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Hi everybody, Im new to this forum and semi new to riding. I just got my license this weekend and go figure now that I can legally ride my bike it isent running well. Ive been trying to find this problem for the past week and I'm goin nuts...nothing will fix it....

The Bike: 1993 Katana 750

The Problem: Riding home from work a week ago and all the sudden I lose half my power and the bike wont idle on it's own. It's been decently maintained and wasnt sitting for a season or anything like that. Upon checking some stuff, I see that cylinders 1 and 4 are not firing. The performance gets worse the hotter it gets and evetually wont idle without constant revving, idle also gets rougher and floats high, then drops and slowly dies

What I've done so far:
*Replaced Coils/Wires
*Replaced all fuel lines/filters
*Oil change (was semi new and correct level anyways)
*Re-cleaned carbs, check diaphragms, all seem to be OK
*Flushed out fuel system
*Ran Seafoam cleaner through carbs (also to help possible stuck valves)
*Checked + cleaned spark plugs, new and not gunked up badly at all
*Checked spark, all cylinders getting spark
-This has all helped a little but not fixed anything


Tomorrow I'll replace the plugs and look around some more, but I'd like to hear anyones opinions on what else I could check. I have not done a compression check (My tool is only for cars), but I dont think that a pair of cylinders went up at the same time. Any suggestions would be awesome, THANKS!

Cylinders 1 and 4 probably use the same ignition coil. I would normally suggest that you test yours. But you already said that you replaced the ignition coils. So color me confused... are you sure that you're getting sufficient power TOO the ignition coils? Perhaps you've got a partially frayed wire or partial short to ground along the way to the coil.

Other then that... 1 and 4 run a little cooler then 2 and 3 normally... so it seems unlikely that the valves would go on them first.

I would say check all the wiring for your ignition system, front to back and see what happens.

I assume your spark test was just to take the plug out of the block set it against the block and turn the engine over? All that did is prove it will spark at atmospheric pressure, the greater the pressure, the tougher it is to spark.

What is common to cylinders 1 and 4? Sounds to me like you have both ignition and carb problems.

I used the method of grounding the plug wires with a screw in them to check the spark, and I checked all of the ignition wiring that I could see, as well as peel off some wiring harness tape, all seemed OK.

The carbs were "professionally cleaned" before I bought the bike, which I believe because they are very clean inside and out. I have also been told that I should have them synced, but I dont see how they could suddenly go out of sync and cause this problem.

Also, Sev, how would you suggest checking the power to the wires going to the coils? I dont wanna hook a voltmeter to something with a few thousand volts, so I dodnt check that stuff yet. I spent all day checking wires and what have not with no problems found. Thanks again guys

Well there should be two wires that plug into the ignition coil? I THINK they carry 12 volts prior to entering the coil Those are the ones that I'm thinking of at any rate. Check the voltage, check for shorts to ground, check for continuity. It'd be a lot easier with a wiring diagram.

Again, a spark in atmosphere only means it'll spark at 14.7psi. Your engine should be reaching about 160psi at the top of the stroke, which makes it substantially tougher to spark.

The 'correct' name for coils is actually, 'transformer'. They take the 12 volts from your battery and step it up to the thousands of volts (with very low amps, so even those volts are not dangerous, just annoying) the coil spits out. So any power readings before the coils will be good ol' 12 volts and nothing to fear. Anything coming out of the coils will be thousands of low amperage volts, and still nothing to fear.

Meter away to your hearts content, eh?

Until you send 10000 volts through a meter that can only measure 2000... Then you need a new meter .

Sev wrote:Until you send 10000 volts through a meter that can only measure 2000... Then you need a new meter .

No, then you need a new fuse in your meter. And a lesson on how to use it.

On a completely un-related note..... how's school?

BuzZz wrote:

Sev wrote:Until you send 10000 volts through a meter that can only measure 2000... Then you need a new meter .

No, then you need a new fuse in your meter. And a lesson on how to use it.

On a completely un-related note..... how's school?

School went well actually. Work is better, if slightly less interesting.

I'll try testing the voltage going into my coils today, and see what I can find. Thanks again