Spark plugs are black

[christopher]

Have a gas/air skrew question

My Haynes manual only specifies for the british suzuki release and not the american for the number of turns to back off the air skrew on the carbs. Does anyone know how many turns to back off the gas skrew and the air skrew for a 77 suzuki gs750? Im going to assume the air skrew is 1 and 1/4 turn from the bottom. Does anyone know how many turns to back off the gas skrew? Thanks for your help

[KEITH KRAUSE]

Black plugs can be caused by many things. Some common basic checks...
If you have a compression tester, is compression within specs?
Are you burning oil? Whitish smoke or black plugs the don't dry in the air means you're burning oil. This must be fixed before anything else.
Are the plugs NGK B8ES?
Are the plugs gapped approx' .027"?
Under dark conditions, and with a new plug, turn the crank and check spark color. Is it a decent bluish color or weaker and orange?
If weak/orange, then you need to verify battery voltage, check/clean all connections including the plug caps, clean points and adjust the dwell if you still have points, and check timing and ignition advance action. You also need to verify coil resistance at the primary side of coils and secondary side (plug cap to plug cap). Even if a good bluish spark is present at all cylinders, the above should be checked.
This is basic maintanance and should be done regardless of what you may think is the problem.
If all above are serviced correctly then you can go on to the intake/carbs.
Verify the filter is clean and the entire intake is in good condition, including the rubber boots (filter side) and the manifolds and their o-rings(engine side).
Check fuel tank venting to be sure it's clear.
Make sure both float bowl vent lines are 100% clear and routed without kinks.
If you can be sure any problem is the carbs, clean completely and install Robert Barrs inner o-ring kit, adjust floats to factory setting (about .95") but verify float needle valve/spring tension condition first. Any worn valve tips and/or sloppy springs must be replaced. Verify choke plungers seat well and the rubber tips are not allowing leakage.
Since it appears the pilot jet and main jet are stock, I'd GUESS the jet needles are at the factory position too but you should verify this. Also verify with a factory manual or trusted source that ALL jet needle assembly parts are present and in factory assembled order.
As for pilot fuel screw (underneath) and side air screw settings, try 3/4 turn out for the pilot fuel screws from LIGHTLY seated and 1 1/2 turns initially on the air screws.
You must then bench synch the carbs as best you can.
If all above is good, the bike should start and you can adjust the air screws using the highest rpm method.
Then you must vacuum tool synch.
To back up just a bit, if you have a 4-1 pipe as your only mod, and it flows better than stock, I'd try 5 to 7.5 larger on your mains. Leave the pilot jet and jet needle stock unless further testing says to richen them.
Lot of work I know, but basic maintanance. Do/check all the above and it will probably save time and frustration.

[Suzuki_Don]

Link To Carb Rebuild Series

Chris this is the link to the carb rebuild series for the VM type carby, the ones that are on your bike.

http://www.thegsresources.com/files/vm_carb_rebuild.pdf

Cheers
Don

[christopher]

Float valves

Ok, thanks for the advice. There is alot of work to do. I believe all my questions have been answered but one was raised with the last post. I have four float valves and only one is brand new. It has more resistance than the other 3 when pushed in by hand because its new. Should i replace the other 3 since there is not as much resistance as the new one? There is spring action there, just not as much resistance. And thanks again for all ya's help.

[KEITH KRAUSE]

Ok, thanks for the advice. There is alot of work to do. I believe all my questions have been answered but one was raised with the last post. I have four float valves and only one is brand new. It has more resistance than the other 3 when pushed in by hand because its new. Should i replace the other 3 since there is not as much resistance as the new one? There is spring action there, just not as much resistance. And thanks again for all ya's help.

Hard to say without seeing them for myself.
Many replacement valves out there are made cheap and I've seen new bargain brand valves leak immediately. I don't know if yours are original or how many miles on them. The best quality factory valves are a good $35/40 each I believe.
First test for any valve is the leak test. If you know for a fact the float level/float assembly action is correct and the valve seat washer (fiber or metal) is good or the valve seat o-ring is good, and that carb still overflows even a little after shut off, then the valve is bad. The valve tip can also groove too deeply and it will need replacing. A slight groove is normal.
If that carb doesn't show any signs of leaking...
As for the spring, in my opinion, if the spring has tension along its entire length then it's probably OK. But if you can gently push it in 1/2 way (no more or you can damage it), gently release it, and then pull up some slack, then it's sagged and needs replacing. The spring would never be fully compressed during its normal life so I'd never push it all the way in, even just playing with it.
Springs can have no sag but still be too weak. Even normal riding/vibration can result in the valve sealing poorly and the bowl level will be higher than intended. A weak spring will allow some leaking.
A sticking/leaking valve may be from a small burr and that can sometimes be gently filed off.
In short, if there are no leaks while off or during riding, you're probably good. But the valves can be hard to determine sometimes, especially for adequate spring strength. Best thing you can do is make a fuel level checker out of an extra bowl drain bolt and some clear tubing. Start the bike, let it idle, and place the tester against the rear 1/3 of each bowl as indicated in the factory manual and see if the level is within that specified range.

[KEITH KRAUSE]

One other thing, though it may not matter in your case due to unknown history of the carbs, don't mix parts, especially the float valves and their respective seat. They wear as a unit and mixing them up can create leaks.

[christopher]

Carbs and leaks

Keith Krause, thanks for the reply. I have a starting point now to begin testing what could be wrong with my bike. It does start right up now where as before it took like 10 tries with the electric start then surged. In your previous post you mentioned , if my bike leaks while NOT running. It has started leaking gas down the front of the engine down the left side, which is the side of the kickstand, and the side my bike is leaning on. Gas moisture is on the front left side by the exhaust pipes and a small puddle on the ground. Pretty much to get it to stop i have to take my gas tank completely off and unattached the gas line. Do you know what could be causing the gas to leak out of the side of my engine? It didnt do that before i started working on my bike?
I did have a small block of wood braced under my carbs while it sat in the garage because gas was leaking into the airfilter box while the bike was off. My airfilter box is in the bike and attached to the intake, but i didnt have the airbox skrewed into its brackets, and therefore the weight of the airbox on the intake was causing my carbs to angle down leaning towards my airfilter box. And i thought this was causing gas to leak into my airbox, so i put a block of wood under my carbs and now the gas is leaking out the front. Even when everything is level it still seems to leak into the airfilter box. Has this ever happened to anyone before? It is smelling up my whole garage and part of my house. This is a minor problem but still an annoyance. Thanks for suggestions.

[tkent02]

Did you leave the petcock in the prime position?
If not does it shut off the flow of fuel when the engine is not running as it should?
Most old petcocks leak, test it and replace it if it fails.
The petcock and the float valves should both be able to stop the flow of fuel, so even with a failed petcock you shouldn't get fuel overflowing unless one or more float valves are weak.

Check also to see if you are getting gasoline added into your engine oil, leaked fuel usually ends up in the oil.

You never really said how well it runs....

Are new plugs turning black, or is it just that the old black plugs are not getting themselves clean?

Are you riding it enough to get the plugs good and hot?

Information is a good thing...

[christopher]

prime position

No, i dont leave it on the prime position when it is just sitting in the garage. Should I ? I either leave it on the "on" position or the reserve position. I thought it didnt matter cuz my bike always was left in the on position without leaks. My bike runs good and sometimes backfires when its warming up but not near as much as it did before. And i usually put new plugs in because they turn so black. But honestly, at this point, my plugs are black but my bike hasnt bogged out yet. Still waiting for that. I put hotter plugs in. Normally i use ngk B8ES and this time i used NGK B7ES because i was told it would burn hotter. So should i leave my petcock in the prime position when parked? A friend told me it shouldnt matter. But he's new to bikes too. THanks for your help.

[tkent02]

No, i dont leave it on the prime position when it is just sitting in the garage. Should I ? I either leave it on the "on" position or the reserve position. I thought it didnt matter cuz my bike always was left in the on position without leaks. My bike runs good and sometimes backfires when its warming up but not near as much as it did before. And i usually put new plugs in because they turn so black. But honestly, at this point, my plugs are black but my bike hasnt bogged out yet. Still waiting for that. I put hotter plugs in. Normally i use ngk B8ES and this time i used NGK B7ES because i was told it would burn hotter. So should i leave my petcock in the prime position when parked? A friend told me it shouldnt matter. But he's new to bikes too. THanks for your help.

Do NOT leave it in the prime position.

[KEITH KRAUSE]

Sounds like you have at least one float valve leaking. This assumes the floats are operating correctly and are adjusted correctly.
Sometimes parking at an angle (sidestand) aggravates a float valve problem. Parking on the centerstand sometimes minimizes the leaking but it's no cure.
Sounds like you have some work to do.
If you can locate a compression tester, check compression because it's quick and simple. If it passes, try to do the electrical tests. Once you know the electrical is allright, then focus on the carbs.