Cleaned carbs - now runs like crap and revs very slowly

[MrZig]

I recently cleaned the carbs on my GSX400 and put it all back together and now the bike runs like ****.

It's extremely hard to start when it's cold, and once it's running it sometimes has a rough idle and dies. When I twist the throttle, it revs very slowly.

I didn't change any sort of mixture screw settings, and everything in the carbs went back together perfectly. What could cause this issue I'm having?

The only thing I changed in the carb's was the float level, they were out by 3mm each - letting more fuel in than they should. I tried removing the air filter for a quick test - no change. The fuel line is straight and has no kinks. I sprayed water around the carb boots and the idle didn't change, nor did I see any bubbling. I'm getting frusterated because I don't know why it isn't running properly. Could it be ignition? I don't see why that would've changed from the last time I ran it, about 2 weeks ago.

[kparkfan]

did you re sync the carbs. i think they need to be sync after a rebuild. im currently in the same boat as you. in the proccess of doing a valve adjustment before i sync.

[MrZig]

did you re sync the carbs. i think they need to be sync after a rebuild. im currently in the same boat as you. in the proccess of doing a valve adjustment before i sync.

No I havn't sync'd the carbs. Would it really cause the problem I posted though?

[reddirtrider]

Did you take them completely apart - even the idle mixture screws? Did you dip, or use spray? Did you blow them out with compressed air? Did you replace any o-rings? Bench sync?

[MrZig]

Did you take them completely apart - even the idle mixture screws? Did you dip, or use spray? Did you blow them out with compressed air? Did you replace any o-rings? Bench sync?

I didn't mess at all with any mixture screws. To clean the carbs I used the baking soda & compressed air method then soaked them in hot water for a couple hours, and then blew out the passages with compressed air.

I didn't replace any o-rings, and I eye-balled the bench sync as best I could (comparing the plate positions against the pilot hole in the carb body).

[MrZig]

Would a big leak between the air box and carbs cause the problems im talking about?

I sprayed some WD40 around the boots there and the idle has gone uncontrollably up. Seems like its leaking. The problem is the airbox is from a GS400 and the engine is a GSX400 so they dont line up properly.

But, like I asked, would that cause the problems im describing if it was leaking terribly?

[spchips]

These bikes are extremely sensitive to changes in intake resistance, such as the smallest leak. It won't run right without the pressure spot on, or rejetting, which wouldn't make sense in this case since it's a leak.

They usually won't run at all or only with full choke without the airbox.

Gotta tighten the leaks up, or if anything is stiff or cracked, replace with fresh rubber.

[greg78gs750]

i would probably replace those o-rings. and dip them overnight in carb dip. also, your valves are in spec, right?

[reddirtrider]

I didn't mess at all with any mixture screws. To clean the carbs I used the baking soda & compressed air method then soaked them in hot water for a couple hours, and then blew out the passages with compressed air.

I didn't replace any o-rings, and I eye-balled the bench sync as best I could (comparing the plate positions against the pilot hole in the carb body).

If you didn't completely disassemble the carbs, then you can't be sure they are clean. You've gotta have a solid place to start.

[MrZig]

If you didn't completely disassemble the carbs, then you can't be sure they are clean. You've gotta have a solid place to start.

What do you mean? The only thing I didn't dissasembler was the mixture screw. I took the floats out, the diaphram out, etc.

The bike revved up fine before I cleaned the carbs. It just had a rough idle once it warmed up. The carbs can only be cleaner than before, and a clean carb wont make it act the way it is..

[MrZig]

i would probably replace those o-rings. and dip them overnight in carb dip. also, your valves are in spec, right?

What O-rings? All the rubber pieces in the carbs looked okay. I didn't take a look at the mixture screw though.

Also I havn't checked my valves because I can't find any sort of valve clearence numbers for my engine. It's a 4 valve (8 total) parralel twin GSX-400. I can't find any.. But I mean the bike should run at least as good as it did before I cleaned my carbs, right? It's running a lot worse..

[reddirtrider]

What do you mean? The only thing I didn't dissasembler was the mixture screw...

Bingo.

You're asking for advice. If you don't like it, ignore it. Fine with me.

[7th day]

Hard starting and poor idle is a clear sign that the enrichener and idle passages are partially plugged, you have to remove the screws and soak the carbs in a good carb cleaner and blow them out. When you cleaned them you probably loosened some crud that is now stuck in there. One other thing to check is that there are no pinholes in the diaphrams.

[reddirtrider]

What O-rings? All the rubber pieces in the carbs looked okay. I didn't take a look at the mixture screw though.

Also I havn't checked my valves because I can't find any sort of valve clearence numbers for my engine. It's a 4 valve (8 total) parralel twin GSX-400. I can't find any.. But I mean the bike should run at least as good as it did before I cleaned my carbs, right? It's running a lot worse..

The o-rings are at the base of the (dare I say it) mixture srews.

You are correct that it should run at least as well (not worse) by cleaning the carbs. The valves may need adjustment, but they are not your problem.

[MrZig]

Bingo.

You're asking for advice. If you don't like it, ignore it. Fine with me.

Sorry but I don't understand? How would not touching the idle mixture screw make it run 100x worse than before I cleaned them?

The o-rings are at the base of the (dare I say it) mixture srews.

Ah, yeah, well I might take a look at them if everything else completley fails.

Hard starting and poor idle is a clear sign that the enrichener and idle passages are partially plugged, you have to remove the screws and soak the carbs in a good carb cleaner and blow them out. When you cleaned them you probably loosened some crud that is now stuck in there. One other thing to check is that there are no pinholes in the diaphrams.

Hmm this is a possibility. The diaphrams were 100% perfect, though. I think I'm going to try and eliminate any possible vacuum leaks before tearing into the carbs again. My airbox-to-carb boots are pretty gross, so I'm going to buy some rad hose and make my own.

No, I will not buy new boots because like I said, my airbox is for a different engine with different carb spacing. What I'm saying is that when I line my air box up with my carbs, the air-tubes on the box are spread out a good half inch than where they should be. The only way to fix it properly is to buy an air box for the engine (from a GS450, or GS250) and I simply can't do that at this time.


Edit: Something to note, the last couple times I started the bike when it was warm, it would idle nicely and at a respectable RPM, and then slowly climb and climb and climb until what I can think is at least 5000 RPM (I don't have a working tach.)
Really sounds like a bad vacuum leak to me.