Problems Tuning Carbs

[Anonymous]

I have a GS650GL(shaftie) with a little under 30k on it. I just got it running by rebuilding the carbs. It runs but refuses to acelerate well, and i have a top speed of about 40-45mph. When i get on the throttle it kinda bogs down and the the engine starts to respond but it wont go all the way to the red line. I cant tell exactly how high it is going cuz the tach is no good. When i got it the cover to the air box cover was missing so i covered it with duct tape, i pretty sure its air tight. I bought a carb sync tool but it doesnt seem like any adjustment i make to the four little screws has any effect. So now i just set the screws to 2 turns out, no real change. Any help...anyone?

 

[Jethro]

The carb synch tool has nothing to do with the 4 mixture screws. To adjust the synch you adjust the 3 throttle body screws. These make a huge difference in the running.

As to your running problems, sounds like your main circut is not right. Does it have the stock jetting? Did you replace the float valves and seals?

 

[Anonymous]

main circut?

But yes it is all stock i did not replace anything i just cleared the carbs of old gas and gunk

 

[DMPLATT]

Just a thought here, but did you cover the airbox top COMPLETELY with duct tape?

 

[Anonymous]

I covered the side that was missing completely, but if your getting at an idea that it cant breathe there is some vents on the opposite side where it is desingened to draw air that are completely free of obstruction.

I think Jethro is right i need to sync it, but this time adjust the throttle screws and not the mixture screws

 

[DMPLATT]

Ok, you have a different airbox than I do. Just wanted to make sure it was getting air. :wink: :wink: 8) 8)

As far as the synch goes, there are some pro's here that can help more than I can. However, this is what I've learned.

Warm the bike up, set idle to 1700 rpm, adjust the throttle valve screws to get all in synch, then adjust the mixture screw to obtain the highest idle for each carb. Then set the idle back down to around 1100-1200.

Good Luck.

 

[Anonymous]

Sounds like you're just going into the mains. So make sure the main jets are the correct size. You need to check them against the specs. unless you were running good before. Lots of these bikes get parked for decades because the jetting got mixed up. Also, make sure you got the float bowls to the correct level. If you have a sync tool, then you probably have adapters that will fit into the bottom of the fuel bowl. Put a transparent tube on it and hold it beside the bowl. Think they are supposed to be approx. 3mm below the top surface of the bowl.(could be wrong on that but it's in the factory service manual). Can start the bike up while watching the fuel level.

 

[Anonymous]

Also, don't forget there are more components involved when you are asking for high volumes of fuel and air. The fuel tank, petcock, fuel filter (if there is one), air filter. If the air filter is becoming partly restricted it will become a factor when you ask for high volumes of air. Unfortunately, you can't just remove it to see if it is the problem, then you will get too much air at all RPMs. I've seen GSs that won't even start without the air box on. With my K&N air box filter elements I can only go around them once with the oil spray at about 12 inches. If I go around twice, I have to clean them up and start over. Same idea with a fuel filter, you're in the high volume area. If you are having problems getting up to 3000 RPMs, then you also have a problem with the vacuum diaphrams, needles, needle jets. But I would look into general air and fuel delivery from what you are saying. If you tanked the carbs with the o-rings left in the float valve seat and the air/fuel mixture screws, then not much of those o-rings exists anymore.

 

[Anonymous]

Huh? you went way over my head with that one. How do i adjust the float level, and what are the repercusions of not adjusting it?

Its not that im too lazy to adjust the float level, its just if i get them sync'ed and everything works fine i will be tempted not to touch anything else. You know how it goes, If it aint broke...

 

[Jethro]

How do i adjust the float level, and what are the repercusions of not adjusting it?

If you don't get the float hights set right, your carbs might be trying to either push too much or not enough fuel, resulting in a lean or rich condition. If your mix is too rich you might not be getting a good burn out of each stroke. If it's too lean, the cylinder might get too hot resulting in pre-ignition of the fuel. The more you open the throttle bodies, the worse the performance gets. To check the float heights you have to pull the carbs off, remove the bowl and measure the distance between the gasket surface on the carb body and the float itself. On my bikes it should be 22.4mm +/- 1mm. This is when the float arm just comes in contact to the float jet.

 

[Anonymous]

This is the passive way to adjust them with the carbs upside down. Bend the tabs to get the right height, they rest against the float needle valve. Myself, I call that a preliminary adjustment of the float height. It's in most service manuals. The Suzuki Factory Manual covers it best. After the carbs are on the bike you can actually check the fuel height by replacing the fuel bowl drain plug with a fitting (might be a short one included with your sync kit). Put a transparent tube on it (like tubing used for fish tanks), and put the tube up beside the carb. Should have the bike on the center stand.
Fuel level needs to be correct before sync but your levels could be correct now, nobody knows without checking. If you set your carbs down on the floats with the bowls off, they are probably out of adjustment.
If you seperated the carbs to clean them, they would certainly be out of sync.

 

[Anonymous]

Being that this I am restoring this bike with him, I am still at a loss on how to do this.

Preliminary adjustment of the floats should be done with the bowls off, upside down (on the CV boot caps), from the gasket on the carb body to the floats. Where exactly on the floats? Height from the carb body to the plate? Where can I/we find the proper distance for our bike?

Then on the bike when attaching the short attachment from the carb sync to the fuel bowl, then a piece of tubing around the bottom of the bowl and up along the side, how far should the fuel rise if any?

I am sorry if I am sounding dumb but we are both getting agrivated with the performance of this bike and are trying our hardest to get it running right.

When syncing the carbs which adjustment should we adjust first? The Throttle Plate adjustment screws then the mixture screws?

How do you get the RMPs for syncing, Use the idle adjust screw? Hold the throttle open?

We appreciate anything you guys are saying.

 

[Anonymous]

Ok i've got it sync'ed and the mixture is just about right, i think (plugs look pretty ok to me). But it still runs like crap. Its a bit more responsive and goes a little faster but i still have it boging down, not reaching red line and there is no acceleration to speak of on this thing. I'm going to try to pull the carbs off open the bowls and work on the float level bu ti could use a little guidence. And if i can check the levels without even taking it off all the better. MidnightRider what level should the fuel be at?

Also, Where can you buy jets and how do i determine what a stock jet size is and how much to go up for certain thing, like k&n pods/ new exhaust...

 

[Anonymous]

Main jet size, you can probably find on "BikeBandit.com" (it's usually stamped on the jet surface). Height of the floats, think you really need a factory service manual, but you can probably get by with a Clymer or Haynes. I think on my model, the fuel level is 3mm below the top surface of the bowl. It's fairly difficult to adjust the floats on the bike, can be done.
Mixture or throttle screws? Good question, there's been a lot of discussion on this. Your problem certainly isn't with idle mixture, so I would set them like 2 or 2 1/2 turns out and move on to the sync. One of the carbs doesn't have a throttle plate adjust so you have to use that carb as a point of reference. I use the idle speed adjust to keep the rpm up during sync.
Most of this stuff has been discussed 1000 times. You might be able to pick it up in a search and save yourselves some time. If you have those modifications (pod,4 into 1 pipes) and you have stock mains, that would cause the bike to run terrable.

 

[Jethro]

Ok, before I start, let's establish one thing. If you are going to touch a wrench to any bike at all, you simply must have it's manual. I suggest the factory manual, no matter what it costs you. I have all three- factory, Haynes and Clymer. Sometimes one has better photos than the other, sometimes one has a better write up of a proceedure. The reason I say this is because I'm not sure what your float heights should be in your model, and the best way to explain how to set the float heights is by looking at the pretty pictures :lol:

Preliminary adjustment of the floats should be done with the bowls off, upside down (on the CV boot caps), from the gasket on the carb body to the floats. Where exactly on the floats? Height from the carb body to the plate? Where can I/we find the proper distance for our bike?

You must measure form the gasket mating surface of the carb body- not the gasket. Remove the gasket and get new ones. The floats are in the bowls in the bottom of the carbs. Take the carbs off the bike, flip them upside down, and remove the bottom of each carb with the 4 screws. Inside you'll find the floats. The distance to measure is from the carb body to the bottom of the float itself- at least thats what my manual says.

Then on the bike when attaching the short attachment from the carb sync to the fuel bowl, then a piece of tubing around the bottom of the bowl and up along the side, how far should the fuel rise if any?

This method is new to me, but seems like a really good way to check your work! I assume the fuel should rise to the line of the gasket for the float bowls. My factory manual doesn't explain this, but I am going to try it next time I set my float heights!

When syncing the carbs which adjustment should we adjust first? The Throttle Plate adjustment screws then the mixture screws?

The throttle plate adjustment screws. In my opinion anyway. In theroy, the mixture screws shouldn't change your synch, just your burn.

How do you get the RMPs for syncing, Use the idle adjust screw? Hold the throttle open?

I use the idle set screw. You'll be fussing with this anyway.

 

[Anonymous]

Make sure to consider the inlet-boot o-rings as a cause of your problem.

 

[Anonymous]

I pulled one of the Jets and it appears to be a 110. Does anyone know if this is the stock size? And if so how big should i go for adding pods?

 

[Anonymous]

I pulled the pin that sets the float height and it is spring loaded and is about 3mm so float height is fine. What else could it be?

 

[Anonymous]

Astra625. Let me jump in here. You have no pin that adjust float height. There is a small metal pin about 3/4" long that the float pivots on. Don't remove it. First of all, you should probably buy a shop manual for your bike which explains some of these procedures but the FIRST step in any carb tuning is to get the amount of fuel in the bowl the proper amount. If you have too little, the bike will starve for fuel and exhibit symptoms of running lean. If you have too much, then it will behave as if it were rich and possibly drool gas out the overflow. You must get the the "Service Fuel Level" correct. The float is suspended by pin and has a "tang" which is a small metal patch that contacts a float needle. You adjust the amount of gas in the bowl by bending this tang. To determine what amount of bend is needed, if any, the carburetors MUST be level. You can put the carbs on your bench in a vise or do them on the bike by putting the bike on centerstand and putting a board under your front tire. Once level, connect a gas hose to the drain nipple on your float bowl. Turn the gas on and open the drain screw. I suggest you should hold the clear hose next to a carb body (doesn't matter which) at the line where your bowl gasket lives... between the carb body and bowl. Gas will fill the hose to the level it exists inside the bowl being checked. DO NOT move the hose upwards as this will give a false reading and if there are bubbles in the line, gently tap them out as this will also give a false reading. The gas in the hose should be 1/8" below the gasket line. If it is HIGHER, then bend the tang on your float upwards just a tad and if it is LOWER, bend it down a tad. It doesn't take much to make this adjustment.

Once you have the Service Fuel Level correct, note that there are screws that adjust the opening of the throttle butterflies. These are NOT the mixture screws. Adjust the mixture screws by turning these closed (tighten) till they gently seat and then turn them two turns out. These affect the air/fuel mixture at idle only and don't usually need any tinkering. In any case, put the hose ends of your sync (manometer) tool onto the vacuum ports. Warm your engine and adjust the screws between the carburetors used for adjusting the butterfly opening. Usually, there are arms that join the carbs with springs in them and the screws will sit in these. The bike should be warm and you will essentially adjust these screws so that the mercury in each tube is level. This indicates the butterflies are opened the same and allowing the same amount of vacuum through the carburetor venturis.

At this point, you can adjust the pilot mixture screws. To do this, you let the bike idle and adjust the #1 screw in and out just a tad to maximize the bike's idle. Get the bike idling as fast as it can, then turn the idle back down using your throttle stop idle screw. Repeat for carbs 2, 3 and 4.

That is about all the tuning you will need to do and as I mentioned, it is all laid out in a shop manual (or Haynes /Clymer). Good luck.

 

[Anonymous]

Ok I tore the carbs apart last night to discover what I believe is the source of my problems. The main jets were loose? all but one. The reason they are loose is that the threading was so corroded that when I tried to tighten one all the way it fell apart. So I ordered new jets and they are on the way, hopefully the stock size will work with my new pods form cycle recycle. If not then o well 16 more bucks for new jets?damn it. My question is why the #%#@ do they make these things out of brass? Why not steal or something at least a little stronger?