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GS850 wont run without choke on

  • Thread starter Thread starter dbarnes42
  • Start date Start date
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dbarnes42

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I have a 79 GS850. Oringinall the #3 exhaust was not getting hot. After a lot of work on the carbs, it is finally getting hot. But now, it won't run unless the chock is on. If I turn the chike off, it dies. I have the needls set in the second position from the top. The air screws are all in different positions. The fule screws are about 1/2 turn out. The bike seems like it is running really lean and I can;t figure out how to richen it up. The bike has new intake boots and boots to the airbox.
 
I'm no pro, but my guess is that your carbs are the only source of your problem. If the bike is running, that meens the electiclal and mechanical are ok. I don't know if this is possible with your bike but, a while ago, I put back together my carbs with the floaters up side down. The needles where not working right and this resulted in constant starving of the motor. Just brain storming here... Good luck!;)


dbarnes42 said:
I have a 79 GS850. Oringinall the #3 exhaust was not getting hot. After a lot of work on the carbs, it is finally getting hot. But now, it won't run unless the chock is on. If I turn the chike off, it dies. I have the needls set in the second position from the top. The air screws are all in different positions. The fule screws are about 1/2 turn out. The bike seems like it is running really lean and I can;t figure out how to richen it up. The bike has new intake boots and boots to the airbox.
Click to expand...
 
when you did alot of work on the carbs, did you clean the pilot circuits? they are probably under some aluminum plugs on the front of the carbs if you haven't done them. i had a similar problem and it turned out to be a combo of dirty pilot circuit and leaky o-rings between the carb boot and head.
 
seuadr said:
when you did alot of work on the carbs, did you clean the pilot circuits? they are probably under some aluminum plugs on the front of the carbs if you haven't done them.
Click to expand...
Seuadr, his '79 bike would have VM carbs. VM carbs don't have the aluminum plugs. They do have separate pilot fuel and pilot air screws.


dbarnes, you are going to have to elaborate a bit on "a lot of work on the carbs". What all did you do? Apparently you still have problems with carburation, so you will likely have to do some more work, but this time, follow a plan. There is a guide on how to clean your VM carbs found in the Garage section of this forum, you can find it by clicking here. The basics involve getting a can of Berryman's carb dip and some o-rings. You can find the dip in most auto parts stores for about $25. Contact Robert Barr, a member of this forum, at cycleorings.com . He can provide you with a set of o-rings to replace all the rubber parts inside your carbs that are undoubtedly hard, brittle, and likely damaged. Also recommended are the intake tube o-rings and the stainless steel hardware for the intake tubes. Get the dip and order the o-rings as soon as possible, you can be dipping the carbs while you are waiting for the o-rings to get there,but it does not take long, he ships quickly. Your total expenditure will be about $50 for the dip and o-rings, but your carbs will run better than new when you get them back together.

.
 
Edit: Steve posted while I was typing. Do what he says.:)

The 1979 850 has VM carbs - this type of carb has a Pilot fuel screw on the bottom, and the Pilot Air Screw on the side of the carb. Starting position 3/4 open on the fuel screw and 1.5 on the air screw.

Hate to say it but unless you took the carbs all the way apart and soaked all the parts in carb dip the carbs are not clean yet. Cycleorings.com sells O-ring kits for both the carbs and the intake pipe boots. Replacing these are mandatory.

Another thing to check is spark on each plug. '79 GS bikes have points which need to be clean and properly set, also the plug caps can wear.

I suggest verifying all these basic things before worrying about why the bike doesn't run right.
 
Steve said:
Seuadr, his '79 bike would have VM carbs. VM carbs don't have the aluminum plugs. They do have separate pilot fuel and pilot air screws.
Click to expand...
i uh.. knew that.. i was, you know, testing you guys :-\\\ :lol:

nah i had a brain fart reading and didn't even connect the date with style of carbs :) thanks for correcting me :)
 
Ok, here is what is going on now. When i took the carbs off, I did soak them in Berryman's for about 45 minutes and i followed the instructions for the VM carb rebuild. I then took air and blew everything out. After that, I used very fine wire and ran it through each passage I could find. I have new intake boots as well as o rings for them. I assembled the carbs carefully, setting the float height, setting the air screw at 1.5 turns out and the fuel screw at 1 turn out. The bike would run, but as soon as the chock was turned off it would die. I finally gave up on it last night and then this morning I tried again. It started with the chock and then about 30 seconds later I turned off the chock. It seemed to run ok, but it did have some popping in the carbs and backfire through the pipe at about 3500 - 4000 rpm.
 
Did you vacuum sync the carbs? Until you do, you don't know where you are at.
 
I did a bench synch on them after they were rebuilt and I did a vacum synch on them this morning. All of them were fairly close after the bench synch so it didn;t take much to get them all lined up.
 
Check the boots on both sides of the carbs and if you do not know when the o-rings between the engine and carb boots were last replaced, replace them now.

But before you do that check that your airbox is propertly sealed both around the entrance doors and between the filter itself and the top of the box. Don't be afraid to use weatherstripping every place a seal or gasket is missing or looks like it could be letting air pass.

My bet would be on air leak.

P.S. I just reread and saw where you have new carb boots. Did you replace the o-rings at the same time? Have you checked the airbox sealing?
 
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popping and backfiring sounds lean to me, might try ajusting the idle screws richer a half turn at a time.
 
i had similar problems. My issue was the fuel petcock. Put it on pri and start it up with choke on. Once it warms up turn choke off and keep the petcock on pri and see what it does. I tried all of the aforementioned advice and stubbled across the petcock. Nice easy fix.
 
I think at least part of the problem is the 45-minute dip. Depending on how bad they were to start with (and if you don't know the history, just assume the worst), I would prefer to dip each carb body overnight, not just for 45 minutes.

.
 
Here is an update. I was finally able to get the bike to run, without the choke on. But not very well. The rpm's would go up to about 3k and then down to idle. I am guessing this means I have an air leak somewhere. I did replace the intake boot o rings when I replaced the boots. I was able to get the bike to idle (very rough) and the idle adjustment screw was all the way in to keep it running. I tried to adjust the air screws and this seemed to have no affect. Every once in a while, I could turn one of the air screws and the rpm's would climb to 3k and then the bike would die. Once I was able to get all of the air screws adjusted and attmepted to give the bike some throttle. It would bog down really bad and then die. I also left the petcock on pri and plugged the vacum hose. This really didn't make a difference either. I am really at a loss of what to do!
 
At this point, we need a bit more information:

1. You replaced the intake boots, did you replace the O rings between the boots and the head?
2. Is your airbox attached and does it have a filter in it?
3. Did you adjust your valves?
4. Are you getting adequate flow from the petcock when you turn it to prime?
5. Did you put new O rings in the carbs?
6. Does your bike have a header or pods?

In the meantime, try this cheap fix. Remove the gas tank and drain the gas from the carbs. Replace the drain plugs and pour (or Spray) Seafoam or some carb cleaner down the gas line until it fills the carbs up. Leave it like that for a day. Drain the cleaner out (you can put it back in your gas tank), put the drain plugs back in and try to start it again. If it's better, but not good, the carbs need a longer cleaning. The take apart and dip each one for a day and reassemble with new O rings cleaning you'll find in the Carb Cleaning pages.

Remember, those carbs are 30 years old and probably have never been cleaned.
 
I did replace the intake boots and the orings, the airbox is attached with a new filter and boots on it, the valves have been adjusted, I did put new o rings in the carbs and it has a stock exhaust. The fuel flow from the petcock is good if it is on prime. But I attached a hose to the vacum side of the petcock and sucked on it and the flow was not so good. Could it really be something as simple as the petcock?
 
id drain the tank, take the petcock off and take it apart and give it a good once over, it could be something as simple as the vacum o ring sticking. If it turns ot to be something with the petcock you can get replacement seals and o rings easily enough.
 
dbarnes42 said:
Could it really be something as simple as the petcock?
Click to expand...

Yep - start by draining the tank, then removing the screws on the face of the petcock. Pull the lever out and see if there's crud back there.

If it's pretty clean, pull the petcock from the tank and check the filter screen for crud.

If it's crudded up, apply carb clean as needed. You'll probably want to replace the O ring and disc after you've pulled it apart, but you can always do that later.

Don't take the diaphragm apart.

If it's clean at both places, buy a new petcock. Rebuilding has a low success rate, including mine, so why toss $20+ bucks to get a failure when a new one is about $50?
 
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