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.

 

[Guest]

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?

 

[Guest]

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.

 

[Guest]

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.

 

[Guest]

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.

 

[Nessism]

Really sounds like a bad vacuum leak to me.

There you go. You answered your own question.:!:

Not sure if your bike has these o-rings, but intake leaks on GS bikes are often from this source.

 

[Steve]

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

Because something you disloged in your previous "cleaning" moved in behind the screw that you did not remove and is now causing problems.

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

Why wait until everything else fails? They might be the cause of it all.

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.

A climbing idle as the bike warms up is a good indicator of a vauum leak. One of the most common leaks is the o-rings that Nessism pictured above. Not all bikes have them, but I think your bike does.


I just looked back through some of your previous posts, and it appears that you have only had the bike for about a month. Based on some of the questions you are asking, you are either new to motorcycles or just kinda new to being a mechanic. One of the things that is necessary when acquiring any 'new' old bike is to thoroughly go through it, making sure that everything is clean and works. There are not too many shortcuts that can be taken. If you take a shortcut, you will just end up coming back again to do it right. When you "cleaned the carbs" with your baking soda blast, all you did was make the outsides shiny again. Even the warm water bath did not do much to clean out the inside. I have seen some rather cruddy, crusty old carbs on rat bikes that worked perfectly because they were clean on the inside, where the fuel has to flow. The best way to ensure that the inside of the carbs are clean is to take them completely apart and dip them in carb cleaner, then re-assemble the carbs with all new o-rings. Dirty fuel passages (which are rather small) and cracked o-rings are the two biggest problems in the fuel systems on our bikes. Once you take care of that, your bike will run like new.

Please keep asking questions, that's the only way we learn new stuff. And, someone else might learn from your question, too. But, when suggestions are offered, please try them before you shoot them down. The collective wisdom on this board is rather phenomenal. We will get your bike running right.

by the way ... how much of a mess did the baking soda blast make? I have thought of doing that, but I have too much stuff that would need to be cleaned if it's a messy process.

.

 

[MrZig]

I never removed the pilot screws because I heard I had to drill the caps out, something I didn't want to do. Now that I know they're so important, I'll clean that circuit.

And I'm not new to being a mechanic, I've pretty much completley rebuilt my own vehicle, but I am incredibly new to bikes and carburetors. I don't have anyone at home to help me, no one, so these forums are all I've got and that's why I ask a lot of questions because I simply have no idea.

Oh and by the way, I didn't just clean the carb bodies with the baking soda. I also throughouly sprayed them with solvent and blew them out with shop air. I'll have to take a look at the pilot circuit though.

The plan is to buy new o-rings, make custom intake boots and to clean the pilot circuit. If that still fails in fixing the issue then I really don't know what's going on. This is why I made the thread, to give a newbie like me some ideas. I obviously overlooked some major issues that I shouldn't have, and that's part of learning.

Edit: The baking soda method is quite messy. You go through a lot of soda. I went through at least 8 of these boxes http://www.ohdeedoh.com/uimages/ohdeedoh/2008-04-14-baking soda.jpg

I wouldn't do it in a shop, that's for sure.

 

[Guest]

no worries mate. these gs carbs are very finicky, i had to dip mine twice to get them clean enough, i should have been more thorough the first time. it also took me 2 valve adjustments to get my #3 ppipe to warm up like it should. learning on your own is a pain. this forum, though, has impressed me time and time again with its patience for all of my stupid questions! thanks guys!

 

[BassCliff]

The plan is to buy new o-rings, make custom intake boots and to clean the pilot circuit.

Hi Mr. MrZig,

It sounds like you are making progress on your bike and gaining valuable experience. I appreciate your patience with us as we try to help.

I found a parts fiche for the GSX400 here (but I don't know exactly what year yours is):
http://www.cmsnl.com/suzuki-gsx400-1984-ee_model13613/partslist/

The intake boots are #18 and #19 (different part#'s for the left and right boots), the O-rings are #20. See the picture below:

(Ignore the "Get these pars at..." message. I was just looking for any parts fiche with illustrations and part numbers. But this particular site seems to have a lot of non-US models. Handy.)

Does this look like your engine? Can your really fabricate those intake boots? Are the vacuum ports on the intakes in the head or in the boots? You'll need these vacuum ports on the intake to sync your carbs.

Or are you going to fabricate the airbox-to-carb boots?

Here is part of the mega-welcome that seems pertinent to your situation.

***********Quoted from Mr. bwringer************
Every GS850 [and most other models] has (or had) a set of well-known issues that MUST be addressed before you have a solid baseline for further troubleshooting. It's a vintage bike, and it's quite common (as in, every single GS850 I have had contact with) that there are multiple problems that have crept up and slowly gotten worse over the years. It's not like a newer vehicle, where there's generally one problem at a time.

These common issues are:

1. Intake O-rings (install NEW OEM or Viton only - common nitrile O-rings will quickly deteriorate from heat)
2. Intake Boots (install NEW -- these cannot be repaired)
3. Valve clearances (more important than most people think)
4. Carb/airbox boots
5. Airbox sealing
6. Air filter sealing
7. Petcock (install a NEW one)
8. On '79 models, install new points or Dyna electronic ignition (or at least verify that the old points are working correctly)
9. On all models, it's fairly common to have problems with the spark plug caps. These are $3 or $4 each, and often worth replacing if you're keeping the stock coils/wires.
10. Stock exhaust with NO leaks or holes -- good seals at the head and at the junctions underneath.

Carburetor maintenance:

Replace the intake boot o-rings, and possibly the intake boots. Here's the procedure:
http://bwringer.com/gs/intakeorings.html
Here's an overview of what happens with this particular problem:
http://cycleorings.com/intake.html
You'll also want to examine the boots between the carbs and the airbox. There's a good chance these are OK, but check them over.
And finally, if things still aren't exactly right, you'll want to order a set of o-rings for BS carbs from the GS owner's best friend, Robert Barr:
http://cycleorings.com
Once you receive these rare rings of delight, then you'll want to thoroughly clean and rebuild your carburetors. Here are step-by-step instructions that make this simple:
http://thegsresources.com/gs_carbrebuild.htm

*********End Quote******************


Keep up the good work. Keep us informed.





Thank you for your indulgence,


BassCliff