GSX400L 1984 possible carb problem

[Hamish Carlson]

I'm not sure whether this is a carb or engine problem, as I've been told by different mates either is the issue...

I recently burnt out my charging electical system and had the stator replaced, new regulator, new battery. While this happened my bike was still revving out properly and I was doing short runs with bike running on battery I charged every night.

NOW however I am having some ultimate pain in the ass. When I went up north after all that replaced my bike kept missing while at revs between 4 and 6.5 thou rpm. by having my hand near the spark plugs while running I found out it was leaking spark, so replaced spark plugs, leads and coils (couldn't get old leads off old coils).

Since then its still not running right - It has adequate power at revs from 2-4 thou rpm, but if I try revving out it just flounders (best description). Back to low revs and its fine again. took air filter out, cleaned it, dried it, back in, no difference. Sprayed crc around join of airbox and carb, and bike died, so looked and airbox wasnt sealing with carb. Siliconed up the gap, as I thought it might have been stopping sufficient airflow into diaphram controlling needles (twin carb). Just went for a ride and its still doing it. Any Ideas? Cleaned carbs.

[mark247]

Mind my ignorance. Im hella jet lagged so cant remember everything. The reg rec and ignitor are two different box's correct? If so, it could be the ignitor?

[Hamish Carlson]

Yes they are, if you mean the rect/reg are in one unit and the cdi is separate. It doesn't run without the battery in it if thats any help, my mate is adamant thats the problem, but I'm sure its not.

[mark247]

Yes they are, if you mean the rect/reg are in one unit and the cdi is separate. It doesn't run without the battery in it if thats any help, my mate is adamant thats the problem, but I'm sure its not.

Well I'd say its the ignitor. I would say finding one wont be too hard. I'm pretty sure the ignitor out of a gsx250 ( older one obviously ) would work as well as I got a aftermarket ignitor made for an old 1983 GSX250 which i had a while back which also worked in my friends 1982 gsx400.

[Hamish Carlson]

By igniter you mean cdi? I don't think they are easily found - I've never found a cheap one anyway. I wanna make sure I have the problem isolated before throwing more money at her, already spent three times what I got her for.

[mark247]

Yea CDI. I just remember that on my GSX250 it said "Ignitor" on the box.

[Hamish Carlson]

If it was the cdi, wouldn't it not fire at all?

[mark247]

If it was the cdi, wouldn't it not fire at all?

Possibly not

[F5 Dave]

There are a lot of GSXRs of that vintage with replacement or aftermarket CDIs (technically not the correct acronym) after the reg/rec alt battery thing flares up. Buy a multimeter & check voltage while running every so often, never run silly big bulbs & keep oil level ok so doesn't overheat alt. That might indeed be your problem.

But it could also be any number of things, coils are ok & use copper (ie not car) leads? Carb jets could be blocked, filter restricting flow, diaphragms perished.

[Hamish Carlson]

From what I can deduce, its probably the carb bowl not getting enough fuel, as it revved out fine when I left it sitting idling for a minute, then went for a thrash. Just as I reached 120, the bike started dying, so slowed down and idled again, did the same thing again, same result. Proper power through all gears, unless I stay high revving, then it starts missing like its outta fuel in a cylinder. Checked the fuel tap for flow, and is flowing perfectly, so guessing it would be the needle or float level in bowl. I haven't tampered with the levels or touched the needle valve, so was wondering whether blowing down the fuel line with an air compressor (at a good 'safe' pressure) with bowl off would clean it out. Not leaking out breather hose, but I've cleaned all the other jets and tested they are working, so thinking its the needle with floats. Might also adjust float level slightly higher.

[mark247]

From what I can deduce, its probably the carb bowl not getting enough fuel, as it revved out fine when I left it sitting idling for a minute, then went for a thrash. Just as I reached 120, the bike started dying, so slowed down and idled again, did the same thing again, same result. Proper power through all gears, unless I stay high revving, then it starts missing like its outta fuel in a cylinder. Checked the fuel tap for flow, and is flowing perfectly, so guessing it would be the needle or float level in bowl. I haven't tampered with the levels or touched the needle valve, so was wondering whether blowing down the fuel line with an air compressor (at a good 'safe' pressure) with bowl off would clean it out. Not leaking out breather hose, but I've cleaned all the other jets and tested they are working, so thinking its the needle with floats. Might also adjust float level slightly higher.

Interesting, the way you describe it there sounds a lot like the problem my friend had with his GSX400. I didnt realise it only happened when going fast.

My friends GSX400 would start to miss and stutter if he was going full speed for too long, say maybe 30 seconds? After that it would just start to miss on one cylinder under you let the gas off and slowed down again.

[F5 Dave]

ahh more of the story unfolds.

ok suzis tend to rust out their tanks. So either the flakes of rust (like slit in the bottom of the bowl) is clogging up the jets (have to disassemble to clear out), or a filter inside the carbs which some odd carbs have.

Or someone has fitted a fuel filter inline. These just love to kink the line so subtly that you can’t see it & will produce the symptoms you have.

Or someone has sealant coated the tank & the breather is blocked. Think there should be a separate hole for the breather, or in the cap.

Or the float heights need to be adjusted by bending the tabs so the floats sit closer to the body when inverted. Do this last as it can affect fueling for what may be an unrelated problem.

[Hamish Carlson]

Tank hasn't been sealed, doesn't have a breather, no inline filter, not blocked at fuel tap filter, standard 80's style diaphram carb. Oh, and this bike doesn't have any speed inhibitors etc, it's before that era, and a cruiser design, if that helps. Was thinking I might go for a thrash, run it till it starts missing, kill it, so no more fuel drops into carb and measure the amounts of gas that come out of each bowl, as if none comes out of one, it will definitly be that carb, and float level. I love the jappas - I have to go through the mudguard at the back to get to the carbs.

[F5 Dave]

ahh, all this time I misread as GSXR, but now I know what you are talking about, the L model.

Try looking at the fuel cap which is where the breather should be, they should come apart ok.

Maybe it happens on near empty tank rather than full?

[Hamish Carlson]

Nope, no breather, the tank cap is loose, and I have already sustained, even with the cap off that it's something in the carb.

[Hamish Carlson]

Found the problem - one of the needles attatched to the floats is sticking, any ideas on how to stop it doing that, as I can't get the floats off for some reason. Guessing its an issue with some crap behind the valve.

[F5 Dave]

Goo from solidified old petrol, or hair. Sometimes the pins are peened in a little bit so removing them is a bitch, but totally possible, but with care. Need a centrepunch & hammer & a sharp edge to support the edge of the pillar. More than that you need to engage brain & lightly tap, better with a helper

[Sparrowhawk]

ahh more of the story unfolds.


Or someone has fitted a fuel filter inline. These just love to kink the line so subtly that you can’t see it & will produce the symptoms you have.



Sorry to bring up an older thread, but my 1990 GPX250 Ninja has started cutting out occasionally. Usually while I'm sitting at 100 for a bit, and most of the time when it's been when I've been changing to Reserve on the tap.

It's happened since I tried to drain the tank by disconnected the hose to the aftermarket inline fuel filter the previous owner fitted. This didn't work, so I syphoned it instead (needed to fix a leak in the tank where I'd put a fairing bolt in too far).

Is it likely that I've affected the way the inline fuel filter works??

GIJoe is gonna give me a hand on saturday to have a look at the carbs, incase there's crud in them, and I've bought a new pair of spark plugs - probably not the problem, but can't hurt aye?

[F5 Dave]

How did you fix the leak?

Sealant?

Does the tank breather still work? usually the cap on older style bikes,

Remove & Clean out tap.
Check lines run largely downhill & without kinks.

[Sparrowhawk]

How did you fix the leak?

Sealant?

Does the tank breather still work? usually the cap on older style bikes,

Remove & Clean out tap.
Check lines run largely downhill & without kinks.

The leak was caused by me putting the wrong fairing bolt in - it was too long & went straight into the tank (the fairing bolt threads into the tank itself, dumb idea). So I put a plug of Steel Putty in the end of the hole, threaded the bolt in while providing pressure on the other side to make sure it sealed properly, then waited for it to harden.

Then I took a new bolt, of the same thread size, and put it in until it was almost against the putty, and used some permanent thread lock. Then I cut the head of the bolt off, meaning it's now a stud in the tank, not a threaded hole.

I thought by doing that, I can't do it again. Perhaps Kawasaki should have thought of that to begin with, I'm not the first mug to do it. I'm wondering if the steel that I pushed through with the bolt to start with has worked it's way into the fuel system?? Or perhaps a little steel putty broke free?

How do I check if the tank breather still works?? I'm not sure if it's the cap or not.

I will have a look for kinks. It's strange that it only does it occasionally. I also noticed a small amount of fuel leaks at the tap when I switch it to reserve. However if I switch it to Off it leaks quite a bit. I guess that could be my issue? :confused:

[F5 Dave]

yeah, but it could just be tank rust blocking the fuel tap, remembering those kawis of that vintage often do rust up the tanks. Pull the tap & check it out.