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HELP! New 1979 GS850GN owner - bike won't draw fuel

  • Thread starter Thread starter Bigko
  • Start date Start date
B

Bigko

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Hello all I am rebuilding a 79 GS850GN with my son forhis first bike. We have hit 2 problems that we can't seem to get around and I'm hoping you can help. The first is a fuel issue. The bike was purchased non running with the carbs off the bike and an assurance they were just rebuilt by a local shop. After making other repairs (non motor) we put the carbs on and tried to fire it up. All the bowls have fuel but only one cylinder will fire (far right #1 I think). The others will light immediately if you spritz them with carb cleaner but will not draw enough fuel on their own to light the cylinder. We can get the bike to run for a minute or two on one cylinder with the choke on but nothing else. I have taken the cabs off twice and disassembled everything under the bowls and blew carb cleaner and compressed air through. Everything seems open but same result in only running on 1 cylinder. The vacuum line is correctly connected to the petcock and we rebuilt the petcock. We also purchased new intake boots. Carbs are the VM26SS original carbs. Any ideas?

The he second issue is with the starter. We can kick start the bike and is has spark on all cylinders. If we use the starter, there is no spark while the starter is running, but the moment I let go of the starter button there is a quick spark. We purchased a new starter button assembly and it has the same issue. Any ideas?
 
First of all,
sgreeting_welcome_sign_general_100-106.gif


Next, #1 is on the LEFT, as you sit on the bike.
#1 is under your clutch hand, #4 is under your throttle hand.
Any time reference is made to "left", "right", "front" or "back", it's as if you are sitting on the bike, ready to ride.

Fuel issue: a local shop might have "rebuilt" them, but that does not mean they were done correctly, so you will have to check them yourself.
There is a possibllity that the passages between the jets (inside the carbs) might be plugged.
The pilot jets might be plugged.
The pilot screws might be mis-adjusted.
The float levels might be off.
The carbs probably need to be synchronized.

Electrical issue: You have a volt meter? Use it. Check the voltage at the battery:
1. before you turn the key ON
2. key ON, before you press the starter
3. while pressing the starter

Let us know what you find, we can make some more guesses.

.
 
As Steve mentioned above your best bet will be to re-clean the carburetors properly. Every PO "says" a shop cleaned them when they really meant carb spray was thrown in their general direction. I suggest going to our master file storage keeper's website, http://members.dslextreme.com/users/bikecliff, where you'll find several useful documents for you. Download the carb rebuilding tutorial from Nessism and follow it to the letter.
 
Also, a note on the carbs. If you screw in the needles to count the rotations till bottom, use very, very slight pressure or the tips will break off. There are two tutorials on carbs (maybe more) finding the one for VMs was harder when I did mine, but it is there. Also would suggest replacing the o-rings on the fuel rail if not done.
 
So, thanks to the electrical section of this site the starter issue is solved. Somehow when making some other repairs we managed to switch the negative starter lead and the negative battery lead. It is working fine now and sparking as it should... Next is the carb issue...
 
twotimeGSr said:
Also, a note on the carbs. If you screw in the needles to count the rotations till bottom, use very, very slight pressure or the tips will break off. There are two tutorials on carbs (maybe more) finding the one for VMs was harder when I did mine, but it is there. Also would suggest replacing the o-rings on the fuel rail if not done.
Click to expand...
Do you have a photo or more info on the o-rings? I'm not sure what you are referring to. Thanks
 
There's O rings in the carbs, between the carb boots and head and maybe on the fuel connections between the carbs. Some, like mine, have plastic connectors for the fuel rails that don't use O rings.

Just follow the carb tutorial and post up some pics if you run into trouble.

Also, don't believe anything the seller told you. You wouldn't be here if everything was perfect. Also, check the Top 10 Newbie mistakes and use that as your guide to getting the bike road worthy
 
Quick update... Ordering o-rings

Quick update... Ordering o-rings

gsrick said:
Order all new orings from Robert Barr. It's a lot cheaper than getting kits off eBay. He also has replacement screws. http://cycleorings.com/
Click to expand...

I have soaked, used carb cleaner through all holes and have blown out with carbs with compressed air. While doing so I saw that the o-rings in the carbs were very brittle and actually broke when I tried to remove some. I am convinced the carbs are whistle clean and will just need to wait for the o-rings to arrive from Robert Barr. I will post an update when I get them back together and on the bike.
 
Did you remove the pilot jets from the carbs and hold them up to the light to make sure the orifice is open?

Check the pilot fuel screws to assure there are no broken tips in the carb bodies?

Check the Newbie Mistakes thread linked in my signature to be sure you don't overlook anything.
 
best to start with a valve adjustment or at least a compression test to verify the health of your cylinders
 
Yes, all 4 carbs were completely disassembled and checked/cleaned. Jets are all open and unrestricted.
 
Problem identified! And continued issue

Problem identified! And continued issue

Hello all, quick update on my carb rebuild... Issue found! As I began to reassemble the carbs, I inspected the slides and linkage to them. I realized that the shop that "supposedly" rebuilt them assembled them incorrectly. Instead of having the spring piece below the linkage, the linkage was on the bottom with the spring above it. In this condition the carbs could not be synched and the throttle was not opening or closing properly. After reassembling correctly, the bike started rit up. I still have an issue with it however that I'm hoping you can help with... It seems to run well at low RPM all the way through the gears but if the throttle is opened more than 1/4 way, it chokes like it is starving for fuel. I have stock main jets, the air jets are at 2 turns and the mixture screw is at 1 turn. Also, I do not have the airborne on the bike, I have K&N individual carb filters. My plan is to turn the air screws back in to 1 turn and "tune" them as per the directions... Then maybe open the mixture screw another 1/4 to 1/2 turn. Any thoughts or opinions on that approach?
 
The above should read "I do not have the stock air box" not airborne...
 
If you are running pods, you will most likely need to adjust your jet needles and go up in main jet size. It varies by bike and location, so finding just the right adjustments and jet sizes can be a pain. But good luck!
 
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