Bike will crank but wont run

[Jpaul26]

Yeah so I am totally new to the motorcycle world, bought a broken bike last weekend and although mechanically we have everything we should need for the bike to run, it wont!

We cleaned out the airbox, bypassed the clutch (just in case that was a hinder), and charged the battery. When we try to start it, the sparks in most start, we plan on changing out the sparkplug cables just in case. Everything connected to the tank for fuel delivery looks fine, but I guess my question is what do I look for when inspecting carburetors, and what else could be preventing the bike from feeding fuel for the sparkplugs to ignite?

[MikeyZ]

Read CARBS 101. They could be all clogged and preventing fuel from entering.

[foxox]

You can check if fuel is getting into the cylinders by smelling the end of the exhaust pipe just after cranking the engine; should smell like gasoline! Might also be a compression problem if fuel/spark all checks out

[Wild-Bill]

The plug wires on these can be trimmed back 1/2" and screwed back into the plug boots. A lot of times, if you've got a weak spark, that's all it takes.

That said, the single most common reason a Kat won't start - especially after it's been sitting for a while - is clogged carbs. Hit the wiki and download the pdf version of carbs101 (or carbs 102 if you've got a 98+ kat). Clean the snot out of the carbs (Don't forget to remove the AF screws. They're under the EPA plugs if they haven't been removed before.), and replace any old, hardened o-rings. If you've got the money and don't mind changing something that may or may not need replacing then I'd recommend just ordering up 4 rebuild kits and 4 new float needles from carbkitcapitol.com. That'll mean you don't have to go back in there again but it'll run you $80. Good insurance IMHO.

Oh, and welcome! Don't forget to head over to the introductions thread and post something. It'd be great if you had a photo ready to post, too. We all like purdy piktures!

[scottynoface]

What do the plugs look like?

[Jpaul26]

Plugs look fine, coils on 1 and 4 doing fine and spark igniting, but apparently it wont try running with just two cylinders :/

[scottynoface]

Well if you've resistance tested the coils just get a new one.

[Jpaul26]

that's the plan to get another CDI because the coils are fine, I think. Memory serves me right, the coils were both able to receive signals just the CDI wasn't cooperating...

I sorta want to take this CDI apart since its claimed to be broken anyway... anyone ever seen the inside of one? its not the entire CDI, just the part that sends the signal to the coils.... I might sound dumb saying all this just kinda bear with me, you've been a great help Scotty!

[phil823]

fuel, air, spark, compression = go!

if it cranks you have compressions (most likely),
pull 1 plug at a time, ground it and look at it while you crank...see spark...your good.

check fuel from tank to carbs, filling?
check air flow...leaks? to much? not enough?

[Jpaul26]

All of those aren't problems though! *confusion* My dad keeps saying its the CDI, he says he's positive it is... :/

[Wild-Bill]

If you've got spark then the CDI is probably fine. Just on general principles, check for spark on all 4 cylinders and see what you get. If #1 and #4 are both sparking though, your CDI and coils are definitely fine. (The Kat uses a "wasted spark" system where 1/3 and 2/4 spark at the same time. 1&3 both spark then 2&4 both spark then 1&3 again, etc. - I think that's the pairing but the wires coming off each coil are labeled and I'm too tired to look it up right now.)

[Jpaul26]

Well the thing is we don't have a spark on 2 and 3. 1 and 4 spark fine, the cables are fine, the plugs look fine, and we swapped cables to see if the spark plug would ignite (to see if it was a bad coil) and the thing like backfired or somethin, shot air out the exhaust pipe....

And trust me I understand, its late. Im just pressed for cash at the moment and if at all possible to see it run without replacing working parts, then that'd be great.

[kevin2502000]

Not your cdi. Pull the plugs and leave them hooked to the spark plug cables. Then switch the wires to the coils and see if your good coil still works. If it does, you have a bad coil, if it doesn't then you have another problem.

[Wild-Bill]

What Kevin said. I suppose it's possible that your CDI lost half the circuit and is firing one coil but not the other. It's just not likely.

[Jpaul26]

I'll try that, at the moment the verdict was CDI simply because he said there was literally no signal coming from the respected circuit (part of the plug to the cdi that goes to coil for 2 and 3), so although I see what you're both saying, is there any explanation to why there was no signal? the wire is fine, and the rest of the CDI sends readable signals...