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79 gs850 carb problems

  • Thread starter Thread starter dhayward312
  • Start date Start date
D

dhayward312

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So i'm in the process of giving the carbs a complete cleaning. I was taking the pilot fuel screw out and noticed the end of it was broken off. Where can i find one of these?? I also lost the spring with it too.:mad:
Finally, I forgot to record how many turns these were set at. Anyone have a good starting point?
 
dhayward312 said:
So i'm in the process of giving the carbs a complete cleaning. I was taking the pilot fuel screw out and noticed the end of it was broken off. Where can i find one of these?? I also lost the spring with it too.:mad:
Finally, I forgot to record how many turns these were set at. Anyone have a good starting point?
Click to expand...

Is the tip still stuck in the hole?
Something like 1 -1 1/2 turns for starters, tweak them for best running.
I think the screws are only available used.
 
Yes, be sure the screw tip isn't stuck in the carb body.
If the intake is stock, I'd start at one full turn out from lightly seated. The majority of these screws are set at 3/4 to 1 turn out from the factory. The adjustment of the pilot fuel screw is intended to fine tune the pilot circuit jetting. Fine tuning will most likely be needed.
As for the spring, it's purpose is to keep enough tension on the screw so it can't vibrate and move.
 
dhayward312 said:
So i'm in the process of giving the carbs a complete cleaning. I was taking the pilot fuel screw out and noticed the end of it was broken off. Where can i find one of these?? I also lost the spring with it too.:mad:
Finally, I forgot to record how many turns these were set at. Anyone have a good starting point?
Click to expand...

I have a set of spare VM26's from a '79 850 so I suspect I have one of the fuel screws and spring you seek. Make sure that's all you need then PM me with a complete list of what you need, then I'll go take a look what I have.

Like tkent02 and Keith say, be very sure the tip isn't stuck in the body otherwise disappointment and frustration are in your future. Ask me how I know... go on... ;)
 
Last edited:
tkent02 said:
Something like 1 -1 1/2 turns for starters, tweak them for best running.
Click to expand...
The '79 850 used VM carbs. The pilot FUEL screw was out about 5/8 turn from the factory, but 3/4 turn seems to work better with a stock bike.
If you have pods or a pipe on there, 1 full turn might be better. The pilot AIR screw is usually about double the fuel screw as a starting point, so start with that one about 1.5 turns out.

The '80 and later bikes only had a pilot MIXTURE adjustment screw, and 1.5 turns on that is almost enough to work. Most bikes will need between 2 and 3 turns.

.
 
Didnt look to see if the end was still in the carb. Its sitting in cleaner now. I'll check it out when i get home from work. Thanks for the quick reply guys! I have pods and straights on this bike btw.....
 
dhayward312 said:
Didnt look to see if the end was still in the carb. Its sitting in cleaner now. I'll check it out when i get home from work. Thanks for the quick reply guys! I have pods and straights on this bike btw.....
Click to expand...

The carbs will need to be rejeted since you changed the stock configuration.
 
Steve said:
The '79 850 used VM carbs. The pilot FUEL screw was out about 5/8 turn from the factory, but 3/4 turn seems to work better with a stock bike.
If you have pods or a pipe on there, 1 full turn might be better. The pilot AIR screw is usually about double the fuel screw as a starting point, so start with that one about 1.5 turns out.

.
Click to expand...

With VMs I find it easier to get it running on the rich side and then go leaner on the screws until it starts to run worse, then back richer just until it runs perfect. It's harder to tweak the screws if you start with a lean setting. It really does not matter where you start as long as you tweak them to perfection.
 
Let me know if you still need any parts, I've got a couple of extra racks and I owe you for the good parts. What ever you do make sure the tip of that fuel screw is not jambed in the hole or all your effort will be in vain. A starting point could easily be 3/4 turn out for the fuel and 1 1/2 for the air, should be fine enough to get her started. From there just use the 'best idle' method of fine tuning them.
 
dhayward312 said:
Do you guys have a starting point with the jetting???
Click to expand...
Hard to guess exactly when you say you're running a straight exhaust and pod brand is unknown. You may also already have jetting that isn't stock.
See what you have now. There are basic changes that can at least get you going the right direction if not right the first try.
A minimum 5 full sizes up (25) on the main jet. If your main is a 95 I'd probably start even richer at a 125, 127.5, or 130. Test the main at full throttle position.
Jet needle e-clip must be at least 1 position richer and that's usually not enough. The stock jet needles should have 5 positions and I believe your factory e-clip position is #3. Most of the time I'd suggest the bottom position. Hard to say because your exhaust isn't tuned. Trying to guess right the first time, I'd suggest position "4 1/2". That means you need to get some jetting spacers. A jetting spacer for your carbs is approx' .022" thick. The spacer is used to make 1/2 position changes. Place the jet needle e-clip in the bottom position and then place the jetting spacer directly on top the e-clip. Install factory plastic spacers in factory order. In your case, the thicker plastic spacer goes above the jetting spacer and e-clip and the thinner one goes under the clip.
Test the needle circuit at 1/3 to 1/2 throttle position. Do what the plugs/performance say. If you have issues at this throttle position, then you may have to go with a different jet needle such as the DJ.
Pilot jet may need changing to a 17.5 but you can try to make the stock 15 work by richening the pilot fuel screws underneath. If up to approx' 3 full turns from lightly seated dosn't work then return the screws to about 3/4 turn and replace the jet with a 17.5. Test the pilot circuit at minimal throttle positions (1/5 throttle to full closed). There is some overlap effect when transitioning from the pilot to the jet needle and some issues may require, again, the DJ jet needle. The DJ needle is actually designed to work with the stock 15 pilot jet so that tells you how it can effect lesser throttle position jetting.
Keep in mind the bike must be otherwise tuned before you an accurately re-jet. Valve clearances, ignition timing, etc, must be spot on first. Otherwise, you may blame the jetting for what is actually another problem.
Also, after jet installation, the carbs must be bench synched carefully. Then, initially set the side air screws to 1 3/4 turns out. Also, your VM carbs will perform better if you remove the two floatbowl vent lines and leave the ports open to breath. This is recommended by Dynojet in their stage 3 jet kits for your carbs.
After full warm up, fine tune the side air screws using the highest rpm method. Adjust idle with the idle knob adjuster to 1,000 rpm's. Starting at any carb, slowly turn the screw in either direction until you hear the motor reach maximum rpm. If the base idle changed enough, return the idle to 1,000 using the idle knob. Repeat to all carbs.
Now you need to vacuum synch with a vacuum tool. After all this, you can go out and accurately test each jetting circuit at the correct throttle position. Testing on level or uphill is fine but not down hill.
 
Ok so i Got all of the parts(thanks Martin)

Where can i get some needle spacers??
 
anyone have info on the needle postion? How and where do i put the spacers?
 
The factory spec for the jet needle clip position is 2nd down from the top for a 79 GS850. Raising the clip up will lean things putting it down will richen.
 
dhayward312 said:
anyone have info on the needle postion? How and where do i put the spacers?
Click to expand...
I typed some of this info in my previous post. I thought the factory needle clip position was number 3, but if AZR is correct (2), then I'd try 1 1/2 positions richer (3 1/2). Place the clip in position 4 from the top and place the jetting spacer on top of it.
 
Of course, I may be wrong and 1 or 2 positions richer may work. You wouldn't need jetting spacers. I just don't think 1 position richer will be enough and I'm thinking 2 may be too much. You could always try 2 positions and test. If too rich, then you go leaner.
But trying to get it right the first try, I'd try 1 1/2 positions richer.
 
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