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Similar to my thread on starting the bike, here are some recurring items from various new carb threads and questions in this subforum. The idea is to round up these chestnuts into a single reference thread.
Before you launch into a specific problem, consider these pre-game issues first.
1. Valves > Carbs. If you are stabbing at starting/idling problems, it may be your carbs, but check and adjust your valves first. The magic formula is compression, air, fuel and spark. If your valves are tight, your compression will suffer and nothing you do to the carbs will change that. Moreover, if your valves remain tight, you will damage the top end, burn valves, etc. When that happens, we'll see you in the Engine/Drive Train forum for more expensive work. Also, valves are either right or wrong. So get them right first.
2. Electrics Matter. You still need to deal with your carbs, but while they are bathing in dip, you should check your coils and timing. Sometimes (but not always), rich or lean symptoms result from weak spark or poor timing. Nothing you do to your carbs will correct this, so verify that your ignition is up to spec and is properly timed.
3. Clean Your Carbs. Before you launch into why the bike acts funny, clean your carbs. Members are not likely to take your problem seriously if you skip the valve adjustment or short-change the carb cleaning. If your carbs aren't clean, you are just chasing your tail. There are comprehensive guides for stripping and rebuilding GS carbs, both CV and VM carbs. Learn them, love them, live them. Don't screw around with "the bowls looked clean" or "I ran SeaFoam through the system" or "I sprayed them real good." There is only one way to clean your carbs, strip them, dip them and replace the o-rings.
4. Don't Use Rebuild Kits. They suck, and you end up paying for crappy parts you shouldn't use. Even if your carbs were stored in the La Brea Tar Pits, the only parts you need to clean the carbs are new o-rings from Bob Barr (www.cycleorings.com) and bowl and top gaskets. Once you pull the carbs apart you may end up with some jets or screws that don't survive, are missing, etc. You can order original Mikuni replacement parts from Z1 Enterprises and other sources for much less than those terrible carb kits.
5. Know Thyself. While you have those carbs apart, note what jets you have. Compare them to the stock specs to see if they've been changed by a PO. Getting a handle on what's in your carbs helps us (and you) isolate a running problem. If you start with a symptom but have no jetting reference point, there is not much to tell you.
6. You Have Air-Leaks. Every carb help post gets an air-leak answer. Don't be that guy. These old bikes are notorious for air-leaks because the intake boots and intake o-rings are old and crappy. If the bike is new to you, change the intake o-rings with new ones from Barr. Check those intake boots as well. New boots are expensive (about $125 for a set of 4), so if they are soft and have no cracks or tears, you don't need to replace them. But if the boots are hard or have any cracks, you must replace them with new ones.
7. Share with the Class. There are a lot of different GS models in this forum, and there are several modifications that make a big difference in your carb settings. Tell us (a) what bike you are working on; (b) what exhaust system you have (stock, 4-1, chopped-straight pipes, etc.); and (c) what air system you have (stock airbox, pods, etc.).
Once you have established a baseline, if you still have problems, consider these details when framing the question:
1. Throttle > RPM > MPH. Your carbs and jets are triggered by throttle position. They are not connected to the tachometer because RPMs mean nothing. The speedo is not connected to the carbs either, so MPH is not helpful in the analysis. You may think you are hitting a wall at 60 mph, or at 5,000 RPM, but unless you have some kind of governor on your engine (you don't), your throttle position is the real clue.
2. Learn to Love the Carb. Familiarize yourself with the basic carb functions here. You don't need to be an engineer to follow this, and the overview will really clue you into what may be amiss in your system.
3. Plugs Know For Sure. Any question that starts with "engine bogs at 6,000 RPM" or "stumbles at 25 MPH" is pretty hard to address. Some symptoms are strong indicators of rich or lean (e.g., hanging idle = lean), but "hesitation" and "stumbling" could describe either condition. Your plugs do not lie, though. Drill into your problem with a plug chop at what ever throttle position (because RPM/MPH are for scrubs) it occurs, if you can. Mid-range and WoT chops can be challenging, depending on where you are. Even if you cannot isolate the problem with a chop, check your plugs anyway. If they are markedly different in color after riding, that also helps narrow down your problem.
4. You are Probably Lean/Still Have Air Leaks. If you skipped the intake boot/o-ring check, we cannot fix you. You may notice that no matter how vague the question, almost every thread includes a "sounds lean" response. I used to scoff at this as just a knee-jerk forum culture thing. Now I have sipped the Kool-Aid. Here's why. Your carbs take two things - air and fuel and give them some "alone time" where they can make sweet, sweet love and produce that stuff your engine needs. Fuel is a meat 'n potatoes guy. He starts in the tank, moves down the fuel line, and shows up to party like clock work. Air, OTOH, is a Babylon whore. Air scoffs at the rules and will show up to the party through the front door, back door, a broken window, etc. So if your mixture is off, the odds favor the culprit to be air, not fuel. That's why you need to verify the integrity of that air system, to keep her honest.
5. Pod/Pipes = Rejetting. Don't bother asking the question, that just feeds the pod-haters. If you change the pipe to a 4-1, you may need some rejetting. Change the box to pods, you will need some rejetting. Change to pods and a pipe, you absolutely need substantial rejetting. Many will tell you to get it running right with stock parts first, before going into the wilds of pod/pipe jetting. To the extent that is part of the pre-game items above, I agree. Lots of us, however, start with bikes that have one or more of these changes, so you at least have to account for them in the rebuild. That's one reason for inventorying your jets - many a PO will change to pods and skip the rejetting, or change back from pods without restoring the stock jetting. Both are bad. Despite the haters, pods and pipe are not mortal sins, but with great power comes great responsibility. Check the factory specs for your bike to gauge where your jets will need to be.
Please add to this with anything I missed.
Before you launch into a specific problem, consider these pre-game issues first.
1. Valves > Carbs. If you are stabbing at starting/idling problems, it may be your carbs, but check and adjust your valves first. The magic formula is compression, air, fuel and spark. If your valves are tight, your compression will suffer and nothing you do to the carbs will change that. Moreover, if your valves remain tight, you will damage the top end, burn valves, etc. When that happens, we'll see you in the Engine/Drive Train forum for more expensive work. Also, valves are either right or wrong. So get them right first.
2. Electrics Matter. You still need to deal with your carbs, but while they are bathing in dip, you should check your coils and timing. Sometimes (but not always), rich or lean symptoms result from weak spark or poor timing. Nothing you do to your carbs will correct this, so verify that your ignition is up to spec and is properly timed.
3. Clean Your Carbs. Before you launch into why the bike acts funny, clean your carbs. Members are not likely to take your problem seriously if you skip the valve adjustment or short-change the carb cleaning. If your carbs aren't clean, you are just chasing your tail. There are comprehensive guides for stripping and rebuilding GS carbs, both CV and VM carbs. Learn them, love them, live them. Don't screw around with "the bowls looked clean" or "I ran SeaFoam through the system" or "I sprayed them real good." There is only one way to clean your carbs, strip them, dip them and replace the o-rings.
4. Don't Use Rebuild Kits. They suck, and you end up paying for crappy parts you shouldn't use. Even if your carbs were stored in the La Brea Tar Pits, the only parts you need to clean the carbs are new o-rings from Bob Barr (www.cycleorings.com) and bowl and top gaskets. Once you pull the carbs apart you may end up with some jets or screws that don't survive, are missing, etc. You can order original Mikuni replacement parts from Z1 Enterprises and other sources for much less than those terrible carb kits.
5. Know Thyself. While you have those carbs apart, note what jets you have. Compare them to the stock specs to see if they've been changed by a PO. Getting a handle on what's in your carbs helps us (and you) isolate a running problem. If you start with a symptom but have no jetting reference point, there is not much to tell you.
6. You Have Air-Leaks. Every carb help post gets an air-leak answer. Don't be that guy. These old bikes are notorious for air-leaks because the intake boots and intake o-rings are old and crappy. If the bike is new to you, change the intake o-rings with new ones from Barr. Check those intake boots as well. New boots are expensive (about $125 for a set of 4), so if they are soft and have no cracks or tears, you don't need to replace them. But if the boots are hard or have any cracks, you must replace them with new ones.
7. Share with the Class. There are a lot of different GS models in this forum, and there are several modifications that make a big difference in your carb settings. Tell us (a) what bike you are working on; (b) what exhaust system you have (stock, 4-1, chopped-straight pipes, etc.); and (c) what air system you have (stock airbox, pods, etc.).
Once you have established a baseline, if you still have problems, consider these details when framing the question:
1. Throttle > RPM > MPH. Your carbs and jets are triggered by throttle position. They are not connected to the tachometer because RPMs mean nothing. The speedo is not connected to the carbs either, so MPH is not helpful in the analysis. You may think you are hitting a wall at 60 mph, or at 5,000 RPM, but unless you have some kind of governor on your engine (you don't), your throttle position is the real clue.
2. Learn to Love the Carb. Familiarize yourself with the basic carb functions here. You don't need to be an engineer to follow this, and the overview will really clue you into what may be amiss in your system.
3. Plugs Know For Sure. Any question that starts with "engine bogs at 6,000 RPM" or "stumbles at 25 MPH" is pretty hard to address. Some symptoms are strong indicators of rich or lean (e.g., hanging idle = lean), but "hesitation" and "stumbling" could describe either condition. Your plugs do not lie, though. Drill into your problem with a plug chop at what ever throttle position (because RPM/MPH are for scrubs) it occurs, if you can. Mid-range and WoT chops can be challenging, depending on where you are. Even if you cannot isolate the problem with a chop, check your plugs anyway. If they are markedly different in color after riding, that also helps narrow down your problem.
4. You are Probably Lean/Still Have Air Leaks. If you skipped the intake boot/o-ring check, we cannot fix you. You may notice that no matter how vague the question, almost every thread includes a "sounds lean" response. I used to scoff at this as just a knee-jerk forum culture thing. Now I have sipped the Kool-Aid. Here's why. Your carbs take two things - air and fuel and give them some "alone time" where they can make sweet, sweet love and produce that stuff your engine needs. Fuel is a meat 'n potatoes guy. He starts in the tank, moves down the fuel line, and shows up to party like clock work. Air, OTOH, is a Babylon whore. Air scoffs at the rules and will show up to the party through the front door, back door, a broken window, etc. So if your mixture is off, the odds favor the culprit to be air, not fuel. That's why you need to verify the integrity of that air system, to keep her honest.
5. Pod/Pipes = Rejetting. Don't bother asking the question, that just feeds the pod-haters. If you change the pipe to a 4-1, you may need some rejetting. Change the box to pods, you will need some rejetting. Change to pods and a pipe, you absolutely need substantial rejetting. Many will tell you to get it running right with stock parts first, before going into the wilds of pod/pipe jetting. To the extent that is part of the pre-game items above, I agree. Lots of us, however, start with bikes that have one or more of these changes, so you at least have to account for them in the rebuild. That's one reason for inventorying your jets - many a PO will change to pods and skip the rejetting, or change back from pods without restoring the stock jetting. Both are bad. Despite the haters, pods and pipe are not mortal sins, but with great power comes great responsibility. Check the factory specs for your bike to gauge where your jets will need to be.
Please add to this with anything I missed.
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