I need help!

[tucker8541]

Long story short!!!

Please excuse my spelling, been up for two days working on the issue...
I have a 1977 gs750 with no baffles and air pods (Don't judge!)

The original carbs got ****ed up! Not my fault, to long of a story! If you want to hear it call me after hours when at the bar!

So I have a set of 1979 GS1000 carbs on my GS750 (They fit). I have the bike running, Idle is a little off not the real issue, will get them synced. Running a little lean, will work on it. The real thing I am having issue's with right now is:

*The bike will run great for the first mile or two then will slowly stall. Seams like it is running out of gas during high rpm riding or in 3rd or fourth gear. While driving, the bike seams to hit a wall (Almost like the clutch got pulled in) around 4400rpms then seams to catch up. The bike stall when I slow down for a light, it will restart after 5-10 mins on own. I don't think it is a battery or coil. Please help!

**Possible reasons I can think off and what I will do next is: (Any other things you can think of)?

-The gs1000 carbs don't appear to have a vacuum from one of the carbs to go into the second small valve on the petcock? Any clues? So running the bike on "pri" without the other lines (Overflow hoses or terbulance) connected. Will I have to modify petcock to run free flow?

-May have a Little gas in oil, I may of floaded the carbs while trying to get it running after carb cleaning/jetting. Will do another oil and filter change.

-Will re-check plug gap, may bring in to allow a richer run?

-Timing?

-Re-check gas tank and petcock to ensure are good and free off rust?

-Check to make sure the fuel line is not collasping while riding?

-Check manifold boots for leaks?

-Re-check float bowl hieght?

-Battery seems ok, may just get a new one just to be safe!

Please feel free to call me because i will not be in front of a computer to check this forum. I will be in the garage in another marathon attempt to get the bike right! Tucker 630-272-854 one. I live in River Grove, IL. if you want to share my pain...

 

[tucker8541]

No oone wants to touch this one huh!? I will see what it looks like after I try some of those things tomorrow.

 

[hampshirehog]

Probably your tank not letting air in and you are getting a vacuum. Try running without the tank cap on and see what happens.

Plus I don't understand that you are not getting a suck on your carb vac hose. If you have the hose connected to the right brass nipple, the one forward of the slide on, I think it's #3 (I can't remember - it's the only one forward of the slide though) then you must have a vacuum.

 

[Guest]

Sounds like a petcock problem

 

[omaharj]

Do you have an inline fuel filter?

 

[tucker8541]

I have a inline filter and the bike ran with the original carbs and without the mods.

Currently I do not have a second hose running to the petcock. I know the petcock is a vacuum type and that is why I was running the petcock on prime. But I can not locate which nipple to run one from. My original carbs had four brass nipples, one for the main gas, one between the 2nd and 3rd carb for the vent on the petcock and the others were vent hoses that ran above the carb filter not attached to anything.

I guess my next question is, where is the brass nipple on the gs1000 carbs that runs to the second nipple or vacuum on the petcock? The gs1000 carbs appears to only have 2 nipples that are used as vents? Or do they? Can I attach one of the vents to the petcock? Should I see if one of them sucks, literially? Is there a hidden vacuum nipple on the carb that goes to the second vacuum nipple on the petcock?

 

[landshark]

If they are from a 79, they probably arent vacuum carbs. Are they round on top?

 

[TheCafeKid]

Ugh..
Pods and modified exhaust system. And you haven't re-jet them have you.

For starters, if you haven't re-jet, you're not a little lean. You're WAY lean. In all honesty the bike may very well be over-heating and that could be the reason it craps out on you. You need to understand that these are NOT cars. They will not tolerate the amount of monkey-Ing around you can get away with on an old car.
Pods introduce a much larger amount of air than the stock airbox did. Therefore the fuel flow capability must be increased to compensate. The window of the perfect air/fuel mix is relatively small and with the pods and modified exhaust you've skewed that way toward the lean side. At that point what mix that will burn will burn extremely hot. This isn't good for many reasons. You can do serious costly damage to your valves, pistons, etc.
So before you do ANYTHING else, I'd suggest a re-jet of the carburetors. This is of course assuming that you've disassembled and cleaned/dipped them, and installed new orings. You also need to replace the carb boot orings. The boots are the rubber things the carbs get clamped into on the motor. Behind those boots are orings that seal the boot to the engine head. They dry out and rot after many years and theyll no longer seal as they should and this will allow the engine to suck more air around them which will further the mixture problems.

Once you've assured you've taken care of this, you can move on to rejetting the carbs for your pods and exhaust. I don't know what the GS1000 used from the factory for jets, but I seem to recall them actually being smaller than what the 750 used (they're the same carbs actually, just jetted differently) so you've not helped your situation by using those even though in your mind it might have made more sense since the gs1000 was obviously a larger motor.

For your setup, I'd suggest purchasing mains in a range of sizes, as we can only really get you in the ballpark without being there. Someplace between 117.5, 120 and 122.5 is likely where you're going to end up for mains. The jets aren't super expensive so get em all if you can. What you don't use, perhaps someone here, maybe even me might buy

Stick with the stock pilot size for now. You should be ok there. The needle clip will need to be moved as well, probably two slots down from stock as a guesstimate.

Set your air screw at 1.5-2.0 turns out, and your fuel screw to 7/8-1 turn out from lightly seated.

Of course...you could put the airbox back on and find some stock pipes if this sounds like too much

It's not easy, and taking shortcuts will end up frustrating long cuts..so don't do that. But if you do it right and pay attention to the details, it wi pay off with a good running, fun bike in the end.

 

[76Mike82]

Just something to think about also, the prime setting on your petcock is a much smaller hole for the fuel to flow meaning at high rpm your going to take more fuel then the petcock can deliver.

Good luck.

 

[Big T]

Tucker

The 79 1000 uses the same carbs as the 750, but on a different mount and a different idle screw set up

So, the #3 carb should have a vacuum nipple, just like the 750 carb

How about a picture of your new carbs?

 

[tucker8541]

I re-jetted the carbs and are basically synced, idles and rides until it runs out of gas. So this is what I have come up with.

I ran the bike with one of the vent tubes connected to the 2nd petcock nipple, then tried the other no luck. These GS1000 carbs do not have a vacuum vent to run to a petcock. They look just like my stock GS750 carbs minus the vent port. So I have kinda 4 choices here:

1-Buy a free flowing Petcock. Kinda pricy and heard they leak
2-Modify my petcock to become a free flow (Heard they are trouble if you do this!)
3-Make a vent port for these carbs! Gonna be rough!
4-Fix my old carbs and start the re-jet over again.

My old carbs have a bad needle in one carbs (No Biggie) and a fk'ed up Throttle Valve. Anyone know where I can find one? They are hard to come bye, anyone willing to part with one? I will buy you a beer!

 

[7981GS]

Perhaps you have the 29mm smoothbore carbs on it. Can you post pic's of the carbs? Does the drain plug take a 17mm socket?
You would need to run a tube in one of the intake manifold sync. ports to the petcock for it to work (BTDT)
or run it on prime and remember to point it down to off (run position) when you are not riding it.

 

[tucker8541]

Didn't think to try to run a tube in one of the intake manifold sync. ports to the petcock. Will this work? Does it matter which one? Wouldn't think it would. Don't have a picture of the GS1000 carb on hand, still at the shop.

 

[7981GS]

Didn't think to try to run a tube in one of the intake manifold sync. ports to the petcock. Will this work? Does it matter which one? Wouldn't think it would. Don't have a picture of the GS1000 carb on hand, still at the shop.

Yes.
The outside left is the easiest to use. The second carb if you don't want the tube to show.

Eric

 

[tucker8541]

Will try that, looking for a throttle valve slide for my bike is been pretty dam tough. Emailed 8 places so far.

 

[7981GS]

It is dark out and the bike is dirty but, it has worked for 17+ years.

Eric

 

[TheCafeKid]

Will try that, looking for a throttle valve slide for my bike is been pretty dam tough. Emailed 8 places so far.

If you have 26s I may have a spare slide...

Is it possible that the carbs weren't put back together in the gangplank correctly??

 

[tucker8541]

I believe the carbs are VM26SS

 

[tucker8541]

Tapped into the manifold and ran a tube to the petcock and it worked! Very gratefull 7981GS! Works and runs great! But, I have a small problem though. After I shut down the bike and let it sit for a little bit, the #3 carb starts to drip some gas? I have tried to move the petcock lever to on/prime and even reserve. Yet it starts to leak a little? Does the bike need some time for the needle to seat or something? Leak is coming from the filter.

Cafe kid, if the throttle slide is for a VM26SS I would love to rebuild my stock carbs and get them in. I will throw you some cash or do a pimp deal. Let me know...

 

[7981GS]

I would say that both your petcock anf the float needle are leaking.
More likely than not, it is just the O-ring that goes around the seat assembly that is leaking there but, your petcock still needs to be replaced.

Eric