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New Guy Carb Issues

  • Thread starter Thread starter kdupont
  • Start date Start date
K

kdupont

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Hey guys, Im new to the forum as well to motorcycles as well. Bare with me as I have absolutely NO KNOWLEDGE of carburetors, however I am an auto tech student so I do understand basic mechanical function. I just bought a 79 GS 850. I believe its a "G" but im not sure of the different years and models. The kid I bought it from had recently removed the carbs and cleaned them and put them back on. At this point it runs but it leaks fuel like crazy. When he assembled it he used the old gaskets, I think its leaking from the float bowl gasket. I have ordered new gaskets at this time. I now have the carbs on the bench waiting for the new gaskets so I thought this would be a good time to adjust all the screws and such, but I have no clue on how to or even what I am dealing with. Any help would be much appreciated!!!
 
Go to Basscliffs website and there you will find the tutorials on the carbs, pictures and all. I am sure he will be around soon with his big mega welcome. I was able to do mine following the tutorials, from dismantling, to synching. I ended up purchasing a small sonic cleaner, well worth the investment. After having dipped them the previous year,I was amazed at how much more stuff came out in the sonic cleaner. You have a lot of studying to do but the time invested is well worth it. Robert Barr (on this site) has the o rings. Send him an e mail and his fee and you will have them in the mail in a few days.
 
go here: Basscliff's Website and you'll find the VM carb rebuild tutorial along with a ton of other information. That will give you a clear guide to how to rebuild your carbs.
 
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The 79 GS850 has VM carbs, so you'd want to follow the VM tutorial

You'll want to clean them properly with new O rings, because you should never trust that the PO actually cleaned them correctly

You'll find that pilot fuel screws (bottom) should be 3/4 -7/8 turn out and the pilot air screws (side) double that, if you have a stock airbox/exhaust

If not post up what you have for better answers

Auto tech? what are you going to plug the computer into? :)

You'll learn more about internal combustion here than at school

as for your leaking carbs, pinpoint where they're leaking from so you can properly address that issue
 
The only place I can find thats leaking is from the float bowl. I believe its just bad gaskets. When I removed the float bowls i had one gasket that was wet with gasoline. I believe thats my problem child. As far as adjusting scews, the only screws I see access to are the main jet, the pilot jet, and one screw that i believe is referred to as an air jet. Its on the left hand side of the venturi opening on the air box side.
 
kdupont said:
The only place I can find thats leaking is from the float bowl. I believe its just bad gaskets. When I removed the float bowls i had one gasket that was wet with gasoline. I believe thats my problem child.
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If your bowl gaskets are leaking, you have a couple other problems, they are just showing up at the gasket.
1. The inlet/float valve is not set correctly or is not working at all. The proper fuel level is a few millimeters below the gasket line, so the fuel is obviously too high.
2. If the fuel is that high, it should be going out the overflow tubes. They might be plugged.



kdupont said:
As far as adjusting scews, the only screws I see access to are the main jet, the pilot jet, and one screw that i believe is referred to as an air jet. Its on the left hand side of the venturi opening on the air box side.
Click to expand...
The main jet and pilot jets can be changed, but are not "adjustable". The pilot air jet is on the side of the intake, the pilot fuel jet is on the bottom, on the engine side of the float bowl.

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Alright so i need to adjust those two screws before i put it back on? Im gonna check the over flow tubes later. How would i adjust the float needles?
 
kdupont said:
Alright so i need to adjust those two screws before i put it back on? Im gonna check the over flow tubes later. How would i adjust the float needles?
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If the bike is basically stock, as in stock airbox and exhaust, you should check the pilot fuel screws (on the bottom of the carb, at the front edge of the float bowl) and turn them to about 7/8 turn out from lightly-seated. BE CAREFUL seating those screws, they are VERY fragile. If you tighten them too much, the tips will break off, requiring full disassembly of the carb.

As a general starting oint, the pilot air screws (the ones on the side of the carb, near the air inlet) will be set to double the fuel screw setting or 1 3/4 turns out from lightly-seated. After the bike is running and warmed up, you will adjust the air screws for the best idling mixture.

To adjust the float needles, you bend the tabs on the floats on which the needle rests. You set the height by holding the carb upside down and measuring from the edge where the bowl gaskets rests (gasket removed) to the top of the float. Specs call for 24.0 +/- 1.0mm. Ideally, you will also to a "wet check" by installing an adapter in the bowl drain screw which has a clear tube attached. You can then hold the tube next to the carb and see the actual fuel level.

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I adjusted the floats yestetday and now it runs without leaking. I believe its running a little rich but in not sure. Whats the best way to determine that? Its my understanding that its om to be a little rich than lean on an air cooled motor. Is this correct?
 
Ive had problems with adjusting the floats on several bikes, leaving them even a bit to high "to much fuel in the bowl" seems to leave it rich all over except when your on the main jet. Ive had better luck setting them so the fuel is at the lowest not the highest.
Just a thought.
 
I drove it today for the first time today. In 1-3 gear at low speeds it does fine but when i get into the throttle it stutters and back fires a bit. I can hear the exhaust on the right side but not on the left?
 
I sent my carbs off to a shop to go through them, he changed my jets from a 112.5 to a 107.5, also was missing the little rubber piece on top of the pilot jets, he added those to my carbs from another carb he had sitting around, he also cleaned everything up real good and adjusted the floats. I took the carbs home and put them back on the bike, and now it runs worse than it did.... before I could get up to about 45 before it started bogging down and now I cant even hit 25 before it bogs down. Any adjustments I can make to try to fix this? I still have the 112.5 jets that I can put back in if I need to. Any suggestions? I was thinking about adjusting the screws on the intake side of the carbs.
 
kdupont said:
I sent my carbs off to a shop to go through them, he changed my jets from a 112.5 to a 107.5, also was missing the little rubber piece on top of the pilot jets, ...
Click to expand...
The '79 850 came with 102.5 mains, I have not seen anything that says you need larger ones. Why the different jets.

Also, the VM carbs that came on '79 850s did not have rubber pieces on top of the pilot jets. The '80 850s (the early ones were made in '79) had BS-series carbs that had rubber pieces over the pilot jets, but they came with 115 main jets.

Please give us some pictures or some more details about your bike. We are getting conflicting information, and I am going to stop guessing until more details are provided.
icon_shrug.gif


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Big T said:
Auto tech? what are you going to plug the computer into? :)

You'll learn more about internal combustion here than at school
Click to expand...

You highly underestimate a modern day auto technician. Motor vehicles may be laced with wires and electronics up the wazoo but they're rock solid and majority of failures are still attributed to things of mechanical nature.

You have to be honest, this forum is filled with a bunch of DIY'ers trying to learn how to work on bikes with some success but we're still a bunch of amateurs making do. For one, my cousin, who is a trained and certified motorcycle tech didn't need to disassemble and clean the carbs or any of that "basic maintenance for a 30 yr old bike" before narrowing down and attacking specific problems - something I don't even think we try for, as if free time is endless and replacing parts and/or making them new until the problem goes away isn't tedious or costly. So yeah a schooled tech is far above our level, they don't and can't just replace or clean stuff until the problem goes away because someone has to pay for the time and parts.
 
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Im beginning to wonder if someone has swapped the carbs out on this bike. Ill get some numbers for you guys off of the carbs before I go any further.
 
I cant find any numbers on the carbs except on the butterfly valve which says 135. Other than that it just says Mikuni Corporation. The GS850103027.
 
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