Now what did i break?

[bherriman]

Got the 400 out today and played around in the field for about 10 minutes on my way to the shed to get the lawn mower out, anyway it took me a little over 3 hours to mow got back on it and rode back to the house and shut it off. About 20 or 30 minutes later I decided to ride back and see how muddy the trails were (we've had like 7 or 8 inches of rain the last 2 weeks) tried to start it and it sounded like a back fire but a little louder and now it wont start. It still turns over it just wont fire. Any ideas?

[bherriman]

No ideas?

[beags86]

did you check spark? does it smell like fuel, have fuel in the tank? check out a few basic things and get back to us.

[slightlybent47]

Yeah I’d say check all the obvious things first. Fuel, plug, kill switch, oil level.

[bherriman]

Yea everything is working right its got spark half tank of fuel and full of oil. Seems like a head gasket problem to me after the whole "back fire" thing it sure seems like it turns over faster and has less compression.

[bkelley]

How old is the gas?

[aDviSol2y]

Take the spark plug out, put your finger over the hole, and try to start it. If your finger does NOT get blown off the hole. You have a compression issue. It shoud get blown off with some force.

edit: it may also be a starter issue.

[bherriman]

Gas is week old 93 pump...and I don't think its the starter because its turning over faster than normal which leads me to belive its a compression issue but I'm not 100 percent..might be time to tear down

[CJM]

Compression test it.

If you have a harbor freight nearby or dont mind waiting for it in the mail they got a nice compression tester for 25 bucks. I just used it on 2 different 400s and it worked really good.

Totally pinpointed my low comp of 90 PSI and my smoke issue and my friends fully rebuilt had like 120 which was dang good.

[exrider12]

My guess is it jumped timing. Check your timing and make sure its ok.

Anything below 100PSI I believe it is said to need a rebuild. Obviously you start modding something internally and numbers change.

[hocman123]

Originally posted by aDviSol2y
Take the spark plug out, put your finger over the hole, and try to start it. If your finger does NOT get blown off the hole. You have a compression issue. It shoud get blown off with some force.

edit: it may also be a starter issue.

people told me this samething when mine was not working and it is stupid. ur finger can't tell u if it is low at all just if there is non. but is u had say 90-95 psi it could still blow ur finger off but is still bad. and comeone other people can push a lot harder then others on the hole. it just seams like a stupid half *** way to go about things

[bherriman]

I know it doesn't need rebuilt I just put her back together about 10-12 hours ago...but I will try a compression test but even if the head gasket is blown and compression is low I figure it would still start? Maybe not though..

[tri5ron]

is your kill switch in the center "Run" position ???

don't laugh,.... Plenty of us have done it,
(but most aren't willing to admit it).

[bherriman]

Haha I laugh because I have done that before and probably more than once lol...I'm gonna check timing when I get home from work/ school today and if its still on I'll probably take the head off to see what the gasket looks like...I just cant think of anything else it could be.

[aDviSol2y]

Originally posted by hocman123
people told me this samething when mine was not working and it is stupid. ur finger can't tell u if it is low at all just if there is non. but is u had say 90-95 psi it could still blow ur finger off but is still bad. and comeone other people can push a lot harder then others on the hole. it just seams like a stupid half *** way to go about things

Most of the time your bike will still run woth 90 psi. His will not start at all. So putting your finger over the spark plug hole is a good way to test if you have compression. Not a half *** way of testing it.

[aDviSol2y]

If you have compression, your starter gear may be stripped. Just a thought.

[ballerchaos]

the stripped gear doesnt explain the loud bang, i wuold have to go with your timing jumped, possibly a head gasket, or blew a ring. i would start by pulling the plug and doing a compression test, if your compression is ok then look into your timing. if you have no compression, like your piston isnt coming up and down, then possibly your starter gear is stripped. pull your starter and check it out. oddly enough my dad ride on did this to him, and it was a cracked flywheel missing a few teeth so that could be your issue also.

[bherriman]

i know for a fact its nothing with the starter..the motor still turns over and turns over plenty fast and I can still feel it pushing air out the exhaust. I've been busy at work and college but I should get some time to tear it down in a couple days..hoping its just a head gasket

[wrekd]

Sounds like it jumped time to me and a valve isn't closing at the right time causing a loss of compression. Did you replace the tensioner when you put it back together?? Make sure the tensioner was installed right??

[f4iracer]

check your air filter and make sur eyou dont' have a bunch of water in there or something, u said you were out riding some wet trails.

[bherriman]

So I finally got time to sit down and look at the bike today and found out my problem. Apparently when it backfired (which I still dont know why it did) it had so much pressure behind it that it actually blew my carb off my intake boot which, in turn, caused it to suck to much air causing the no start condition. At least it only blew the carb off..I've seen a guy get in his race car to back it off the trailer and when he tried to start it it back fired and it bent a couple rods..now that would suck!

[tri5ron]

Originally posted by bherriman
So I finally got time to sit down and look at the bike today and found out my problem. Apparently when it backfired (which I still dont know why it did) it had so much pressure behind it that it actually blew my carb off my intake boot which, in turn, caused it to suck to much air causing the no start condition. At least it only blew the carb off..I've seen a guy get in his race car to back it off the trailer and when he tried to start it it back fired and it bent a couple rods..now that would suck!
Yea !!!
Tighten a couple of screws, and your ready to ride !
That's a good thing!