue starts after 20 minutes?
Is this 20 minutes after you clean the plugs?

 

[Travis]

I would start from the top.

Check the valve clearances
Check compression
Check timing and points if you have them. (you haven't told us the year yet I don't think)

That should take about 20-30 min.

Pull carbs and clean them (clean like you could eat off of them). Check all jetting and float heights. Make sure the needle and seat are good so they aren't flooding.
New plugs - check for good spark
Check for air leaks
Sync carbs

That could take you anywhere from about 1 hour to 4 hours if you don't know what you're doing.

If that doesn't work I would start to suspect the coil. Check the coil using a multimeter when it's cold and hot.

What year bike do you have?

Have you read through the manuals? www.xs400.com/forum/showthread.php?t=4503

 

[OliverB]

Welcome to the forum. Sorry you are having problems. All of the above plus: have you taken time to read back through the posts to learn about the issues with these old bikes? A great investment that won't cost you anything but time!