Erratic running but not all the time

[Katana 750]

Hello.

Not sure if this is fuel or ignition related, but...

Bike : GSX750S Katana
Year : 1983
Condition : stock air box, Marving "race" slim exhaust, all electric components stashed under the seat.

The bike ran great as is for a year or so. Then started messing around. Checked the carb bowls and saw grime, so i had the carbs ultrasound cleaned and redone by a good guy.

Fitting the carbs back, it was not running good, on 3 cyl. Turns out no3 was cold. I swapped no1 and no3 plugs, and doing that, no1 was cold and no3 was good.

So i ruled out a plug issue, and while i was there, changed all four.

Ran like a dream for 1 week or so. Great power, tickover and revving.

One day I rode to work no problems. 12h later, i leave. Started fine, but choppy and no power all the way home.
Put it on reserve and filled her up, thinking maybe it was because I was low on fuel.

But no result.

Since that, its been on and off during my road tests. Some times its fine, some days its not. Some times it goes off fine and halfway through the run it starts messing around.

Any tips for this overnight breakdown ?

Thanks

[alke46]

My 1st thought would be to get out the ohm meter and check the resistance between pairs of plug leads. Also check the plug caps for proper readings. Caps should be around 5 ohms I believe, and the pairs of plug leads should show around 11k ohms.

Someone with more knowledge than me will chime in soon. Good luck.

[tom203]

I'd just start by replacing all the spark plug caps - they are cheap: corrosion can cause spark issues.

[Guest]

Broken pickup coil wires is a possibility. Runs fine, then bad, then fine. Not sure if this is a known GS problem but I am putting an XS11 back on the road and had issues and sure enough 3 out of the 4 pickup coil wires were bad. maybe the hot box going out?

[Katana 750]

Thanks for the input.

Indeed it does sound electrics related. I derusted the tank, put an inline auto fuel filter after the petcock, also checked that the filter of the petcock wasnt blocked.

Not sure what you call the hot box though ?

Are all the ignition elements the same between the 750 and 1100 ? Because i have a GSX1100 if I can used that ones parts to test on the Katana

[Guest]

... I ..., put an inline auto fuel filter after the petcock, ...

This might be part of your problem. Most of the automotive fuel filters are designed for cars with fuel injection systems, so they have a rather high-pressure pump to push fuel through them. Our bikes only rely on gravity for a drop of 25-30 cm. The filter element might just be too restrictive. Look for a filter made for a lawn tractor, as many of them also have gravity-fed systems.

[Katana 750]

Ah hadn't thought of that. There was one on the bike that the previous owner had fitted, i put a new one in just because when i put the cleaned up carbs back on the bike. I can always try running without one on at all for a bit to see if it improves but from what it feels like on the bike it seems more like an intermittent spark issue, definitely need to look into whats been proposed previously

Thanks

[alke46]

The consensus on fuel filters is: "we don't need any stinkin' filter". Seriously, most of us don't use them. That's why there is one integrated with the petcock.

[Guest]

The consensus on fuel filters is: "we don't need any stinkin' filter". Seriously, most of us don't use them. That's why there is one integrated with the petcock.

The fuel filter debate is an interesting one. If your on the XS11 forum their consensus is you must run filters and their petcocks have the same filters as ours. They say too much small stuff can get through the petcock filters.

[Rijko]

The fuel filter debate is an interesting one. If your on the XS11 forum their consensus is you must run filters and their petcocks have the same filters as ours. They say too much small stuff can get through the petcock filters.

+1, my GS1000 petcock filters allow a lot to pass that the inline transparent filters do catch, and i like the fact i can see pollution at a glance instead of having to unscrew the petcock to see what's up.

[Katana 750]

Guys

Doesn't cost much to test without, so I removed the filter and in doing so changed the sections of fuel line by a single length. I noticed the line on it when i had the filter seemed like its layers were like separating as if the fuel was breaking it up.

So i replaced it and since i have not yet had running issues.

I'm still doing test runs but so far it seems ok, no running problems.

I'll keep you posted with any updates if i find anything else or if it stops running again

[Guest]

When I first got my bike I had similar problems. There is not a lot of room for the extra filter I had. That in combination with an improper size and type of fuel line was causing it to collapse intermittently and interrupt fuel flow. You can't beat the Suzuki fuel line. I replaced the mess I had with it and have had no problems since.

[Guest]

Gunk in the bottom of the tank?

[fixmybrokecomputer]

My GS1100GK started stuttering a while back so it's not been getting ridden lately. The plan was to pull the carbs and go through them and replace all the o-rings while I was in there. Went all the way and ordered a new petcock, intake boots, all new clamps and airbox boots. I had run most of the gas out of the tank, so I added a couple of gallons from the gas can. Primed the carbs and eventually got it started. I backed out of the garage and it died. Couldn't get it to fire, so back in the garage. Next day it still wouldn't fire. I disconnected/reconnected the wiring plugs under the left side cover a few times to scrub the connections. Tried to start again and it fired right up. Took it for a ride and it ran perfectly with none of the stuttering that I had experienced in previous rides. I believe what I thought was a carb problem turned out to be crappy connections on the plug for the igniter. I'm still going to replace the petcock, but thankfully I don't have to pull the carbs and go through them!

[Katana 750]

Right. It's back in limp mode as from leaving work today.
Worked fine all the way to work and is now not running from when I took off back home.

Same detail in the situation is that it has rained on the bike all day after I parked it.

Next move will definitely be changed the plug caps and wires.

Does anyone have a generic cap reference ? And also is it possible to change the wires on the coils or are they stuck on the coils ?

Thanks