Yamaha XS400 Won't start

Message

plchamb · #1 Unread post by **plchamb** » Tue Feb 07, 2006 5:34 pm

Alright, I have been scratching my head for a while now and i am close to given up and take it somewhere but maybe someone has an idea here.
Here is what i have:
When i got the motorcycle, i changed the battery and now it turns over but won't catch. Always go back to the basic. Compression, Ignition, Fuel.
I think the fuel is coming in and i have compression but here is what makes me think i have an ignition problem.
2 days ago before getting new spark plugs, i had a spark with the old ones but it was very weak.. now i have no spark with the new ones. If i ground them to the engine then i get a spark. Am i spposed to get a spark even if i don't ground the spark plug to the engine?
NO matter what it should spark inside the combustion chamber cause it would be grounded then? But doesnt start!
Do i really have an ignition problem? How can i fix that
I have a fully charged battery, good fuses. And when i get the spark by grounding the spark plugs, it looks pretty good. Strong and at the right frequency so my electronic igntition, trigger and coil should be good!
Please help... it is driving me crazy!! I just want to go for a ride!!!
Thank you so much!!!

BuzZz · #2 Unread post by **BuzZz** » Tue Feb 07, 2006 5:45 pm

Yes, your plugs must be grounded to spark. And yes, they are grounded when installed. Sounds like you got spark.

So it's time to verify the other components of successful combustion. Your sure you have good compression? And is the fuel making it's way all the way through the carb to the intake tract, and in the correct amounts? If the bike has CDI ignition and not points, chances of the timing going off are slim at best. Unless you have recently disturbed the pick-ups or triggers....

plchamb · #3 Unread post by **plchamb** » Tue Feb 07, 2006 5:53 pm

I just talked to someone form this forum and he told me that since the bike has been sitting for a while it is most likely the carbs so i got to clean that! GOod compression... Well how can i tell if i have GOOD compression. I mean got some, i can feel it but i am not experienced enough to know if it is GOOD or weak.. any suggestion to get a better idea?
You guys rock on this website... you are so fast and you make my life so much better! : )

BuzZz · #4 Unread post by **BuzZz** » Tue Feb 07, 2006 6:04 pm

Beg, borrow or buy a compression gauge. They aren't too expensive and will tell you exactly what the compression of any cylinder you own. Don't drop, kick or soak it, and it will do that for years.

But I would also say it sounds like you got some carb issues to deal with.

plchamb · #5 Unread post by **plchamb** » Tue Feb 07, 2006 6:07 pm

Thanks man... i will do that!
Also... how much compression should i get and if i don't get enough what's the problem? Leaks? what to do?

BuzZz · #6 Unread post by **BuzZz** » Tue Feb 07, 2006 10:47 pm

Compression readings can vary depending on the original design of the engine, wear and such.... but you want something between 120ish-180ish for most engines, more is better. More important is the amount of variation between cylinders on the same engine. You want as little of that as possible.......

One place that will give a good target range for your bike, and is the single best tool you can buy for your bike, is a good service manual. It will also tell you causes and cures for lost compression and most other problems you may have with it. Like carburation..... you see where this is going, I'm sure......

plchamb · #7 Unread post by **plchamb** » Wed Feb 08, 2006 7:41 am

thank you : )

plchamb · #8 Unread post by **plchamb** » Wed Feb 08, 2006 11:08 am

When i ground the spark plug... i have a spark.
When i do the compression test: i get exactly 150 PSI on both cylinders
I just finish cleaning my carbs put them back on the bike...
It won't start
I don't understand... Any Idea?
Could the carbs have a problem?
Please help me! : )

Wed Feb 08, 2006 4:08 pm

Does the starter turn over alright?
Does the battery have a good charge?
Are you using new fuel?
Did you pull the choke out?

If it's cold where you are, because you didn't list it and it's protect your balls freezing here, your bike might need a bit of loving to get her going. When my xs400 gets worked on in the cold, I first prime the carbs, then pull the choke, then crank her while twisting the throttle a bit. It's a religious ceremony that if isn't followed just right, won't get her started when it's below 40 degrees.

Wed Feb 08, 2006 4:08 pm

Oh yeah

How sure are you that you cleaned the carbs well? One small obstruction and that's all she wrote.