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gs750 carbs are killin me

  • Thread starter Thread starter liftedresarch
  • Start date Start date
L

liftedresarch

Guest
Hello,

Im brand new to this forum, and motorcycles in general. I just bought a 78 gs750, she ran pretty well, but what do i know. So i was trying to learn about the carbs and like an idiot, i pulled them and proceeded to"learn" by taking them apart and cleaning them. Now i have them back in and she wont start. I have no idea what i did wrong. Thank you in advance
 
didja follow the tutorial at all?
are the plugs dry?
any kick at all when you crank?
 
What Jeeprusty is trying to say is go to http://members.dslextreme.com/users/bikecliff and read up on the carb rebuilding tutorial. Make sure you follow those instructions about putting them back together.

Also, what kind of condition is the electrical system in? What are the readings when you turn the ignition switch on and while you are pushing the start button? Is the Run/Kill switch in the run position? Did you bench sync the carbs before you put them back in? How many turns out are the idle mixture screws?
 
I havent used the manual because i didn't think i would change anything, i was obviously incorrect. I looked at the manual from the link, there is a picture of the float bowls and 4 screws, in a caption next to it said to not disturbing these screws, or something to that affect. Well i did mess with screws, is there a certain number of rotations that has to be screwed in/out?
 
did you Prime the carbs before trying to start the bike?

Turn those 4 screws in gently, then turn out about 5/8 of a turn

You're learning the wrong way. Read 1st, practice 2nd
 
liftedresarch said:
Hello,

Im brand new to this forum, and motorcycles in general. I just bought a 78 gs750, she ran pretty well, but what do i know. So i was trying to learn about the carbs and like an idiot, i pulled them and proceeded to"learn" by taking them apart and cleaning them. Now i have them back in and she wont start. I have no idea what i did wrong. Thank you in advance
Click to expand...

Well we have no idea either, we can't very well help if we have no idea what you did, see where I'm going. Love to help but when you just tear a rack apart and put it back together without a manual or any knowledge of how a rack goes back together, well that just spells trouble. I hope you at least understand the function of a carb. Once I learned how they worked it made better sense on how they function and in what way they should be put back together. Follow a guide and put it back together correctly. We can be more helpful and be able to trouble shoot allot better if your putting the carbs back together correctly.

I will state that if something isn't broken don't fix it especially don't blindly fix it.

Your better off reading the guide and starting from scratch...

Good luck, unless you can give us more info we really can't give you that golden answer of; your bike doesn't run because...

Welcome to the site... Good luck.

Where is your location? we have member's all over the place that might be able to help out.

Oh some Carb 101, I know your bike doesn't have a diaphragm but you'll get an idea.
 
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Thank you all for the quick responses, so all i did was remove the carbs, unscrew the bowls, take off the floats, unscrew and spray all jets, and unscrewed what i believe is the gas screw for the pilot circuit, and thats about it. i also messed with the idle screw a bit, but i feel like a bit of an impulsive idiot
 
Slow down and dont get fklustered.

Here are the links that youll need for the bike and carbs. You have VM26 carbs,

http://members.dslextreme.com/users/bikecliff/images/vm_carb_rebuild.pdf

http://www.mtsac.edu/~cliff/storage/gs/GS750_Service_Manual_early8valve.pdf

IF you break a pilot screw....http://members.dslextreme.com/users/cbsaunders/gs/pilot_screw_removal.pdf

Jetting chart...http://members.dslextreme.com/users/bikecliff/images/carbspec_float_height.html#A01

Pilot Screw ( bottom ones ) if you find a broken tip..http://www.siriusconinc.com/pro-detail.php?pid=&product_id=4245

Fuel tee and crossovers in case you have the junk plastic or rubber coated type, get the metal oring style..

http://www.siriusconinc.com/pro-detail.php?pid=&product_id=2737
http://www.siriusconinc.com/pro-detail.php?pid=&product_id=2742

Carb bowl and top gaskets..

http://www.siriusconinc.com/pro-detail.php?pid=&product_id=2767
http://www.siriusconinc.com/pro-detail.php?pid=&product_id=2769

And finally, the carb oring kit from our own member here Robert Barr. Note that the intake manifolds ( carb holders ) have an oring in them that needs replaced also. Measure the INSIDE diameter of yours and order them accordingly from page 3. ONE KIT will do all 4 carbs and fuel tubes..of course get the VM kit.

http://cycleorings.com/
 
Nice work on chuck's part. Tons of great info to get you started.

Owning a 40 year old motorcycle is (I'm told) a lot like a wooden boat. There is always some maintenance tasks to perform. Cleaning the carbs is just the beginning. If you are kicking yourself for tampering with the bike you best just sell it now and let someone that isn't so timid perform the upkeep. You have tons more to do like perform a valve adjustment, clean the braking system, check the charging system, etc. Unless you have lots of money to pay a mechanic, you bet get mentally ready for more work ahead.
 
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Dammm Chuck. Some of those links I've never seen before. If I has seen that carb matrix it could have saved me a lot of trouble over the last few years.
That chart should be a sticky at the top of this forum. The current sticky on collecting carb specs is a little difficult to sort through.

Thanks for the post.
 
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The chart is posted in Bikecliffs website. On the home page there are links on the left side. the CARB SPECS thing is the one to select,

Head over to Bikecliffs and check out the many links just below the manuals menu board.
 
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I've been all over Bikecliff's site in the past few years and somehow missed that link. Glad you posted it. It's now in my favorites listing. Still think it should be a sticky on this site as it provides a quick reference to the answer to questions I see posted all the time.
 
And another VERY IMPORTANT fact to remember is that as the EPA crap came into being, they changed jetting on the 750s a few times. This chart shows that era of chaos and notes that the jetting is subject to CERTAIN ENGINE NUMBERS as well. Check down on the flat spot on top of the tranny on the right side to see what your engine number is and compare to the chart below.

NOTE >>> The chart shows the MIXTURE SCREWS ( side ones ) settings. Pilots ( bottom ones ) are set at 3/4 to 7/8 out.

carbs.jpg
 
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Thank you again for the responses. When you say "turn in gently" how gently are we talking? And im in the san fernando valley just north of Los Angeles
 
Like hold the screw driver with your thumb and finger.....gently turn them in till they stop...DO NOT force or torque them down. Then count out 3/4 to 7/8 for the bottom ones and 2 out for the side ones. These are starting points and you do the fine tuning of the fuel to air mixture with the side ones. Leave the bottom ones alone once set.
 
So i turned all the screws out to what was recommended, and still, nothing. Im not sure what else it could be.
 
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