1983 GS400 carb rebuild - advice needed

[Mat]

Hi,

I've been wanting to dismantle my carb for a good cleanup (no major issues with it apparently though, bike runs always well except for some long steep hill climbs).

No experience with that. I've read guides for four cylinders engine that I guess could probably adapt for my model (mikuni BS34 I think).

Here's the list of unknowns that I need advice:

1. I have no idea how to order the correct o-rings before opening the carb and worry I will have trouble finding some once I will have broken the old frayed ones while dismantling. Is it probable the o-rings will be the same as in the kits Nessism sells for four cylinders? I'm not touching a screw before I figure this one out.
2. I don't have access to an ultrasonic basin, what cleaner do I use and how long
3. What else could go wrong? what might be easy to break?

P.S. It's a 2 cylinder 8 valves, two carbs

[rphillips]

I've always believed in "if it ain't broke, don't try to fix it". If something is wrong and it isn't running right, yes. but just thinking I haven't cleaned this carb for a while, I think I'll take it apart, just doesn't seem reasonable. But that's just my opinion.

[Nessism]

The drain and float valve O-rings are common with other GS bikes. Can't tell about the pilot screw O-ring, because Suzuki didn't sell those parts for the most GS models, so you can't do a reverse part lookup.

I think dealers can get the various O-rings, or I can help you figure out what sizes you need if you decide to take on the project. All you need is a pair of digital calipers, and the old O-ring, to figure out what's needed.

[Rob S.]

I've always believed in "if it ain't broke, don't try to fix it". If something is wrong and it isn't running right, yes. but just thinking I haven't cleaned this carb for a while, I think I'll take it apart, just doesn't seem reasonable. But that's just my opinion.

And my opinion. And my mechanic's. If it ain't broke...don't break it!

[Mat]

Well, I'm pretty satisfied with how the bike runs except on specific occasions (long steep hill climb at full trottle, the bike suddenly seems to be gas starved and stutter). Wish I had better understanding to diagnose this.

I just drained the two floats and there was some dirt in there:
PXL_20230710_155732542.jpg


I just wish I could make the bike perfect but likely won't break anything as it is I guess.

I can wait for winter to come and enjoy the riding season as it is for now.

Appreciate very much your input all of you, thanks!

[Nessism]

It's clear that your carbs are full of debris...which means your gas tank is also.

[Mat]

...and this is the dirt from only one float

here's the other with similar debris:
PXL_20230710_160409437.jpg

Must admit I was surpised this dirt was not causing too much running problems.

Ed I can't find Gunk, Berrylman or Yamalube parts cleaner, do you know if this Spray Nine product would do: https://www.canadiantire.ca/en/pdp/s...w.ds#store=692

otherwise I will use Pinesol.

Would this be a good idea to clean the rust inside of a gas tank? https://www.canadiantire.ca/en/pdp/g...ml?rq=gunk#srp

[Nessism]

To clean the carbs, you need carb cleaner. Spray may work, as long as the carbs aren't all scaled up inside. Shoot, and soak, all the passages. Make sure all the internal passages are open, by comparing your carbs side by side. For example, shoot into the pilot jet passage, should come out the tiny passages in the carb throat.

For tank cleaning, do they sell Evaporust in Canada? If so, get some. Realize, though, the petcock, cap, and fuel sending unit (if your bike has one) must be removed, and caps created out of aluminum plate and rubber for sealing. If no Evaporust, check similar alternates. Next best, is some phosphoric acid sauce, diluted. This is what I use. It works great, doesn't need to be neutralized, and will derust fast. Or, yet another option, maybe best yet, on further thought, is vinegar. It's slower, but works fine. It's slower, several days or longer, and the tank surface needs to be kept wet, but it will do the job.

Good luck and don't hesitate to PM me with any questions.

[rphillips]

There should be a very fine screen on the pet cock inside the tank, if this screen is clogged enough, running wide open throttle up long hill could cause bike to suck more fuel through than the clogged screen will let flow through. Would be starving for gas. Just say'in. Also a tiny bit of some of that crud could possibly start to build up in a jet or tiny passage. Run a tank of gas with a half can of Sea Foam through it, give it a chance to dissolve any possible beginning of a build up, before it gets bad enough to cause a problem.... Not say'in it will help anything, but what have you got to lose?..

[Nessism]

There should be a very fine screen on the pet cock inside the tank, if this screen is clogged enough, running wide open throttle up long hill could cause bike to suck more fuel through than the clogged screen will let flow through. Would be starving for gas. Just say'in. Also a tiny bit of some of that crud could possibly start to build up in a jet or tiny passage. Run a tank of gas with a half can of Sea Foam through it, give it a chance to dissolve any possible beginning of a build up, before it gets bad enough to cause a problem.... Not say'in it will help anything, but what have you got to lose?..

Sea Foam doesn't dissolve rust. The only way to fix the bike is to derust the tank and clean the carbs.

[rphillips]

Sorry, I never meant to insinuate Sea Foam would dissolve rust, that's why I intentionally never mentioned rust. Crud (varnish like) build-up can hold micro rust particles and gradually grow to an obstruction, if Sea Foam can dissolve this crud and let the micro particles flow through without causing an obstruction, it seems this would prevent that problem from ever happening. The only problem mentioned here was starving for fuel on long steep uphill runs at wide open throttle, other than that all was just fine. For me that would seem more like fuel not getting to carbs rather than carbs needing cleaned...That being said, I'm no carb mechanic and from everything I've read, ED has the reputation of being one of the best around.

[Mat]

I understand I need to do a torough job on this one (and Seafoam might help or not, but won't hurt).
Found a couple products similar to evapo-rust:
https://www.canadiantire.ca/en/pdp/m...p.0477920.html
https://www.canadiantire.ca/en/pdp/r...38.html

I haven't found a proper part cleaner to dip the carb yet (only spray cans) but will do. Fellow canadians that can help on this you are welcome!

I've read many of Ed's publications and must say it helped me a lot to get to the point where I understand the how's and why's.
Still I have so much to learn about the mysterious ways of the carburated bikes

So thank you Ed for giving me the correct fix and rphillips you helped me figure out what might be occuring on those steep hill climbs.

Next time I get the same "gas starved problem on steep hills" I will try to run the bike on PRIME petcock position for a moment to see if that helps (must remember not to leave it that way after the ride not to flood the carter)

Riding season in Canada is short though and as the bike runs not too bad I will make this a winter project and enjoy my only bike as it is for this summer.

Ed you will probably hear from me when I'll have this carb dissassembled and o-rings figured-out this winter.

[kochic]

I need to do mine on my 400 too, with bad luck my ultrasonic stopped working, it just blow fuses. I have tools to synchronize the carburetors if you don't want to go to the dealer, but i'm 2.5hours from you.
Marc

[Suzukian]

You could take the petcock out and clean the screen inside. Make sure the valves are adjusted too. I've seen a lot of people chase carb problems when it was tight valves causing the issues.

[Mat]

Well I've done some compression test lately and discovered I (probably) have some very bad valves on the left cylinder. I remember the valves were tight when I did the adjustment about 500 miles ago...

When cold or hot I had 90 psi on left cylinder...
on the right 170 psi cold and 120 psi when hot

That's probably the reason my top speed is around 88mph when it should be more like 105mph

Definitely, I've got some more work to do

Hey Marc I didn't even know I'd have to sync the carbs