GSX400L 1984 possible carb problem

**Hamish Carlson** · 21st July 2008, 17:29

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** · 21st July 2008, 17:48

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** · 21st July 2008, 17:52

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** · 21st July 2008, 18:15

Originally Posted by 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.

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** · 21st July 2008, 18:25

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** · 21st July 2008, 18:29

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

**Hamish Carlson** · 22nd July 2008, 21:03

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

**mark247** · 23rd July 2008, 07:57

Originally Posted by Hamish Carlson

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

Possibly not

**F5 Dave** · 25th July 2008, 14:56

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** · 27th July 2008, 16:29

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** · 27th July 2008, 16:37

Originally Posted by 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.

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** · 28th July 2008, 10:11

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** · 28th July 2008, 16:57

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** · 28th July 2008, 17:01

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?