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Carb Question

  • Thread starter Thread starter minime
  • Start date Start date
M

minime

Guest
I have a 77GS550L with Mikuni Carbs. I need to know what the adjustment screws are on the side of the carbs and also the ones on hte bottom of the carbs. I also would like to know what the stock ammount of turns are as well as the ammount that will work when jetting with pods.

I checked some of the history on the site as well as my manual, but could not find a definate.

Also, I am waiting for my jets to come in but with the pod setup is it normal to have to run fully choked for the bike to NOT be falling all over itself?

TIA.
 
You will be running lean with pods and not rejetting. Rejetting means main jet and possibly pilot jet. Also richening your adjustment screws. I don't know too much about the VM carbs. There are alot of VM gurus here and the king is Keith Krause.
 
minime said:
I also would like to know what the stock ammount of turns are as well as the ammount that will work when jetting with pods.
Click to expand...

It sounds as if you are assuming that you can make the adjustments for your pipe and pods with these screws. It doesn't work that way.

The screw on the side is the pilot air screw. The one underneath is your pilot mixture screw. In general they help control your idle and just off idle transition. There are stock settings (a place to start) but they won't apply in your situation.

As Chef said, its a virtual certainty you'll need new pilot jets and main jets, plus you'll need to adjust your needles. Pilot circuits are generally assocated with idle and off idle, your needles from about 1/8 throttle to 3/4 throttle, and you main jets come into play from there on. There is overlap of course and getting it all right will take some trial and error.
 
Okay. I'm not worried about Idle just yet (Although not haveing to gas at a stop would be nice.

Its funny though because normally with choke on your idle goes up. In my case its the exact opposite.

I guess I wont know for sure until I get the Jet Kit in. Where do I start when adjusting my needle? Also can I do this before or after replacing the mains?

Thanks

Vinny
 
Do a search for "plug chop". This is how you jet a bike with mods.
 
Basics.
Be sure carbs are clean and float levels are good and all inner o-rings are good.
I suggest replacing the manifold o-rings at this time.
Valve clearances and ignition timing must be correct.
Pods oiled correctly (if oil used).
All electrical connections clean/good plugs/gapped correctly/battery good.
Now you're ready to re-jet.
For pods only(?), I'd try something close to 100 mains. Stock is 80, so I think 95 would be the minimum and 100 the maximum needed. Hard to guess the first time when running pods with a stock exhaust because they're not a good flow match. Test at full throttle.
Pods will require you to raise the jet needles AT LEAST one position richer. I believe your stock jet needle position is 3 (middle position). Go 1 lower and test at 1/3 throttle. Every time you change the needles, you must re-bench synch the slides at the very least. This should be followed by a vacuum tool synch for accurate test results.
Try an additional 1/2 turn richer (CCW) on the pilot fuel screws (underneath). The factory generally sets them about 1 turn out, so I'd try 1 1/4 to 1 1/2. Fine tuning will probably be necessary. Test the pilot circuit at minimal throttle.
Try initially setting the side air screws at 1 1/2 to 1 3/4 turns out.
REMOVE the two floatbowl vent lines and leave the ports open when running pods.
After all the above is done, warm up and adjust the side air screws using the highest rpm method.
 
Keith... I must concur with everyone on this forum... YOU ROCK!

I took apart my slides (After finally figuring out thats where the e clip was) and set them to the 2nd position from the bottom. I bottomed out all the needles and eyeballed the slide height (Per your bench sync results found on the boards here) and jetted with 110 Mains. I am riding a new bike! It still spits from time to time (Not all the time I think it may be a petcock issue)

Thanks again!

-V
 
minime said:
Keith... I must concur with everyone on this forum... YOU ROCK!

I took apart my slides (After finally figuring out thats where the e clip was) and set them to the 2nd position from the bottom. I bottomed out all the needles and eyeballed the slide height (Per your bench sync results found on the boards here) and jetted with 110 Mains. I am riding a new bike! It still spits from time to time (Not all the time I think it may be a petcock issue)

Thanks again!

-V
Click to expand...
OK, thanks. I'm glad it's running better.
So, it appears you didn't buy a jet kit. OK.
Also, I assumed you were running pods only when I suggested 100 mains. You chose 110 mains which I would think are a bit rich for pods only/stock exhaust. But if you do have a pipe those 110's would seem right. Either way, I'm glad it's running better.
My stock jet needle position suggestion was also based on pods only. If you have a pipe too, you're probably on the lean side, based on my experience. A quality pipe/pod change usually requires 2 positions richer on stock jet needles, if the stock needles work well enough at all. Please let us know what exact mods you have because the info may help others in the future.
Did you do any plug chop/tests?
You really do need to synch with a vacuum tool before you can truly test performance and trust the plug reads. As I've told others, the valve clearances and ignition timing must be correct before the synch.
As for the spitting out the pods, that's a lean condition. For me to give advice means I need to know the exact mods. I also need to know at what throttle position it spits and/or what speed and gear you are in. How much does it spit, etc?
Spitting can be pilot jet or jet needle related. Actually, it can be cut-away related too but we rarely mess around with the cut-away and we can generally come up with some jetting that works well enough so the only spit you ever get is very slight and usually only on colder mornings/the leanest condition you'll typically be in. Even then the spitting should be gone by the time it's fully warmed up. Sometimes spitting is gone completely. It varies from bike to bike, some will spit just a little and richening the pilot or jet needle can create bigger issues because it really is a cut-away problem.
In your case, it could be lean jetting due to incomplete mod info from you. It could be because the carbs aren't synched with a vacuum tool.
It could be caused by still having the 2 float bowl vent lines attached??
It could be the pilot fuel screws need to be adjusted better and possibly the side air screws are opened too much.
If richer screw adjustments don't help, then you do need a 17.5 pilot jet.
It could be valve clearance related.
Or any combo.
I just want your bike to be running well and not fooling you. Lean mixtures can deceive you into thinking there's plenty of power and it's running right.
Be sure the bike is tuned as above and ready for the re-jet.
Then test at the throttle position needed for each jetting circuit. Chop off.
Do what the performance and plug reads say. The plugs tell the truth.
 
One thing that you can do to adjust fuel mix is raise the float level up to richen and lower to lean slightly.Approx equal to one jet/needle position.The only way you can get an accurate fuel level you KNOW is good is by the actual level in the bowls.The floats in my exp. can be very light in weight or heavy which will affect your fuel mix.The way I do it is by hooking a small line to the drain on each carb and see where the fuel comes to in relation to the carb body/float bowl surface.Start low and work higher trying to keep all equal.Taking the bowls off is a LOT easier than adjusting the needles on VM carbs.
Sorry Keith for my "butting in" because you ARE the expert on carbs IMHO !!:-D
 
82 GS1100E carb parts..............

82 GS1100E carb parts..............

Where is the best place to get carb part's. My bike is an 1982 GS1100E with jetted Mikuni BS34SS carb's.
My thought is to have some extra parts on hand.

Thanks,

Tony
 
zuzu said:
Where is the best place to get carb part's. My bike is an 1982 GS1100E with jetted Mikuni BS34SS carb's.
My thought is to have some extra parts on hand.

Thanks,

Tony
Click to expand...
Fleabay!..................
 
hoyterb said:
One thing that you can do to adjust fuel mix is raise the float level up to richen and lower to lean slightly.Approx equal to one jet/needle position.The only way you can get an accurate fuel level you KNOW is good is by the actual level in the bowls.The floats in my exp. can be very light in weight or heavy which will affect your fuel mix.The way I do it is by hooking a small line to the drain on each carb and see where the fuel comes to in relation to the carb body/float bowl surface.Start low and work higher trying to keep all equal.Taking the bowls off is a LOT easier than adjusting the needles on VM carbs.
Sorry Keith for my "butting in" because you ARE the expert on carbs IMHO !!:-D
Click to expand...
Well, I can understand what you're thinking, but what you're suggesting is a form of compensation jetting, which really never works and just causes more problems.
Raising the bowl fuel level will make it easier for the jets to draw fuel, but if the level is beyond the factory high range, you won't get correct atomization of the fuel. Also, you would actually "richen" every jetting circuit, not just the jet needle as you're suggesting. And if you're above the factory level limit at all, there will be some fuel loss through the overflow lines. It may seem a small amount, but it shouldn't overflow at all.
Honest, it would cause problems. Now if you're only suggesting setting the floats to the maximum factory level to help the jets draw fuel, that's fine but you won't have any margin for error and ANY wear or rough driving conditions will soon result in a higher than maximum level and poor fuel atomization and fuel loss will occur.
 
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