GS400 (1981) Won't start and I can't figure it out

[Guest]

The engine turns over but it won't start.
The bike always had a ****ty idle where sometimes if I didn't just always give it throttle it would die. Last week I was riding and came to a stop, I turned off my bike but it wouldn't start back up, it didn't even sound like it was trying. I left it parked for 30 minutes and when I went to try again it started right up and I rode home. On my way home the bike randomly started to slow down until a stop and it failed. It wouldn't start up at all again and hasn't really since.
I've charged the battery, replaced the spark plugs, taken apart and cleaned the carb but still nothing. The engine turns and turns but never ignites. There spark plugs produce a spark but it looks like the spark on the right cylinder has oil fouling on it, even though it's brand new.
Last but not least, every once in a while with the choke open the bike will start for a second - even yesterday I was able to ride it around the block but as soon as I came to a stop it failed again. That was the only time I've been able to ride it since it first failed.
Sorry for the long winded post, I'm new to biking and literally just picked this up in October.
Any advice would help, thanks!

[BigD_83]

Welcome to the forum from another Vancouver member.

This sort of story is a pretty common one for new members. There are some similar problems that everyone has to address early on in ownership of these 32+ year old beasts. Your description hits on at least four things you'll need to check:

1. charging system
2. valve clearances (* a big problem that seems to underly many starting problems)
3. carb synch and
4. engine compression

Most of what you are saying sounds like dirty passages in the carbs. Can you please describe the method you used to clean them?

[leakybreaks]

Hey thanks Big!

Hearing that this is common amongst new members is at least a little encouraging.

I followed the manual's steps in taking apart the carbs (removing the float, the jets, and pretty much anything that wasn't fixed to the carbs) and cleaned with a carb cleaner, a toothbrush to scrub, and pressurized air to dry and get the tiny holes before I put it all back together. I followed these processes (https://www.youtube.com/watch?v=p44VNddZ7Zc)

I'll look into these four things, the valve clearances is actually what the previous owner said I'd want to look at but I have no idea where to start - I guess I'll see what I can find in the manual!

[Gorminrider]

add to that list- "Petcock".
Test:
Disconnect fuel hose , get a jar under the outlet and turn tap to PRIME . Fuel should flow freely (into a jar! eh) Next, test the RUN and RES positions of the tap. To do this, disconnect the smaller hose (that goes to one carb's intake side), attach a piece of hose to suck on- fuel should flow freely. There should NOT be fuel in this small vacuum hose. That would mean a perforated diaphragm in the tap... but you can run around well enough using "Prime "tap-position given your Float Needle is restraining the gas properly...

More to say, fuel supply is important. and in that vein, of course there are fuel inlet needles and seats,float-levels, etc. to look at. You mention the tiny holes in your carb cleaning which points to jet removal. That's good. They MUST be clean.
There's many more options to "fix" Many find their inlet manifold rubbers are leaking at the engine (makes LEAN running).... but start at the tap. Cross the easy ones off your list.

[John Park]

Hey thanks Big!

Hearing that this is common amongst new members is at least a little encouraging.

I followed the manual's steps in taking apart the carbs (removing the float, the jets, and pretty much anything that wasn't fixed to the carbs) and cleaned with a carb cleaner, a toothbrush to scrub, and pressurized air to dry and get the tiny holes before I put it all back together. I followed these processes (https://www.youtube.com/watch?v=p44VNddZ7Zc)

I'll look into these four things, the valve clearances is actually what the previous owner said I'd want to look at but I have no idea where to start - I guess I'll see what I can find in the manual!

While it's fashionable to curse the previous owner - PO - for whatever hasn't been done or done right, sometimes they are passing on the right info. These 400s are screw adjust valves so you don't have to source shims and all that. When they tighten up, which is what happens, running at low speeds gets erratic. Plus, it wrecks the valvetrain.

You will need a tool for the screw head which is square and fortunately fits a #2 Robertson screw. I just bend one at right angles and screw it into a small block of wood for a handle. The locking nut is a 9mm as I recall, but you'll need a slim open ended one, which can be a fat one ground down. That and a set of feeler gauges and a gasket are all you need.

The biggest hurdle is getting the old gasket off the head, unless the last guy put grease on it so it wouldn't glue itself on. The gasket itself is particular to 80-82 so later ones, which seem more plentiful, won't fit. I'm not sure of the exact years and differences, but they moved some bolt holes around in '83 as I recall. In Vancouver you might get the right one from Modern Motorcycling - 12th and Commercial. You can check part numbers on cmsnl.com. This motor never got to the US, but I've bought gaskets from Canadian sellers on Ebay.

Below the cylinders, the rest of the motor is the same as the the GS450 in almost all regards. Is yours an L or an E?

[leakybreaks]

add to that list- "Petcock".
Test:
Disconnect fuel hose , get a jar under the outlet and turn tap to PRIME . Fuel should flow freely (into a jar! eh) Next, test the RUN and RES positions of the tap. To do this, disconnect the smaller hose (that goes to one carb's intake side), attach a piece of hose to suck on- fuel should flow freely. There should NOT be fuel in this small vacuum hose. That would mean a perforated diaphragm in the tap... but you can run around well enough using "Prime "tap-position given your Float Needle is restraining the gas properly...

More to say, fuel supply is important. and in that vein, of course there are fuel inlet needles and seats,float-levels, etc. to look at. You mention the tiny holes in your carb cleaning which points to jet removal. That's good. They MUST be clean.
There's many more options to "fix" Many find their inlet manifold rubbers are leaking at the engine (makes LEAN running).... but start at the tap. Cross the easy ones off your list.

I've tested the prime and it's working well. I'll test the RUN and RES positions next. It's funny you say that I can run around on Prime, I actually was doing that for a bit because it was having trouble idling back when I got it and I found that PRIME really helped but then I read that I shouldn't be running in PRIME because that can just destroy the carb and in turn the engine.

Also, you say LEAN running, I've been told my bike is RICH which I believe is the opposite.

Forgive my vocab, seriously just learning all of this now.

[leakybreaks]

While it's fashionable to curse the previous owner - PO - for whatever hasn't been done or done right, sometimes they are passing on the right info. These 400s are screw adjust valves so you don't have to source shims and all that. When they tighten up, which is what happens, running at low speeds gets erratic. Plus, it wrecks the valvetrain.

You will need a tool for the screw head which is square and fortunately fits a #2 Robertson screw. I just bend one at right angles and screw it into a small block of wood for a handle. The locking nut is a 9mm as I recall, but you'll need a slim open ended one, which can be a fat one ground down. That and a set of feeler gauges and a gasket are all you need.

The biggest hurdle is getting the old gasket off the head, unless the last guy put grease on it so it wouldn't glue itself on. The gasket itself is particular to 80-82 so later ones, which seem more plentiful, won't fit. I'm not sure of the exact years and differences, but they moved some bolt holes around in '83 as I recall. In Vancouver you might get the right one from Modern Motorcycling - 12th and Commercial. You can check part numbers on cmsnl.com. This motor never got to the US, but I've bought gaskets from Canadian sellers on Ebay.

Below the cylinders, the rest of the motor is the same as the the GS450 in almost all regards. Is yours an L or an E?

This is great, I'll look into the valves. I actually have no idea if my bike is an L or E, the owner just knew it was a GS400. Can you tell by the photo what the bike is?

Here's a photo:
IMG_3471.jpg

[Steve]

From that photo, it's an E.


Going back to your original question of not starting, the primary causes are (in no particular order):
1. Dirty carbs. I watched the video you referenced. Not too bad, but very incomplete for a GS carb. There are other things that need to be addressed, as well.
2. Mis-adjusted valves. Especially if they are tight, which is common.
3. Weak battery. Which is sometimes caused by a weak charging system, but you can connect a larger battery to the bike for troubleshooting. If that larger battery happens to be installed in another vehicle, make sure the other vehicle is NOT running while connected to your bike.

.

[John Park]

This is great, I'll look into the valves. I actually have no idea if my bike is an L or E, the owner just knew it was a GS400. Can you tell by the photo what the bike is?

Here's a photo:
[ATTACH=CONFIG]53341[/ATTACH]

Looks to be a T, but the vin ticket on the steering head should give you the info. I didn't think they made the T until '82, but Ts are a bit scarce and maybe I haven't seen an '81 yet. The '82s often have a build date from late '81. The wheels should be 17" rear and 19" front but they interchange and it looks like your front might be an 18" or the fender is from something else.

I've had all sorts of bikes over the years and the 400T is what I'm riding - quite happily. In the long run you'll end up doing some work and upgrading a few things, but it's well worth it and I can't think of a better old style bike to start with.

If you haven't yet, the o rings on the manifold boots to the head should be replaced; they get hot and lose their elasticity and leak which makes for funky low speed running and hanging idle symptoms. The hardest part of that is getting the screws out as they are hard to get to and can be rusted in. I've always managed to get a vise grip on them and crack them loose; then replace them with allen heads.

You'll also end up getting familiar with the fuel tap and the charging system. The rest of the bike is pretty hard to fault and pretty open ended for lifespan.

[Redman]

lb,

Welcome to GSR.

Your post is not long winded.
(and you did use sentences and punctuation, so that puts you ahead of some)

Looks like you are meeting some of the BC members (there are others) and are also getting some good help.

Spraying carb cleaner and brushing is fairly good, but dipping in carb cleaner for 24 hours is better.

Do study up on the valve adjustment.

If You have a bike from the 80s you might need a multimeter for checking the charging.
You have a GS from the 80s, so you will need a multimeter for checking the charging.

.

[Gorminrider]

I didn't think they made the T until '82

It's an 81 T. I have one.Registered as 81 and per the VIN 10th letter is B and per the wheel rims too.

but they moved some bolt holes around in '83 as I recall

yes they did change the valve cover. Again, I have one. perhaps change is co-incident with the newer tubeless rims..

[Gorminrider]

then I read that I shouldn't be running in PRIME because that can just destroy the carb

How?

"Prime" is same as a lawn mower's fuel tap and many motorcycles too that don't have vacuum taps.... Float and needle should stop the flow. However, it is generally a good idea to shut these simpler fuel taps to OFF when not running.

Also, you say LEAN running,

just as an example of the multitude of little things that will buzz around ...ie: bikes with history can show up at your door tuned or bodged to run despite other issues...Example: It's easy to head off on a deadend fiddling with idle mix and float levels and "carb synch" when the real problem is somewhere else. So, my general advice is to try to use the manual's settings in all regards to start. Wide variations will indicate bodges.

Do you have a Shop Manual? Haynes is ok. NOT clymer for 450s as it does not cover the differences of this GSX vs GS450 very well.
Also get the Suzuki shop manual It is in two parts. You need the GS250-350 (91mb) AND the GSX400 (7.5mb)...which last is an addendum that describes what differences there are, these all being GSX engine types.(the X means 4valve per cylinder)

Go Here

http://members.dslextreme.com/users/bikecliff/

There is much confusion partwise as your GSX is called a GS400 in Canada, but unknown in 99% of the US catalogues where they got a GS450 instead.

When you need a part number, Go Here

https://www.cmsnl.com/suzuki-gsx400_model13612/

[jwhelan65]

Fresh gas, carbs cleaned properly, good spark, good battery = fire in the hole.

[Redman]

....
I shouldn't be running in PRIME because that can just destroy the carb and in turn the engine.
..

No, not destroy carb.
If leave it in PRIme position when parked for too long, and if the carb float needle valve does not completly close off (which is doesnt have to, only needs to mostly shut off) then what can happen is the carb float bowls overfill and gas runs out the carbs and into the air box (and probably on the ground) and maybe into the cyclinders and then into the crankcase and then your oil is not oil it is oil and gas.

Leaving it on PRIme when engine running is not a problem either. THe problem is if levae it on PRIme when bike is parked for some time and even then only if the carb float valves leak some.

.

[jdvorchak]

If you have to run it on prime, to get fuel flowing, then fix the petcock or better yet replace it. Not only do you run the risk while leaving it in prime, while not running, and contaminating your oil, you will most likely run out of gas. That usually happens a mile or so from a gas station. Prime position is the same a Reserve. Once you're out, you're out.