General advice regarding carbs, '93 GSX600F

[paul.miner]

I haven't had my Katana for very long, and after my most recent ride, I have a list of new issues to work on:

1. Tail light is out (brake light works).
2. Install centerstand. Need to buy/make bushings and find the right bolts.
3. Make some sort of rubber bumper for the gas tank so it doesn't bang around on little bumps.
4. Tighten chain (just installed new chain and sprockets, so I think they're still breaking in).

And the unknown:

5. Fix problem with carbs/vacuum. Symptoms are poor economy (about 35mpg), and engine idles low and often dies after coming to a stop after running it hard for a while. The first couple times I thought I had just killed the engine when I was about to take off from an intersection, but it happened several times while in neutral recently, so I know it wasn't me. I had been riding hard for 15-30 minutes, and after that, whenever I was stopped at an intersection, the engine would idle very low (under 1000 rpm) and sound rough, and usually die. It would do the same thing immediately after restarting, so I'd have to start it and immediately rev a bit to keep it alive.

It has been suggested to me that a couple possibilities are vacuum leak or rich fuel mixture. I haven't messed with carbs much, so I'm rather new to this, but I have a service manual and I'm ready to dive in.

Any thoughts/suggestions? Do's and Don'ts?

[Kfreak]

Since it is a 93, it just may be time for a carb overhaul. Or for now try bumping up the idle to around 1200/1300 rpms.

[diavolo]

Not enough info regarding the carbs, but try dumping in a can of Techron or some Sea-Foam and see of that helps clear up the problem. Other than the low idle speed after a few minutes, how is her top end throttle response? Might just need a few good runs with detergent to get any varnish cleared out of those carbs.

[scottynoface]

The first couple times I thought I had just killed the engine when I was about to take off from an intersection, but it happened several times while in neutral recently, so I know it wasn't me. I had been riding hard for 15-30 minutes, and after that, whenever I was stopped at an intersection, the engine would idle very low (under 1000 rpm) and sound rough, and usually die. It would do the same thing immediately after restarting, so I'd have to start it and immediately rev a bit to keep it alive.

Sounds like overheating to me. How much time are you spending at a stop?

[shadowhunter04]

I would +1 the carb overhaul. I had the same issue a couple weeks back and couldn't figure what the problem was or what had changed since it had been running so well. I even went with the sea-foam approach and figured that it must be able to clean it out a bit...apparently not. I ended up taking the carbs apart, and letting the jets and parts soak in some carb cleaner. When I got it all back together, started right up and worked fine... Sea-foam is great, but it doesn't replace a direct jet of carb-cleaner

[paul.miner]

Or for now try bumping up the idle to around 1200/1300 rpms.

I think that's roughly where it idles normally, just not after a hard ride.

Other than the low idle speed after a few minutes, how is her top end throttle response?

Good AFAIK, but this is my first sport bike. Another oddity is that on some mornings, it will idle very high (4000 rpm?) at start up, no choke or throttle, and won't drop until I fidget with the idle adjustment screw. I don't actually have to turn it, I just have to touch it and push on it a bit, and suddenly engine speed will drop to normal (between 1000 and 2000 rpm, can't remember exactly what).

Sounds like overheating to me. How much time are you spending at a stop?

It's noticeable pretty much immediately after stopping, usually dies before even 30 seconds have passed. I do notice that I feel a lot of heat during normal riding at the time, like the radiator is really pumping the heat out. Would this be related to the fuel mixture being rich?

[paul.miner]

Update...

I've replaced the tail light, ordered bushings for the centerstand (I have an '05 GSX750F centerstand I'm trying to install on this '93 GSX600F), made a rubber bumper out of garden hose to fit in the little semi-circle at the front of the tank, and tightened the chain.

I took the carbs off and followed the carbs-101 guide to completely disassemble one of the carbs. Went on an all-day ride with my dad Sunday, so I should be back on the carbs tonight. I replaced a few O-rings, but I don't know what to do about the rubber plug over the pilot jet (page 11 of the carbs101.pdf). It fits loose, so I need to replace it -- any suggestions on something cheap and easily available that I can adapt to this purpose?

Also, the PDF says stoppers -- there was only one in the first carb I took apart. Should I be concerned?

[steves]

The 05 center stand will not work without cutting/re welding parts.

If the rubber plugs are gone/missing order new ones.

[paul.miner]

The 05 center stand will not work without cutting/re welding parts.

Can you tell me what is different? Mine didn't come with a centerstand, so I don't have one to compare with.

If the rubber plugs are gone/missing order new ones.

That's what I'm not sure of, are they gone? I looked at an online parts catalog, and for "J" and "K" model carbs, there doesn't appear to be plugs. For "L/M/N/P/R" carbs, there appears to be one plug per carb. I guess the guide may have been talking about plugs because it assumes you're working on all four carbs at the same time?

[steves]

Look at the parts fiche for the center stand. You'll see it mounts very differently.

If it's a 96, there should have been rubber plugs covering one of the passages. Check out carbs 101 in the wiki for pictures.

[paul.miner]

Look at the parts fiche for the center stand. You'll see it mounts very differently.

I looked, and the main difference just seems to be the bushing. I think the hook for the spring may have switched sides, but I think I can take care of that if necessary.

I held it up to the mounts on the bike frame and it looked like it would work. I didn't inspect it closely because I'm going to have to pull the exhaust down to even get a bolt in there. As it is, I can't even test thread a bolt in there because the exhaust pipes are in the way.

If it's a 96, there should have been rubber plugs covering one of the passages. Check out carbs 101 in the wiki for pictures.

Yeah, mine looks like that, I was just wondering if one plug per carb was correct. After further thought, I think it's just worded that way because the guide assumes you're taking all the carbs apart.

[steves]

One per body, not one per rack.

[paul.miner]

Got the carbs cleaned, various o-rings replaced, replaced the rubber plugs over the starter jet, and put it back together last night. Today I'll probably work on getting them adjusted and synced.

In the meantime, I've got a question about the A/F screw. My jets appear to be stock; I wrote it down at home, but IIRC it was 112.5 main and 32.5 starter, with a needle with one clip position. The A/F screws did not have a plug over them, and they were adjusted to 3.5 turns out, which seems pretty lean. I put them at 2 turns out when I reassembled the carbs, and I may try the idle drop technique outlined in the sticky.

Would 3.5 turns out make the engine run excessively hot? From what I've read, even jetted bikes don't have that many turns out. And how does 2 turns out sound?

I seem to be reading conflicting opinions -- is more turns out leaner or richer? Or is there more to it than that...?

[Psycho1]

The more turns out you go the richer it is. 2 1/2 turns is stock settings, try 2 3/4 or 3 turns out for a stock engine and jetting with a stock air filter.

[paul.miner]

Well, got it back together and running again! I had set it to 2.5 turns and forgot to put in the additional 1/4 turn, but hopefully it'll be okay. A guy I met on another forum came over and we put the carbs back on and synced them. The A/F mixture screw looked to be a real pain without a tool, so I'm going to skip that for now.

It seems to take off from a start a lot easier now, I don't have to rev it as much, like it has more power at lower RPMs. The real test will be when I get to go on an extended high-speed ride, and then see if it dies when coming to a stop.